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Newish Stella 4T engine stalls/dies while riding

Posted: Wed Sep 12, 2018 1:29 am
by johnk
Hi everyone. My Stella engine stops running every time I ride it recently. I'm hoping to get it back in shape, so this post is both to document my attempts for posterity and to solicit your advice. I'll describe the situation and the steps I'm taking; please feel free to ask questions, suggest treatments, and correct me.

I am a very new Stella owner with zero prior automotive knowledge. I am planning to take my motorcycle-license test in about three weeks, so this is slightly urgent—if it dies while I'm testing, I'll have to put a foot down, which will make me fail.

—2012 Stella 4T
—purchased "new" (unused) recently
—under 30 miles on the odometer

—after driving for about an hour (neighborhood cruising and parking lot practice), the engine acted like it was out of gas (sputtering and then losing power), but it still had over half a tank (both according to the gauge and peeking in the tank)
—it would start back up, but then die again every few minutes (seeming to increase in frequency)
—the next day, the idle was uneasy for a few minutes, and the bike died again after a few minutes of riding

—after about a week of driveway practice when I first got the bike (maybe 15 miles total), I noticed that the choke had been out since I bought it
—the seller says the battery is brand new and the bike never had any gas in it until I bought it (and I'm still on the first tank)
—I have seen a drop or two of dark liquid on the garage floor under the carburetor vent tube and/or the fuel bowl drain tube (not sure if this is relevant)

—posts on this forum about similar symptoms suggest that the problem could be vapor lock, a kinked fuel line, a coil problem, an air filter problem, a carburetor problem, a fuel/air mixture problem, a fuel-tap (AKA petcock) problem, a fuel filter problem, or an EVAP problem
—a motorcycle friend told me that riding it with the choke out probably ruined the spark plug

—opened the gas tank to test for vapor lock (no sign of pressure or suction)
—double-checked the petcock (it was set to ON when the bike died)

—add Sta-bil to the gas
—change the spark plug

—check for kinks in the fuel line
—check coil/coil bracket
—remove the air filter and clean the carburetor
—rebuild the carburetor
—adjust fuel/air mixture
—unclog fuel tap
—replace fuel filter
—unflood/unclog EVAP

If you have any advice, or have the patience to instruct me on any of the possible treatments I don't know how to do, I would greatly appreciate it! I have a copy of the service manual, but all of this is still very foreign to me. If you know of videos that might help, I'd love a link. I will update this thread as I go. Thank you!

Posted: Wed Sep 12, 2018 1:48 am
by Point37
To test for pulling a vacuum loosen the gas cap a little before a far as the rest of the possible the easy things first...pull spark plug and clean it with a wire brush...

get something to clamp the fuel line off with like forceps and pull the fuel hose off the carb and put the hose end into a bottle then loosen the clamp to verify you have good fuel flow...that should narrow down if it’s a fuel flow issue...then go from there

Posted: Wed Sep 12, 2018 3:07 am
by Mr.FixIt
Fuel, Air, Compression, Spark.

Fuel flow is number one check. If it trickles out slowly, then find out why.

Its been sitting around, make sure nothing has taken up residence blocking the air filter or passageways. (including the exhaust... dang mud dobber wasps)

Its basically new... compression shouldn't be an issue. We can skip that.

The porcelain of the spark plug will pick up metallic particles from a wire brush. Throw it away and get a new one for a couple bucks if it is fouled. The after affects of riding with the choke on will be apparent. If the rubber has deteriorated from sitting around, perhaps the spark boots or wire has developed a carbon track. Start it in the dark and watch for fireworks jumping around from the high tension wire to the frame!

The coil has to have a good ground to work, so yes, that's a good thing to check as well.

Your list of things to do is right on track. 4T owners will have to jump in and get the specifics.

Fuel line, spark plug, died again today

Posted: Sun Sep 16, 2018 5:46 pm
by johnk
Thank you for your advice, Point37 and Mr. FixIt.

Is the fuel line the one indicated by red arrows in the attached photos? (If so, it doesn't look like it's kinked, right?)

To check the fuel line, am I correct that I should (1) clamp it near the carburetor, (2) disconnect it from the carburetor, (3) put the end of the line into a bucket, (4) unclamp it, and (5) observe whether it flows quickly or slowly? If it flows slowly, what's my next move?

Although spark is fourth priority on your list, Mr. FixIt, it was the easiest thing for me to check (photo below). It doesn't look too bad, and I checked the gap before reinstalling it. But just to be safe, I ordered an NGK C8EH-9 (7473) and I'll install it when it arrives.

I added some Sta-bil and a fresh tank of gas and rode for about an hour today. It was idling low at first, then ran great for about an hour. After that, it started sputtering, then died. I kick-started it, got another block, and it died again. (And repeat until I made it home.)

The owner's manual says that leaving the choke out (as I did accidentally) can cause "flooding of petrol in the carburetor causing erratic running and high fuel consumption." That might be my problem. If so, what do I need to do to the carburetor to fix it? EDIT: I just spoke on the phone with a scooter mechanic who said the carburetor would have cleaned itself out by now. He advised me to replace the spark plug and air filter, change the oil, and replace the fuel filter.

EDIT: An old post here recommends that, in addition to getting a vented gas cap from a 2T, I should install a one-way valve in the EVAP line going into the gas tank, like this. Any thoughts?

I appreciate any guidance anyone can provide. Again, I have zero automotive knowledge, and I'm a little nervous about messing with fuel and/or any part of the scooter that I might damage. So if you think it would be safer to have a mechanic do any of this for me, feel free to say so!

Posted: Mon Sep 17, 2018 5:07 pm
by Stanza
So, you really need to clean the carburetor. If the bike was (according to the dealership) new, and never had gas put in it by them, then it's a sure thing that it will still have had the small splash of fuel left over from when they were test ridden at the factory (look up the videos of the LML factory, it's a hoot).

My guess is that your carb has debris in the bowl, likely fuel varnish and whatnot from it sitting all these years with old gas. When you're riding along, it's getting sucked up against the mainjet, and the bike starves for fuel. The 4t shifter stella has probably the easiest carb of them all. Two screws, two bolts, and it's off. Take it off, remove the bowl (two phillips heads screws) and report back with what you find.

Carburetor cleaning

Posted: Wed Sep 19, 2018 5:55 pm
by johnk
Thank you, Stanza, for the advice and reassurance!

I opened up the carburetor following the Genuine 500-Mile Check-Up video (starting around 2:40). The bowl doesn't look too bad as far as I can tell (see attached photo). There are some tiny blue flakes, but no apparent gunk.

I removed the small (idle?) jet and couldn't see any light through it. I sprayed carburetor cleaner and compressed air through it, and now it looks clear (but impossible to photograph). I gather that this is very likely the source of the problem.

I removed the large (pilot? main?) jet and it looked pretty clear. I cleaned it the same way and reassembled/reinstalled everything.

The only thing that looked grimy was something directly to the right of the air/fuel mixture screw (photo also attached). I'm not sure what it is, or what it's supposed to look like.

I'm planning to ride for a while this afternoon, so I hope to discover whether that did the trick. Thanks again!

PS. Here are a few more things I picked up that might be helpful to others working on a carburetor for the first time:
—carburetor cleaner is a nasty chemical that will spray in unexpected directions when you spray it through a jet, so protect your skin and eyes
—carburetor cleaner will make rubber swell up, which will cause leakage, so don't let it come into contact with rubber
—I've heard that an E string from a guitar (the smallest string) is good for cleaning carburetor jets, but many guitar strings are made of steel, and steel can damage brass jets
—a nontrivial amount of fuel will dump out of the carburetor when you open it up, so have a rag or two sitting under the carburetor before you open it

New spark plug, another ride, stalled again

Posted: Fri Sep 21, 2018 6:03 pm
by johnk
I went for a longer ride today and the engine stalled again after about an hour. I was going about 30, I felt it start to sputter, and by the time I pulled over, it was dead. Then it ran for another few minutes, then stalled. (Repeat until I got home, decreasing in running time between stalls.)

In addition to cleaning the carburetor jets recently, I replaced the spark plug yesterday.

So the fuel system seems most likely to be the problem. I have a vague picture of what I can do to check it, but I'm not sure what I'm really looking for, or what to do about what I find. Can I trouble anyone to give me a step-by-step?

Thanks again!

Posted: Fri Sep 21, 2018 6:49 pm
by Point37
did you try loosening the gas cap and riding any of those times it stalled to confirm you're not pulling a vacuum or cavitating fuel lines?...have you tried to pull the hose to the carb to confirm uniform fuel flow...i don't know a ton about the stella in particular but i do know my way around small engines a bit...check/replace the fuel filter...check/clean any fuel screen (if there is one, may be in the tank?)...check for kinked in fuel hoses...fuel is gravity fed since it's not fuel injected so there is no fuel pump...your fuel lines look like they go up and bends horizontally as well more like a water park slide and then down into the carb which isn't good...can you shorten the hose the it's a more direct path between fuel shutoff and're not trying to overfill the fuel tank correct?...i don't know that there is a ton else that could restrict fuel flow

edit: try shortening the fuel line so it's a more direct path to the carb from the shutoff always pitched in downstream

one way fuel valve

lots of threads on this topic... ... e&ie=UTF-8

Posted: Fri Sep 21, 2018 9:56 pm
by Stanza
Hi John, you said that you tested for vapor lock by loosening the fuel cap. Have you checked the fuel flow to the carburetor? Take the bike to an area that won't mind getting messy, remove the fuel line from the carburetor, and turn on the petcock. It should be a solid steady flow. If it's barely trickling out, you may have a blocked filter. As long as this bike had been sitting before you purchased it, the old filter could be coated with old fuel varnish.

As for the carburetor cleaning, when it comes to such things, it's never a bad idea to do it again. If you feel up to it, I'd take the carburetor apart once more, now that it's stalled a few times, and inspect the jets once more. If you had caked on grime in the lines from the old gas, some may have detached and plugged the jets all over again. I would strongly suggest replacing the fuel filter, if you haven't already. It's just held on the fuel line by spring clamps, and a good set of pliers should knock it loose.

Oh the joys of revitalizing bikes that have sat for years.....

Next steps

Posted: Fri Sep 21, 2018 10:53 pm
by johnk
Thank you for all of this information, Point37 and Stanza.

In the attached photo, the red line is the fuel line as is, with a pretty clear incline under the tank. When I replace the filter, should I replace/shorten the segment between the tank and the filter, too (blue line)? Or should I replace/shorten the entire thing so that it runs directly to the carburetor (green line)? In other words, must the fuel line run through the hook on the body right next to where the filter is now?

It would make the most sense to re-clean the carburetor after replacing the fuel filter, right?

Aside from that: in all the excitement of trying to avoid stalling in intersections, I forgot to try loosening the gas cap. And because I'm presently riding on a permit, I don't yet have total freedom to test these fixes with long rides. I figure I'll try these fuel line fixes first, and if they don't solve the problem, I'll move upstream and install a 2T (vented) gas cap and a one-way filter in the EVAP line.

Vented gas cap and one-way valve

Posted: Sun Sep 23, 2018 10:56 pm
by johnk
While I'm waiting for a fuel line to be delivered, I went ahead and installed a one-way valve in the EVAP system and a vented gas cap from a 2T. As Point37 pointed out, a potential cause of my stalling problem is a vacuum in the gas tank. With the stock (sealed) 4T gas cap, air only enters the gas tank from the EVAP. But it's easy for fuel to splash into the EVAP line, preventing proper airflow. So the one-way filter is intended to prevent that, and the vented gas cap is intended to provide even more airflow. (As far as I can tell, the "vent" on the 2T gas cap is only a teeny tiny hole in the very center. Many people have recommended just drilling a hole there in the stock 4T cap.)

When I cut the EVAP line to install the valve, I discovered that the line is not really wide enough to fit onto the valve (Fig. 1), so I had to slice the line a bit lengthwise, shove the valve in, and zip-tie it closed as well as possible (Fig. 2).

My next step will be to replace the fuel line and filter between the petcock and the carburetor. If I have everything right, it's a 3/8" interior-diameter line from the petcock to the filter and a 1/4" interior-diameter line from the filter to the carburetor. To prevent a waterpark effect (ups, downs, and loops), I'll route the line directly, as illustrated by the green line in my previous post. I got some Helix Racing transparent fuel line to be able to see the flow better.

I couldn't find much information on the "best" fuel filter for the Stella, so I just went with stock. I gather it's a pretty low-tech part, so the relevant specifications are just the diameters of each side (3/8" in and 1/4" out). But I couldn't find any generic/aftermarket filters with those specifications. Can anyone link to a reliable option, given that the stock filters probably won't be available much longer?

Posted: Mon Sep 24, 2018 12:39 pm
by Point37
with the proposed green fuel line i can't really tell which way the connectors are pointing between the carb and the don't want the connectors to not be pointing at each other and run those hose directly from one to the other cause you may cause a kink/obstruction right at the connection...personally i would cut the dip out of the fuel line upstream of the filter first and see what the downstream side looks like after shortening the upstream side it may fix the downstream side enough to be effective

as far as that one way valve goes...i would get rid of that zip tie and get a very small hose clamp from a hardware store if you can find one that fits or just use a metal zip tie...i would also cut that slice out of the hose...that's asking to just tear open...and i would hog out the hose with a drill so the filter fits but make sure the hose is angled down when drilling so the rubber comes out of the hose

Posted: Mon Sep 24, 2018 9:59 pm
by Stanza
When you re-run the fuel line, be sure to leave enough slack in the line to account for the engine moving with suspension travel. Those bends in the line are meant to flex as the engine tilts when you hit a bump. If you run them as a tight straight shot, you will end up yanking the line on each bump, which will make for a short and frustrating ride.

Fuel line layout

Posted: Mon Sep 24, 2018 10:56 pm
by johnk
Here are my best approximations of the stock fuel line layout and the improvement I will attempt. The connector coming out of the petcock is horizontal and pointed toward the left side of the bike. When the fuel line runs through the hooks connecting it to the frame, the fuel filter is parallel with the bike. The connector going into the carburetor is vertical, going down into the left side of the carburetor.

In the stock layout, there is a sharp curve in the segment coming out of the petcock, and then a noticeable incline in the bend leading to the fuel filter. My plan is to simplify the route and let the filter hang freely (detached from the frame).

I got the one-way valve to fit better in the line by drilling it out a bit.

Thank you for the tips, and feel free to keep them coming! (I have also read that pressurized lines get shorter, which is another reason for leaving some slack.) I'll update with progress.

Posted: Tue Sep 25, 2018 5:06 pm
by Stanza
Pressurized lines do get a tiny bit shorter, but your stella uses a gravity feed system. No pressure to speak of, beyond what's flowing out via gravity. In a fuel injected bike, that might be a factor.


Posted: Sun Oct 28, 2018 6:58 pm
by johnk
When I last complained, my problem was that my Stella could only really handle about an hour of riding. After that, it would die, and if I could get it started again, it would keep dying.

Since then, I have replaced the stock gas cap with a vented gas cap and installed a one-way valve into the EVAP line going into the tank. (I had also planned to replace/reroute the fuel line, but I had a motorcycle mechanic look at it recently, and he said the fuel line layout looks perfect as it is, and messing with it would almost certainly make things worse.)

Now, my problem is a little different. The Stella still dies while riding it—after as little as half an hour. But it starts right back up and runs strong immediately. Then, a little later, it dies again, and starts right back up again.

As far as I can remember, it only dies when I'm downshifting. As I close the throttle and decelerate, the engine winds down below idling speed and shuts off. This mostly happens at red lights, but it happened once while I was trying to maintain a steady speed. If I keep the throttle open a bit (which isn't always easy to do when coming to a stop), that seems to prevent it from dying.

Is it possible that this is a problem with my downshifting technique? Might I be stalling the engine somehow, even while rolling?

If it is a mechanical issue, where is the next place I should investigate?

Posted: Mon Oct 29, 2018 1:23 pm
by Stanza
You might have a little bit of debris in the float bowl that's getting pulled up into the idle jet. Then, when the engine cuts out, suction stops, and it falls back off the jet.

Posted: Fri Nov 02, 2018 2:49 pm
by BuddyRaton
It is starting to sound electrical to me. I can't see being able to ride for an hour with poor fuel delivery problems.

Many intermittent electrical issues do not repeat until components are warm to hot. I have more than once chased a "fuel issue" extensively only to later find it was a bad electrical component

Posted: Fri Nov 02, 2018 4:49 pm
by Stanza
Have you verified that it actually does have spark? Pull the plug, and hold it up against something metal on the bike (hold it by the cap) to see if it's even sparking while you crank the bike.

Another ride

Posted: Fri Nov 02, 2018 7:08 pm
by johnk
Thanks, Stanza and BuddyRaton! I haven't looked at the carburetor or spark plug yet, but I took another ride today that might provide a little more information.

BEFORE THE RIDE: I used a Battery Tender Jr. to make sure the battery was fully charged. I made sure there was plenty of gas—but not too much—in the tank. I pulled out the choke to start it (it was about 40° here overnight), and it took a couple of kicks before idling nicely.

10 MINUTES IN: The engine died while I was coming to a red light. I had been going about 30 MPH in 3rd gear. Started right back up with one kick.

15 MINUTES IN: Same thing. At a different stop, it seemed like I saved it from dying by revving the engine with the clutch in while coming to a stop.

40 MINUTES IN: I was going 30 or 40 in 3rd or 4th, and the engine just died while rolling (I was not downshifting or intending to come to a stop). When I noticed it dying, I tried to rev the engine with the clutch in to keep it alive, but it had the opposite effect—the engine would momentarily cut out completely while the throttle was open. It took a few kicks to get it started.

50 MINUTES IN: Same thing, but it wouldn't start at all until I pulled out the choke.

60 MINUTES IN: Same thing; required choke again.

I hope this data tells you something. (It sure sounds like a carburetor issue to me.) In any case, I will clean the carburetor again as soon as possible, I'll check the spark, and I'll get the battery load-tested professionally. (It's at least as old as the bike, and it sat for six years.)

BuddyRaton: Given that the choke seemed to help it start back up, and that it died earlier in my ride this time, does that tell one way or the other about whether it's a fuel or electrical issue? Do you have any guesses about which electrical component could be at fault?

Posted: Sun Nov 04, 2018 3:42 pm
by jimmbomb
Re-route your fuel line to ensure that the flow is always downhill and no short turns.
Also, spray out your float needle and needle seat. Make sure that the float moves up and down freely and the needle valve goes up and down (opens and closes).
Good luck.


Posted: Tue Nov 27, 2018 6:37 pm
by johnk
I haven't yet done any more work on the scooter, so this is not a full update, but to my surprise, it's running extremely well now. The only thing that might have changed is that the Stabil 360º I added a while ago has had a chance to work all the way through the fuel system. (Unlike regular Stabil, Stabil 360º claims to clean the fuel system in addition to stabilizing the fuel.) If I'm lucky, I just had a clogged jet that's now cleared.

I'll keep you all posted if anything changes. Thanks again!

Posted: Sat Jul 06, 2019 11:49 pm
by G-Rod
Hate to bring this deal up again but I’ve been wrestling with exactly the issues noted in this thread. Honest...I’ve done everything suggested and everything I can think of even remotely responsible. One thing....seems to run better until I reinstall the cowl. I’m starting to think I might fix this problem with a match.

Posted: Sun Jul 07, 2019 12:23 am
by johnk
G-Rod: Have you tried disconnecting the EVAP line, as jamisfoes recommends here?

I'm having the same issues again this season, but I haven't done any experimentation yet, nor have I tried many of the recommendations above. It really seems like the carburetor just isn't getting fuel, and it happens after I've been riding for a bit, so it would make sense that I'm getting a vacuum in the fuel tank that prevents fuel from flowing. My motorcycle mechanic also recommended that I disconnect the EVAP line.

I'm optimistic that we can figure this out!

Posted: Sun Jul 07, 2019 10:51 pm
by G-Rod
Thanks for asking. Yup, I’ve done ALL the recommended items and more. In fact, I’ve cleaned plug and carb half a dozen times. After each, the scooter starts nicely, idles and runs.....for fifteen minutes. Have a “one last time� search and destroy mission scheduled for sometime next week. Just looking for something new to check. Thanks again. I’ll post any new developments.

Posted: Sun Jul 07, 2019 11:40 pm
by Stanza
When it dies after fifteen minutes, does it shut off like you're hitting the kill button, or does it idle lower lower lower die? Or is it a cough stumble cough die?

Posted: Tue Jul 09, 2019 12:47 pm
by G-Rod
Combination of the two. Usually idles and runs well enough then starts missing under load finally coming to a sputtering stop. Restarts but the situation gets worse and worse until restart is impossible. However, I’ve also experienced occasions when it simply dies when coasting to a stop. In either case, finally, the scooter won’t start again until it’s cooled and the carb is dismantled, cleaned and reinstalled. Weird.

Posted: Tue Jul 09, 2019 1:42 pm
by Stanza
It almost sounds like vacuum lock, where the tank is building up vacuum and not letting any fuel out. For your next ride, can you try running it with the gas cap in, but loose? Like, set it in the hole, but don't lock it down. This should let it breathe. If the problem goes away, then you need to vent the cap, or install one.

Posted: Tue Jul 09, 2019 4:39 pm
by G-Rod
Thanks for the tip. Unfortunately, I’ve already done everything mentioned in this thread...including the gas cap venting and vapor system removal. No help. I’m getting a little desperate. Honestly, I’ve been doing my own basic trouble shooting and wrenching on dozens of scooter, carts and bikes over the past fifty or so years. This is the damnedest deal I’ve ever seen. :roll:

Posted: Tue Jul 09, 2019 4:43 pm
by Stanza
Here's a hail mary then. Stellas have a kill button on the handlebar, and it tends to short out partially as they get older. You'll still seem to have spark, but it will be weak and inconsistent. Take the horn cover off, and disconnect the plug/socket that is a two wire, green and black deal. This bypasses the kill button. If this fixes it, then you were dealing with a classic stella problem of the kill button being twitchy.

Posted: Wed Jul 10, 2019 12:56 pm
by G-Rod
Did have a problem with that a while ago. That time it was pretty much a go/no go situation after riding in the rain. Replaced the switch with one off another scooter I had. Still, certainly worth taking another look. Thanks again.

Posted: Wed Jul 10, 2019 3:17 pm
by scootERIK
I don't know anything about the Stellas but is there a chance the stator is bad?

Posted: Thu Jul 11, 2019 11:47 pm
by G-Rod
Certainly a possibility. I’m a little weak with electrics. Did a couple of checks with the multimeter and found everything apparently optimal. Factory manual calls for replacement of electronic parts from non-working to working scooter as ultimate test. Easy for factory/dealers, not so much for me. In my real world, I’d be chasing a problem with very expensive parts. If I do that, first, I might get fuel issues completely off the table with a new carb. Already have more than enough flow from the rerouted lines and have cleaned the original several times. Thoughts?

Posted: Thu Jul 11, 2019 11:47 pm
by G-Rod
Certainly a possibility. I’m a little weak with electrics. Did a couple of checks with the multimeter and found everything apparently optimal. Factory manual calls for replacement of electronic parts from non-working to working scooter as ultimate test. Easy for factory/dealers, not so much for me. In my real world, I’d be chasing a problem with very expensive parts. If I do that, first, I might get fuel issues completely off the table with a new carb. Already have more than enough flow from the rerouted lines and have cleaned the original several times. Thoughts?

Posted: Fri Jul 12, 2019 1:52 am
by tenders
I’m out of my league with Stellas too, but have you checked valve clearances? “Stalls with increasing frequency as the engine warms up� suggests to me coil, valves, or stator, probably in that order, if the carb has been rigorously checked and cleaned.

Posted: Sun Jul 14, 2019 5:02 pm
by BuddyRaton
So what I would do is a full carb rebuild and check the fuel line as suggested. Don't just spray it but take it all the way apart and replace components.

It's still sounding electrical and I agree either coil or stator but I'm leaning more towards stator or pickup. I would start with stator and pickup, I may be right but I could just as easily be wrong. That's what sucks about these kind of issues and how we wind up with spair stators and coils and switches and...

Using a VOM is great when it's a major stator/pickup issue. "I got the readings that tell me it's bad so let me order one." Then you're good, order a part, change it out go ride.

I think it's the stator or pickup. Was it cold when you took your readings? I think the problem is electrical and related to running temperature.

Sometimes these types of problems I have resolved by changing one component at a time. I think it is the stator and would change it out. Now that is easy for me to say since it isn't my coin.

Please keep us updated

Posted: Sun Jul 14, 2019 5:58 pm
by BuddyRaton
If you are looking for instructions Scooter Help is a great place to start but personally I would not be putting too much money into that scooter...but I would do the stator.

There are tons of videos for anything you want to do all over the place. Start with the basics and work your way up. We all started out knowing nuttin! If you want to learn there is plenty of help!

Posted: Tue Jul 16, 2019 1:55 am
by johnk
I had an interesting ride today that gave me some more information on my problem.

Right around twenty minutes into the ride, as expected, I started losing throttle. As usual, it sputtered a bit while I was cruising around 30 MPH. When I came to a stop, I couldn't get going again. It was as if the throttle functioning was somehow backwards: rolling on the throttle made the engine starve out until it died.

Again, I'm working with the hypothesis that I have a vacuum problem (fuel stops flowing out of the fuel tank because no air is flowing into it to take its place). I have a vented 2T cap installed, as well as a check valve in the EVAP line to prevent fuel from splashing up into it.

So I just cut the EVAP line, which is supposed to supply air to the fuel tank. Interestingly, fuel leaked out, which confirms that fuel can splash up into that line. I started back up and it suddenly ran like a whole new bike. I was thrilled.

But then it died out again, in exactly the same way as before. I started to wonder whether any air is even getting under the seat to flow into the vented cap or the now-cut EVAP line. I popped the seat open for a second, closed it again, and it ran just fine. For a minute. I popped the seat open for another second, closed it, and it ran just fine for another minute.

My sub-hypothesis is now that air can't get under the seat. (NCJ8 was having precisely this problem.) To test this hypothesis, the next time it died, I just pulled over for approximately the amount of time it would take me to pop the seat open and close it again. And it did still wouldn't run! (This supports my sub-hypothesis!) And then, when I did pop the seat open for a second, it did run again!

In the next few days, I will try some of NCJ8's tips for getting more air under the seat.

G-Rod: Have your fixes gotten into this territory?

Posted: Fri Jul 19, 2019 10:38 pm
by G-Rod
Sorry to have been out of touch. Took some time riding one of our “working� bikes for a bit. First of all, thanks BR. Good, sound input and advice. I think you’re right about chasing the electrical issue. I just wish I didn’t love that Stella so much....dangerously susceptible to spending good money after bad getting her well. Frankly, johnk, I haven’t had exactly the issue you described. I did, however, check the seat pan carefully by chalking the gas cap to see if there might be any contact...none noted. Have found that once I’ve had the scooter running and apparently dialed in with the cowl off, once I replaced the cowl the same old symptoms recurred. That been leaning me towards more of the heat-related issue direction. Hope to get some time to work on the Stella next week. I’ll be in touch.

Posted: Sun Sep 29, 2019 11:30 pm
by G-Rod
Okay...I’ve done everything I can think of short of chasing electrical issue with expensive parts. I’m in Western NY. This Stella is for sale. Make an offer. Perfect except for the stalling engine.

Posted: Tue Oct 01, 2019 1:51 pm
by srbbnd
It looks like it has been mentioned in the thread already but I had a similar problem.

It was the kill button and the evap system.

The fix was replacing the kill button and removing the hose on the evap system to the air hose and sealing the hole on the air hose.

This fixed the vapor lock issue and the random stopping after starting was the kill button replacement.

Posted: Wed Oct 02, 2019 10:45 pm
by G-Rod
Thanks but done it all. However, following my little meltdown I think I might be falling back on draining fluids, putting it on the tender and letting things go until spring. After all, it’s been a learning experience...even approaching 60 years of two-wheel obsession....and I just can’t give it up. Plenty of other rides in the collection, especially our newest Ural, so I guess I can keep occupied until we thaw again. I think I’m just a little spooked by any electrical issues beyond a switch. :wink:

Posted: Thu Jan 09, 2020 5:14 pm
by artfull dodger
To me, a 20+year small engine mechanic on lawn equipment, that you have a CDI coil breaking down. Seen this many times on lawn equipment, even from new. The coils get hotter as the motor runs, both from the engines own cast off heat and from how the coil functions to make the power for the spark. As the heat increases, a break in the coil's winding opens up gradually(the sputtering) then opens far enough to kill the spark(the stall), by the time you start trying to restart the coil cools off just a bit and that gap in the wire closes back up and she fires up again, only to repeat this process again. As you have been thru the fuel system and cannot see the spark plug wire easily like on a lawn mower(I used an inline spark checking tool to watch the spark go away while the engine was running as i mowed the grass), I would look into a new CDI coil and see how she runs this coming spring. Mike

Posted: Thu Jan 23, 2020 11:35 pm
by G-Rod
Thanks Mike. Replaced the coil just after the situation started. However, I’m going to give your in-line spark check suggestion a try if and/or when I get it running again. Who knows; wouldn’t be the first time I’ve gotten a bad electrical component right out of the box. Taking a break from this deal has put me back in the “WTF is going on� mode. Could be dangerous. Promise I’ll be back with any news.....good or bad. Thanks again.

Re: Newish Stella 4T engine stalls/dies while riding

Posted: Thu Sep 07, 2023 11:43 pm
by G-Rod
It’s been a while but I saw a reference to a BGM high-flow fuel tap for a 2012 Stella 4t. I can’t find it. Hope someone remembers.