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Newish Stella 4T engine stalls/dies while riding

 
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johnk
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Joined: 03 Sep 2018
Posts: 41

2012 Stella 4T

PostPosted: Wed Sep 12, 2018 1:29 am    Post subject: Newish Stella 4T engine stalls/dies while riding Reply with quote

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.

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

SYMPTOMS:
—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

THE FACTS:
—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)

RESEARCH:
—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

ATTEMPTED TREATMENTS:
—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)

PLANNED TREATMENTS:
—add Sta-bil to the gas
—change the spark plug

POSSIBLE TREATMENTS I DON'T KNOW HOW TO DO:
—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!
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Point37
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Joined: 08 Mar 2018
Posts: 237
Location: MA
'13 Buddy 125 Seafoam

PostPosted: Wed Sep 12, 2018 1:48 am    Post subject: Reply with quote

To test for pulling a vacuum loosen the gas cap a little before a ride...as far as the rest of the possible causes...do 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
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Mr.FixIt
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Joined: 01 Aug 2018
Posts: 34
Location: York, PA, USA
Stella 2T

PostPosted: Wed Sep 12, 2018 3:07 am    Post subject: Reply with quote

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.

_________________
Eric
(aka Mr. Fix It)
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johnk
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Joined: 03 Sep 2018
Posts: 41

2012 Stella 4T

PostPosted: Sun Sep 16, 2018 5:46 pm    Post subject: Fuel line, spark plug, died again today Reply with quote

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!
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Stanza
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Joined: 29 Jan 2018
Posts: 219
Location: Chicago
Puch Maxi

PostPosted: Mon Sep 17, 2018 5:07 pm    Post subject: Reply with quote

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.
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johnk
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Joined: 03 Sep 2018
Posts: 41

2012 Stella 4T

PostPosted: Wed Sep 19, 2018 5:55 pm    Post subject: Carburetor cleaning Reply with quote

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
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johnk
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Joined: 03 Sep 2018
Posts: 41

2012 Stella 4T

PostPosted: Fri Sep 21, 2018 6:03 pm    Post subject: New spark plug, another ride, stalled again Reply with quote

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!
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Point37
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Joined: 08 Mar 2018
Posts: 237
Location: MA
'13 Buddy 125 Seafoam

PostPosted: Fri Sep 21, 2018 6:49 pm    Post subject: Reply with quote

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 carb...you'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
http://www.modernbuddy.com/forum/topic22538.html

one way fuel valve
http://www.modernbuddy.com/forum/topic25298.html#320363

lots of threads on this topic...
https://www.google.com/search?q=site%3Awww.modernbuddy.com%2F+stella+stalling+while+riding&oq=site%3Awww.modernbuddy.com%2F+stella+stalling+while+riding&aqs=chrome..69i57j69i58.12910j0j4&sourceid=chrome&ie=UTF-8
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Stanza
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Joined: 29 Jan 2018
Posts: 219
Location: Chicago
Puch Maxi

PostPosted: Fri Sep 21, 2018 9:56 pm    Post subject: Reply with quote

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.....
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johnk
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Joined: 03 Sep 2018
Posts: 41

2012 Stella 4T

PostPosted: Fri Sep 21, 2018 10:53 pm    Post subject: Next steps Reply with quote

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.
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johnk
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Joined: 03 Sep 2018
Posts: 41

2012 Stella 4T

PostPosted: Sun Sep 23, 2018 10:56 pm    Post subject: Vented gas cap and one-way valve Reply with quote

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?
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Point37
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Joined: 08 Mar 2018
Posts: 237
Location: MA
'13 Buddy 125 Seafoam

PostPosted: Mon Sep 24, 2018 12:39 pm    Post subject: Reply with quote

with the proposed green fuel line i can't really tell which way the connectors are pointing between the carb and the petcock...you 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 that...by 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
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Stanza
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Joined: 29 Jan 2018
Posts: 219
Location: Chicago
Puch Maxi

PostPosted: Mon Sep 24, 2018 9:59 pm    Post subject: Reply with quote

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.
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johnk
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Joined: 03 Sep 2018
Posts: 41

2012 Stella 4T

PostPosted: Mon Sep 24, 2018 10:56 pm    Post subject: Fuel line layout Reply with quote

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.
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Stanza
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Joined: 29 Jan 2018
Posts: 219
Location: Chicago
Puch Maxi

PostPosted: Tue Sep 25, 2018 5:06 pm    Post subject: Reply with quote

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.
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