"Vapor lock" on 4T Stella

Thadsgood · Post by **Thadsgood** » Sun Jul 31, 2011 11:07 pm

Is there something like a vapor lock thing with the stella 4T, like there is on the buddy? I was cruising around in my brand spanking new Dijon 4t stella when it started coughing and sputtering at top speeds (50+mph). It would sputter down to around 30....then I could build speed back up....only to sputter down to 30 again. If I pulled up to a stop it would stall, but I could restart it without issue and get up to 50 again before it would act up.

I'd just added a new tank of gas so it can always be a carb gunk problem, I just wondered if any 4T owners had experienced anything like a 'vapor lock' issue on their scoots.

Silver Streak · Post by **Silver Streak** » Mon Aug 01, 2011 4:57 pm

There definitely can be a fuel starvation problem on a Stella 4T if an overfilled tank or a steep hill allows liquid fuel to enter the evaporative emissions system canister via the hose at the top of the tank.

This is not really "vapor lock" in the traditional use of the term. Vapor lock is really a condition that occurred in older vehicles where heat actually vaporized the fuel in the fuel line to the carburetor while the vehicle was parked, creating a bubble in the line that prevented the vehicle from being started.

What happens on the 4T Stella (and many other scooters with this type of evaporative emissions system) is that -- once liquid fuel has clogged up the canister -- no air can enter the fuel tank to replace fuel being used by the engine, and the vacuum building up inside the tank prevents fuel from reaching the engine.

The problem can be solved in one of three ways: never filling the tank anywhere close to the top, disconnecting the evap emissions hose from the black valve mounted behind the tank and rerouting it to serve as a tank vent, or plugging the hose and installing a vented gas cap from an older 2T Stella.

desmolicious · Post by **desmolicious** » Mon Aug 01, 2011 6:59 pm

Silver Streak wrote:The problem can be solved in one of three ways: never filling the tank anywhere close to the top..

I don't recommend this one because the gas tank - no matter the claim - only holds 1.1 gallons (from full to the brim to pushing it to a gas station!).
Not a big amount, and I wouldn't want it to be any less than that!

Anyway, lots of threads on this topic. Here's one:

topic19337.html

Lovelandstella · Post by **Lovelandstella** » Wed Aug 03, 2011 5:47 pm

Silver Streak wrote:...The problem can be solved in one of three ways: never filling the tank anywhere close to the top, disconnecting the evap emissions hose from the black valve mounted behind the tank and rerouting it to serve as a tank vent, or plugging the hose and installing a vented gas cap from an older 2T Stella.

Fun fact: the stella 2T cap is not an "end all" solution. it just has a different side effect of filling to the top.

on the 4T the fuel will go up throught the evap hose and result in the problems we've all described.

on the 2T, when fueled up to the top, after putting the gas cap on and starting the scoot, the gasoline can pressurize and shoot up through the "vented hole" in the 2T gas cap much like a geiser. It's kinda neat- until you realize that gasoline is not the best thing for paint, as its soon to be dripping over the tank unless you happen to see it and have a bunch of rags handy. otherwise you simply turned your performance problem into a cosmetic problem. and hopefully not a "scoot on fire" problem.

rondothemidget · Post by **rondothemidget** » Thu Aug 04, 2011 3:41 am

I've been having issues with my 4t and I don't believe it is related to the evap system. I think it is the carburuetor not getting enough gas into the bowl when running WOT for a few miles. The engine will cut out and actually die. Then it starts right back up again, probably after the bowl fills up again. It has done it with the evap hose hooked up and unplugged. And it works fine going 50 or less

I'll be taking it to the mechanic next week and will keep you posted.

desmolicious · Post by **desmolicious** » Thu Aug 04, 2011 4:57 am

rondothemidget wrote:I've been having issues with my 4t and I don't believe it is related to the evap system. I think it is the carburuetor not getting enough gas into the bowl when running WOT for a few miles. The engine will cut out and actually die. Then it starts right back up again, probably after the bowl fills up again. It has done it with the evap hose hooked up and unplugged. And it works fine going 50 or less

I'll be taking it to the mechanic next week and will keep you posted.

My PX did that because the previous mechanic put in an incorrect (too long) carb needle.

You could also have some junk blocking the fuel flow.

Silver Streak · Post by **Silver Streak** » Thu Aug 04, 2011 2:55 pm

Lovelandstella wrote:
Silver Streak wrote:...The problem can be solved in one of three ways: never filling the tank anywhere close to the top, disconnecting the evap emissions hose from the black valve mounted behind the tank and rerouting it to serve as a tank vent, or plugging the hose and installing a vented gas cap from an older 2T Stella.
Fun fact: the stella 2T cap is not an "end all" solution. it just has a different side effect of filling to the top.

on the 4T the fuel will go up throught the evap hose and result in the problems we've all described.

You'll notice that my exact words were: "... plugging the hose and installing a vented gas cap...".

desmolicious · Post by **desmolicious** » Thu Aug 04, 2011 5:29 pm

Well, I've never had a fuel geyser issue, but I have had the stalling EVAP connected issue.
I can see how the geyser would happen though if you really over fill the tank, so the protruding end of the gas cap is immersed in the gas. The excess fuel will have no where to go but up through the vent hole!
If it didn't you wouldn't be able to close the gas cap!

Disconnected/plugging the EVAP hose is to prevent the stalling, which for me happened when the fuel tank got anywhere near full. Since it only holds 1.1 gallons, using less fuel is not a satisfactory option.
If you still insist on overfilling, then you deserve a nice refreshing 87 octane spritz!

trumptonriot · Post by **trumptonriot** » Fri Aug 05, 2011 12:29 am

So do you just disconnect the hose or just plug it? There seems to be competing theories on this. I already have the 2T cap.

Silver Streak · Post by **Silver Streak** » Fri Aug 05, 2011 2:27 am

Disconnect and plug where it comes out of the tank. If you leave it open, fuel will dribble out all over the back of your scoot when you accelerate or go up a steep hill with a full tank.

Len · Post by **Len** » Thu Aug 18, 2011 7:13 pm

Personally I wish that LML/Genuine would install a REAL gas tank in their scooter. 1.1 gal is a joke. I mean really, there should be plenty of room in the frane/body for at least 2.5 gal

Len · Post by **Len** » Thu Aug 18, 2011 7:14 pm

Personally I wish that LML/Genuine would install a REAL gas tank in their scooter. 1.1 gal is a joke. I mean really, there should be plenty of room in the frane/body for at least 2.5 gal

desmolicious · Post by **desmolicious** » Thu Aug 18, 2011 7:21 pm

Len wrote:Personally I wish that LML/Genuine would install a REAL gas tank in their scooter. 1.1 gal is a joke. I mean really, there should be plenty of room in the frane/body for at least 2.5 gal

1.1 is small, but that is about 100-130 miles in range. In one sitting that is plenty as you'd want to get off waaay before that!

But for numerous short trips it would be cool to fill up less -once every 2 weeks vs once a week - I guess.

The Vespa PX 2 strokes (and I think Stella 2T) have gas tanks double the size. My Vespa gets about 70mpg vs 100 so it's real range is about 150 miles vs 100 for my Stella (with my usage)

Keith · Post by **Keith** » Fri Aug 19, 2011 10:47 am

My 2T comes in at 2.1 gallons.

Modern Buddy

"Vapor lock" on 4T Stella

"Vapor lock" on 4T Stella

Gas Tank size

Gas Tank size

Re: Gas Tank size