Stella 4T hesitation / carburetor problem?

[lifebeat]

Hello again, here is my other big issue with my Stella.

Since I bought it used (with 10,000km on it) it always has had a weird hesitation on accelerating and/or being under load on anything that isn't a very flat road. It almost feels like missfiring, but it only happens at higher rpm's and under load.

Here are the steps that I did, to try and fix this, but I am sadly at the same point as in the beggining:

-At idle, when I reved, it would almost stall before reving up. Cleaned all the jets, not much results, so I ordered main and idle jets
-After no results (the bogging down on idle was a bit better, but the hesitation was still there) I took the carb appart and dipped it in Gunk carb cleaner for 24 hours.
-This fixed the hesitation problem for about 3 rides... then it came back again
-So today, I replaced the fuel filter, idle jet and main jet (all to original size), while blowing all the passages with carb cleaner. The idle is now really smooth, but I got the boggin down on reving again, and the hesitation when accelerating is still there. By the way, the needle clip on the main jet needle is in the central position, and the spark plug seems nice enough.

This feels like the carb is starving for fuel at higher speeds, so I checked the fuel line to make sure no kinks can develop with the suspension range of movement.

Another piece of info that might help. WHen I took my scoot out of the garage after winter, and noticed these problems, I drained the tank to put it fresh gas. I pulled the fuel line before the filter and drained it into a bottle. With the gas valve at the ON position it would run gas almost drip by drip, but in the RES position it would then flow at a reasonable trickle. I thought this could be the problem, so I tried running on Reserve for a while, but this doesn't help the hesitation at all.

So I am now lost with all of this, I can't see what my next move should be. This is really anoying because the scooter takes forever to get up to speed and when it does get close to 50mph, it hesitates like crazy, and anything resembling a slight incline will make me lose speed to around 30mph (I weigh 135lbs).

Thanks for any help you could provide.

Luc

[fisher1]

I've read of issues like this if the fuel tank is not venting/breathing properly and the fuel draw at speed creates a vacuum in the fuel tank which prevents fuel draw.

[lifebeat]

I've read of issues like this if the fuel tank is not venting/breathing properly and the fuel draw at speed creates a vacuum in the fuel tank which prevents fuel draw.

I've read this too, and tried running with the cap not twisted in, just droped into place, and the hesitation is still there...

I can add that whenever I hold the throttle still long enough, this stabilises, and there is no hesitation. But if I open the throttle, hesitation comes back...

[gar1013]

I wonder if there's something wrong with the evap system. I know you're not supposed to tamper with emissions related equipment, so I'm not going to tell you to disable it even though that could be a simple solution. What I will say is that would be an excellent spot to try looking, and to see if you can solve the problem by fixing that particular setup.

[lifebeat]

I wonder if there's something wrong with the evap system. I know you're not supposed to tamper with emissions related equipment, so I'm not going to tell you to disable it even though that could be a simple solution. What I will say is that would be an excellent spot to try looking, and to see if you can solve the problem by fixing that particular setup.

Very good point, that I forgot to mention. I did disable all the EVAP system, and plugged the inlet in the carb entry pipe.

[jason]

I have these same issues.

It was really frustrating a couple weeks ago when my friend (2T) and I rode a ride with long stretches of 50mph and anytime there was an incline my speed dropped by 10mph and I quickly ended up 1/2 a mile behind him before he even noticed.

but I just chalked it up to the 4T just not having the same oomph as the 2T.

If it's not a limitation of the 4T design, I'd love to know what I need to do in order to correct it as we talked about going on a long road-trip but there's no way I'm going to be able to keep up with him.

[lifebeat]

I just ordered a 22mm Polinin carb, and a 165cc cylinder kit from SIP-Scootershop, because i'm fed up with this, and you end up not trusting your ride...

But before I do the swap, I saw these two little interesting bit on the same site, that I think I will try right before (it's cheap and easy to try) and this just might solve the fuel starving, if this is what's happening.

First thing is a fast flow fuel valve : 15878000
And second is an elbow fitting that redirects the fuel line right off the valve, so it doesn't have to do this 180 degree bend... : 15877000

I'll let you know what happens with this.

Thanks!

[3angieyou]

I just ordered a 22mm Polinin carb, and a 165cc cylinder kit from SIP-Scootershop, because i'm fed up with this, and you end up not trusting your ride...

But before I do the swap, I saw these two little interesting bit on the same site, that I think I will try right before (it's cheap and easy to try) and this just might solve the fuel starving, if this is what's happening.

First thing is a fast flow fuel valve : 15878000
And second is an elbow fitting that redirects the fuel line right off the valve, so it doesn't have to do this 180 degree bend... : 15877000

I'll let you know what happens with this.

Thanks!

Noooo!! I was hoping for an easier (read: cheaper) fix seeing as I am having the same problem

[lifebeat]

Well... The elbow fitting and the fast flow valve are rather cheap components, I just have my doubts as to how effective this will be considering that I can't imagine where my line is kinking up at the moment... Once I try this, I will at least be 100% positive that the fuel is getting there properly...

[Eojnommas]

I was having the same trouble. Just had to pull the choke out a bit. I've had similar problems on my vw bus and tweaking the carb always helped. A loose manifold or spark plug will cause a lean situation and make the engine run like crap under load.

[lifebeat]

Well, I'm finaly done with this problem.

I changed in sequence :

-Fuel outlet, elbow fitting : no better result
-Fast flow fuel valve : no better results
-Polini 22mm carb : YEP, It was indeed a carb problem. No My Stella runs fine. The only little issue I have now is some stalling when twisting the throttle for takeoff from standstill. It seems like it's lean or something the rpms go down (sometimes stalling) but then it runs fine throughout the rpm range.

Only coment I could say is the Polini carb kit is a bitch to install. The intake manifold supplied is really far from being the right size. I ended up using the original manifold, but the diameters are different, so when I get to fitting the 165cc cylinder kit, I need a final solution because this diameter difference will create quite a restriction. Will be on the line with SIP people tomorrow to see what they can do.

Also had time to fit the Polini pipe on the Scoot. Sounds very nice to me. Probably even less loud than the original, more of a "round" sound.

[Cellarrat]

Seems like I have a similar problem and have heard a lot of talk about venting issues. Wouldn't the new carb require more air since you are burning more fuel? This would seem to indicate that it isn't a venting problem.

Do you have a vented gas cap?
Thanks