Erratic acceleration issue on a vespa bravo

Issue at hand I'm having is acceleration at stop to 1/3 to 1/2 throttle is up and down then accelerates to 30 and nothing else no attempt to hot a powerband or anything. Setup is as follows: polini 43mm race kit, polini speed case, mazzuchelli crank, malossi cdi, dos six roller variator and dellorto 13.13. Plug is chocolate brown. Temps hold at a max of 372 degrees. I'm completely baffled on the issue. Advice or help on wtf is going on would be rad.

Re: Erratic acceleration issue on a vespa bravo

what ignition and exhaust?

Re: Erratic acceleration issue on a vespa bravo

Malossi cdi and proma

Re: Erratic acceleration issue on a vespa bravo

i guess air leak.

Re: Erratic acceleration issue on a vespa bravo

Belt slipping and grabbing.(edited)

Re: Erratic acceleration issue on a vespa bravo

How far into the rear pulley cheeks does the belt need to be? It currently rides with the top of the belt level with the outside diameter of the rear pulley cheeks.

Re: Erratic acceleration issue on a vespa bravo

> Robert Emery Wrote:

> -------------------------------------------------------

> How far into the rear pulley cheeks does the belt need to be? It

> currently rides with the top of the belt level with the outside diameter

> of the rear pulley cheeks.

It needs to be down in the rear pulley a little. Around 3/16"? I'm not at mine to measure. Also take the front variator off and look at the cheeks. If they are shinny get some really fine sand paper and lightly sand them until the shine is gone.

Re: Erratic acceleration issue on a vespa bravo

What ratio transmission gears do you have?

Did you sharpie a line on the variator cheek to see how far the belt is traveling up at 30mph.

Re: Erratic acceleration issue on a vespa bravo

How heavy are your variator weights and what contra spring are you running. I’ve had that variator bounce running weights that were too heavy on a light spring. I use the silver/white polini contra spring with (3) 4g (3) 5g weights in my bikes.

Re: Erratic acceleration issue on a vespa bravo

Dirty30 Dillon /

It's either slipping belt, or it's sticky variation

Re: Erratic acceleration issue on a vespa bravo

Joe is on the right track to your trouble. If your variator kit came with alternate sets of rollers swap in some lighter before you go after the contra.

This adjustment could give you the smooth variation you would be comfortable to live with.

Re: Erratic acceleration issue on a vespa bravo

I was running the 2.5g polini weights. Switched over to 3g weights. Stock contra spring.

Re: Erratic acceleration issue on a vespa bravo

> Robert Emery Wrote:

> -------------------------------------------------------

> I was running the 2.5g polini weights. Switched over to 3g weights.

> Stock contra spring.

Is it better? Running malossi belt?

Re: Erratic acceleration issue on a vespa bravo

So I sprayed a but of carb cleaner to look for leaks base gasket was good, head gasket was good the intake where the carb slides onto killed the bike immediately. So where carb meets intake I'm assuming is a leak. I do not have an oring in the carb because it never came with one

Re: Erratic acceleration issue on a vespa bravo

Where the screwdriver is pointing

20191018_135211.jpg

Re: Erratic acceleration issue on a vespa bravo

Between the clamp and carb killed the bike immediately

Re: Erratic acceleration issue on a vespa bravo

Mine does that too

Re: Erratic acceleration issue on a vespa bravo

I assume the 8 mm nut is tight? Maybe a loop of Teflon tape to see if that spot is somehow the problem. And the intake casting isn't cracked ?

Re: Erratic acceleration issue on a vespa bravo

That case has a separate intake that bolts on , correct ?? Make sure the surfaces are flat and make a new gasket I would consider.

Re: Erratic acceleration issue on a vespa bravo

Double Trouble Dan /

Take some permatex non-hardening gasket sealer and smear it on both sides of the plastic bushing that goes inside the carb and over the intake. It doesn't take much .

thin even coat is best.

I have fixed 2 vespa's this way .

https://www.permatex.com/products/gasketing/gasket-sealants/permatex-form-a-gasket-no-2-sealant/

Re: Erratic acceleration issue on a vespa bravo

Dan I agree but that polini speed case is slightly different. Much greater areas of leakage because the intake directly bolts on to the case. If I'm not mistaken. With the speed of conking.out when sprayed I suggest that the plate with the two bolts for the 13 mm intake is warped.

My question is if that area was checked for perfect flatness before assembled. I hope this area can be worked on once the engine is pulled without further disassembly. I wouldn't just trust a gooey layer of yamabond on this btw. This is no different than any typical intake on non Vespa designs.

Re: Erratic acceleration issue on a vespa bravo

Dirty30 Dillon /

I've never tried running a small skirt (43mm) kit in the larger opening, but I'm guessing all that increased case volume is not doing you any favors.

What belt are you running?

Re: Erratic acceleration issue on a vespa bravo

So updates on the issue at hand I made sure the intake was level as can be I found a piece of marble I had with all my chef stuff got really fine grit sandpaper and sanded flat the intake matting surface, made new gasket for intake, I added an oring to the carb got the killing issue to stop, updated to a 66 seemed to run a bit better, I'm trying different weight sizes. As for the belt type I'm running it's one of those malossi ones that's 13.4mm wide. I'm high reving while going and not even reaching a top speed. I have not tried a different contra spring as I do not have stiffer ones. If I cannot get that figured out I'm going to switch over to my single speed set up for new Orleans rally. So hopefully I see some of you all there

Re: Erratic acceleration issue on a vespa bravo

Yes new contra spring. I've been playing with that area of vespahood. There are a bunch of different contra/ drive shoe units each a bit different. Some have a hole to stick the bottom end of the contra spring to afix and some do not. The classic yellow spring if no bottom hole has to be cut so it lies flush into it's bottom race which malossi makes a nice holder for. It's critical when messing with the spring not to deform the pulley cheek , so if using say the OEM Vespa contra spring compressor deal to only compress enough to loosen the nut so make sure you already have bent the locking tabs off the washer.

I own the 46 mm polini jug which is on a ghetto bored stock case that I bought from someone who pretty much knew if would require crazy work to make right. I might be willing to sell you that kit ,maybe. Pm me at some point. I probably still want to get that thing air tight , it's all rebuilt with an anticipato in there. So it's on the back burner. Let me know .

Re: Erratic acceleration issue on a vespa bravo

> Robert Emery Wrote:

> -------------------------------------------------------

> So updates on the issue at hand I made sure the intake was level as can

> be I found a piece of marble I had with all my chef stuff got really

> fine grit sandpaper and sanded flat the intake matting surface, made new

> gasket for intake, I added an oring to the carb got the killing issue to

> stop, updated to a 66 seemed to run a bit better, I'm trying different

> weight sizes. As for the belt type I'm running it's one of those malossi

> ones that's 13.4mm wide. I'm high reving while going and not even

> reaching a top speed. I have not tried a different contra spring as I do

> not have stiffer ones. If I cannot get that figured out I'm going to

> switch over to my single speed set up for new Orleans rally. So

> hopefully I see some of you all there

Wait a minute. You updated to a 66 main jet? What did you have in it before? Either way you're still lean. You should be between 68-72. I'm running a 68 in one of my bikes and a 69 in the other. Basically the same set up but stock cases.

Re: Erratic acceleration issue on a vespa bravo

Is it variating all the way? You may have a really low set of gears keeping the max mph low even if your variating all the way.

Re: Erratic acceleration issue on a vespa bravo

Here’s a video on how to determine the trans gear ratio. Are you running a euro clutch with 100mm cheeks or are you on the standard 90mm cheeks?

(edited)

Re: Erratic acceleration issue on a vespa bravo

Nice Joe. Put that in the wiki.

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