Gramde problems

O.K. here's the situation. I bought a high performance pro curcuit performance pipe for my stock vespa that was going 20 miles per hour. The pipe made the bike go 5 miles per hour faster. So then I put a kit on it a 64 cc polini. I didn't pick up any speed, still going max about 25 miles per hour. I thought it was the jets so I tried a 65 - way too much. There was only a 39 in there to begin with. So then I bought some 40's. The 45 worked ok but still only going 25. I tried a 49 and it seemed to big only went about 20 mph with the 49. I'm going to put the 45 back in tomorrow. Any suggestions to make this 78 vespa grande go faster? Thanks in advance please help!

Joshua Porter

Re: Gramde problems

is it possible you have a 10mm carb, or smaller?

stock airbox restricting airflow?

how does the belt look, is it riding fully up in the variator.

use sharpie on the inner surfaces, front and back to measure travel.

is there a white sticker on the left side of the subframe with the mph numbers on it, 20, 25, 30?

how are the brakes, wheel bearings, tires, need attention?

will it pickup more speed going down a slight decline?

hills are a wonderful tool to remove engine power from the tuning EQ.

lets you focus on gearing, variation, chassis issues seperate from hp / torque.

pipe and CC's are like 25% of the speed formula, maybe less.

Re: Gramde problems

Joshua Porter /

Thanks for the responce Glenn, I have a high flow filter. And I'll chevk the variator tomorrow. There's no white sticker on the sub frame. Brakes wheel bearings and tires are good. It does pick up a little more speed on a slight decling but the engine sounds like its maxing out at 25. What do you mean by focussing on the gearing, variation chassis isues separate from torque? Doesn't the variator increase torque? I'm still learning. You say pipe and cc's only make up 25% of the speed formula what makes up the rest? Again, thanks Glenn.

Re: Gramde problems

Joshua Porter /

forgot-- it's a stock carb. 13.13. I believe.

Re: Gramde problems

Maybe you have bad bearings or bad seals/gaskets somewhere. Or the ignition is borked. Did you rebuild the engine when you kitted it? Did you case match to the kit? Did you bore out the intake? Gap the points?

I've got a stock cylinder Vespa running a 63 jet so you might want to upjet. It should have the model number of the carb printed on it, on the clamp part that goes on the intake.

Re: Gramde problems

i recently upgraded to a 13.13 from the stock 12.12, no intake modding.

running a 68 jet with polini top one pipe.

>40mph, but i exhaust port matched to taper to the pipe, removed the lip down to an edge.

belt tension will keep you from reaching full variation, also a worn skinny belt.

i did a mod similar to grahams, except i didn't mod the piston, just the cyl spacing, deck height and head milling, think 155 psi cranking.

lighter vario weights help with accelleration, not top speed.

a good % of speed is getting everything to work together, i have a lot of time into tuning this.

speed rating sticker?

Re: Gramde problems

Joshua Porter /

the bike does fine intil I go past 20 then it sounds like it reving really hard.

Re: Gramde problems

Joshua Porter /

the kit was bolt and go. I made sure the points were gapped correctly.

Re: Gramde problems

Sounds like variator weights are super light, or rear clutch is stuck. Basically you're constantly in 'low gear'?

Re: Gramde problems

Joshua Porter /

the belt is riding up the variator and the rear clutch seems to be functioning normally. But it does feel like I'm in low gear.

Re: Gramde problems

Pull out your variator weights and see what you have. I've seen solid brass, and steel with a hole in the center, both encased in a plastic roller.

Re: Gramde problems

Joshua Porter /

they're solid brass

Re: Gramde problems

Joshua Porter /

12.7 carb

Re: Gramde problems

Joshua Porter /

variator weights weigh 9 grams 10 with the plastic on em.

Re: Gramde problems

my stock rollers were 10g each, 50g total, aftermarket were 8g, so 40g total, plenty light for mild modded stock, 3 rollers, or 30g was too light.

low gear too long feeling.

use sharpie on the inner surfaces, front and back to measure travel

sharpie, ride, then look to see if the marks are worn to the center of the rear pulley, and within 5 or so mm of the outer edge of the front pulley.

tha's here mine stop, not gonna cut the windows to "fully variate"

i have a better plan in the works.

other than that, tuning to get the HP to spin and get up in the higher gearing.

Re: Gramde problems

Joshua Porter /

thanks Glenn

Re: Gramde problems

i'm betting that 12.7 carb has a lot to do with it. that's only a 7mm whole for air that you are allowing into your engine, while most of us are running a whole 13mm. that's a pretty big difference.

and if your variator is untouched stock, it will have a speed governer brass bushing on it, limiting your variator not to close all the way. grind that mutha down

Re: Gramde problems

Joshua Porter /

cool will do Mat

Re: Gramde problems

Joshua Porter /

ok so I ground down the brass bushing on the vartiator, but am only picking up 2 miles per hour. Every time I put a higher jet 45+ the bike runs like shit and alot of smoke comes out of the exhaust... What's going on?

Re: Gramde problems

changing 1 variable at a time is a hard rule to follow.

it allows you to see cause and effect.

i'll say this, modifying the vario didn't cause / cure "runs like s#!& and smokes"

bad gas?

basically, you're focused on top speed as a measure of success.

derestricting the exhaust gave you 5 mph.

brass bushing, 2 mph picked up.

put a kit on it a 64 cc polini, didn't pick up any speed.

i'll bet it's not spinning any more rpms then stock.

hmmmmmm?

Re: Gramde problems

Joshua Porter /

My measure of success is getting the most out of my money and yes that does include increased speed.

Re: Gramde problems

Joshua Porter /

So what do you think? I ordered a 13.13 carb and some 60's jets. Do you think that will make a difference?

Re: Gramde problems

some mods inprovements are measured in inches, but every little bit helps.

i was commenting on speed vs acceleration with the polini.

Re: Gramde problems

what ratio are you mixing your oil, and what oil are you running?

Re: Gramde problems

Joshua Porter /

I think I figured out the problem! The guys at 77 mopeds informed me that the grande was made with seven different transmissions. Mine has 47 teeth on the large gear. I bought a 37 toothed gear. We'll see if this fixes the problem. I'll keep you all posted. Thanks for all the input.

Re: Gramde problems

Wow, 47 is one of the biggest I've heard of

Re: Gramde problems

Joshua Porter /

Yeah, man it's super slow

Re: Gramde problems

You must have a 20mph version then. I need to crack open my 3 transmissions and see what gears I have.

Re: Gramde problems

12.7 carb, and 47t gear? Definitely sounds like a 20 mph version..

Fyi, I have the same polini kit and its really not "bolt and go" . Yes it will fit in the stock cases and bolt on with out modification, but that doesn't mean that's all you should do.. If your gonna spend the cash do it right. AT LEAST match the transfers.. Also its not a bad idea to file all the windows/ports in the cylinder. Mine were razor sharp, and don't forget about ring gap!

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