1981 Grande Backfireing

Backfireing on decelleration is the problem of the day. Here's whats goin down...

After cleaning the carb good, readjusting the idle screw and checking for (what i see as) good gas flow, i took the ped out for a quick test run. Everything seems to be okay, speeds up to about 20 (which is as good as i can get it running so far) on decleration the ped is backfiring. Before i cleaned the carb it sounded and felt like it was backfireing from the airbox (felt rushes of air on my right ancle) Any thoughts? I thought backfire usually came from the exaust no?

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Re: 1981 Grande Backfireing

Plllleees? Anyone?

Re: 1981 Grande Backfireing

backfiring comes out the carb, and it isn't good at all, that's about the extent of my knowledge.

Re: 1981 Grande Backfireing

Check the points for proper gap, Check the plug and the HT connection to it.

Re: 1981 Grande Backfireing

Hi Jason, off topic, but just incase you didn't know...that sticker that says 25 on your subframe indicated that, that grande is the 25 mph model. You'll have to make some mods to go faster. I think one big one is changing the gears in the rear tire hub to the faster model gears....

Re: 1981 Grande Backfireing

I actully have an 1980 Grande that has the "30" sticker on it. Could i swap out the hubs between the two (1981 and 1980 Grandes). I'd swap the entire wheel but there is a giant chunk taken out of the rim. :(

Re: 1981 Grande Backfireing

Will do, thx for the reply. I'll post the outcome tonite.

Re: 1981 Grande Backfireing

Whats other mods besides changing the gearing would help me get a bit faster. I was looking at cylinder kits on 50cc.com. But i not quite sure what i'm looking for. I guess i'd like a 70cc kit. Anyone local have kits for sale to put on my Grande?

Re: 1981 Grande Backfireing

What is the proper spark plug gap for a Grande?

Re: 1981 Grande Backfireing

.020

Re: 1981 Grande Backfireing

you can up to a 13.13 carb, and bore out the intake if you don't want to get a kit. If you are looking for a kit, I got mine at 50cc.nl, but if you're going to do that you'll need to cut the crank in your engine, and replace the bearings with once that can take higher rpms. Thijs Apekop made a really nice post about the whole process a while back...

Re: 1981 Grande Backfireing

Jordan Caughey /

I think that backfiring comes from timing being advanced too far. Maybe you could check the timing and perhaps mark it so if it ends up getting worse you can always go back to the mark.

Re: 1981 Grande Backfireing

vespas dont have stator plates. the timing is set.

Re: 1981 Grande Backfireing

Jordan Caughey /

oh goodluck to ya then

Re: 1981 Grande Backfireing

hmm, well,......hmmm.

i dunno

Re: 1981 Grande Backfireing

I am not to shure about what your bike is like but when my tomas was backfiring I cleaned out a very dirty exhaust. with easy off over cleaner . soaked it for two days . cleaned it throughly . no more problem. its cheep and it could not hurt.

Re: 1981 Grande Backfireing

Ah sweet, I'll mos def try that ASAP as well.

Thx

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