Re: '78 vespa bravo new carb still wont idle

I was just reading about having a leaking decomp valve and the solution was lapping. If I can clean it and it works I’m fine with that. I didn’t replace the mounting bolts I just cleaned them up while I had them off to replace the tires. But as you guys can probably tell this is my first time getting into things like carburetors and engines I didn’t really understand an air or fuel leak before I started getting into this so bear with me lol

Re: '78 vespa bravo new carb still wont idle

I appreciate the explanation and I have a better understand of how that works now. However i never replaced the mounting bolts with longer ones. I just cleaned up the stock ones while I had the tires off and was changing the gear oil. I don’t think the oil was ever changed before me and it had been leaking as there was oil everywhere and little left in the hub. I most likely over tightened them or they were already like that. I wrapped them and they seem to we holding. I don’t have a problem cleaning instead of replacing, I much rather do that. I was just reading about a leaking decomp valve and it seemed the solution was lapping. This is my first time ever even opening up a carburetor or engine. In fact I didn’t even understand air or fuel leaks before this so bear with me lol

Re: '78 vespa bravo new carb still wont idle

Took apart the decompression valve and cleaned it good, finally tested the compression multiple times and only got about 45 psi. I thought that seems really low as it isn’t very easy to turn over but it should be around 120 correct?

Re: '78 vespa bravo new carb still wont idle

> Colin Onda Wrote:

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

> Took apart the decompression valve and cleaned it good, finally tested

> the compression multiple times and only got about 45 psi. I thought that

> seems really low as it isn’t very easy to turn over but it should be

> around 120 correct?

Yes you should be around 120. Anything under 90 is no good

Re: '78 vespa bravo new carb still wont idle

I used a pretty cheap gauge to test it. Wonder how accurate it is. Anything I should replace besides piston rings?

Re: '78 vespa bravo new carb still wont idle

So ive been reading on here that a short in the brake light wiring will kill the engine when the lever is depressed. My brake light works, but I have noticed that i am missing the plug in the rear brake handle and my wire is dangling unconnected. Could this be part of the problem or would this not affect grounding.

Re: '78 vespa bravo new carb still wont idle

For anyone one who’s interested, I pulled the motor. All of the wiring seems to be in good condition, I have a new crankshaft seal to pop in, as well as a condenser. My question is do I need to do anything to the cylinder when I replace the rings?

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Re: '78 vespa bravo new carb still wont idle

Pull that piston and clean it good , including the ring landings .

Anytime rings are replaced the cylinder should be honed to establish fresh cross hatch . That to help the rings seat in better .

Re: '78 vespa bravo new carb still wont idle

Great, thanks!

Re: '78 vespa bravo new carb still wont idle

12.12 carb has a stock 48 49 jet

maybe crankseal gone bad

happens alot

stock no headgasket

and alu base gasket

timing / condenser is also possible if its not a cdi version

Re: '78 vespa bravo new carb still wont idle

So after cleaning the piston good I see it’s got some pretty good scratches. Is it worth reusing?

Re: '78 vespa bravo new carb still wont idle

> Colin Onda Wrote:

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

> So after cleaning the piston good I see it’s got some pretty good

> scratches. Is it worth reusing?

Pics . The internet is a great tool , but , we still can't see through your eyes .

Re: '78 vespa bravo new carb still wont idle

Only on the bottom, my fingernail catches on them. Yes it’s on the kitchen table lol

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Re: '78 vespa bravo new carb still wont idle

I'd run it after a light buffing with emery cloth or very fine sand paper . Just enough to take ridges down .

Insure there's free play for the rings . I'd remove them and clean the landings with brake cleaner after being done with the skirt .

Give the whole piston a good shower with brake cleaner to insure no grit remains .

Re: '78 vespa bravo new carb still wont idle

Great thank you I’ll give it a try

Re: '78 vespa bravo new carb still wont idle

Alright anyone who is still interested, I put the motor back together and back in. To recap, I replaced the crankshaft seal, condenser, cleaned at gapped the ignition points at .4mm. (I did this with piston at top center, didn’t actually time it) and new external coil. Also new piston and rings (I couldn’t find rings for my old piston) and honed the cylinder. I started it up today no problem but it’s getting about half power at full throttle, which is worse than before and still not idling.

Re: '78 vespa bravo new carb still wont idle

I should also mention I had to sand down the woodruff key to get it to fit back in the slot on the crankshaft. It was a pain to get out. In the process I chipped off a little corner of the plastic side wedge that the coil sits in

Re: '78 vespa bravo new carb still wont idle

well A for effort. but the thing is you've taken apart a motor n put it back together, where do you think you've gone wrong? did u hone cylinder? did u do compresssion test again? did u check for air leaks? alotta times its something that i've done that i systematacaly forget that makes figuring out whats wrong hard.

Re: '78 vespa bravo new carb still wont idle

Finally got some time to mess around with the Vespa. Yeah I admit I kinda just threw some new parts at it and kinda hoped for the best lol. But yeah I did hone the cylinder, well my uncle did. It wasn’t the best job as the blades were too small. I re checked the compression with a better gauge and it’s at 95psi. I checked for leaks and doesn’t seem to be any but I had to keep on the throttle as it won’t idle. I don’t know if that will effect the results. I swapped the 42 for a 46 jet in and it brought it back up to 20 mph, still no idle. I never measured the cylinder, possibly that’s out of spec? I’m going on vacation in September, hopefully I can get it in shape to take with me I’d love to ride it to the beach. Thanks again guys.

Re: '78 vespa bravo new carb still wont idle

Compression might be a little low. Squirt a little 2t oil in the cylinder and check it again. I'm hoping for 125-150 with a lubed cylinder. If it's still low, try lapping your decomp valve.

Re: '78 vespa bravo new carb still wont idle

Why are u making this so hard just to save a scored piston. Get a new piston and rings , set ring gap , hone, reassemble , ride. Use the current piston as a paperweight.

Re: '78 vespa bravo new carb still wont idle

Really not trying to make it hard. I did get a new piston with new rings and honed the cylinder and those were my results. I will set the ring gap.

Re: '78 vespa bravo new carb still wont idle

Great thanks Seth, I’ll try that

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