exhaust leak By famousbyter (Read 442 times)

[famousbyter]

most of the time when I let go of the trottle, I get some very unwanted backfires. I have tried several gaskets and have been very careful to seal it with high temp silicone. I have done this three times and always get the same results. My question is this..... Can there be other reasons why i'm getting these leaks? Please advise........

[sprocket]

yes.. the automatic cut-off valve (AVC) on the carb may be stuck or the diaphram is cracked...check the vacuum hose that goes to it... on this pictures it is called the de-accleration vacuum line...

use a full gasket on the exhaust... the copper rings are terrible..

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[sprocket]

full face gasket..by the way high temperature silicone will last about 30 minutes on the header...useless

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[famousbyter]

hey sprocket, i got that same exact gasket now, my first two were different. I did not realize that the silicone I was using is useless. Well I will check out that cut of valve. Am I just checking for a tight connection, no cracks ......or is there something else I need to do with that valve?

[Bashan]

If the vac line looks good you need to remove the two screws and take the little diaphragm out. If it's dry and cracked you'll either have to replace it or get a new carb, whichever is cheaper. Rich

[sprocket]

Rich has you covered.. be careful taking the ACV valve apart there is a tiny spring in there.. I always open it and loose the spring and tiny O-ring and have to go buy a new carb... you would think I would learn... right

[famousbyter]

so I checked the diaphragm out inside of the ACV. No cracks, all in one piece.....vac lines are good as well.
I did notice that the diaphragm did not seat properly when tension was put on the spring. I tried to kinda sorta re-shape it but I just ordered a new carb .....I hope this resolves my backfire issues.....anyways thanks for all the scooter wisdom.....

[terrilee]

now you regulars know
im NOT a mech

but couldnt it also be valves ?
specifically exhaust

[sprocket]

Backfires on de-acceleration usually are caused by air getting into the exhaust at the header or the engine is running very lean or very rich (fuel to air mixture) and raw fuel is exploding in the muffler...

Basically a backfire is an explosion...you need fuel, oxygen and a hot ignition source like a manifold...

Usually carb backfires are caused by the intake valve, and I suppose the exhaust valve can do the same thing in the other direction...