Backfiring G3LS

AlanRSmith · Post by **AlanRSmith** » Sun Aug 31, 2008 3:13 pm

Am having problems with backfiring on deceleration on my G3LS. I have cleaned the carb fully and checked plug and points setting. It looks like the exhaust has an air leak round the cylinder junction. I note from previous forum exchanges this could be the cause.
Looks like a number of options re getting a tighter fit.
Any recommendations on the most successful to try?

paul knapp · Post by **paul knapp** » Sun Aug 31, 2008 3:34 pm

Fit the pipe in the head with a cushion of auto grade silastic to seal the joint.
Your idle mixture may be on the rich side, try screwing out the idle mixture air screw 1/4 turn at a time.

AlanRSmith · Post by **AlanRSmith** » Sun Aug 31, 2008 3:50 pm

Thanks for the info Paul -any suggestions re stockist -have looked on the Web and am not sure what product you are recommending. No clear reference to Auto silastic?

SPRIDDLER · Post by **SPRIDDLER** » Sun Aug 31, 2008 4:24 pm

Alan
I've always used exhaust paste on my G3LS - mainly because I already have a supply. It's lasted 3 or 4000 mls so far.
Wrap (masking) tape around the exhaust pipe at its entry point into the head to save having to clean off the excess.

paul knapp · Post by **paul knapp** » Sun Aug 31, 2008 4:42 pm

The auto silastic I refer to is the one sold in car accessory/spare parts shops, other than the silastic range sold for bathrooms etc.
I have found R.T.V. silastic to be almost indestructable, and it also is a handy adhesive.
Paul

AlanRSmith · Post by **AlanRSmith** » Sun Aug 31, 2008 8:08 pm

Neville/Paul - Thanks for your suggestions - I will see what I can get tomorrow. Good tip re masking tape.

AlanRSmith · Post by **AlanRSmith** » Tue Sep 02, 2008 4:20 pm

Am having problems sourcing the RTV silastic - can anyone suggest a source on the web?

HALL · Post by **HALL** » Tue Sep 02, 2008 8:17 pm

I had this problem on my 16MS and it was driving me nuts for a while.
I played about with the exhaust using various sealants. Also I had tried tuning the carb as per "surrey cycles " handy guide. All to no avail, so in exasperation I screwed the air screw fully home and bingo! Never had any more problems.
Best of luck

Charlie

itma · Post by **itma** » Tue Sep 02, 2008 9:11 pm

The air leak that causes this is not necessarily at the head, it could be at the silencer joint, or a hole in the exhaust system, ie the bracket at the back of some repro silencers splits.

AlanRSmith · Post by **AlanRSmith** » Tue Sep 02, 2008 10:25 pm

Looks like the backfiring was fixed by sorting the air leak in the exhaust manifold joint. but now I have a bigger problem. Much blue smoke so assume I am burning oil. Have run it for a few mins so its not just sump oil build up. Seem to get more smoke after running on tick over then open the throttle (i.e was ensuring the mixure wasn't too rich). Any suggestion? Don't want to run it if a have some bigger engine fault & needing a strip down. Not sure what I should do next. Help!