Backfiring G3LS

lawrence · Post by **lawrence** » Tue Sep 02, 2008 11:54 pm

Hi Alan
On a G3 you may have to run it more than a few minutes to clear the sump. Their pumps are SLOW!

iF THIS HAS ONLY OCCURED SINCE IT HAS BEEN STANDING AND PROVIDED THERE IS A RETURN FLOW TO THE OIL TANK a ten minute run down the road and back should clear it.

I use Gun Gum exhaust paste. It is a greyish putty and excess wipes off with a damp rag though the tape idea sounds easier!

AlanRSmith · Post by **AlanRSmith** » Wed Sep 03, 2008 4:27 pm

Still no joy - I have drained the sump and this stopped the smoking. Have sealed the exhaust and tried every way of setting the pilot mix and the slow tick over. No joy at all the bike is backfiring and spitting on deceleration.
Seems to be missing as soon as I set tick over slower and cannot solve it by adjusting the pilot screw.
The carb has been stripped and cleaned with new gaskets.
Am loosing the will to live. Not sure what else to do other than assume its in the electrics e.g. the timing is somehow out or the mag is playing up. Any ideas? Really do not know what to try next.

itma · Post by **itma** » Wed Sep 03, 2008 5:03 pm

Have you checked Tappets?

AlanRSmith · Post by **AlanRSmith** » Wed Sep 03, 2008 7:19 pm

Ok I will check the tappets next. Thanks for the suggestion Ken

clive · Post by **clive** » Thu Sep 11, 2008 10:36 pm

A number of thoughts. Oil leaking past the pump is rare on singles but when it does happen if the bike has stood for long it may not clear from the sump easily. Also the plug is likely to oil up whilst you are running it to clear and then not run properly even if you drain the sump.
I also had problems with spitting back on my G3L which is a WD motor with later H lift cams. These have a slightly different cam timing and I had to change the inlet cam timing by one tooth and all the problems went. No decernable effect on performance. Totally ignore this if you have the correct cams for the year or if the problem has developed. If so I would suggest you just haven't tracked the leak yet. Happened to me on a different bike recently only to find that I had a spark plug that had vibrated loose!

AlanRSmith · Post by **AlanRSmith** » Sun Oct 12, 2008 1:22 pm

Help - still no joy - bike pops and bangs on deceleration. Cannot get the bike to tick over at slow speed (it pops and fails) hence I am having problem even setting the mixture (have done the basic 2 turn out).

The list of fixes I have tried is as follows:-

1) Checked and set the plug.
2) Checked the HT lead and connection (twice).
3) Set the Mag points (twice).
4) Removed and resealed the exhaust (twice).
5) Stripped the carb (twice second time using gasket seal) and cleaned pilot and main jets replacing gaskets including inlet gasket plus using gasket seal. Inc checking the choke and throttle slider.
6) Set the tappets.
7) checked the Mag chain.

Am really at a loss re next attempt at sorting this out - any ideas or suggestion are welcome.

I do get the some smoking from the exhaust from time to time when its warm. Could I have a problem with the engine internals (valves or piston) - power and compression seems fine?

Note:the bike ran fine until I went for a 80 mile run when it developed the popping after about 40 miles. Sinced then I have carried out the above attempts to fix the problem.

RogerNorman · Post by **RogerNorman** » Sun Oct 12, 2008 5:20 pm

One other place you could try and its one that is often overlooked but it worked on mine years ago and its solved the problems on a number of other bikes since - take the carb off and look in the inlet tract on the engine side of the carb. On the bottom of the tract there is a very small hole that is the pilot feed from the jet into the tract. If this is blocked it will cause a backfire. Your eyesight will need to be good to see the hole and you will need a very thin piece of wire but it can be the problem. Obviously take the pilot jet out before you do it so that the piece of gunge (if its in there) doesnt then go into the jet then as soon as you start up, block the hole again

56G80S · Post by **56G80S** » Mon Oct 13, 2008 10:05 pm

Have to own up that I get a little of this popping on overrun, usually when cold and as it is relatively mild and the spark plug is a nice colour and the G80S starts well --- I just ignore it.

I'd thought it was front pipe in head fit and as most of my use is currently the run to work and back (72 miles) mainly in the countryside it doesn'y seem to matter. Of course, if there was more urban use, I would.

Good luck - not much help though.

Johnny B

AlanRSmith · Post by **AlanRSmith** » Tue Oct 14, 2008 5:09 pm

Finally sorted the backfiring - it was air leak in exhaust to manifold. Took me three attempts to fix it.

However the carb I cannot fix.

This is what I have tried (time and time again):-

1) Set mixture screw in fully- then 2 turn out
2 Warm up engine
3) Set tick over up a little using the throttle stop.
3) I Attempt to screw mixture in and out a little to see if it improves tick over .

At this point I can get no further as the more I turn the screw in the faster the engine goes. Screw it out too much and it stops. So I cannot get past the basic 'two turns out'. This sounds like the pilot hole is blocked but I have cleaned it time after time. If I take the screw out I can see a very small amount of fuel.
Also I cannot get it to run on slow tick over - it tends to run fast or it stalls.

Any ideas on what to do?

AlanRSmith · Post by **AlanRSmith** » Tue Oct 14, 2008 5:32 pm

Correction its still backfiring !!

Anyone got any other ideas as I have tried all the suggestions so far and still no further forward