GS850 Backfiring

[Chris Finlay]

Hi All.

I have a 1979 GS850 and it backfires through the left exhaust. I swopped over the coils but made no differance. It is also very hard to start from cold even with full choke. Will start with a shot of easy start. Would appreciate any help.

Regards.

Chris

[tom203]

Once it does start (with difficulty) does it backfire all the time ,or just when you let off on throttle? Have you checked your exhaust manifold to make sure you don't have a leak?
Hard starting could be many things-let's start with....have you checked your valve clearances ?

[Chris Finlay]

Thanks for the reply. It backfires all the time on tick over. I replaced the exhausts with new gaskets. I have done nothing with the engine. I also rebuilt the Carbs.

[tom203]

Sounds like this is new-to-you bike??? best to figure that maintenance is way overdue. You must check valve clearance and while you have cam cover off. it's also easy to check cam to crank timing (maybe this is ok but you need to be sure).Once you know this is good, you can move on to other issues. Have you seen bwringers common issues in this link?

http://members.dslextreme.com/users/bikecliff/images/GSR_Greeting.html

rebuild carbs means- clean them and new o-ring stuff ? or aftermarket "repair" kits?

[Steve]

I also rebuilt the Carbs.

As Tom asked, we need you to elaborate on this.

Did you do the full "strip and dip" method, which includes replacing all the o-rings with the kit from cycleorings.com, or did you simply use "rebuild kits" (which are generally a waste of money) and change a bunch of parts?

Unless you did the "strip and dip" method, you can still expect to have some problems, so get ready to do them again.

Regardless of which way you "rebuilt" the carbs, you need to properly set the adjustment screws. If your bike has stock airbox and pipes, the fuel screw (the one on the bottom) should be about 7/8 turn out, the air screw (the one one the side) should be double that, or about 1 3/4 turns. After the bike warms up, slowly adjust the air screw for best idle.

.

[spyug]

Backfiring is indicative of air leaks either on the intake side or the exhaust side. On the exhaust side its usually only noticeable on deceleration.

I would follow Steve's advice and make sure you have fresh O-rings in the carbs and on the intake boots tot he head. Also do check that your pipes have no holes and are tight to the head.

Good luck and let us know what you find.

[Chris Finlay]

Thanks for all that. I will start at sorting out air leaks and go from there. I will keep you posted.

[SqDancerLynn1]

Also make sure you have 12V on the coils, if not check the ign switch

Also adjust the valves !!!