New guy, have questions about my bike

[tateG]

I bought a 79 GS1000L a few months back that had been sitting for a few years for the nice price of $200. I have got the bike running and driving good for the most part, took a few months to find the right tank for the L model, thought I could use any GS tank, I know better now. I wish I would have found this forum earlier. Anyway, I got the bike to run, but it takes forever to warm up and usually only runs on two or three cylinders until it finally warms up. Once I get it to rev up and ride it around a bit it idles fine and has good throttle response across the rev range, but it backfires when coasting down and at idle. I did take off the carbs and thought I cleaned them out well, but maybe not good enough. It has a stock airbox and stock exhaust. I just replaced the points with a Dyna S unit today, stock coils, and it didn't really make any difference. It did start easier, but still only running on three cyclinders cold and backfiring. It seems if I have the choke in a midway position it will only idle on two cylinders at about 2000 rpms, with the choke pulled out all the way it idles on three at about 3000 rpms. Until a lengthy warm up it will die if you try to roll on the gas. Am I right in assuming this is a carb related problem?

The exhaust does have a couple of holes, but way back at the mufflers. I would like to eventually put a different exhaust on, will putting on a 4 into 1 constitute a jet change if I keep the stock airbox?

I have not adjusted or played with the carbs at all except for blowing out the jets and putting them back in. If this is a carb problem, is it a dirty carb problem or an adjustment problem?

I have to say, once it is warmed up and running good, it runs GOOD, and has quite a bit of get up and go, but still backfires a bit on coast down and idle as I said before.

Thanks for any help you can give.

Tate

[DimitriT]

Tate,

my guess is you have a lean condition on your idle circuit. You need to look for any intake air leaks and if you don't find anything, you will need pull the carbs and look at the choke circuit and idle jets (and pay close attention to the very small holes on those). Perhaps you can identify the problem cylinders by looking for a cold pipe or by pulling the ingition and looking for no change in idle.

I'm assuming you've already tried adjusting the idle mixture and have done a carb sync. You can try this too, but if you haven't removed and cleaned those jets you may be just fixing the symptom by playing with the mixture.

Look for the link on this site which instructs on cleaning the carbs. It is excellent.

Good Luck.

-Dimitri.

[humhead]

Sounds like dirty carbs. Unless the previous owner stored the bike properly, there's gum/varnish in your carbs. You can try using Sea Foam or Berryman's B12. These are strong gum & varnish dissloving fuel additives.
The best thing to do is find a second set of carbs & have 'em renewed. That's what I'm doing. Try http://www.wgcarbs.com/ He's a member of this group & comes highly recommended.
You should also check the rubber boots that attach your carbs to the engine.
27 year old rubber can leak, causing all sorts of problems. New parts are still available.
Also check your ignition system. Points, condensers, coils & wires.
Holes in your exhaust will change your backpressure, but what you describe shouldn't be the cause of your problems. A 4 into 1 exhaust will require jetting changes. consider something like this http://www.denniskirk.com/jsp/produc...1755#altImages
Stock jetting should work fine with this type of exhaust.
Did you check your brakes & tires? Old brake lines are an accident waiting to happen. Same goes for tires. If they're more than 3 years old, they should be replaced.

[qslim]

Backfiring during engine braking is usually caused by a leak at the header. I just solved this problem myself with a new set of gaskets.
And congrats on finding this forum. My 850 wouldn't be anywhere near the running shape it is in now without this place, and everyone here will see that your 1000 gets up and goes soon.