1981 GS100E backfires an pops

[Mitch from Everett Wa.]

I just bought me a 1981 GS100E. Its a great bike and I love it but it has a couple of isues.
My first and bigest issue is that it pops and slightly backfires when I am riding it. To be more specific; it ran like crap whe bought it. I constantly backfired and popped really loudly.
First I put some 92 Oct gas in.
Then I changed the worn out throttle cable and that made a BIG difference in the response time when turning the throttle.
Then I changed the spark plugs.
Then I put in a new air filter

All of this signifcanly reduced the amount of pops I was getting.

Now it pops (not very loudly) when I am engine braking or running at higher RPM's.

I have VERY little experience with carburetors but am enthusiastic and illing to learn. I just don't know what to do.

Can anyone help me??

[nvr2old]

Have you checked the timing? Adjusted the valves? The first thing I've always done after buying a used bike is to do a complete tune and service. That way you've pretty much covered all the bases and you can go from there. If it's completely stock and everything is set to factory specs, Japanese bikes will run correctly 99% of the time.

[argonsagas]

There are several possibilities.

There are gaskets between the carbs and engine head. You may still have original ones on there and the O-rings that fit between them and the engine deteriorate with time. Air intake leaks are common with old O-rings. They result in incorrect mixtures that cannot be fully corrected by carb adjustment..

You could have bad ignition timing

You could need valve work.

A compression check will give you a fair idea here, and a leak-down test will add to the findings.

[reddirtrider]

That's a pretty small motor.

DO what they suggested - good advice.

[chef1366]

The 1100E doesn't have intake o-rings. The carbs probably need a good carb cleaning.

http://www.thegsresources.com/gs_carbrebuild.htm

[Bill Humphreys]

GS pops and backfires.

All of these replys are good ones. They didn't mention a simple test you can run without pulling the tank etc.. Get a can of WD-40 or carb cleaner or really any flammable aerosol spray that you will not mind spraying on your engine. Start your bike and let it idle, with the choke off. Using the red tube that comes with WD-40, for accuracy, spray a very quick shot at each manifold. If the idle speed changes, up or down speed, then that manifold is leaking where the spray hit. Sloppy shots can hit the air box and if the rubber neck is not fitted well, you will get a false indicator. Remember, that box sucks, so if you spray close to it, you failed. Check all manifolds top and bottom at the head and at the carburator. Good on you. Tip: West Marine sells something called "Creeping Crack Cure", you can order it online. It is a latex based liquid that looks like millk, is water soluable before drying, and wicks into cracks like you won't believe. Use brake cleaner spray (no oily residue) on the manifolds and then flow on some "C.C.C.". Crank the engine throttle closed to suck it in. Don't start it. Give it a couple of coats. It still is working on my bike. Does anyone supply new manifolds (or Carb mounts) for 1982 GS1100GK engines? Does GK stand for Good Kind?

[TheCafeKid]

The 1100E uses TUBES rather than manifolds like your GK. but, that doesnt rule out the possibility of cracks in them. However, if they are pliable and clean, and when the motor is running you can see them flex in and out, you should be good there. Assure that your screw clamps on both sides are good and tight, but not OVER tight, as this can pinch the boot and cause a free air sucking gap.

[Mitch from Everett Wa.]

I forgot to add, aftermarket Kerker 4 into 1

I forgot to add that it has an aftermarket Kerker 4 into 1 pipe on it. It seems in good condition.

I will do the things that you recommended. We'll see what happens

[reddirtrider]

That alone may cause you to run a bit lean. When the carbs are apart check to see if there's a kit in it.

[chef1366]

Kerker recommends
47.5 pilot jet
117.5 main jet
remove air box lid (are you using a stock air box?)

[Mitch from Everett Wa.]

aftermarket Kerker 4 into 1 exhaust

I have a brand new K&N air filter in it.