GL1200, one cylinder doesnt fire until 2000 rpm

codyhartikainen said:

one cylinder doesnt fire until 200 rpm, then engine jumps to 4000 rpm....
spark is good on all cylinders... the tach bounces at 0-500 rpm at first then jumps to 3-400 rpm , bike is idling on 3 cylinders
gl1200
any ideas?

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I'd start out swapping things.
First off switch the spark plugs on the two cylinders served by that spark coil. If the miss moves to the other cylinder you've found the problem.
Switch the two spark leads across from the missing cylinder to the opposite side and vice versa. No change in the missing cylinder it's time to check out the spark plug leads and the connection to the plug and coil.

Plugged idle circuit in the offending carburetor?

the left rear cylinder is the offender... initially the bike would not idel, but with a few smacks to the carb with a wrench the idle smoothed out,, now idles. but hesitates and spits and coughs at low rpm, then clears up ..
looked at spark on all cylinders all strong and blue... removed each plug wire one at a time at idle, all made rpm drop except for rear left cylinder had no effect on idle speed when removed..
swapped plugs with front left had no effect...
tomorrow will do a full dignostic with electrical..

but due to the fact it is one cylinder not 2 .. I think it is a fuel related problem...
how do I go about unplugging the idle circuit in the offending carb?

have to find out weather its fuel or electrical related. swapping plugs is a good start. once you have eliminated all the electrical causes then the only thing left is fuel. if the bike has been sitting for awhile it may be a stuck float but one step at a time. eliminate one thing then move on to the next.

the bike has been sitting for 2 yrs

if you're getting spark at all 4 plugs then i think you can move on to the carbs.

Ken Bergen said:

Plugged idle circuit in the offending carburetor?

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That's the first thing that came to my mind, too.

And that was before I read that the bike had been sitting 2 years...

About a year or so ago I was having what sounds like the same problem with my 1200.I used several cans of carb cleaner in the gas,and I removed the seat and sprayed carb cleaner in the intake.All this helped some but the left rear cylinder would not come in until about 2000 rpms.While going through this someone on this forum recommended Yamalube ringfree shock treatment,don't be put off by the name ringfree because it is a carb cleaner also.I looked it up and was kinda hesitant because of the name.I bought a bottle and after about 20 miles I slowed down on a back road,just letting it lug and skip kinda let down about the bike that I had just bought a few weeks ago.Then I heard that rear cylinder pop,pop pop, poppoppop hum.I still remember exactly where I was when it started humming.This is the story of my 1200 coming back to life.What ever the problem is with yours I know you will forget all about the troubles once it starts running right

Remove the sync port screw at the base of the intake runner. With a plastic nozzle attached to a can of CARB cleaner, push a couple squirts into that cylinder and it should make a dramatic change if the idle circuit is plugged. Be careful. You working with combustibles.

Since you have spark at all four plugs it does sound like the low speed circuit in the carb may be plugged. 2000 rpm is where the mid range circuit should be supplying most of the fuel.

so any recommended carb cleaner?

I think carb cleaners are all pretty much the same,I buy the cheapest brand I can find