The mysterious cylinder shuffle

So I've had my old 1983 GPz 550 for about a year or so now after rescuing it from a backyard bush where it had sat for at least 2 years, uncovered.

It has numerous problems but I am slowly working through them.

Last year I finally managed to get her running, as discussed in this thread kzrider.com/forum/2-engine/483547-yet-an...ke-wont-startq-query

Before I had to stop tending to the bike (work and studies took priority), I got two cylinders running, curiously these were 1 and 2 (recall that 1 and 4 are a pair as are 2 and 3) and only on full choke. As indicated in the other thread, all 4 cylinders have good compression, it has fresh plugs, fresh oil, fresh gas, I replaced the spark plug leads and boots and tested the spark pick-ups and the resistance was normal.

The conclusion was dirty carbs.

I have since cleaned the carbs and they seem good to go. One problem was that the fuel-air mix screw on carb 2 (one of the ones that was running) had been abused by the previous owner and tightened until the tip snapped off in the hole.

Re-installing the carbs and the problem persisted ... only 1 and 2 firing and only on full choke. Adjusting the idle and, very curiously, bike will sit and idle (althogh rough and high) on cylinders 1 and 4! If the choke is on or the bike is revved higher, 2 and 3 start to kick in a bit. I suspect this is simply the compression at higher revs forcing combustion in those cylinders.

This is very confusing.

At first I thought the 2/3 coil had blown, but I switched the coils and still onyl 1 and 4 fire.

I thought the air-fuel mix screw may be hampering 2 and 3, so I knocked it out and retried. Still only 1 and 4 fire. Regardless of how I adjust the air-fuel screws on 1, 3 and 4, 2 and 3 refuse to run consistently.

Any thoughts, ideas or suggestions? If you need more info or want me to test something, just shout

Thanks!

PS - An additional point which may apply ... the tachometer does not work. When the bike it running it sits and jitters around it's resting position. I recall from the manual that the tach picks up it's readings from the same mechanism responsible for firing the plugs ... I think. So this may be relevant.

Do you have spark at 3 and 4?
Are the spark plugs wet with fuel on 3 and 4?

I confirmed sparks on all 4 cylinders before my break, but can check again.

Yes, all 4 cylinders are getting fuel. 1 and 4 run consistently, 2 and 3 only when revving high (as measured by spritzing water at the headers).

.

What are your compression readings? Have you checked your valve clearance?
Have you sprayed some carb cleaner around the intake manifolds looking for vacuum leaks? Are all of the hoses hooked up properly, or are the vacuum nipples capped? On the vacuum line to the Petcock, is it hooked to one of the offending cylinders? It would normally be hooked to cyl #2, with the fresh air switch hooked with a Tee to 1 & 4. Make sure these are all in good shape, and that the petcock does not have a hole in the diaphragm, as that can let fuel into the cylinder that the vacuum is hooked up to.

Thankd for the input guys

Martin - I switched over the coils and got the same results, so don't think it is the coils. They are the stock coils though, so will measure the resistances (just across where the signals from the igniter enter the coils, right?) next time they warm up.

Motor - I think you're onto it! Attached are two photos of the carbs (pod filters removed [previous owner swapped airbox for them, not me!] for clarity). The vacuum port is on carb 3, all other carbs have their ports capped and the caps look good. But ... I did NOT have 3's port capped off! Feeding the carbs with a coke bottle IV of gas, I didn't notice that vacuum port on the petcock. This will explain why carb 3 isn't working, it's pulling in WAY too much air and no gas

Could carb 3's struggling be hampering carb 2 as well?

The second photo is of a black plastic tee-piece connecting carbs 3 and 4 (there is another between 1 and 2). What are these for and where should they connect to?

Thanks again