only 3 of 4 cyclinders are firing...HELP!!!

[Anonymous]

Don't overlook the possibility of a bad sparkplug boot. I had #1 plug boot bad and if I put a plug in it and grounded the plug to the head it would spark but, if I put it back on the plug in the head it would arc to a cooling fin and kill the cylinder. I only found this out while starting it one night after it started to get dark so I could see the spark. I had cleaned the carbs twice and adjusted the valves and was getting very frustrated about the loss of power. Hope this helps. I have a 1983 GS 550L with the double throat carbs.

Interesting possibility....How would I check to see if my "sparkplug boot" was bad?

Rudi

[Anonymous]

I found mine by starting the bike in the dark and could see the blue spark jump from the boot to the head in the darkness. It was killing #1 completely and seemed to make #4 exhaust cooler than #2 and 3. I sprayed water from a bottle on the exaust pipes to see which were hotter.

[simon lambert]

Well I can relate to this, My 1980 GS1000s (2 valve) started misfiring at the end of a ride. I had just filled up and put it down to crappy fuel.
The bike was sputtering and eratic. I got it home, checked the fule for water and junk, changed the plugs and washed the foam air filter.
For the next ride I stuck a paper filter back in the bike. On the next ride after about 60kms it was back to misfiring. I coould still ride it but it was missing quite bad. Since then I have cleaned out the carbs, checked the shims, checked compression ( around 150 psi accross the board, even used two different compression guages to check) I have changed the coils one by one, taken lead from number 4 which fires to number one which misfires, didn,t fix it. I have changed CDI boxes, 3 of them, checked with a spare in the shed and took another of another bike I have. I took the igintion exciter of a bike and checked that. I have changed the resisitors in the plug caps. What I have noticed is that if I lift the lead from number and hold the cap close enough to arc to the plug it runs smoother. Once the cap is put back on the plug it runs erratic. This bug has just about sent me insane. I have checked and rechecked and now I am starting to question what I have already done.. I had to stop myself from taking the head off to checked the valves, but triple checking the compression says there is nothing wrong. I have another set of 29mm Mikunis in the shed so I will kit and clean these to try solve the problem.. the carbs on the bike have been balanced with a set of mercury vacum guages..
One thing the bike does now is backfire both exhaust and carb backfires.. not constant but more often than the norm..
SO ANY IDEAS??
Regards Simon

[HiSPL]

Simon, I would look at cam timing for your problem....Possibly even cam chain tension.....


Rudi, Great to hear that the bike sorta runs .....I know how frustrating these things can be. Here are some thoughts on the subject.

Stuck ring? I dunno could be.... We know your valves are good. We know your carbs are clean. Could be a stubborn ring, caused by the bike sitting for years.... Maybe all it needs is to be ridden for some miles...

Stuck float needle? Just because its clean doesn't necessarily mean it works.... take the bowl off of that carb and move the floats up and down and look if the needle is moving with the floats....


The carb sync thing is pretty easy. You'll pay less for the tool than to have a mechanic do it, so it really pays to do it yourself...

Keep at it Rudi, we'll be here to help.