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

  • Thread starter Thread starter Anonymous
  • Start date Start date
A

Anonymous

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Hey everyone! 11 long months have come to a close. I have finally gotten my bike to start! However, I still have a problem.

Only 3 of the 4 cylinders appear to be firing. If you're sitting on the bike it would be the one on the far left.

-I checked to see if I got a spark or not...I did. The plug WAS providing a spark. So that's not the problem.

-Secondly, I left the plug out and tried starting the bike (I wanted to see if I could smell the gas fumes)...I couldn't. It appears that gas is not getting to that cylinder. Although, I'm confused about that possibility because I thoroughly cleaned the carbs out.

-I then tried unscrewing the "air screw" a bit (approx. 1.5 turns). Not sure if this was a good or bad thing to do (I admit it, it was a desperate move :-) ). However, I did try starting the bike again without the spark plug in and I did smell gas (can't guarantee it was coming from that hole). Put the spark plug back in and tried starting the bike. It started fine, but when touching the exhaust pipe relative to that cylinder it wasn't as boiling hot as the others.

NOTE #1: I DID just take my carbs apart and clean them...also, I put all new O'Rings in...The carbs looked fantastic..there wasn't a speck of rust or dirt anywhere. With that said, I have NOT syched my carbs. Not sure how "out of whack" they could be in that department. I'm still relatively new to all of this.

NOTE #2: I should mention that the bike dies when in neutral (or if I slow down to a speed close to zero mph. If I get it into first and take off, it stays running. I would assume this phenomina is due to only three cyclinders firing.

What do you think the problem could be? Is it possible that this is just a symptom of my carbs not being synched? I am absolutely positive that my carbs are cleaner than my baby's butt (after a bath...haha).

Appreciate your help.

:D Rudi
 
Rudi, get a compression Gauge and measure the compression on all four cylinders. My guess is your compression is pretty low in the one "not firing". Without compression, no gas gets into the combustion chamber and you will end up with a cold cylinder. Within a minute of starting all those headers should be too hot to touch. If one can still be held onto while the others are hot it is probably compression. It may not be due to bad rings or burnt valve, might just be the valves are too tight. and not closing. Get a feeler Gauge of the proper size, check your valve clearances and replace the shims if needed. Bet that is your problem. Some if not all your compression will return.
 
I agrre with Micheal but think you should go a bit further, Valve clearances are vital to compression, so check them and a cab synch is definitely needed, one c=arb be out of whack with the others could be your problem.
Dink
 
Oh boy...you guys are starting to scare me here. Sounds like if my compression is off, then I'll need to have the engine rebuilt.....Is this a safe assumption? Is it possible that my carbs not being syched is the main problem here?

And the hits just KEEP ON COMIN'

:evil:

rudi
 
Rudi I think it is more likely a carb issue particularly as that is what you have changed by disassembling them.
Dink
 
Dink said:
Rudi I think it is more likely a carb issue particularly as that is what you have changed by disassembling them.
Dink
Click to expand...

bless your soul....I hope you're right. :-)

btw, is it relatively cheap to go to a bike mechanic and have my carbs professionally synched?
 
It is no where near as cheap as buying a set of mercury sticks and doing it yourself!!!!
Dink
and no amount of money equals the satisfaction of doing it yourself.
 
Dink said:
It is no where near as cheap as buying a set of mercury sticks and doing it yourself!!!!
Dink
and no amount of money equals the satisfaction of doing it yourself.
Click to expand...

Dink,

I was just outside with a guy who agreed with Michael F. on this one. He didn't think the carbs could cause what I described...only a lack of compression. As much as it pains me, it sounds like I have more work to do...like rebuilding this engine. Any thoughts?

Rudi
 
I believe you need to do the valve clearances first then a compression check then look at carb synching as it is a waste of time if everything is not right.and doing the other stuff first will ensure a positive result from synching and reassure you the rest is right or if it is another problem it should show up under these previous tests.
Dink
 
Listen to Dink Rudi. Check your compression and valve clearances first. also make sure there is no air leak between the carb and the intake manifold. that will keep you from pulling in the fuel air mixture needed to ignite in the cylinder.
 
I'd also check that carb 1 is even getting fuel. It's a pretty slim chance that no fuel is getting to it but it's easy enough to check. Just loosen the drain plug on the bottom of the carb. If you have a real shallow and small pan put it underneath first or at least a shop rag to keep as much gas contained as possible.
 
Rudi, I lean towards a carb issue. I know you checked the valve clearance (I was there when you did it) and if it is a rings issue you would probably see evidence of oil burning. Do a compression test to ease your mind and to get a benchmark on your compression. Dink is right about getting everything right before synching the carbs. I lean towards what Pete was saying about fuel not getting to the carb...could be a float needle stuck in the up or closed position.


Hap
 
I had same problem once and it was because the carbs were not synchronized. Really!!! When you put the carbs back on, did you set them. If you have a repair manual, check it out. If you don't want to pay some one to synch your carbs and don't want to buy mercury sticks, check the book for the location of the carb screws (which need to be adjusted to synch them) and start turning them, especially the one for the dead cylander. (what have you got to lose? If you notice a difference then you know you're on the right track and can follow up at repair shop etc. You can usually adjust them while the bike is running.
 
Ok..ok...I'll take a DEEP breath and go with your suggestions. :-)

For those of you who don't know, I've worked on this bike for months...never quitting as new problems kept arising. Sort of figured it was finally over...then this.

BUT, I'm not stopping now. Besides, I've never done a compression check before...it will be a good learning experience.

Thanks for all your ideas. Will post in here with an update as soon as I know something more.

Rudi
 
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.
 
Tool Twister said:
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.
Click to expand...

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

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


Rudi, Great to hear that the bike sorta runs :D .....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.
 
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