one cylinder not firing (or so it seems)

[mikeanw]

Good Evening All

I will explain my challenge and what i have done to isolate the issue. I would appreciate your collective feedback. Prior to my activities i spent 2 hours scouring the forums for support as well.

Issue:

Bike seems to be running rough (especially at low RPM). I can get it to idle at 980, but it struggles when I try to take off. I have the bucket of bolts syndrome happening. After about 2600RPM, It smoothes out a little.

For context, the Bike has new PG's and new timing belts and a new alternator (Brilliant). It also has a Randakks Carb kit.

I acknowledge that I have NOT Synced the carbs yet and that is contributing to my issue.


Actions:

One by one I pulled the plug wires while it was running. Each one made a noticeable difference except for number 4. When I pulled number 4 it made no difference at all.

I replaced all 4 plugs. Still #4

I stuck a plug on #4 and held it against the valve cover and the spark it showed was as good as the others.

I swapped the coils and the wires from the ECU. Still #4

I replaced the plug wire for #4. Still #4

I checked the float bowl for #4 and It had gas.

Conclusion:

I have a problem with the #4 carb. At idle and low speed it does not seems to be providing fuel.

I would appreciate any thoughts or other steps I might try. If none I will pull the carbs tomorrow night.

Thank you in advance for your patience and experience.

M

[Charlie1Horse]

I don't know about the Randakks carb kit but I had the same problem with my 1986 1200A and after taking the carbs off the right side three times I finally came to the conclusion that I had a float valve not opening to get enough gas into the cylinder. I went to ebay and ordered a pair of aftermarket float valves and changed both right side valves and then the problem was fixed. Have you tried checking the drain plug on the offending carb? The plugs are hard to get to but, with a long screwdriver you can loosen and find if there is actually gas in there. Have you done a complete compression check? Perhaps the offending cylinder is low of compression.
Russell

Those who say it cannot be done should try not to interrupt those who are doing it.

[virgilmobile]

Same comments from this peanut gallery too.
Spark,compression,fuel.Check the easy stuff first.
Spark confirmed...Next compression then the carb.
Although unlikely a compression problem,do check it.
So far with all of mine,every non firing single cylinder on these bikes (noticeable at a idle)has been a plugged slow speed jet.
By all means,when you have the carbs off,do a mechanical throttle plate sync.Eg..all 4 plates open at exactly the same time and amount.Set the idle down jets by the book...even if you have to drill out and pull the caps off to get to them.
Polish the slides and bore...inspect the diaphragms for pinholes and ensure proper positioning.Shop vac each carb to watch the slide action one at a time with operating the throttle.

[mikeanw]

Compression check this afternoon

Then out come the carbs.

I will document the outcome.

Thanks again.

[mikeanw]

130 lbs of compression. Not to bad for 32 yrs old

Carb time.

Thanks again

[virgilmobile]

Good compression.Good diagnosis.Expect the slow jet circuit plugged.Clean it out with a fine copper wire.It won't damage the tiny hole.Be sure fluid gets through it all the way to the idle ports by the throttle plate.The one with the slow speed idle adjustment needle and the 3 or 4 tiny holes at the edge of the throttle plate.

[mikeanw]

All done

Seems I forgot to drill out and remove the air mixture screw. I removed it and cleaned it out.

Carbs all tested with a shop vac. All back in and now firing on all 4 cylinders.

Thank you all.

Carb sync tool arrives later in the week. Looking forward to finalizing that.

[virgilmobile]

Yeaaaaa.Your getting good at this.

[mikeanw]

Ok, tool arrived.

Carbs Synced....much nicer.....so smooth, lots of power.

Thanks again to all who chime in and support.

If anyone in the Ottawa area needs to borrow sync tool, PM me!!!!!

[virgilmobile]

Borrow?
Why not rent it out and recoupe a few bucks
Na.I suppose not.
Glad the bike is all better now.
Onto the next project right?