Cylinder 1&4 misfire 1980 gs750l

[Guest]

I’ve been chasing this problem around for weeks and need some help. I’ve got the bike to idle finally but can’t seem to get cyl 1&4 to come alive. When I pull the plug cables on 2 or 3 the bike will die, and when done to 1&4 no change. I have spark on all cylinders, all cylinders are getting fuel, no air leaks, possible exhaust leak at the header not sure which cylinder. I need to check valve clearance again it’s been a long time. I’m going to test compression this week but am wondering if there’s something I may have missed. Any suggestions? Thank you!

 

[zed1015]

Unless you have very low or no compression the problem can be spark related or manifold air leak.
Spraying easy start around the 1 - 4 carb boots would get a result if there's major leaks there but It would be a big coincidence having air leaks or no compression on the two cylinders that are also served by the same coil.
The fact that pulling 2 or 3 kills the engine is because it is only running on those cylinders , if all four were firing it would not die.
The strength of the spark is crucial , even if it sparks in the atmsphere the compression of the cylinder will suppress a weak spark.
Once you have ruled out the other causes i would be looking at the ignition circuit and coil associated with 1 - 4 and start by switching coils to see if the fault follows to 2-3.

 

[Guest]

i would be looking at the ignition circuit and coil associated with 1 - 4 and start by switching coils to see if the fault follows to 2-3.

+1 on switching the coils, sounds exactly like an ignition/coil issue with it happening on 1 and 4 only.

Mark

 

[Guest]

Update: After swapping plugs and playing around with tuning I got both cylinders to fire by taking out the stacks that connect them to the air box. I noticed an abundance of fuel in the air box from 1&4 and decided to try running it without filters and they fired up. Sounds like I have a float issue, correct? I don’t own calipers or any good way to measure float height so looks like I’ll be doing some trial and error, wish me luck. Thank you for your responses I will be swapping coils to see if anything changes.