1979 GS1000L Spark but not firing on Cylinders 3 and 4

[dubwicht]

I am trying to trouble shoot this problem. The first day I started the bike it fired on cylinders 1-3 and now it fires only on 1 and 2. I didn't do a complete tear down of the carb the first time but am doing that now. Just wondering if folks can recommend other troubleshooting to rule out something else. I adjusted the valves nd timing over the winter and installed new points.

[Nessism]

I am trying to trouble shoot this problem. The first day I started the bike it fired on cylinders 1-3 and now it fires only on 1 and 2. I didn't do a complete tear down of the carb the first time but am doing that now. Just wondering if folks can recommend other troubleshooting to rule out something else. I adjusted the valves nd timing over the winter and installed new points.

You're learning the hard way.

Read the Newbie Mistakes thread linked in my signature. If you can't see my signature, go into your profile and turn on the feature to view signatures.

What you will learn is to do maintenance first, before hitting the starter button. Old motorcycles need love. They don't do their own maintenance. I don't even bother to try to start the bike until all the standard maintenance is up to date. And YES, that includes valve adjustment.

[dubwicht]

I have completed a good number of the recommended newbie stuff including brakes, new rectifier/regulator, tank cleaning, petcock rebuild, new intake boots and o-ring, Rotella oil etc. I have the other type of Mikuni carbs and not the CV type. I installed new coils as well. I didn't do the full dismantle because they were very clean.

The cylinder 3 and 4 plugs were wet with fuel. I have read that it could be a carb sync issue in that the two cylinders were so far out that they were not getting fuel. It didn't look that way when I dismantled them. Partially plugged fuel passages? Not the issue. Idle jets for 3&4 seemed to be partially blocked but no material came out during cleaning. It may have been my imagination.

I was experiencing fuel overflow from carb 1 - the float was slightly higher.

Ultrasonic cleaning is next. I will check compression as well.

[dubwicht]

Wow - one of the needles was bent in an S shape. Yikes.

[salty_monk]

That might explain some things…

[dubwicht]

Perhaps but I haven't managed to get the bike into the mid-range yet.