Topic: Exhaust 1 is hotter than 2,3,4 and much more issues

[Jbosma]

I bought a 1981 Honda CB650 that...kinda runs. So here’s what I’ve done: I cleaned out the carbs with some carb dip and replaced the Jets. I have a pressed in idle jet so I had to unclog it and blew some air through it. I was able to feel some air come out of the float valve I’ve heard this is good, it wasn’t much air but it was something. I put the carbs back on and give it about 3/4 choke and the bike starts up. It will not Rev by itself and I have to constantly give it throttle in order for it to run. Exhaust 1&2 run very hot while 3 is warm but 4 is cool enough to where I can grip the exhaust (my Exhaust is a 4INTO1). I feel like I might have seen a small amount of smoke come from the exhaust after It ran for about 15 seconds (this scares the living #$%* out of me) I’ve already changed out spark plugs and oil. Not sure what to do next any advice is appreciated.

[lafindufondu]

Now I'm still learning but I'll try and help out if I can.  I would first check for spark on cylinders 3 & 4 by removing wire from spark plug and then attach a spare plug to the free wire and ground it on the engine.  Turn the engine over and look for spark.  Do this for both 3 & 4.  If you're getting spark then move onto the carbs, drain the bowls and make sure you're getting enough fuel in there.

[Don R]

 Swap the plug to a cylinder that's firing now. See if the cold cylinder follows the plug or stays there. A wet cylinder can be difficult to dry out. I've left a plug out for a while. It sounds more like not enough fuel than too much.

[cjespersen]

Sounds like 4 is not firing if the header isn't hot. I had the same problem with cylinder 3 not firing. I sprayed a can of starter fluid in the number 3 carb while running and it fired up so I knew I had a fuel problem. Also swap the spark plugs so you can rule out spark. Those carbs are a pain in the ass.

[RustyF]

Jbosma, When I installed the 4 into 1 exhaust on my bike I jetted up 1 size on both pilots & mains.  It ran rich and I had a hard time tuning with an inconsistent idle and hot stalling occasionally at stop lights. I noticed that #3 was @80F colder than the other 3 cylinders and I could not "tune it out". After trying everything I swapped the guts (all brass parts) from #3 to #4 and the problem moved to #4.  This was a start but with all new jets I was confused but on the right track.  Pulled carbs again and jets found that the after market pilots had burs in the jet passage causing restriction and a messed up flow pattern that I confirmed by spraying carb spray thru them. My fix was to clean & reinstall the stock jets (pilots & mains) and the bike runs great. With the stock airbox & filter I did not need to upjet for the pipe.

I am sharing this story because you may have a pilot circuit partially obstructed causing the cold cyl. If you have already swapped spark plugs and still have the cold cyl then I would look at pulling the carbs, giving them a clean and verify all the pilot & main circuits are clear.