2 hot, 2 warm

What would cause a bike to have 2 hot cylinders and two luke warm ones? I'm thinking it might be the plug condition. She runs on all four, but not as well as I would like. Carbs are spotless, good spark.

 

If you are checking at idle, it could be two lean cylinders for the warm ones. How do your plugs look?

I had something similar and was checking at idle. When I pulled the plugs, I could tell the two 'cooler' cylinders were lean.

 

the lean cylinders should be the hot ones.

 

Sounds counter intuitive, but I promise that is exactly what I observed. This was not using the throttle, but at idle during warm-up.

Agree completely during actual running that the lean ones will be the hotter ones.

 

Someone else was having this problem and I was wondering if it couldn't be something with the plug wires going to that side or a coil problem.

 

Idle (all) mixture screws are set at 3. These pipes are on the same coil, but the spark appears to be the about the same as the other two cylinders. The plugs were changed in favor of the old plugs (new ones were fouled bad from fuel) and we got better response. I'm wondering if it is in need of new plugs.

 

Coils are 1 and 4 -- 2 and 3

 

I know that Bill.
I was wondering if perhaps the wires to that side were damaged.

 

MiCarl could probably offer some insight here, but if you have a cylinder that has a poor idle mixture (in your case, possibly very lean) what can happen is that that cylinder won't fire every time. This leads to a poor idle, and would probably cause those cylinders to have cooler pipes than the other.

The reason the pipes would be hotter during actual running (open throttle) with lean pipes is that extra fuel is actually added to the cylinders to cool the flame, otherwise the engine would melt in a heartbeat. This happens to also give favorable performance when you hit the throttle hard.

What I'm thinking, though is that you're not quite dialed in on the idle mixture. What happens when you use the choke?

 

when you use the choke, it runs fine, but the cylinders (on the same coil) are just cool. She idles fine, but comes down slow between 2-3k which tells me she's lean somewhere even though the mixture screws are set at 3 or whatever I posted before. I'm wondering if the air fuel channels are clogged?

 

Can you run a continuity test on the associated plug wires for those two cylinders? You was the cylinders on the same coil - so either 1 and 4 or 2 and 3 - that is how they are paired. From what you said earlier, I thought you said it was on one side, such as 1 and 2 or 3 and 4 ...

Someone else was having this same problem with one side cool and the other hot and his airbox was disconnected - he was doing testing. After attaching the airbox properly then both sides came up to temp - see "And it starts - '81 650 Maxim"

Could be that you don't have good seal on the carb intake boots?
Similarly, how about the channel the fuel goes to connect the 4 carbs?
I don't remember, have you done a complete strip down of the carbs?