one cylinder hotter than the other

After the rebuild of my 1972 750 commando with most engine parts new plus electronic ignition the motor runs and sounds really great with super acceleration especially after fitting new carbs but I have one cylinder that is running hotter than the other, any ideas what can be the cause and what can be the cure. Help me out guys..

How did you determine that the one is hotter than the other? Have you verified that the carbs are in sync?

Nathan

Thanks for your reply Nathan.
The carbs were set up using a mercury column and so are in perfect cync, the exhaust pipe of the left hand cylinder has discoloured blue and brown whilst the right hand one has still retained its chrome colour. indicating that the left cylinder is running hot. Any more suggestions would be most welcome..
Kingcole

Tight exhaust valve clearance?

The only time I've experienced one pipe hotter than the other, I had a blocked idle circuit and I thought the bike was idling on both cylinders, but it was only idling on a single cylinder. Once I accellerated past the idle circuit range, the other cylinder would begin to fire and I had normal power. That normal power had me assuming that both cylinders had to be firing all the time, but they weren't.

I could get the bike to idle at about 1100 rpms on one cylinder with no problem. The side that wasn't firing was popping and farting occasionally and I thought it was because of ignition issues (I thought the spark was cutting out. The air coming out of the exhaust seemed warm on both sides at idle so I also wrongly concluded that both cylinders were firing. If I spit on both header pipes, one would instantly boil off the spit, the other didn't smoke at all... That made me realize that I wasn't getting any firing on that cylinder until I was at about 2800 rpm. I realized that it was the idle circuit that was clogged, so I wasn't getting combustion on one cylinder at an idle. I unclogged the idle circuit, fired the bike up, and spit on both header pipes which both boiled off the spit instantly in a puff of smoke at idle.. fixed... If it's not hot enough to boil off your spit, it's not firing.

kingcole said:

the exhaust pipe of the left hand cylinder has discoloured blue and brown whilst the right hand one has still retained its chrome colour.

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Any air leaks in the manifold on one carb could do this too, or even on the exhaust side (but this usually causes popping in the exhaust).

Have you spit on the pipes to make sure they are different temps though - could be bad chrome on one.

Maybe the discolored one is okay and the other is too cold. What do the plugs look like? Both my pipes are blue and gold on my 3 running bikes.

htown16 said:

Maybe the discolored one is okay and the other is too cold. What do the plugs look like? Both my pipes are blue and gold on my 3 running bikes.

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+1 ..... Chrome normally turns purple/blue at the head, then fades to gold/yellow further down the pipe. the color graduation is an indicator of temperature. The pipe that is not turning color, or barely turning, is probably cold. See oOnortonOo's post above.

Slick

You can buy stick on strips of an approx. heat range that could be applied to the cylinder head before you go for a run that would confirm if you are 100% correct. :shock:

Thanks for all your comments you guys they have certainly helped and I now have a direction to go in..

Take a control to:
- the spark plug, may be is on ground because too much gasoline goes from the carb (set the float like x manual);
- low battery, switch off the light.
Ciao
Piero

I could add, Check compression on both cylinders, set ignition with a metal timing disc ( plastic ones will disintegrate above certain revs :!: ) and strobe, on both cylinders no matter which ignition system you have and set carb idle /air screw with a colour tune in the DARK for clarity :idea: