Left side running hotter, right running cooler

[Dmwelch]

Hey guys I just got my 1980 XS 400 running, but noticed that my left cylinder is running hotter than my right, I checked with a laser thermo (left running 300+, right running around 120).

I pulled the plugs and checked the spark and there both getting good spark, I noticed the right plug is a little more wetter then the right.

Any thoughts on how to get those more even in temp or at least get the right side hotter?

Thanks

 

[xschris]

Make sure the carbs are clean and compression is the same on both cylinders. After that sync the carbs with a manometer.

 

[drewpy]

also jetting was slightly different on each carb on some models, maybe to compensate for this.

 

[xschris]

That was for the dohc bikes only.

 

[Dmwelch]

Got another question, I was attempting to sync the carbs and am trying to figure out exactly what to set the idle air needle(see photo), screw it down until it's snug then back it out 3 and a half turns? Or 1 and a 1/4? Also after I pulled my carbs off and looked at the right side, and notice the right butter fly valve open slightly higher then the left side, would this cause more fuel to flow in and flood the cylinder?

 

[xschris]

With a stock bike it is around 2-3 turns out. But from your pic it looks like you need new boots for the carbs If one valve is open more than the other it will put the carbs out of sync. Use a manometer to sync them after you replace the boots. It may be also a good idea to replace the butterfly seals as well.

 

[Dmwelch]

What exactly are the butterfly seals?

 

[xschris]

There are shaft seals at each end of the carbs for a total of four per set. Over time they dry and crack or become deformed. Sometimes the outer seals plastic washer breaks or it missing altogether.

 

[Dmwelch]

Thanks for the input, I pulled off the carbs today and reset them a small needle (per some YouTube video I saw) I got them set, I also compression tested it and left side 135, right 145, puts everything back on the bike figuring that I would be able to get it running with having just bench sync the carbs, tried to turn it over and couldn't get it to start up ( I know the carb boots look terrible, but I don't think there the current problem because when it was running I sprayed them with a punch of carb cleaner and didn't notice the engine do anything different, I will though be replacing them.

My questions now are: what should that idle screw be set at or do I just have to play with it while trying to kick over the bike?
What would bad butterfly seals do to the carbs?

Thanks!

 

[ArtursF]

Bad butterfly seals might cause vacuum leak and engine will be running leaner (especially on idle).
As Xschris said 2-3 turns should be OK. That is a good benchmark to start. For finer adjustment I usually use ''dead cylinder'' method. These settings may vary from bike to bike, and that is why you should check plugs and off idle/ back to idle performance of your machine

If bike is not starting:
1. Are carburetors really clean? (there is a reason why we have T-Shirts stating "Telling XS400 owners to clean these things Since 2010".)
2. Check fuel bowl levels. Incorrect setting may cause problems with fuel mixture.
It is better to use plastic pipe method on the bike (bench set levels may differ due differnet angle they are installed on the bike).
3. Check condition of idle mixture screw O-Ring. If it is worn out or is cracked, that may cause problems adjusting idle mixture (learnt that the hard way).
4. Check plugs

Also it is a good idea to adjust valve clearances before carb sync.

 

[Dmwelch]

Ok guys so update to this thread, just broke the carbs apart and cleaned them again, and I have reversed my problem....... now the left side is cold and right is hot and it will only run on when I have the choke pulled out and dies when I let off the choke (also I have the plunger style choke and I think I might have lost one of the ball bearings that goes in the shaft when I took them apart, any one have any ideas where I could find another?)

And back to the drawing board

 

[xschris]

You can find them at the end of a grease fitting. Just go to a hardware store and pick one out then pop it out of the end. Did you replace all the o-rings and seals then sync with a manometer?