Blow back?

Here is what is going on. I measured the shims on the X and ordered replacements before winter hit. Waiting till warmer weather to put things back together. The carbs were tilted up to provide access to the chain tensioner. I finally removed them completely so they wouldn't distort the intake boots during the long winter sleep. When I looked at the butterflies, which were completely normal looking during initial tear down/cleaning, I see what I'll show in the pictures.



Carb #1 above.



Carb #2 above.



Carb #3 above.



Carb #4 above.

You will notice the butterflies in #1 and #3 are now discolored. What would cause this? Maybe a valve not fully closing and hot blow back hitting the butterfly? Funny thing is that there was no measurable clearance at some intake cams at cyl. #2, #3, and #4, but smallest clearance at the cyl. #1 intakes was .06 mm. Ideas?

 

well, if there is no clearance at the intake, (or any) of the cams, then they need to be put in spec, simple as that.
no clearance will end up with burnt valves.
Bigfitz's AIRHEAD VALVE ADJUSTMENT with Pics - parts I & II

 

Waiting on warmer weather to put the new shims in. Was more curious about the discoloration and if anyone else has had it happen.

 

Here is a wild, wild guess......Do you have stock pipes or after market? You may be experiencing reversion which comes as a result of poor scavenging and exhaust gas is blowing back into the intake tract. Could be result of deterioration of the inside of head pipes/mufflers.

Good luck!

 

Nope, everything is stock. Now that I have the rack off again I'll break it and replace throttle shaft seals. I can then also clean up the discoloration so I will have a color baseline for any future removal and inspection.

 

why are the butterfly screws buggered up on #1?
looks to me like someone has taken it apart previously, if that is the case then many possibilities why it might be discolored.

 

I went to church on them previously and some screws were very hard to remove with JIS screwdrivers. The butterflies were all the same color at that time. The discoloration occurred between then and when I tore into the shim work.