Motorcycle Repair: 1978 Yamaha XS750 Compression Pressure, eamil address, compression pressure

Question
Hi Mark:  I have a 78 Yamaha XS750 3 cylinder that pops from one of the pipes when you start it up.  I found the RH cylinder (sitting on the bike) was not firing at idle.  As the engine revved up the cylinder started firing (Pipe got hot).  I removed the carbs and did a thorough cleaning.  (I didnt remove the diaphrams for the slides).  Reassembled and it starts and runs on all cyls.  Went to syncronize the carbs and the RH cylinder has real low vacuum.(5 in of mercury)  (That is the carb the other two must be synced to).  The other carbs (center and left) will snyc exactly to each other at about 25 inches of mercury. The RH carb dosnt make any difference where the pilot screw is set.  While I had the plugs out the left cylinder and center cylinder had 125 PSI compression.  The RH cylinder had 160. Yamaha does not give a PSI number for compression.  Such a spread dont sound right.     Any help will be appreciated  Thanks in advance.  Dan

Answer
Hi Dan,

I return tech files by email. There was no eamil address with your question as requested and explained in my instructions.

Include your email addy with your reply. We'll go from there. The tech files will help you troubleshoot and repair the problems.

By chance are you in or near Louisville, KY? Dan Cook Sr. or Jr.? FOP member?

Respectfully,
Mark Shively
Dayton, Ohio