valves won't seal...ideas?

so i just picked up a well-used '87 honda xl600r
I have cleaned the carbs, but it will not start.
It will pop every 5-6 kicks though.
If I open up the throttle, then it will push air back through the carbs.
I am fairly certain the valves are not sealing due to it having sat for a good long time.
The previous owner said it would start with starter fluid but then die...but that was a year ago.

Anyone have any tricks to help them seal? Like, could putting oil/pb blast or anything like that help clean the valve seat? I have worked on smaller OHV engines but nothing as big as this beast and it also says it has RFVC...radial valve. I don't know how that differs from other OHV engines I have worked on (briggs, gy6 and other small engines)
 

SRAD97750

Moderator
Staff member
Howdy!
Anyone have any tricks to help them seal?
I would check the valve clearance first. Then decide if the engine need a valve job.
If there is a lack of compression, as read by a leakdown tester, then only a valve or ring job will fix the issue.
Start with clean carbs and valves in spec. -BIG DAN:thumb:
 
Remove valve covers and rotate engine . check to see if lifters and valves move . . Free stuck valves with PB Blaster . Then check valve clearance . And of course clean carbs ....
 
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