2004 yamaha 150 four stroke backfires

[joerc2002]

motor has always ran super with no problems
now when i hit the key it drags slow and when it his it backfires loud
had it out on the water 2 days ago when it got hot and started loosing rpm's
so i shut it off and broiught it home
after it cooled down was when i noticed the back fire when cranking
any ideas????????????????????

 

[99yam40]

Re: 2004 yamaha 150 four stroke backfires

so it overheated and you alarm system came in reducing RPMs to about 2K?
And now it is binding up and backfiring?

Leak down test should show if cylinders are sealing properly and if valves or rings are a problem.

Checking spark and timing

4 strokes have a timing belt that can jump

 

[joerc2002]

Re: 2004 yamaha 150 four stroke backfires

if timing belt jumps canit do damage to valves????