Yamaha c75tlrs, 1994

[DAVECAD2.0]

1994 75 hp 2 cycle.
Could someone tell me what the fuel pressure and cylinder pressure should be?
Did a compression test but don't know the base line.
Top = 80 psi
Middle = 90 psi
Bottom - 100 psi.

Thanks, Dave.

[robert graham]

The compression readings should be ideally within 10% of each other but the tests can tend to vary with methods, equipment, etc....so you may want to run them again to double-check your readings...

[99yam40]

20PSI is too much difference in my opinion.
shock treat with ringfree or seafoam to see if rings are stuck with carbon

Might try a different gauge just to be sure you get the same readings

[DAVECAD2.0]

Yes, I know. Need to know pressures.
Is it safe to run Seafoam in two cycle? Will it not "wipe" the cylinders?

[99yam40]

There are no specs for compression on those motors
I usually see a little higher than what you posted on 2 strokes, but it could be the gauge you used and some motors may run higher compression by design.
Fuel pressure to carbs is usually around 4 or 5 psi I think

Sea foam can be used on 2 strokes. do a search on the web for shock treatment with seafoam

[DAVECAD2.0]

Thank you.
I just disassembled the intake and exhaust heads looking for the cause of my over heating issue. Found excessive calcium scale on the exhaust side blocking water flow. The intake was clean. There was also a lot of carbon deposits on the exhaust side. On the intake the only carbon was on the piston tops. About fifty percent on each. This after flushing twice for an hour with a strong solution of Muriatic acid. Part #50 (Exhaust outer cover) was fifty percent blocked. Part #47 (Exhaust inner cover) about the same. Exhaust side of the block about 30 percent coated and some sludge like gunk. I mechanically removed all the carbon deposits as flushing has nothing to do with that issue. I'm thinking stuck rings as the engine has low hours. I'll try the Seafoam.

[rodbolt17]

be aware that there are no specs and quite a bit of the old 3cyl motors were designed with varying compression.
got bit on one just like you may about 25 yrs ago.

do a leakdown test.

[bajakeith]

compression

And if your gauge is from harbor freight or a china POS you would also get those numbers....Don't Assume a compression gauge always good....I HAVE TO REPLACE MINE EACH SEASON''OOPS damn caps