Yamaha 30hp 92 compression question

[Backchannelmako]

I am looking at a 1992 30 hp 2 cylinder. I was wondering if 82 and 89 were decent compression numbers or not. Thanks.

 

[JB]

Re: Yamaha 30hp 92 compression question

Howdy, BCM.

Welcome to iboats.

Assuming you used a good gauge and correct procedure, those numbers are acceptable.

You might check your procedure against the one in the Engine FAQs Forum.

 

[Backchannelmako]

Re: Yamaha 30hp 92 compression question

Ok, thank you.mthe person who did the test said it was an old compression guage and that he thought he could hear a leak.

 

[Ldavidgrover]

Re: Yamaha 30hp 92 compression question

Warm the engine first, Use a good gauge and advance the throttle to wide open and retry and you will see the number increase

 

[JB]

Re: Yamaha 30hp 92 compression question

Throttle position will make no measurable difference. That is a myth. At cranking speed the cylinder reaches ambient pressure via the exhaust ports.

Use the procedure explained in the Engine FAQs forum

 

[99yam40]

Re: Yamaha 30hp 92 compression question

Sucking air through a closed throttle will take longer to get up to max pressure in my opinion and experiences, but a lot of my experience came from automotive and not the 2 strokes. But I still think it is better to at least get the throttle off of the closed idle stop

 

[JB]

Re: Yamaha 30hp 92 compression question

That theory has been tested many times by many competent wrenches, 99yam40. No difference has been measured.

I invite you to test your theory.