Need quick Yamaha 40 info...

[deedledog]

Can anyone tell me the good compression range and the spark plug gap for a 40 HP Yamaha ETLF (Year model is I think 89 or 90)? I am going to try to get a service manual ordered today, but it seems to just need some minor tweaks to get it running right.<br /><br />Thanks.

 

[marquette]

Re: Need quick Yamaha 40 info...

did you ever find out the proper compression because i am looking for the same information for a 1989 40 hp yamaha? could you let me know or post the compression.<br /> thanks

 

[deedledog]

Re: Need quick Yamaha 40 info...

I never got around to ordering the manual, I sort of wanted to make sure I could get this one running smooth before I spent the money. Obviously I never got a reply here. I measured 105, 95, and 105 on mine if that helps at all. I also found a tag under the cowling that gave the spark plug gap at .040". The plugs that were in it didn't appear to have ever been gapped--they ranged from .020" to .030". I cleaned the carbs too but I haven't ran it yet to see if it has improved.

 

[w2much]

Re: Need quick Yamaha 40 info...

My 1986 Yamaha 50, which is essentially the same as the 40 HP has compression of about 100 + per cylinder.I too would like to know what these engines might have been when new or rebuilt.100 does not seem very high to me.

 

[rodbolt]

Re: Need quick Yamaha 40 info...

there is no published spec, usually the 3 cyl yamahas vary some from top to bottom but stay within 10 PSI of each other. if you suspect a cyl sealing problem the only definitive test is a leak down test.<br /> there are occasionally some big differences in the 40 and 50 HP motors. but those are old enough I would have to have the model numbers to try to find them.<br /> the object is to use the service manual to properly tune and adjust the carbs and ign systems to insure correct running.