Help 150 yamaha

[djarrett]

I have 1984 150 ETLN yamaha outboard. When the plugs are pulled out they all look damp, and the top of the pistons look damp(with fuel or oil or both). The insulators have a light tan color and as i understand they should. BUT spark plug #3 always has black soot on it and the top of the piston for it never looks damp. If you pull any of the spark plug wires off while its idling it seems to barely effect the rpms.

Should the plugs look damp or black and sooty? Which way should the piston tops look when you shine the flashlight in there?

Do you think i'm only running on 5 pistons? I have been told its hard to tell if you only lose one.

I have recently rebuilt the fuel pumps and took the carbs off and cleaned them and set the pilot screws back to the specs in the seloc manual. I also decarbed it yesterday with seafoam and thats when i really noticed the one plug looks so different.

Am i going to ruin my powerhead with the #3 piston?

Please help---i don't know how to troubleshoot any further.

 

[JB]

Re: Help 150 yamaha

My first reaction is that it is normal for plug and pistons to look damp after shut-down. The engine doesn't stop turning or pumping fuel instantly when shut off, it just stops firing the ignition.

That #3, however, is a mystery to me. Sounds like a question for rodbolt.

 

[djarrett]

Re: Help 150 yamaha

I borrowed a compression tester from a friend at work. I was kind of disappointed at the results.
#1-100
#2-105
#3-100
#4-103
#5-100
#6-102
Are these numbers to low for this engine? This was on a cold engine, maybe it would be better if i let it warm up?

The motor does have a little cough at idle but it is sporadic. I'm just worried about #3 being drier than the others unless it won't hurt anything. I really don't want to pay for a rebuild right now.

This engine is on a 16.5 foot procraft tournament style bass boat. It will turn 4400 rpm before i start trimming it up. I have only trimmed it up enough while running to get the rpms up to 4900. The speed was pretty hairy as it starts to chine walk at this speed. What i'm getting at is i've never had it at WOT and trimmed up, so i can't tell if the rpms are down if #3 isn't firing.

 

[JB]

Re: Help 150 yamaha

Forget rebuild, djarrett. Your engine is mechanically healthy. Absolute psi numbers are of little importance in 2 strokes. They never get leaky valves like 4 strokes. What matters on a 2 stroke is that the numbers are close for all cylinders. Your engine passes that test very well.

Sounds to me like your engine is also performing well and that you have the outboard version of hypochondria.

I don't think your engine is broke. rodbolt may disagree, and if he does he is the Yammy Man.

 

[djarrett]

Re: Help 150 yamaha

Thanks for your time JB.

Its great to hear that my engine is healthy and the "outboard version of hypochondria" --thats funny. I'm sorry that i'm anal about maintenence but thats just how i am. And its really not that i thought i was due a rebuild now , i was worried the drier hole might be syptoms of some oddity causing #3 to be lean, as i'm not sure what signs to look for if you are.

I also thought people looked for compression numbers higher than those so any time i can learn something i enjoy it.

 

[brodmann]

Re: Help 150 yamaha

I think the tem is Hydrocondriac!!

 

[JB]

Re: Help 150 yamaha

A hypochondriac is a person suffering from hypochondria, Brodman.