94 yam 2 stroke 150 carb

[esteym]

Hi,

My engine is pretty much brand new (rebuilt). I finished breaking in the engine about 2 weeks ago. I changed the spark plugs last weekend. Friday it was running great at all rpms. We trolled for 8hrs and then 2 hours of 3600 rpms commute to/from fishing grounds. Sunday my bro takes the boat out and the engine sounds like it is losing a cylinder or 2 at 3400-3600 rpm. 4000 ok, no stutter, putting in and out of harbor is fine (500-700rpm), no major vibration. No alarms.

We have alcohol additive in our gas here so water shouldn't be a problem and I dont think that it would cause it act like that. The plug wires look brand new, but they have oil/grease inside them should i go ahead and replace them? What could be causing this?

Thanks!

Mike

 

[rodbolt]

Re: 94 yam 2 stroke 150 carb

test compression first.
test spark.

 

[whiteman]

Re: 94 yam 2 stroke 150 carb

Never lend your boat or your wife.

 

[rodbolt]

Re: 94 yam 2 stroke 150 carb

fact

 

[Ray Neudecker]

Re: 94 yam 2 stroke 150 carb

It is not unusual for that vintage Yamaha to have a slight stutter at the high 3000 RPM range. The timing is wide open and the fuel is not. if there are no other symptoms of a problem, chances are you don't have one other than loaning out your boat.

 

[esteym]

Re: 94 yam 2 stroke 150 carb

Apparently, it was more than just a stutter, it was more like it would bog down then off to the races. "it would jump forward and I almost lost my balance sometimes". I'll go ahead and get a compression tester and then check the spark.

I hope it is the spark. I took a look at the wires again. They don't seem to want to go on fully, two seem down right loose. I would push them on all the way and they would pop back a bit.

I'll let you know how it goes.

Mike

 

[boatmon345]

Re: 94 yam 2 stroke 150 carb

What happened that lead you to have to rebuild?