plug fouling 90hp Yam 2 stroke

[Bud_man]

Hi All,

I've got a plug fouling problem on my 2000 Yamaha 90 hp 2-stroke that's creating some terrible idle at times. I've cleaned the carbs, the float height is at spec, and the pilot screw is at the recommended 1-1/4 turns out (6H107 stamp). I can't hear an RPM change to fine tune the pilot screw.

Below is a link to some photos of the plugs. The plug on the left is from the top cylinder (#1) on down. #1 seems light the culprit, right? Or is #2 and 3 too wet and clean?

http://bellsouthpwp.net/b/u/budhoward/boat/plugs.htm

Any thoughts are greatly appreciated.

Thanks,
Bud

 

[BruceAML]

Re: plug fouling 90hp Yam 2 stroke

What make and number spark plug, what gap and did you torque the spark plugs? Also you need to give us the complete model number from the data plate.

 

[Bud_man]

Re: plug fouling 90hp Yam 2 stroke

Thanks for the reply...

I can't look at my notes now, so this is from memory... pretty confident it's the correct info:

1. Plug is NGK B8HS-10 or BRHS-10
2. Gap is from Yamaha service manual (0.039 comes to mind; NGK seems to ship this plug at proper gap - I always check though)
3. Torque plug to spec (18 ftlb)
4. Model is C90TLRY

Thanks again,
Bud

 

[mikesea]

Re: plug fouling 90hp Yam 2 stroke

Id bet your oil injection pump is going,they over oil as they wear

 

[Bud_man]

Re: plug fouling 90hp Yam 2 stroke

No oil injection - this one is premix. And I've been spending the extra money on Yamalube. Strange...

Probably a simple weekend-warrior-rookie-shade-tree-wanna-be-outboard-mechanic mistake on my part.

Thanks for the suggestion.

Bud

 

[BruceAML]

Re: plug fouling 90hp Yam 2 stroke

The correct spark plug is an NGK B8HS-10. You have the gap set correctly. I would get some Yamaha Ring-Free additive. That should clean out the deposits. Do you have the correct thermostat, pressure valve, compression spring and grommet? They are all located under the thermostat cover. If the motor is not running at the correct temperature you can have spark plug fouling. What oil/gas ratio are you using? Did you use a Yamaha carburetor repair kit?
6H1-W0093-10-00 is the correct carburetor repair kit.

 

[Bud_man]

Re: plug fouling 90hp Yam 2 stroke

Thanks for your reply.

It's been a few years since I've replaced the thermostat so I'll swap that out and replace the associated parts you described.

I simply cleaned and inspected the carbs and didn't replace any parts - I'll go ahead and get the carb kit too.

I'm running 50:1 mix as indicated by the manual.

Thanks again.

All the best,
Bud