25 Hp Mariner WOT issue

[shaunknee]

Hi

Looking for a bit of advice..

Motor is a '89 Mariner with a WBC carb. Runs great until WOT, where the power definitely drops off without any noticeable detonation. I've always assumed it is lean condition. Pulling choke at WOT makes no difference.

Once the motor has been run hard for 30 mins it can then be opened up wide.

Have manual, link and synch done to the letter, new fuel, new plug, cleaned filter / separator.

I'm going to try replacing the diaphragm in the fuel pump next.

Open to other suggestions

Thanks

 

[Laddies]

Re: 25 Hp Mariner WOT issue

That's not a choke, it's a primer so it won't help with a lean hi speed condition. You would have to remove the cowl and air silencer and choke it with your thumb but it sounds like a dirty high speed jet.

 

[shaunknee]

Re: 25 Hp Mariner WOT issue

That's not a choke, it's a primer so it won't help with a lean hi speed condition. You would have to remove the cowl and air silencer and choke it with your thumb but it sounds like a dirty high speed jet.

Very good point ? I never considered that there wasn?t a choke butterfly.
I?ve got a high speed jet on order. I?d like to disassemble as little as possible to avoid additional problems so I?ll try a new jet first.

I?m thinking that pumping the primer while it hesitates at WOT should confirm a dirty high speed jet.

Thanks for your response

 

[shaunknee]

Re: 25 Hp Mariner WOT issue

Well I replaced a shinny & clean high speed jet today without any change in the motor?s behavior.
Still hesitation at WOT for the first 15 minutes. I?ll try the fuel pump diaphragm next.
A friend of mine suggested that it could be the crank seal that becomes more supple when it warms up and leaking air when it?s cold.
I?m always open to suggestions.

 

[shaunknee]

Re: 25 Hp Mariner WOT issue **solved**

Re: 25 Hp Mariner WOT issue **solved**

I hate reading through threads just to have them end without a conclusion.
I picked up 4 used but much newer coils and wires on ebay because my original magnets were clearly broken. I changed the coils and wires, took the motor out and no change. Full bog between ? and wot.
I also purchased an aftermarket switch in case the capacitor had reached the end of it service life after 22 years. I?m assuming they are electrolytic.

It?s like a young motor again. Screams right out of the hole full throttle.

It was a good learning experience. I was amazed how easy it was to rebuild the carb.

Thanks Laddies for your response.