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Mariner 25 WOT problem

S

shaunkee

New member
Hi - first post & 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's lean condition. Pumping the carb primer at WOT makes no difference.

Once the motor has been run hard for 30 mins it can then be opened up wide without any bogging.

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

I've replaced the diaphragm in the fuel pump, replaced a perfectly clean highspeed jet and replaced the mixing chamber gasket as the manual suggested with no change.

I'm starting to think about the coils or magneto. A buddy suggested I consider the crank seals, but tearing apart the power head would be last resort.


I’d appreciate any comments / suggestions

Shaun
 
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you can do a leak down test to see if you have a seals problem, or as your running the motor, spray carb cleaner on the seal and see if the rpms increase, if so you got a seal problem. I think you are saying the motor bogs down at WOT, but after 30 mins the problem goes away,I have never seen an ign problem clear itself up unless it was grounding itself out and then got moved and was no longer grounding itself out, have you adjusted the carbs? if so what are they set at?
 
Thanks for your response

A leak down test isn’t discussed in the manual. Do I use a compression gauge ? I’m not sure how to pressurize the crank area and measure the drop.

As to the low speed jet, I followed the instructions –pretty straight forward. I didn’t think the low speed jet would affect the WOT mixture. I replaced the high speed jet with the correct size 080 according to the dealer and the chart in the manual. The timing and synchronization was done step by step.

Your point about an ignition problem going away makes sense. I’m not sure what to look for with a bad magneto / stator
 
do a google search for leak down test,
need to do DVA and Ohms check on your motor.
did you try the carb spray? (i don't think it's a leak but who knows)
 

Thanks for theDVA suggestion. There is no mention of it in the factory manual - stupid omission.
I will definitelytry spraying carb cleaner around the crank seals.
Thanks againfor your suggestions.
 
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 ¾ 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 to everyone who responded.
 
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