86 25-ESJ Yamaha low rpm/ low power.

[cheesehead4]

I'm new to this group and have enjoyed your forums. I've now come across something I'm having trouble fixing/troubleshooting. Please help.
Here goes. 86 25-ESJ Yamaha. Main trouble. Engine has great hole shot but will not come up to speed. Compression is very close to 120 in both cylinders. Carb has been cleaned and set. (It was VERY clean. Engine/fuel is well maintained.) New spark plugs. Fuel bulb is firm and squeezing it has no effect on the running engine. Tank vent is open and clear. Fuel filter and lines are clean and open.
It's seems to be maybe electrical in nature like timing is not advancing. Just opening the throttle to WO with out advancing the ign. gives me obvious low performance but allowing timing advancement seems to not help alot either. The timing ring does move to the stop position at WO throttle. It comes up to about a mid speed then just settles in there. It's running smooth......It just will not speed up. Any help will be appreciated. Thank You.

 

[cheesehead4]

Re: 86 25-ESJ Yamaha low rpm/ low power.

Was talking to another Yamaha guy today and he said it might have an over temp. sensor bad. Does this engine have that sort of creature? Will it allow engine to idle fine? have a good hole shot? and limit top rpm?

 

[cheesehead4]

Re: 86 25-ESJ Yamaha low rpm/ low power.

Ok....Just tried something. Was told to check if it overheats. It's just the opposite. It never gets warm. The most you see if ran hard is maybe 115 to 123. Where is the thermostat on these?

 

[cheesehead4]

Re: 86 25-ESJ Yamaha low rpm/ low power.

Note to myself........... Found thermostat. It was stuck open.. Cleaned out debris and allowed it to close. Will not close completely. I wonder if this is normal to remain slightly open. Ran engine in large trash can for extended time. Water flow was alot better then before but it still will not come up to temperature. Put my 25 johnson in the same tank and within several seconds it was coming up to temp. Should the two act the same as far as coming up to temp? I'll write myself a follow up tomorrow. Goodnight me.

 

[Ray Neudecker]

Re: 86 25-ESJ Yamaha low rpm/ low power.

It has to close completly to work properly.

 

[cheesehead4]

Re: 86 25-ESJ Yamaha low rpm/ low power.

Ordered thermostat today. Is there a temp. sensor on this engine. If so where is it? What color wires go to it? I can't find anything that looks like a sending unit screwed into the block.

 

[cheesehead4]

Re: 86 25-ESJ Yamaha low rpm/ low power.

Ordered thermostat today. Is there a temp. sensor on this engine? If so where is it? What color wires go to it? I can't find anything that looks like a sending unit screwed into the block.