15hp Evinrude won't reach max RPMs

[AlTn]

Re: 15hp Evinrude won't reach max RPMs

wot drop to idle and it wants to die points towards a loss in crankcase pressure...try this sequence, wot, quick drop to idle, quick snap to 1/2 throttle....if the engine won't recover and dies this points towards leaking or loss of crankcase pressure in 2 strokes < this assumes the ignition and fuel delivery are ruled out >...causes?...crank seals, crankcase halves seam leaking, worn piston to cylinder tolerances, loss somewhere else.
A fishing buddy and I used to run ~18 mph. in a 14' aluminum monark semi v <total weight gear and all ~400lbs> with a 1978 9.9 hp....weight distribution is important as well
If you decide to replace the seals Leeroy's articles should help you pull the powerhead and seals...best of luck

 

[racerone]

Re: 15hp Evinrude won't reach max RPMs

A test prop is listed on Flea-Bay right now part # 386537------$55.00-----try searching for test props there.

 

[Humperdink]

Re: 15hp Evinrude won't reach max RPMs

I agree, eliminate fuel and spark and then go for seals.

 

[gabebp]

Re: 15hp Evinrude won't reach max RPMs

Thanks all. There's some real knowledge on this forum!

Another thing I didn't mention, this motor starts like a champ if I only use the choke once. It consistently starts on the first or second pull if I choke it then immediately push the choke in after it starts otherwise it sputters and dies in seconds. Not sure that helps diagnose... It also starts immediately after it's warm without any choke and without multiple pulls.

Ater I get parts, I'll put it back together after I put on the rebuilt carb, new fuel lines, fuel pump and readjust the throttle timing/cam follower screw. Then I'll see if I need to replace the seals based on performance. $ for test prop may be better spent toward seals since it sounds like I have an engine problem if things are still at just north of 5k rpm. I hope there's something to do do with the fuel pump or perhaps I knocked something loose from the carb even though it appeared clean. I don't relish the idea of tearing it all apart again and buying a seal kit.

The seals seem like a pretty involved operation compared to the simple carb rebuild. Looking at LeeRoy's page, I need to figure out how to pull the flywheel, and come at the seals from the powerhead side. If I come from the intake side, there's two bolts that are really hard to get at on the bottom (minimal clearance), plus there's clearance issues between the throttle plate (cam area) and the intake housing. Sound the power head side is the best approach if I opt to take the plunge and replace the seals and possibly leafs? Or did I misunderstand LeeRoy?

Anyone ever done the seals on a 79 era OMC 15?

 

[AlTn]

Re: 15hp Evinrude won't reach max RPMs

pulling the powerhead is a necessity to get to the lower seal...depending on what you decide I'd suggest you just buy a gasket set as it'll include the powerhead to exhaust housing gasket which you'll need anyway as well as the exhaust cover gaskets, intake gasket, etc. and just do them while the powerhead is off < much easier to get to > but it's your money,huh?
Also, if you remove the powerhead, you'll be able to inspect/replace the upper water tube grommet which is known to be a problem child causing some overheat problems.

 

[gabebp]

Re: 15hp Evinrude won't reach max RPMs

I was looking for any visible signs of blown upper seal (oil/fuel stains) and didn't see any but I ended up spinning the flywheel. I noticed the cam plate will move a bit when I spin the flywheel. It seems to happen more at mid-throttle on the twist grip. I can sometimes get the plate to rotate a significant amount with the flywheel. At idle and WOT it doesn't seem to move when I turn the flywheel. Any movement in the cam plate/link assembly resulting from flywheel movement doesn't seem right. Right? What could that mean?

 

[racerone]

Re: 15hp Evinrude won't reach max RPMs

Well, the flywheel does have some strong magnets that might be pulling on something ??

 

[gabebp]

Re: 15hp Evinrude won't reach max RPMs

Think you're right. Idle and WOT throttle settings position the cam arm in a way that make it easier to move. Sometimes it moves in the opposite direction, so the mystery of magnetism may be at work. Sounds normal if that's what going on.

Parts should be here next week, so I'll post an update when I get it back together.

Have a good weekend everyone.

 

[gabebp]

Re: 15hp Evinrude won't reach max RPMs

UPDATE:

I put it all back together and it didn't make a notable difference at WOT. The engine runs very good though. I got the idle fine-tuned and can go from idle to full throttle to half throttle to full throttle and back to idle again and the response is instant without hesitation.

I placed a business card in front of the carb before I put the airbox back and at idle and at mid-throttle (neutral in water tank) the card "sucks" toward to carb and vibrates just like LeeRoy mentioned it should. There was no gas spitting back at idle or at mid throttle.

I did a drop test on the plugs and it definitely makes a difference when I pull each plug.

I did a test at idle with a propane torch around the intake to see if the idle change and it didn't.

I've come to the conclusion my boat is heavier than I thought for an aluminum boat. I tested the boat with a newer 20 hp motor and I had it up to 23 mph max compared to 16 max in the old evinrude.

Thanks all for the advice. Let me know if you have any closing remarks.

 

[Bosunsmate]

Re: 15hp Evinrude won't reach max RPMs

Yep ive got one,
Whats the propane torch around the intake at idle for?
I havent heard that one ever before

 

[gabebp]

Re: 15hp Evinrude won't reach max RPMs

Unlit torch to see if idle steps up when propane gets sucked in through leaky intake gasket. Propane and WD-40 were mentioned in LeeRoy's Ramblings

 

[gabebp]

Re: 15hp Evinrude won't reach max RPMs

Maintaining Johnson 9.9 Troubleshooting