[EvinrudeBill]

I'm stumped and need some help here guys..... over 30 days and counting.

On the hose(muffs) it starts and runs great all day.... but idles very high (2400 rpm). When in the water it starts very hard, idles very poorly at best, and does not take acceleration very well. Boogs down and quits 50% of the time. (reverse is the worst) Quits evertime. Seems as if the motor loads up. On mid and top end, if you can get it there, it runs out perfect all day. Basically it's not happy with back pressure..... and idles high out of water. Also, the motor does not sound right..... its sounds raspy out of water and muffiled and restricted in the water.

O.K. here's what I've done so far. Complete carb. rebuilds with OMC carb. kits and cleaning. I found nothing. Next, I checked all hose and connections. Again nothing. Did the link and sync according to the service manuel and checked the timing. All good to go. Next, I found another 87 120 that runs good. Compared linkage and timing between both motors and found everything is up to par with my motor. Compression tested 124-126 psi on all 4 cylinders. For a goof, I pulled the heads. Cylinders look great and exhaust ports are clean as a whistle. Again nothing out of wak here. Installed new head gaskets, thermostats and thremostat diaphrams. Next, I pulled the intake manifold off to check out the reeds. Yup... you guessed it looks like it came off the assembly line. The VRO pump was replaced two yrs. ago... so I can't hardly believe my problem lies here. I have fresh gas in the tank and am using Merc QuicSilver TCW-3 oil.

Not that it matters but this motor has very low hours and it has never seen salt.. fresh water only.

I'm thinking bad crank seal next..????? What do you guys think??

Any help here would be greatly appreciated! : )

Thanks!!!! Bill

[Daviet]

A couple of things to ponder, you did not say anything about checking spark. On muffs at that high of an idle it could run on two cylinders. Try pulling one plug wire at a time and see if all cylinders are firing. Squirt fuel mixture into carbs and see if it makes a difference. If a motor is not firing correctly and you put it in the water, because of backpressure,it will crapout on you. What is causing the high idle? Air leak? Try spraying carb cleaner around carb bases and manifold to check for air leak. AS last resort, quit using mercury oil,haha.

[jonesg]

Agree with above, its not firing on all holes.
If you have a timing light that will show the problem, try swapping coils with the bad one and see if the problem follows the dead coil.

An auto part store will sell you a $10 spark GAP tester, thats the best way to see spark strength, it should be set to 7/16th inch gap and spark should jump with a bright blue snap.

I suspect you'll find a dud coil or two.