Losing a cylinder

[78Randallcraft]

I have a 1978 Evinrude 35hp that I got a few months ago. It was seized when I got it (later to find out it had sunk) but got it freed up and has 95 psi in to cylinder and 93 in bottom. When I crank it it runs fine but a few minutes into ride it losses a cylinder at full throttle. I have to rev it up in neutral to clear it out then it goes for another minute or so and repeats. I know it isn’t the coils I have swapped top to bottom and it is always bottom cylinder. I’m running brand new spark plugs. All I can think it is is the cdi box. If anyone has any advise I would be very thankful for that and appreciate it.

 

[Faztbullet]

Recheck compression...reving it up to clear it is not a CDI issue..

 

[racerone]

Revving a motor in neutral can be an expensive trick.----Inspect fuel pump.-----Test run with another tank and hose.------Perhaps bottom crankshaft seal is bad..----My bet is that there are internal corrosion issues.----Seized motor that sat with water on bearings needs to come apart.

 

[78Randallcraft]

Well it’s not acting lean because the spark plug is always wet when I pull it

 

[78Randallcraft]

Wet with gasoline

 

[racerone]

Find out what is wrong..----There is a reason for loosing the bottom plug / cylinder.----Do some trouble shooting !

 

[kbait]

Swap spark plugs in case you got a bad one out of the box..

 

[kbait]

Also, pull fuel pump mounting bolts, and put the bolts back through pump..pump not mounted to block. Add nuts to those 2 and tighten. Now pump primer bulb. If ant fuel leaks out the pulse port on back of pump, you have a faulty pump diaphragm, and you will flood out the cylinder that it’s drawing pulse from.. Good luck

 

[78Randallcraft]

Ok never would have thought of that thanks a lot

 

[78Randallcraft]

Not the pump I’ll try swapping plugs if I run it today.

 

[78Randallcraft]

Not the spark plugs either

 

[kbait]

Test run with one of those in-line, light-up spark testers (pic). Spark indicator bulb will flash brightly when firing correctly, dim flash or nothing if you have a spark issue. At least narrow it down to fuel or spark. Good luck!

 

[kbait]

Also, check for chafing on signal wires running from under armature plate to CDI box..

 

[78Randallcraft]

Definitely not fuel will check wires and spark. I have used one of those but don’t remember how bright it was. Thanks for the advice.

 

[oldboat1]

Inline tester is too subjective imo, with no offense to kbait. An adjustable open air tester will better tell you if there is acceptable ignition output. You need to see (and hear) a bright snap at something around 1/2 inch, or a bit less. Pull it over with the plugs out if the starter isn't turning it fast (200 rpm or so). If it was dunked, the carb should be cleaned and rebuilt and the starter should be serviced -- both of which you can do yourself.

 

[78Randallcraft]

I’ll try to find a gap testers but I’ve already done a lot to the motor like starter and carb. I’ll probably put new coils new cdi and maybe new stator on soon If I can find decent reasonable prices. Thanks for the advice

 

[racerone]

Not interested in testing the parts first?

 

[78Randallcraft]

Well there are two different coils on there and they both look really rough ones about rusted out cause they both went underwater I think. I’m almost certain the rest of the electronics were on it when it sank.

 

[78Randallcraft]

The cdi has mini barnacles on it

 

[webbd]

Does it run well at any speed, at any operating temperature?

After reading your initial post, I thought "heat soak" in the electronics. I'm not certain of that though.

My 1997 J50spl engine is very timing-sensitive. I need to have the link-and-synch set almost exactly perfect for it to run on both cylinders at all RPMs. Yours doesn't sound like this though from your description. It sounds like either a weak spark, bad gas, compression failure, or poor mixture.

I'm going to start with mechanical.

• You mentioned that it had sank. Do you know if it was hot or cold when it was submerged?
• Have you tested compression while hot?
• Also do you know if it was completely submerged or only the lower cylinder?
• I had a car with a compression leak on one cylinder that was impossible to manage until I replaced the head gaskets.
• Are all the head bolts correctly torqued? Would it be worthwhile to pop the head off and take a look, then replace the head gasket for good measure?
• What condition is the reed valve in?

Ignition:

• If you have an inductive timing light, you would normally time the engine off the top cylinder. This is a good idea to check the timing either way, and make sure all the rollers have their clear vinyl coatings because the timing synch mechanism doesn't work right without correct roller diameters (at least on my '97 motor).
• Again, with the inductive timing light, do you get signal after the bottom cylinder drops out? If yes, and if you get a hot spark, then it's probably not ignition. If no, then you might have a latent failure in one of your electronic components (CDI or coils). You mentioned that the coils are good, but if they're old, they could still be suspect. In either case, a poor connection will heat up and exponentially increase resistance until you can't flow enough electirity to generate spark. It might be worthwhile to run all the tests with electronics hot and cold.

Carburetion:

• Doesn't sound like it, but if the lower carb is tuned to compensate for a clogged passage, you might expect to see a fouled plug.

- DW