one cylinder out but have good spark

Hey everyone,
I have a 1993 115 hp Evinrude outboard, My motor has been dropping a cylinder, it has been going in and out for a while. I put new wires and plugs in her today, and it was running a little better, I ran out into the bay a ran her up to about 4500 rpms ran good for about a mile then the rpms were up and down, and finally lost one cylinder altogether, I checked the spark it has great spark in all cylinders, one of the new plugs was a little dirty I cleaned it and put it back in. has good spark but wont fire, could it be a reed valve? or something else? I not sure where to look next.
Thank You
SwanpFrog

Re: one cylinder out but have good spark

A compression test will probably tell.
If a cross engine, check that spark is not jumping to the cover latch.

Re: one cylinder out but have good spark

A busted reed STAYS busted, it doesn't come and go. Could be crud in the carburetor associated with that cylinder. Or could be getting water into that cylinder. Or could be internal engine damage. Check compression first, to rule that out.

Re: one cylinder out but have good spark

You said you checked spark and it was ok. Did you mean that you checked spark with an inductive timing light when the engine started to drop one cylinder and all 4 plugwires had normal spark? FR has some good recommendations.

Re: one cylinder out but have good spark

I did a compression check and #1 only has 40 lb.plus has a lot of carbon on pistion 1 #3 has 75 2&4 have 95 lb. She starts up and runs good and them the skip starst after a minute or so.
is it possible that the head gasket on starboard side has a leak? Some one told me that if the timing is messed up (and it is) I also could lose compression.
Thinking about pulling the heads off to look at 1&3 cylinder.
SwampFrog

Re: one cylinder out but have good spark

You are on the right track. Pull the head and see why you lost compression on that cylinder. Could be a blown head gasket or could be a blown piston. If it isn't a blown head gasket, the next step is to pull the exhaust covers and bypass port covers for a looksee at the rings.

Timing certainly can affect compression, but it does it by destroying the pistons. If that is what happened here, the pistons are the immediate concern and the timing was the cause of the damage.

Re: one cylinder out but have good spark

#1 piston is all messed up. Shes had it I'm sure. I found an old Evinrude 85hp it runs good but may need some parts here and there, or any of my 1993 115 parts enter changeable? Carbs, the foot or electrical stuff?
Thank You
Swanpfrog

Re: one cylinder out but have good spark

It depends on what year the 85 is. The 78 and older 85 hp engines are small bore 92 cubic inch engines. The 79 and 80 85 hp engines are the same 99.6 cubic inch size as the 1993.
The 73-77 and older mechanical lowers shift backwards from the 1978 and newer models.

Re: one cylinder out but have good spark

I thought long and hard about this question, If the bore size is the same on 1980 Evinrude 85hp and 1993 115hp, what componet of the motor makes the 85hp a 85hp and not a 115hp?
Will my 93 115hp carbs fit the 1980 85hp, mid section and foot? I'm bringing the 1980 85hp home Sat. but someone wants to buy my busted 115,
If 115 parts fit on the 85hp I think i should keep it for awhile or use the parts to beef up the 85hp.
Thank You
SwampFrog

Re: one cylinder out but have good spark

A 1980 block is the same cubic inches at the 1993 block. There are many common parts between these engines. All of your internals should swap ok. (crank and pistons.) Here are the performance differences: The 1993 115 block is a high performance block, with different exhaust and intake porting and the bubble back performance exhaust system-all different from the 85. The 115 uses larger throated carbs that are jetted differently to flow more fuel than the 85. You may get the 85 to run with the 115 carbs, but they may also overfuel-so it is possible you may have to rejet the 115 carbs down somewhat. Helps to know what you are doing when you rejet carbs. You will have to decide which ignition system you plan to use (they are different) and what you plan to do about which fuel pump you want to use- they are also different. Also, the black control boxes for the trim system are different. You may want to consider using the 115 as the surviving engine by replacing the 115 powerhead with the 85 powerhead.

Re: one cylinder out but have good spark

that was very good, and clear, thank you. I understand much more, will the 85hp power head bolt to the 115hp mid section ok, the shift arm and all? because i like the idea you have given me.
Thank you
Swampfrog