help rough running

[jeff6898]

1979 evinrude 85 hp

Replaced all 4 coils, new wires, plugs. Compression 130 all cylinders. Was running great about 5500-6000rpms. Tonight heard a thump and it wouldn't run over 4000 rpm's. It runs rough like its missing.CHecked spark and compression again all the same. Has fresh gas in it.Any ideas?
Also there is 2 holes above just below the engine cover. ONe has a great flow of water coming out of it the other nothing comes out. IS it supposed to come out of both holes?

 

[wildmaninal]

Re: help rough running

Well I broke out my manual under the trouble shooting section when I seen this thread but when you said "Tonight heard a thump and it wouldn't run over 4000 rpm's," I got lost. I have a '78 Evinrude 85hp.

Did this thump come from the lower unit? Or do you know where it came from?

Water should come out both holes I would think, I was worried about mine at one point because I was only getting water out one side until a minute or 2 later it started coming out both.

 

[wildmaninal]

Re: help rough running

Here is a list under the "Loss of power (providing that ignition is OK)" Section out of my manual.

POWER HEAD:
1. Carburetors and timer base not Synchronized.
2. Throttle control lever (won't advace)
3. Air leak at the manifold gaskets - warped manifold (backfires)
4. Broken leaf valves (backfires)
5. Excessive carbon on pistons and cylinder heads
6. Stuck Piston rings, or scored cylinder or piston

Carburetor
1. Old fuel - too much lubricant (dirt in carburetor)
2. Spark advance stop screw loose
3. Choke not operating properly
4. Float valves and seats worn or stuck
5. incorrect carburetor float settings
6. Incorrect orifice plugs
7. Altitude horsepower loss

There is allot more. Could this thump be a backfire?

 

[jeff6898]

Re: help rough running

I'm really not sure where the thump came from I was full speed ahead when I heard it. Guess I need to invest in a manual. I just got this boat about a month ago. IT has been sitting unstarted since last September. I will look into getting the carbs rebuilt and see if that might help.
Thanks for taking the time to look it up and post it. Sure gives me some things to look at.

 

[wildmaninal]

Re: help rough running

I'm really not sure where the thump came from I was full speed ahead when I heard it. Guess I need to invest in a manual. I just got this boat about a month ago. IT has been sitting unstarted since last September. I will look into getting the carbs rebuilt and see if that might help.
Thanks for taking the time to look it up and post it. Sure gives me some things to look at.

Your welcome. I don't know if you noticed when I asked "do you think this was a backfire instead of a thump". If it was a backfire then one of the listings below may explain it right on the money.

Tips on cleaning the carbs from my own experience, soak the carbs in carb cleaner over night then the next day blow them out (each hole) using an air hose with 120psi.

 

[DMAN1968]

Re: help rough running

Hello,

Did you happen to loosen or remove the flywheel recently? Maybe that thump was the flywheel key shearing and throwing the timing off. Just a thought.