Rough running 20 hp Evinrude

piscesplaypen · Sep 17, 2003

I own a 1984 20hp manual start Evinrude. The motor was purchased on ebay and was a rough running motor from the start. I've had the complete fuel system redone carb rebuild, fuel pump replaced and all hoses replaced. The kill switch in the tiller had a high resistance short and we replaced it with a new switch mounted on the motor like the earlier model motors. The motor has a problem at medium rpm and trolling speed in that it will intermittently cough or sputter. Adjusting the carburator a little rich helps but the motor is still rough and idles worse at the richer setting. It runs fine when opened up to full throttle. The mechanic who redid the fuel system says that either the carb is still not working correctly after rebuild or there is an inherent problem in the 20 hp configuration of this motor and I should consider changing the intake and carb to a 25 or 35 hp configuration to solve the problem. I'm wondering also if I might have a power pack malfunctioning at a certain rpm.....?? What do you suggest? Does the 20hp foot print for this generation motor have carburation problems more so then the larger configurations? This motor has excellent compression and a spark gap test showed spark on both cylinders although one cylinder appeared to have s lightly weaker spark while hand cranking the engine. I would expect after the fuel system rebuild that most fuel related issues would be eliminated. What do I do next??

alcan · Sep 17, 2003

Re: Rough running 20 hp Evinrude

Hi George I just repaired an older model 20hp last week that had some what the same symtoms. I found the problem to be a leaking crankshaft seal. It sure wouldn't hurt to check both top and bottom. Also check linkage syncronizing. Double check fuel system for air leaks and make sure the carb was put back together correctly. I know this is hard to believe, but I have been distracted and forgotten to tighten screws before or just plain screwed up.

piscesplaypen · Sep 17, 2003

Re: Rough running 20 hp Evinrude

Thanks Al, I will check on what you suggested. How did you find a leaking crankshaft seal?? What should I look for? The motor is extremely clean under the cover and I haven't noticed any obvious oil or residue anywhere. The carb and fuel system was rebuilt by a professional mechanic who specializes in OMC two and three cylinder older outboards, but that's not to say the carb jets could still have blockage problems after the dip treatment. I think he dipped the carb for three days before reassembly. All the hoses were replaced and have all new tie wraps around. Thanks for your response.....GeorgeN

ByteWalker · Sep 18, 2003

Re: Rough running 20 hp Evinrude

George, Does your motor have high and low speed needle valve adjustments? I have a 30HP 1956 RJE-18 Johnson and your problem sounds like what I ran into. If you have those adjustments, read the thread currently by me about "1956 Johnson RJE-18 30HP Carb Info Needed". Turns out it's probably a problem with the low speed needle valve.

piscesplaypen · Sep 18, 2003

Re: Rough running 20 hp Evinrude

Bytewalker, No this is a 1984 model Evinrude. The only adjustment on the carburator is the mixture screw on the front of the carb. There is no other adjustment not even an idle screw. The low speed circuit consists of fixed jets in the carburator. There is a transition between those jets at low speed and the max fuel circuit for high speed. The carburator has been professionally rebuilt but the engine still has the coughing symptom somewhere in the transition area while under load. Engine runs great in high speed mode. I'm stumped at this point. The entire fuel system from the gas tank thru the fuel pump, the carb and all the hoses have been replaced. I'm wondering if something else is going on here?? Thanks for you response, GeorgeN

Solittle · Sep 18, 2003

Re: Rough running 20 hp Evinrude

Your symptoms point to: http://www.outboardrepairs.com/carburetors/

piscesplaypen · Sep 18, 2003

Re: Rough running 20 hp Evinrude

I've looked in that section and found nothing specific to my symptoms given what I have already done about this problem.......I really need some fresh ideas as to what else could be causing my symptoms.....they point to fuel, but everything in the fuel system has been addressed. The engine coughing occurs at an above idle mid range rpm and improves slightly with a richer setting on the carb, but if the carb is set according to the standard setting procedure the coughing occurs. I have to solve this because the speed at which this happens is the speed I use while searching with my fish finder or several trolling applications Please someone out there must have had this problem with this generation Evinrude 20 hp motor.....Thanks for your responses so far

G DANE · Sep 18, 2003

Re: Rough running 20 hp Evinrude

Hi George. Own one now, and had 2 of the 25 - 35HP 1981 - 88 twins. They are very good motors. I had the same problem on a 35HP, and my brotherinlaw similar on a 1973 25HP. On mine, it was caused by too rich iddle misture, letting the motor 4stroke when running just above iddle, after iddling, it would not appear when going from wot down to above iddle. Is yours like that. ? Soaking a carb isnt always enough, sometimes it is neccesary too to run a little piece of wire up thru iddle and intermediate openings above throttle butterfly. Another problem I had, is airleak around low speed adjust screw. Replace the grommet to the new red type and VERY carefully do the sync´n linc procedure in manual, clean carb the way I said and do a carefull lowspeed adjustment with boat moving in water. Oh I forgot: on my brother in laws, it was the manifold bolts ( assy behind carb ) that had come loose. Try and post again. Once OK, this motor will run for ages.

piscesplaypen · Sep 19, 2003

Re: Rough running 20 hp Evinrude

Thanks G Dane, I'll try and check out what you suggest. I was told that it is vry hard to get to the jets witha piece of wire???? Also how did you detect the air leak around the low speed mixture screw? I had this carb rebuilt professionally and I would assume the grommet was replaced. I know for sure that the guy who rebuilt the carb did not clean out the jets with wire. Maybe I should just replace the carb with a new one...expensive fix, but if it works I would be happy. I have to have this motor smooth for trolling. Thanks, GeorgeN

G DANE · Sep 20, 2003

Re: Rough running 20 hp Evinrude

I have never, ever experienced need for a carb change. Unscrew carb from motor. Look in the carb throat from motor side. Rip a hair from a steel brush. Hold the hair with a thin, long plier and run it carefully thru the 3 or 4 small holes just above throttle butterfly. After that remove gaskets, floater needle valve and gasket and low speed adjustment screw + grommet from carb. Turn carb upsidedown and submerge in cleaning solvent. Next morning blow thru with compressed air, especially thru threaded hole where low speed adjust needle goes. Assemble carb. Change grommet around low speed needle, if not new red type. Test needle valve function ( blow thru gas hose, turning carb upside down. Screw lowspeed needle in, seat gently. Reverse 1 3/4 turns, thats initial setting. Adjust low speed mixture with motor in gear, boat moving in water - described by Joe Reeves.

piscesplaypen · Sep 20, 2003

Re: Rough running 20 hp Evinrude

G Dane, Thanks so much for these tips I will try what you say and respond back to you as soon as I get this done and tested. Your help is greatly appreciated as we are sooooo frustrated with this engine right now......Thanks GeorgeN

alcan · Sep 20, 2003

Re: Rough running 20 hp Evinrude

Hi George I understand your frustration. These things usually turn out to be something very very simple. When this happens to me, I start over from step one. Take nothing for granted, don't assume anything. First check compression, or recheck. Then rule out the ignition system. When that proves good procede to the fuel system. inspect everything from the tank to the carb. Check your link and sync adjustment. Check all wires and grounds. After you have made double sure all of the above is in order. Test your crankshaft seals using soapy water our oil. also check for carbon build-up in the exhaust.

piscesplaypen · Sep 20, 2003

Re: Rough running 20 hp Evinrude

Thanks Alcan, I'm really trying to be methodical and logical trying not to miss the slightest detail, but all things and almost everyone points to the fuel system. I will take your suggestions and try to be patient until we get this right. Will keep you posted Thanks GeorgeN

ezeke · Sep 21, 2003

Re: Rough running 20 hp Evinrude

Just a thought, but you could still be running too lean. If you choke it very slightly while running, and it smooths out and accelerates, you will at least have narrowed down the problem some. Wondered also if you have checked the plug wires. What spark plugs are you using?

piscesplaypen · Sep 22, 2003

Re: Rough running 20 hp Evinrude

ezeke, That's another part of the mystery.....my plugs are always wet when I check them whether I have the engine set lean or rich. I'm running the plugs the engine calls for Champion L77JC4(s) gapped at .030 WE put new plugs in last night and ran the motor on the garden hose and played with things for about 30 minutes. When the plugs were removed they were both wet. I beginning to think maybe we may have a weak spark. I measured the plug wires with a multimeter and both measured good continuity. We are thinking of changing the power pack to illiminate the possiblity that it may be flakey. If not we'll have a spare which really isn't a bad thing. I guess it could still be the carb but the dang thing adjusts and I have held my finger over the throat to choke it a little and the motor still has the problem sooooooo??? the beat goes on. Thanks for you input, GeorgeN

piscesplaypen · Sep 23, 2003

Re: Rough running 20 hp Evinrude

FYI for all my help, FYI I also just noticed this morning that my link/sync adjustment looks slightly off. There are two little marks on the ignition cam about 1/4" apart. The book I have for my motor calls for the cam follower for the carburetor linkage to contact the cam midway between the two marks. At this time my cam follower is contacting the cam to the left of the two marks about 1/4". Looking at the front of the engine: *|| instead of |*| The asterisk being the point of cam contact. This appears to mean that the carburetor linkage is not moving soon enough at the low end speed. Could this be causing my symptoms? I would assume that would have somewthing to do with spark and fuel working together at lower rpms and perhaps cause the engine to run rough?? In this case perhaps trying to rich up the carburetor to fix the problem might cause the plugs to run a little wet?? Can someone please comment on this for me.....I'm really to much of a novice to know for sure. Thanks, GeorgeN >*)))><

G DANE · Sep 23, 2003

Re: Rough running 20 hp Evinrude

Hi again GeorgeN It is essential to get a good combustion that the timing sync is correct. You have to adjust so the throttle butterfly starts to open exactly in the middle of the two marks. There is a screw at the end of the axel. Loosen it a bit and you can move the outher bracket to make the throttle open earlier. On some, there is a little bracket on arm, making it possible to extend or shorten arm instead. Check several times to be sure throttle opens exaxtly where it should. Look at throttle axel while moving timer base. If it opens too early, it will sneeze and cough. It it opens too late it will run rough. If your plugs are always wet, apart from cold iddle where they usually are, you might have a leaking needle valve. Was a rebuild kit installed when the carb was cleaned ? - very little cost, 10 $ I would always do that. Instead of changing powerpack, make sparks jump some kind of gap, i.exa put a big nail in plug wire and make somebody pull rope, while you hold hold nail 7/16" from ground with a dry clouth. If they both jump strong, leave ignition out.

piscesplaypen · Sep 23, 2003

Re: Rough running 20 hp Evinrude

G Dane, Thanks for your response. I have already corrected the link/sync by adjustment, but have not tested motor yet. Yes the carb kit was installed but the mechanic admitted that perhaps the three day dip he did to clean the carb was not enough and suggested we try one more time to soak the carb for a week to ten days. I will try and build a 7/16" gap tester or use a nail as you suggest. I have been all over this motor check for any possible air leaks as well and have not found anything obvious. I will not give up until we all fix this problem. I will keep you posted from here........Thanks Again, GeorgeN >*)))><

G DANE · Sep 24, 2003

Re: Rough running 20 hp Evinrude

GeorgeN Usually soaking overnight is enough. I normally run a little wire through the lowspeed and intermediate orifices too. Then everything is usually OK. As your plugs look wet, I think correcting timing and carefully adjusting lowspeed mixture will cure your problem.

piscesplaypen · Sep 24, 2003

Re: Rough running 20 hp Evinrude

G Dane, Thanks again I will give you an update as soon as I run the motor again after the link/sync correction. GeorgeN >*)))><

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