Johnson 9hp problem

capitan · Mar 7, 2009

I have just bought a non running Johnson 9hp 1979 and had 50psi in one cylinder and 65psi in the other, i could only eventually get it started and running on full throttle, renewed the head gasket as it was knackered between the bores and then i had 90psi in the top and still 50psi in the bottom piston. After a few attempts of running it, i tested the compression and the 90psi piston had dropped to 50psi matching the other piston. I have now given up trying to start it. Can anyone shed any light? I have spark and i must have fuel for it to run on full throttle, i know it has been stood for ages.

tashasdaddy · Mar 7, 2009

Re: Johnson 9hp problem

i think what i would do it tilt it up. put some marvel mystery oil the the cylinders, let is sit a couple of days. then drain it. i would try to get it started, and do a decarb on it. this cleans the built up carbon out of the innards, frees up rings.

Decarb, take a can of seafoam put 3/4 of it in the gas tank, with only 1 gallon of premixed gas. put the rest in a spray bottle. start the engine, and let it come up to temperature. then remove plugs, and them some real good shot of seafoam into the cylinders, replace plugs, let sit 15 minutes. restart, and spray the rest of the seafoam into the carbs, so the the motor almost stalls, wait and repeat until the seafoam is gone.then take for a wide open spin. then put in new plugs, ad premixed gas to the tank, and take it for a wide open throttle spin. it is going to smoke like a house on fire, during this process.

afterwards compression.recheck

capitan · Mar 7, 2009

Re: Johnson 9hp problem

marvel mystery oil, is that some thick engine oil, do i level the pistons before i put it in? I don't think we can get seafoam here in the UK

tashasdaddy · Mar 7, 2009

Re: Johnson 9hp problem

i would level them. if you can get seafoam, BRP Engine tuner from a Johnson dealer.

http://www.evinrude-parts.com/oil_engine_care.html

Vic.S · Mar 7, 2009

Re: Johnson 9hp problem

Redex. The original Redex upper cylinder lubricant is what used to be used but these days there is a range of Redex products to choose from. The nearest I guess is Redex petrol treatment.

I am sure that if Sea Foam was available in the UK it would be dismissed as "snake oil" but I have put a question on The YBW.com Reader to Reader forum, one of the leading boating forums in the UK

Go to http://www.ybw.com/forums/showflat.php/Cat/0/Number/2213548/ and see what replies I get during the next few days

tashasdaddy · Mar 7, 2009

Re: Johnson 9hp problem

Vic, add these to your post. http://www.seafoamsales.com/motorTuneUpTechGas.htm

http://www.seafoamsales.com/deepCreepTech.htm

Vic.S · Mar 7, 2009

Re: Johnson 9hp problem

Done

CATransplant · Mar 7, 2009

Re: Johnson 9hp problem

One other thing to consider. You said that after replacing the head gasket, one cylinder was up to 90 psi compression, but that it dropped to 50 after a short time.

Your cylinder head may be warped or have some other damage. Check this carefully, using a metal straightedge to check for gaps all across the head. If you find a slight one, you can resurface the head on a sheet of glass, using a fine emery cloth sheet. Rub the head on the abrasive in a figure 8 pattern until the entire surface is evenly abraded.

Be sure to tighten the head bolts according to the recommended torque setting and in the correct pattern.

This may take care of at least part of your problem.

capitan · Mar 7, 2009

Re: Johnson 9hp problem

Thanks catransplant, i must have read one of your posts before now because i have done that to the head, still have the 50psi in both pistons

CATransplant · Mar 7, 2009

Re: Johnson 9hp problem

capitan said:
Thanks catransplant, i must have read one of your posts before now because i have done that to the head, still have the 50psi in both pistons

OK. When you had the cylinder head off, did you see any scratching of the cylinder bores? If not, then the suggestion to use an additive to help dissolve deposits that might be making the rings stick might do the job.

Also, different compression testers often give different results. Further, if you don't pull the engine through enough times, you may see a low reading. I generally pull the engine through five or six times with the compression guage attached to maximize the reading. That you have equal readings between cylinders is a good sign.

You said this is a 9 hp outboard? What is the model number?

Finally, how is the spark?

capitan · Mar 7, 2009

Re: Johnson 9hp problem

I didn't see any noticeable signs of scratches in the bore although i'm no expert in recognising subtle scratches. I was using a drill and socket to turn it over. Again as to the spark, i have a spark, weather it is the right spark would be down to a professional to diagnose but i would have been under the impression that if you have fuel and spark it should go. Am i right to think that there is no need to be trying to check the timing as it is all electric and no need to adjust? I was starting to think maybe the problem was at the bottom of the engine, the leaf valves, if they may be leaking compression?

Rick. · Mar 7, 2009

Re: Johnson 9hp problem

I looked that up and it is a 79, 9hp. Funny though they don't list it on the parts list. I wonder if it is a 9.9 with a minor revision? Not sure about that. Rick.

capitan · Mar 7, 2009

Re: Johnson 9hp problem

Yes Rick, i believe it is basically a 9.9 or 15hp but with a smaller carb on it.

Rick. · Mar 7, 2009

Re: Johnson 9hp problem

It could be a problem with a leaf valve but I wouldn't think so. I would chase the decarb solution offered earlier. That may well un-stick a ring or two and balance out your compression. 50/90 is no good as I'm sure you know. After the decarb and your still getting those numbers I would open it up and look at the leaf valves and then the pistons. I always thought a 9.9 was a 15 with a smaller carb. I learn something every day on this forum. Rick.

capitan · Mar 7, 2009

Re: Johnson 9hp problem

Thanks, yes, i've poured some oil into the bores as suggested while i get some engine tuner (seafoam), i may check the throttle/cam roller settings etc. I can't get my head round the reason the thing will only run on almost full throttle when i do get it started. The plugs seem to be wet!

Rick. · Mar 7, 2009

Re: Johnson 9hp problem

Why don't you open your slow speed needle valve a turn to let it have a bit richer fuel setting. May be that it wants a bit more gas due to a bit of a dirty carb. Rick.

capitan · Mar 11, 2009

Re: Johnson 9hp problem

Thanks for all your help, combined i have managed to raise the compression a bit and have had it running long enough to get a little closer to the final problem. If i unscrew the slow running screw by about 5 full turns i can get it started, then i try and find the smoothest running position and that can be as little as a quarter turn from completely seated but if i go that bit too far, it stops and i seem to have to unscrew it a few times to start again! If anyone knows the cure for this, i'm sure the problems will be solved?

Rick. · Mar 11, 2009

Re: Johnson 9hp problem

You definitely need a carb. kit and a thorough cleaning. Then you should be able to set your slow speed to where you can idle right down to too slow and all points in between. Rick.

capitan · Mar 11, 2009

Re: Johnson 9hp problem

thanks Rick, come to think of it i had swapped needles with another carb, the needles were slightly different as in the original one had a shoulder near the end and the other didn't, not knowing what should be inside the carb as i can't see inside the needle hole! Are you saying the carb kit comes with a new needle or do you think there is dirt somewere in the needle area?

Rick. · Mar 11, 2009

Re: Johnson 9hp problem

I'm saying your slow speed idle fuel circut is clogged somewhere in the carb. but......... You have just opened another can of worms in your last post captain. Those needle valves are very engineered and precisely machined for every model of carb. You can't just take one from one carb. and put it in another unless the carbs. are identical. That might be the reason your having this trouble in the first place. Why did you change them? Was the original damaged? Can you get it back? Rick.

Johnson 9hp problem

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