1992 40 horse Johnson idle problem

[gimli1977]

Hello all...I've gotten great advice in the past here and now I have a new issue I was hoping someone could enlighten me on.

I have a 1992 Johnson 40 horse that I rebuilt the powerhead on. I put it all back together, went through the carbs, disconnected the oil injection system and am now running 25:1 for the breakin period. I had the motor idling great in my driveway and it was reading 135psi on both cylinders at this point, took it down the lake last weekend, and it ran like a top. I went in and out of coves for at least 2 hours twice taking it pretty easy with no problems at all, running about 5 gallons through it in all. Ran it down to the dam to trailer it and still ran fine, so I'm very happy at this point. My brother and his friend (a marine mechanic, btw) put it in this morning, and it started right up. They run it to get to their fishing spot, saying it ran great, then start fishing. When they go to start it back up to come back, it won't start.

Seven hours later........I'm considering using the trolling motor to get me out to the middle of the lake so's I can pull the plug. It will not start unless at least 1/2 throttle. Last week it would start if you looked at it funny, and I never had to give it any throttle to start it! Plugs are sparking good, gas only 1 week old, 25:1 mixture, fuel pump is pumping, pulled the carbs off and took them apart and they seem to be fine. None of the reeds are stuck open or closed, it just will not idle! Revs up fine with great response, but the lower the RPM, the rougher it gets. Idle adjustment screws on carb seem to have limited affect, at least they don't help it idle better. I will check the compression again when I get it home tomorrow, but I'm not sure what could have happened in a week. I don't suspect that anyway, as its moving a lot of air through the carbs and out the block if I pull a plug. This has really thrown me for a loop, especially considering how great it ran last weekend. Any ideas???

 

[tashasdaddy]

Re: 1992 40 horse Johnson idle problem

did you replace fuel lines with alcohol resistant lines? it is not unusual for the carbs to pick up something, after messing with the fuel lines.

 

[gimli1977]

Re: 1992 40 horse Johnson idle problem

No sir, I didn't replace the fuel lines at all. They looked new, and I have good flow going through them up to the carbs. It does seem like something had to have gotten in the carbs the way it all of a sudden did this, but I took both of them apart, checked the floats and everything I could yesterday on the boat and they both looked very clean.

One thing we tried at the suggestion of the marine mechanic was to remove the spark plug and crank it to see if we're getting any fuel back into the cylinder, letting the compression blow the gas out the spark plug hole, and he didn't think we were getting near what he would expect. At the end of the day, he was as stumped as I am.

 

[tashasdaddy]

Re: 1992 40 horse Johnson idle problem

i think we found the problem you have fuel hoses that are probably 18 years old. ethanol in the fuel softens the inside of the fuel lines, when you handle them they sluff off on the interior. this stuff that sluffs of can clogged the screen in the fuel pump, some gets thru and settles in the bottom of the carbs, blocking the pickup for the low speed jets, and can clog the high speed jets.

 

[gimli1977]

Re: 1992 40 horse Johnson idle problem

You know, I would have thought that I'd find some remnant of fuel line or something somewhere in the carbs if that were the case, but I will certainly replace all the fuel line, fuel filter, and clean the carbs again and see how that goes. At the very least I'd say I've gotten my moneys worth out of the current plumbing. I'll come back and let you know if that fixes the problem. Thanks a lot for all of your responses so far, it's been a great help to me!

 

[gimli1977]

Re: 1992 40 horse Johnson idle problem

To give a bit of an update, I just got the boat back home and tore the carbs apart, and I didn't find so much as a speck of anything in either one. They're clean enough to eat out of. I've got them soaking in carb cleaner and I'll blow through them again tommorow with air and cleaner. I'm going to replace the fuel line, primer bulb, fuel filter, spark plugs, and check compression also tomorrow. Both carbs had fuel in them, so I know it's getting to the bowls.

As an aside, I do realize from the other posts on here that you can't make a 40 horse a 50 by changing the carbs, and that's not my intention. However, I saw a set of 50 horse carbs on ebay and was wondering if the carbs themselves would work on my motor? I'm thinking about just buying another set to try out in the event that mine are just plain cursed and I saw them.

Thanks a lot!

 

[gimli1977]

Re: 1992 40 horse Johnson idle problem

Hello and my apologies for a long post....just trying to give all available info...

Since Sunday night I have replaced every bit of fuel line, fuel filter, and spark plugs on this motor. I did a compression check and both cylinders read 145psi. What I have found that is interesting has to do with the coil. It tests OK as far as ohming it out like my Johnson manual says. Both primary terminals to ground are shorted, and both spark plug terminals to primary leads are around 295 ohms. Both respective primary terminals are ONLY shorted to the ground tab on its own side where it bolts to the block, and I'm not clear if that should be the case or if it even matters.

Either way, when I have the coil connected, the spark plug wires off, and I crank the motor with my Fluke checking voltage between the spark plug terminal and ground, the top terminal sends my fluke off the chart, which I would expect. The bottom one, however, shows NOTHING on the meter, and I tested this out several times for repeatability. Somehow I'm getting a spark on both plugs, though, if I lay them on the block and crank the motor. I'm pretty sure I'm getting near the problem, but now I don't know whether I have a coil problem or an ignition module issue. Any troubleshooting advice in this area? I'm going to call our OMC dealer here in Northern Kaintucky tommorow to see if he can test the coil, and I hope that's it, because I certainly don't want to have to remove that flywheel again!

Thanks a lot!

 

[gimli1977]

Re: 1992 40 horse Johnson idle problem

Marina says they can't test the coil without the motor, so I'm kinda at a stand still. Was thinking about switching the primary lead from the top to bottom, which I think would tell me if my coil is good, or if I need to go deeper.

 

[gimli1977]

Re: 1992 40 horse Johnson idle problem

The situation has now deteriorated to the point where the motor will not start no matter what I do. Using two inline spark testers, I'm seeing both light up, but I don't have the Stevens tester my manual suggests, and ebay wants 90 bucks for one. I'm going to make the load tester my manual calls for with the 10 ohm resistor tomorrow and test voltages to the ignition coil.

Right now it just cranks. If I hit the key to prime it, I occasionally get a backfire out the exhaust, but that's it. What in the world could be causing this problem and why all of a sudden?

 

[TLL]

Re: 1992 40 horse Johnson idle problem

Sounds like maybe your flywheel key is sheared, you have spark, but you say now the engine backfires when you try to start it. Plus the condition has changed from the first time it occured, indicating that the flywheel maybe moved on the shaft some more. Also, find a new marina if they can't test the coil off the motor.

 

[gimli1977]

Re: 1992 40 horse Johnson idle problem

I will check the flywheel key when I get home. My manual did mention the backfiring as a symptom of being out of time. I soldered up a load tester today and I'm going to try it this evening. I still can't tell for sure whether or not I have a spark or fuel issue

Thanks a lot!

 

[gimli1977]

Re: 1992 40 horse Johnson idle problem

Well, I just pulled the flywheel off and the key is definitely sheared in half. The variety of difficulties I've had make a lot more sense now. Thank you very much!!

 

[gimli1977]

Re: 1992 40 horse Johnson idle problem

Just installed a new woodruff key, put everything back together, and it runs very well now. Going to put it in the water tomorrow and see how it does

Thanks again!