79 Johnson 140hp throttling up problem

[jaxstas]

Okay just to start I replaced the fuel lines and fuel pump and that helped with some other issues. Now I've got this happening consistently. 10hrs on new rebuild. Chokes rebuilt year before. Use 91 Octane Non-oxygenated fuel 50-1. Plugs l77jc4 gapped at 35.Compression on left side Cylinders 115 and 115. Compression on right side cylinders 95 and 90. Guy who did the rebuild says this is normal for a rebuild as it is breaking in.

1. At Dock Cold
a. Prime bulb
b. choke and turn over till it starts and dies
c. turn over with no choke and starts right up.
d. Lift throttle bar all the way up till I get about 1500 RPMS max. then back down and let it warm up. With Idle bar all the way down it sits at about 1100 RPM's.
e. Take off and go fishing.

2. Fished for about 1/2 hour and want to move.
a.Turn it over with no choke and no priming.
b. starts up and I am able to idle away no problem.
c. Give it gas and it throttles up a bit and then dies.

3. Lastly to get it going.
a. Prime bulb which is somewhat firm and might only get to give it a pump or two and its hard.
b. Won't start good now, have to turn it over till it is sputtering and then after about 3-4 seconds I can let go of key and it runs. Choking only seems to make it not fire off at all.
c. Pull idle bar up and let it sit thinking it'll get to 1500 RPM's and stay there.
d. Hear engine racing up up to 4100 RPM's and then put Idle bar down back to about 1500 RPM.
c. Idle away slowly for about 10 seconds and then I can give it gas but have to slowly throttle up.
d. After about half throttle it will run like a charm again. Drive away like normal.

Why is this happening? Did check on power packs and coils and while cold at least all ohm readings are normal. As stated replaced all gas lines and pump. Took carbs off and everything looks clean, but didn't actually go as far as checking float area, or disassembling them. Let me know what you advise. I was thinking of purchasing a small gas tank to see if that changes anything just to rule that out. I did check gas pump and bulb and gas flows out well. Seems like the engine has to be somewhat warm for this to happen. Never happens at home on the muffs. Will start up fine even when warm although I've never let it sit as long as I do on the lake. Also once it is restarted after sitting on the lake the RPM shows about 650-700 with the throttle bar down. Why would this change from 1100 at the dock? Thanks Jack.

 

[jaxstas]

Re: 79 Johnson 140hp throttling up problem

Okay me again. I have been reading through some of the other posts here with similar issues. Some are pointing to heat soak. Does anybody think this might be true in my case? If so are there any other ways of cooling the engine besides idling for awhile before shutting it down? Thanks

 

[jaxstas]

Re: 79 Johnson 140hp throttling up problem

Anyone, any thoughts?

 

[basspirate]

Re: 79 Johnson 140hp throttling up problem

it sounds like an ignition problem. buy an adjustable spark tester (they run about 6 bucks) test each cylinder at a 7/16 gap on the tester while cold then again after heated up. if you are loosing spark on one cylinder first swap the plugs. see if that solves it then swap the wires, then the coils, and the wires from the powerpack to the coils. if you are loosing spark on one bank (one side of the engine) then swap the powerpacks and see if the spark loss changes with the powerpacks. if the spark changes on one bank with the powerpack swap then then you have a bad powerpack. if it stays the same i would suspect the stator is bad. if its one cylinder and after swapping everything i would suspect the timer base. just make sure as the stator is about $275 and the timer base is $ 350 from evinrude. they are much cheaper aftermarket. i just went through the same problem and it was the timer base

 

[basspirate]

Re: 79 Johnson 140hp throttling up problem

just to add on the resistance of coils changes from hot to cold. and remember stators have coils as does the timer base

 

[emdsapmgr]

Re: 79 Johnson 140hp throttling up problem

Assuming that the powerhead has the original heads on it, the compression is pretty low for a recent overhaul. Normal on that engine from the factory would be over 130 lbs on each cylinder. Compression will change with break-in, but if you have 10 hours on it, you won't see much change from now on.. Any chance that you have two completely different heads on the engine? Check each plug wire with an iductive timing light when you are under load in the water (in gear at idle.) You should see strong, constant flashes from each plugwire.

 

[jaxstas]

Re: 79 Johnson 140hp throttling up problem

Thanks for the suggestions, I'll be taking it out this weekend so I let you know what happens.

 

[henrye718]

Re: 79 Johnson 140hp throttling up problem

Compression on left side Cylinders 115 and 115. Compression on right side cylinders 95 and 90.

That doesnt seem right, thats way far off fresh build or not. I think I would try new plugs on that low side to see what happens when the problem shows up. My friends engine did just about the same thing when we swapped plugs on the water. It seemed to undue it till the plugs got wetted again very quickly due to the compression dropping out even more. From heat? or lack of fuel/oil going to those cylinders. Never did get it fixed he went new after that.

 

[jaxstas]

79 Johnson 140hp throttling up problem

henrye718 interesting you mention this. I performed this test on the muffs last night with NEW plugs. I started it up and let it idle for about 10min with the cowl on. Then I let it sit for about a half hour or so. Then primed the bulb, and turned it over and it did the same thing as before where I turned it over and over and it spat and sputtered until it started. After that it started up right away every time. I was going to do a spark test, but didn't have time. This really makes me suspect a fuel delivery issue like heat soak when the engine is hot. I guess it seems to me that if it were an electrical component I'd see it consistently when the engine is hot. That is just not the case being it runs fine and I can stop and start it over and over after it gets going with no problem. What do you think?

 

[henrye718]

Re: 79 Johnson 140hp throttling up problem

Do you have a compression tester, test that low side when its hot. If it drops compression even more I would lean on that as the cause. My friends engine would lose compression when it got hot and that side just stopped firing. This doesnt sound liek the case since your able to start and stop after you get past the hard start. I am thinking here more in line that the engine builds compression back up by filling with unburned oil and fuel then fires since it gets enough to back to hit again. I am in no way sure that mixed fuel oil is thick enough to do this tho. :redface:

It does also sound like a fuel problem. You say fresh rebuild. I guess that means the carbs too? If not at least open them and inspect them. Adjust them also? If so do you trust the guy that did it to spend the time and do it right? So many little things can cause these engines to act very eractically. We have to check everything especially the small easy to do things first. The spat sputtering also sounds like it could be flooding during that time and once its started clears and takes times to build up that condition again.

How about spraying some fuel into the carbs to see if that hard start problem is from not enough fuel? The more tests you do the faster you will find the problem.