More 135 Johnson problems

[wiscoboater]

Hi Guys,
I’m still working on this 1975 Johnson 135. It still has running issues. Yesterday had it out, idles very poorly, will not stay running. When I got it to go in gear and stay running (sort of) I tried to accelerate. The motor lugs and stumbles along at about 8MPH. If I leave it wide open, it takes about a full minute and the RPM’s SLOWLY creep up to where the boat will come on plane, flatten out and take off. When wide open like that it seems to run OK. Sounds like its hitting on all cylinders and runs fairly smooth. If I bring it back down slowly it just cuts out and dies. Restart it and it idles like crap again and the process repeats it’s self.
So far I have replaced the stator as one charge coil was dead
Replaced the rectifier as it was not working
Replaced all 4 coils, plug wires, plugs
Replaced the screen and gasket on the fuel pump
Bought the correct manual (OMC) and followed the link and sinc directions to the letter
Replaced both control cables and adjusted per the OMC manual

This morning I am rebuilding both carbs with OMC kits with new floats. When I reinstall the carbs I will do the link and sinc again (about the 10th time)

Now to the questions. The gasket between the carb and manifold that came with the carb kit is not the same as the old gasket. It has an extra hole (see photo) that lines up with the slot in the manifold between the 2 carb throats (see 2nd photo).
Is it OK to use this new gasket with the extra hole, or should I reuse the holeless old gasket?
2nd question. At the bottom of the air box there is a nipple with a hose on it that dissapears under the power head. What is the function of this hose?

Thanks to all that have helped me with this motor. If I can’t get this thing sorted out soon, I’m going to use it to anchor a sail boat mooring buoy. 🙄

[frankr]

How about the carburetor? Does it have a matching hole? If not, then the gasket doesn’t need one either. If there is a hole in the carburetor, I’m not smart enough to know exactly what it does. The cross slot in the manifold is sort of an equalizer or balance between the cylinders.

I believe the hose you are speaking of is a drain for the air box. Captures and recycles the drainage instead of doing it the old way, which was to dump it into the boat or overboard.

[RICK EICHRODT]

The hole in the top gasket is for the primer system port on the later OMC motors that had the primer hose routed up to the top of the carb. Since your motor does not have a primer system but instead has a choke system, the gasket hole is not needed. What OMC was doing at the time was trying to make one carb rebuild kit fit many V4 and V6 motors. Hence the two humps on the top carb gasket, you can install it either way and with the old style gasket, it would only fit on one way, to cover up the reed cage mounting screw.

[RICK EICHRODT]

As for the rough running part of your 135…have you checked the compression? It MUST be up around 120 psi and no cylinder can be 10% less than the highest psi. These motors needed to run the UL77V spark plug. If someone installed the L77JC4 or QL77JC4 spark plugs, it would run too hot and burn a piston, causing the dome to melt and ruin the motor. How do you "know" the motor is running on all 4 cylinders? Do you have a spark checker that can test the gap at 7/16th of an inch? Do you have a peak reading voltmeter that can read the voltage of the triggers and the power pack? My guess is that you replaced 4 ignition coils and wires for no reason. You have another problem, if the issue is ignition related. Make sure you remove the high speed jets and clean them out. There are 4 of them, two on each carb. This is just my opinion and the normal disclaimer applies.

[kerry]

Just asking… did you check the timer base? Trust me, they do cause symptoms similar to yours, including the urge to scrap it. ’74 70hp was saved a fate worst than death by a very savvy OMC tech.

If you have too many, AND not enough, you're a collector.

[wiscoboater]

Thank you rickrodt.
Compression is 154 on #1, 150 on #2, 149 on #3 and 151 on #4.
I replaced all 4 coils due to all of them being cracked. They were working, but it was just a matter of time before failure.
When I rebuilt the carbs today I found them to be very dirty inside. Lots of crud in the upper carb bowl, and one idle circuit blocked completely in the lower carb. Upper needle and seat was very worn as well. Taking out the welch plugs on the idle circuits showed some dirt in there as well.
Not having the proper tool for jet removal I blasted the high speed jets with OMC power tune and 15lbs psi compressed air and gently cleaned with a pipe cleaner. When done I soaked entire carb body in carb dip.
The idle jets I blasted out with power tune and compressed air until they flowed like new. Re assembled with the new kits and floats and test fired.
The motor is running and idling beautiful. It’s like it’s not the same motor. Throttle response is instantaneous and it comes back down with no stumbling or popping. The idle is smooth and even with no more surging. I can’t get it idle below 1200RPM right now so I’ll have to re adjust the cables again and see if I can remedy that.
When I fired it today it was with the UL77V surface gap plugs. I was told by a few members not to use them due to fouling issues. Before that I was using NGK B7HS-10 standard electrode type plugs. They both seem to run about the same, as in I can not tell a difference swapping one for the other.
The stock timing spec for this motor is 20 degrees. I currently have the timing at 18 degrees set at 4200RPM. I was told to back 2 degrees of timing out of it due to the melted piston dome issue this motor sometimes has.
So I guess another lake test is in order to see the final results of the days work. Hopefully I am getting this going in the right direction.

[fleetwin]

Well, kind of hard to say, could be just about anything. Are you sure it is running on 4 cylinders? What pitch prop are you using? Those engines were not the smoothest idling engines, but it should at least stay running. Like others have said, that hole in the gasket is for newer engines with the primer port on top of the carb, and is the correct gasket for your engine.
I know you have checked the sync a few times, but are you sure the timer base is moving smoothly in both directions? I had an interesting case, that I wasted many hours on years ago, all because I overlooked the basics. The old 115hp like yours was mounted too low on the boat, which kicked up considerable rooster tail spray, that ended up being ingested through the lower pan. I had wondered why such a nice looking trailered boat could look so rusted under the hood! In any event, the engine would run fine when at idle and when accelerated to WOT, the problem occurred when you backed off on the throttle, the engine would sneeze/fart stall out every time. I thought I had check most everything, finally theorizing (grasping at straws) that the pack was misfiring, needless to say the new pack changed nothing. Finally, by accident, I discovered the problem while rechecking the sync. The constant salt water bath had stiffened up the vertical throttle linkage pieces. So, the engine ran fine while accelerating. But, during deceleration, the stiff linkage would retard the timing completely before starting to close the carb butterflies, causing the lean spit stall situation. Normally, the carb butterflies start to close first while the timing is still advanced on these engines.
So, be sure the sync is right and that throttle mechanism is working correctly. The only other relatively simple thing I can think of is a sheared flywheel key, which will cause erratic timing that wont show up on a timing light. I thought of retarded timing only because you mention it won’t idle and is real slow to accelerate, which sounds like retarded timing. It is easy to check for a sheared key with the OMC TDC tool, but am guessing you don’t have that. Are you sure you retorqued that flywheel correctly, to 105 foot pounds?

[fleetwin]

OK, you were writing your results as I was writing my post….
So, the engine is running OK now? You did not remove the jets, correct? I’m assuming you don’t have the correct tool. In any event, sometimes a pipe cleaner can be run through those high speed jets removing any little bits of gum that might be left over after blowing them out with cleaner/compressed air.
And yes, you do want to use the surface gap UL77V plugs on that engine. These engines were high compression, and prone to detonation/preigntion damage, even when "good gas" was still available. So, please be sure to use at least mid grade gas running today’s fuels. Yes, the surface gap plugs are more prone to fouling at low speeds, but you won’t be using this engine/your boat for trolling I’m sure!

[wiscoboater]

Hi Don,
I can say I have spark on all 4. Since the new coils went in I get a fat blue/white spark on my open air tester set at 7/16". After running and pulling the plugs out they all look identical. They all have the same amount of soot and color to them, none wetter or dryer then the others. Attaching a timing light to all the leads and watching the flashes shows an even flash all around.
The timer base does move freely in both directions and the key and keyway are good. I did torque the flywheel nut to 105 per the manual.
The prop I was running before is a 3 blade no name 13 X 21 stainless. Yesterday I was running a 3 blade 13.25 X 22, custom cupped and drilled with ventilation holes at the base of the blades. It’s an OMC Raker I got from Dan Anderson at Tomahawk.
I’m almost convinced most of my head aches were with the carbs. Rebuilding them today made a world of difference in how it’s running. I will have to wait till I can get it back on the water for the real test.

Do you think the 18 degrees is OK with the timing? And what about plug choice?

[wiscoboater]

Dang… now you were writing while I was reading. Oh well, more info is good.

Thanks Don!!

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