We can sove this one today!

[karlow1]

I have a 1990 40 HP tracker Johnson.
I do not know a lot about it's history but it has never ran right.
I have worked on and owned it for almost 2 months now.
It runs great at speed, but has never been willing to idle on the water.
It idle on the muffs, usually not great. The VRO was injection way too much oil at idle.
To date, I have gone through the carbs twice.
I have a manual. I have properly adjusted the carbs, synced, and checked the timing at idle.
The latest change was to delete the oil injection and go to premix. the could is gone.
Here is the issue, at idle on the muffs, it pops, when it's up to temperature it runs about 2 sec. and pops. Adjusting the carbs does not seem to effect the poping. If I use the timming light I do not see anything wrong when it pops on ether cylinder. When it pops, there is a little cloud of oil smoke and the engine slows down. This problem is being caused by the top cylinder only. If I disconnect the top plug (and ground it) it idles much better better, no poping.
You can adjust the lower carb with no problems. It seems the poping is the upper cylinder firing out of phase at idle. I do not see any other evidence of this. No stray arcs, no mis located timing light firing. On Sunday she would run at 5200RPM across the lake and die at idle. If it run on the top cylinder only she will not start, she jsut runs about 1 sec and dies.
That is a bunch of info guys, so what is wrong? I will take another look for arc in the dark. My next test will be to switch the connections on the coil to see if I can move the problem to the lower cylinder.

Hellllllllp!

 

[iwombat]

Re: We can sove this one today!

Is it popping out the exhaust or out the carbs.

 

[karlow1]

Re: We can sove this one today!

It seems to be out the exhaust, you get a little smoke cloud ,most times.
Yea, I replaced the top plug too.

 

[karlow1]

Re: We can sove this one today!

Same story in the dark. Then pop is definaly from the exhaust. I can not swap the positions on the coil, the wires are too short on the bottom cyln.The engine runs notably faster on both cylinders. I did swap the plug wires, no help. Sometimes the pop will stall the motor. I see some corona around the plugs, but it is the same on both cyln. No stray arks. No misfire can be detected with the timming light. It;'s solid at 2 deg retarded. The upper cyln is effected by adjusting the carb, you can change the idle speed and make it run worst!

Any help?

 

[karlow1]

Re: We can sove this one today!

A little help please. I'm plaining on another fishing/boat repair trip on Sat.
I like to keep my fishing tow free w/o drifting into other boats!

 

[SKEETR]

Re: We can sove this one today!

Maybe I missed something in your post but did you rebuild your carbs yet? A gummed up carb can't be adjusted.

 

[SKEETR]

Re: We can sove this one today!

My bad, twice got it. All the jets correct to factory spec or did the previous owner rejet for different altitude? You pulled the core plugs while serviceing right?

 

[iwombat]

Re: We can sove this one today!

Might want to try a spray bottle with premix into the carb throat and see if the miss goes away.

 

[karlow1]

Re: We can sove this one today!

That's a thought I will try it after work.
I did try useing the cold start botton, but it did not seem to stop the pop.

Thanks

 

[tashasdaddy]

Re: We can sove this one today!

power pack have been known to fire both plugs at the same time when they are going bad. i have several 2 cylinder motors that size, you do not have an adjustable carb, the jets are suppose to be seated, and fixed. did you do this when you cleaned your carbs. http://forums.iboats.com/showthread.php?t=244013

 

[karlow1]

Re: We can sove this one today!

Update!
I tried the spray, it can make the engine run worse, but not better. I checked the connections and grounds, they look good. I swapped the coil connections. It ran the same. Here is the big clue. After I swapped the coil connections I noted it would run on the top cyln. I adjusted the carb. It will also run on the lower cyln. It is not related to swapping the coils, I swapped them back. Same results. It runs better on ether cylinder than on both. On a single cyln it will run pretty smoothly at a lower speed. With both cylinders it will run smoothly for about a min, them it will start to pop. The pop seems like an out of phase firing. it slows the engine. It produces a little cloud of smoke. If they occure in sequence the engine will stall. If the engine is cold it is much more likely to stall. With the timming light, I have not been seeing a missed shot. I replaced the plugs, set the gaps at 0.03. I ran it a little while. It seemed to have a little bump or hitch in it's step at first. But soon enough, it was pop run run run run pop, run run run run pop run pop run run run pop.
Come on guys what's wrong here?

 

[oldrudedude]

Re: We can sove this one today!

There are only so many thing that can go wrong. If the compression is good on both cylinders and the ignition is solid, what is left? Bad reed valve? Bad air/fuel. I suspect air/fuel because my old twin cylinder was demonstrating a similar problem when I got it. Would not idle in the water. Top cylinder idle mixture screw did not seem to affect idle speed or smoothness except to make it worse. Changed plugs, set timing, etc. Ran nice at throttle but ran lumpy at high idle and would stall at low idle even in neutral.

Solution for me was: I noticed that there was a tiny bit of slop in the throttle linkage between the two carbs. The lower carb was opening slightly sooner than the upper carb such that the carbs WERE NOT in sync. Would idle for a few seconds then pop and stall. After I tightened up the linkage it idles in the water well.

Are you sure the idle circuit orfices a clean? Experience has taught me that I have to be meticulous about cleaning them.

Have you checked for a vacumn leak?

 

[cdoliver]

Re: We can sove this one today!

check your carb float levels, sounds like one is too rich.

 

[woody66912]

Re: We can sove this one today!

just a thought .but run both cyls tdc mark flywheel on both .check with timing light the marks should be close to timing pointer.maybe you have a timmer base going out.also pop the flywheel and check the center magnet closely for cracks.

 

[Joe Reeves]

Re: We can sove this one today!

Your explanation of the problem time and time again indicates a lean running carburetor. I'm assuming that the popping you feel is exhaust related is really not a loud explosive backfiring type pop shooting wildly out the exhaust area BUT rather a slight occasional pop accompanlied by a mild jerking of the engine which would resemble a very mild backfire.... but not actually a backfire as one would think of a backfiring engine.

A engine out of time, if it was possible for it to run at all, would sound like shotguns constantly firing out the exhaust.

Remove the carburetor face plate cover, and with the engine running and the popping problem encountered, stick two fingers into the carburetor throat acting as a manual choke. If the engine smooths out and the popping ceases, the carburetor is running lean.

The cause, if it can not be adjusted out via the mixture adjustment on the top starboard area of the carburetor, would be a loose or improper size idle air bleed jst that's located at the top front portion of the carburetor.

 

[jay_merrill]

Re: We can sove this one today!

My 2 cents is that what you describe as a "pop" can also be called a "huffing sound." Its hard to put a word on a sound, buts that's always been mine for this problem.

 

[CharlieB]

Re: We can sove this one today!

There should not be any 'corona' around the spark plugs, it is time for new ends/boots. But that is NOT the cause of your problem.

What fuel mix are you using?

Did it have this problem BEFORE you removed the VRO?

A carb jetted for a 100:1 VRO idle mix running NO VRO and a 50:1 fuel mix can/will be slightly lean at idle as the richer oil mix displaces fuel.

Try Joe's advise of sticking a finger or two in the carb throats to slightly richen the mixture at idle, when you prove that cures the problem then increase the idle jet size.

Joe sent me a note reminding me, that to increase idle fuel you REDUCE the idle air bleed size.