'89 15hp bogs down under load

[reelistic2650]

1989 - 15hp J15RCEC.

At the lake running about 75-80% WOT for 20 minutes. All of a sudden the motor drops to 25-30% and will not go any faster, regardless of tiller position. It will idle, start, and run fine at low RPMs. But after you hit that 30%, it will not go any faster. Here's what I've tried so far, with the same results after each step.

Removed carb, cleaned completely, and reinstalled.
Removed carb again, soaked metal overnight, and resinstalled.
New spark plugs - old and new were both are getting fire.

Motor will rev up in the bucket, but it takes it an additional second or two over the way it used to run. Lots of smoke, more than I remember from it running before.

One note about the timing: the throttle cam seems to have a lot of play in it. The (single) mark will not line up with the roller follower unless you push the cam clockwise.

Any ideas?

 

[oldcatamount]

Re: '89 15hp bogs down under load

Do a Link and synch on the carb linkage. Adjust the linkage so that the roller and the timing mark line up at the same time the throttle plate begins to open. I made a little tool for that with a small alligator clip and a short piece of stiff wire. Clamp the clip to the end of the throttle rod. that will make it easier to see when the throttle plate is starting to move.

 

[reelistic2650]

Re: '89 15hp bogs down under load

Thanks - I messed with it some and now the mark is almost at the center of the roller. Still acts a little sluggish but better than before.

Have you ever heard of a motor having the timing get suddenly off time while under way like I described above? Or is there something else to check for?

 

[jmendoza]

Re: '89 15hp bogs down under load

If i recall correctly, the 1989 15 has a plastic cam for the throttle which is prone to cracking, so check it carefully near where it bolts to the magneto plate. Normally all you have to do is replace it and re-adjust it so it opens the carb fully. Click on this link and go to the bottom of the page for a nice photo and description:
http://www.sschapterpsa.com/ramblings/Johnson_9.9_carb-fuel_pump.htm

 

[johnreidb]

Re: '89 15hp bogs down under load

sometimes a coil will short out when it warms up and the metal inside of it has a chance to expand. when that happens, you are running on one cylinder only.

one way to check if you have a bad coil is to look carefully at the rubber/plastic seal on the flat side of it. if you see any holes or cracks, replace it. you can also do a spark test when the engine is hot and starts to bog down. or you can stay home and heat the coil up with a hair dryer to try to mimic the symptoms. finally, if you are really ambitious, buy an ohm meter and a service manual. the manual has resistance values and specific instructions for testing your coils.

i keep a vacuum-sealed, back-up coil in my boat. they cost $30, and it takes 3 minutes to swap them out on the water. that seems a lot easier to me than any of the above options.

good luck.

 

[reelistic2650]

Re: '89 15hp bogs down under load

The motor does have a plastic cam plate so I'll check that for cracking. Good info at that link, thanks.

I'll check the coil as well but it was doing that after sitting for several hours. It would start right up but would not go more than 30%. I'll check the coils anyway.

Thanks again for the replies.

 

[reelistic2650]

Re: '89 15hp bogs down under load

Cam plate is not cracked and still will not line up unless you push it clockwise. First pic shows what it looks like when you close the throttle all the way. The throttle roller cam rests against the bottom of the flywheel until you push the cam plate clockwise (second pic). Third pic shows the roller cam after is "snaps" into place.

The tiller handle gear seems to have a lot of slop in it ("jumps" while turning), and I'm not sure if that is keeping the cam plate from being pulled all the way back counter-clockwise so it will line up with the throttle roller cam.

I'm not sure what to do next to try and get the cam plate and throttle cam roller aligned. New tiller handle gear?

After putting the new plugs in and running for a few minutes, the top plug was clean like new but the bottom plug had sludge around the gap and on the threads. The piston heads look like they've got some build-up. I've never done a de-carb, time for one?

 

[reelistic2650]

Re: '89 15hp bogs down under load

Update - not getting any spark on top cylinder, no matter what speed the motor runs at. Have ruled out the spark plug and wire. Removed both coils. How do you test them to see if they're working?

I replaced the power pack with a new one in January of this year because of a cylinder not firing. I hope the new one isn't already shot.

 

[boobie]

Re: '89 15hp bogs down under load

To test the coils properly you would have to take them to a dlr who had a coil tester. A coil tester will load the coil as under operating conditions. The next thing you could do is swap the coils and see which cyl has spark at that time.That will eliminate your power pack.

 

[reelistic2650]

Re: '89 15hp bogs down under load

Now I'm really confused.

Swapped the coils to see if that made a difference. Now I'm not getting a spark on either cylinder. Moved the coils back to their original position and still no spark on either one. The #1 coil looks like it may be the original but the #2 coil has definately been replaced.

An electrical tester gave these results:

Spark plug wire post on coils
#1 coil output - 2.5-3.0mV while turning flywheel
#2 coil output - 2.0-2.5mV while turning flywheel

Small boots from power pack
to #1 coil - .145V constant / .170V max while turning flywheel
to #2 coil - .195V constant / .200V max while turning flywheel

Earlier today, the #1 cylinder was the one that was not firing.

Not sure if this info is worth anything but wanted to post in case someone sees something in those numbers that looks good, bad, or otherwise.

 

[reelistic2650]

Re: '89 15hp bogs down under load

Switched the wires from the power pack to the coils and had spark on the top coil but not the bottom. I guess this means the power pack is bad, unless someone knows of something else that could be causing this.

I just replaced the power pack in January with a new one and didn't expect it to go bad this soon. Assuming I'm going to have to replace it, is there anything else to look for/replace while the flywheel is off?

Any recommendations on where to get another power pack from?

Thanks.

 

[boobie]

Re: '89 15hp bogs down under load

If the power pack is definately bad you may want contact the place you purchased it from and check into any warranty. Usually they are guaranteed for 1 yr. You have to remember one thing though, If you have a bad coil it can take out a power pack.

 

[johnreidb]

Re: '89 15hp bogs down under load

here is what dr leeroy (www.sschaptersa.com) has to say about your problem:

"You might laugh at this question, but if it runs and has no power, or dies at an idle, is it running on both cylinders? It will usually also be a harder to start when cold. You would be amazed at how good it may seem to run one cylinder when not in a tank or under power by just using muffs. I have even trolled all day long on just one cylinder firing.

The tried & true method of checking whether it is running on one cylinder is while it is running at a low or medium speed, pull one spark plug wire off, replace it & then pull the other. If it is running on just one cylinder it will die when you pull off the spark plug wire that is firing.

If it is only running on one cylinder, there could be many possibilities, and I would look at them in the simplest order first (1) bad or fouled spark plug. (2) bad (loose or corroded) spark plug wire connections from the coil. (3) bad electrical connections (again loose or corroded) in the rubber plug-ins or wire leading to the coil. (4) bad ground wire connection (needs to be clean & with no paint where it touches the block under the coil. (5) the coil itself is bad. (6) leaky cylinder head gasket allowing compression leakage. (7) I have never seen a power pack on these 2 cylinder engines go dead for just one coil, (however it is possible, as have seen it happen on a 3 cylinder unit)

If you get to #6 & it is still dead, swap the coils from top to bottom & see if the non-firing follows the coil, if so then that coil is bad."

i say that the easy way out is to buy a new coil (or two) and test by replacing them. you can always vacuum seal the old ones for later if that doesn't solve the problem. also, dr. leeroy says that your should tighten the bolts on the powerpack to make sure that is is grounding out correctly.

good luck, john.

 

[bktheking]

Re: '89 15hp bogs down under load

You have a shorted wire going to your powerpack by the sounds of it, move the wires around while someone is cranking the motor, you'll probably find spark comes and goes. I had a motor do that to me, replaced the pack and all was well.

 

[mikesea]

Re: '89 15hp bogs down under load

disconnect the kill button,its probably bad

 

[reelistic2650]

Re: '89 15hp bogs down under load

Checked kill switch, its okay.

Pulled the flywheel and checked power pack bolts and wire connections. They were all tight.

Checked with vendor and the power pack is still under warranty so I'll be sending it back.
Right in the middle of duck season.

Anything else under the flywheel that should be changed while I'm at it? The charge coil is pretty cheap at $20. Could it be part of the problem and is there any way to test it?

 

[reelistic2650]

Re: '89 15hp bogs down under load

Got ready to disconnect the power pack and saw that one of the wires coming from the coil has a pretty deep cut. Stupid question - could this cause be the cause of the spark issue?

Looking at a diagram for the ignition system it looks like the coil assembly (#36) is pretty cheap and easy to replace.

 

[oldcatamount]

Re: '89 15hp bogs down under load

If that's not the problem, it certainly looks like it is. If it were mine, I'd replace the driver coil like you said.

 

[bktheking]

Re: '89 15hp bogs down under load

You just found your problem or part of it.

 

[reelistic2650]

Re: '89 15hp bogs down under load

Did a decarb with the old power pack and a spliced charge coil wire while wating for the new parts. Installed new plugs, power pack, charge coil, and plastic carb cover (old one was warped).

Seated needle valve and backed out 1-1/4 turn. Sarted right up but was starved for fuel. The sweet spot for idling in and out of gear (in the bucket) ended up to be between 2.5-3 turns out from seated. Unusual? The motor would idle in gear as long as you wanted it to and would explode (in a good way) when the throttle was opened with no hesistation. There is not an excessive amount of smoke either. I was suprised that the needle valve needed to be turned out that much and wanted to get some feedback.

Checked compression - 100 lbs on both cylinders. Had 90 and 105 a year ago - does this seem reasonable? I assumed the decarb helped the 90 cylinder and that the 105 cylinder lost 5 psi just because of age, but again wanted to get some feedback.

Thanks for all the help.