Engine bogging down?

[tmosgood]

I just purchased a 1979 Evinrude 9.9 2-stroke outboard, model 10924B, serial#06656. I replaced the plugs, changed the gear oil, ran it with new fuel. Started on the second pull, accelerates and planes nicely. That was last week.

This week, again, I put it into the water. Started right up - but now it won't accelerate. I turn the throttle and it just either bogs out or stays at a very low speed, RPM. I put in new plugs (the newer Champion version of what the outboard recommends, as they do not make the older ones) and it has plenty of oil/gas, etc. I had a compression test done and it all checked out fine.

What would caused this motor to all of the sudden just not be able to accelerate and get gas? The gas bulb is firm when running and the lines/hoses are all secure. Thoughts???

Thanks!

 

[OptsyEagle]

Re: Engine bogging down?

Most likely you have lost a cylinder, probably due to loss of spark. You said you put in new spark plugs but could not find the ones specified. The ones specified are QL77JC4. What spark plugs are you using?

In any event, if you are not using the right plugs, my first investigation would be to see if one perhaps fouled. Put in another set and see if the problem goes away. If it does, then you did foul a spark plug. To resolve your fouling problem (if that is what it is) you will most likely have to find the correct plugs.

The other test I might do even before I looked at the spark plugs is to start it up and let it warm up for a few minutes. Then, using insulated plyers, I would pull the spark plug boot off each cylinder, one at a time. So pull the top boot and see if the motor keeps running. Put it back and pull the bottom boot. If the motor runs when you pull one boot and not if you pull the other, then the one you pulled when it died was the good cylinder and you have just confirmed that you are only running on one cylinder. These motors idle quite well and run reasonably well on only one cylinder (although with significantly reduced power and speed).

If you are using the right spark plugs and have lost a cylinder (or have not), just return with that information and we can direct you in the proper direction to take, from there.

By the way, the insulated plyers above, is to keep you from shocking yourself. These motors put out a very high voltage to the spark plug and it will seep through the insulated boot onto your fingers and be reasonably annoying to you. This is normal, so use the plyers if you are conducting this test.

 

[tmosgood]

Re: Engine bogging down?

I am using the QL82C's, as recommended by http://www.sschapterpsa.com/ramblings/Johnson 9.9_15.htm. Had no problem running on them a day or so ago, ran wide-open. I just took the plugs out, seemed oily, and one of them seemed brownish. Thoughts?

 

[OptsyEagle]

Re: Engine bogging down?

Those are the alternative plugs and they are probably hotter then the QL77J4C plugs so they, in themselves, should not cause a fouling. Obviously the plugs will work real well right up until they don't, so the fact that they worked before is not really that relevant.

At this point we don't even know if you are dropping a cylinder so I would suggest you either run the test I mentioned above or run a proper spark test on both cylinders to see if they will jump a 7/16" gap. If you want you could change the plugs and see if the problem goes away to confirm or eliminate a fouling. Oil on plugs can be fairly normal with a 2 stroke and over time some brownish can occur. Fouling of course, is carbon deposit on your insulating component creating a conductive short on the spark plug and ending the sparks. This comes from the improper burning of the fuel. I am starting to lean away from the fouling theory, from the new info you have given, but it is still a possibility that has not been eliminated.

Again, we don't even know if you are losing a cylinder yet.

 

[tmosgood]

Re: Engine bogging down?

OK,
Switched to the QL77JC4 plugs and there was no difference. In fact, the engine failed to remain in idle, with the engine dying out before I could even put it into forward, unlike this morning when I could at least run it at full in neutral.

I will have to buy some insulating plyers tomorrow and check out the plugs. Extremely frustrating, especially since it ran so well yesterday and the other times I used it, even with bad gas and plugs.

If a cylinder is out, how much time/cost am I looking at to fix/replace it?

Thanks again!

 

[OptsyEagle]

Re: Engine bogging down?

OK, it is perhaps starting to sound like a carburetor issue. When the engine was bogging down before was it also difficult to idle?

In any event, rule out the fouled plugs since you said you just changed them and the problem is the same or worse. If it was me I would do a spark test (external spark tester set to confirm a 7/16" gap jump) on each cylinder and I would do a compression test (which you did) and if it passed both of those, I would look to a fuel problem (which it is starting to sound like). Most likely a dirty carburetor. If you run it again and it starts to bog down you could try to squeeze the primer bulb to rule out fuel pumping and air leaks. At that point it almost must be a dirty carb.

Until you have determined the cause of the problem it is impossible to tell the time and price of repair. The motor needs compression, timed spark and fuel to run. It is just a matter of eliminating those to find your problem.

 

[tmosgood]

Re: Engine bogging down?

Looked at the engine again today. Starts on first pull - idles smoothly, seems to misfire a couple of times (or seems like there may be debris in the fuel). Again, shifted into forward, engine would not fully rev, stayed at one speed, and bogged a couple times. I realized, is this something that could be occurring because of the lean/rich adjustment? Currently, it is at the 6 o' clock position - However, it has been on this setting since I bought the engine so maybe I am just crossing my fingers it is something that easy. Fuel bulb stays full. Compression is good. Timed spark is next, I suppose.

 

[OptsyEagle]

Re: Engine bogging down?

OK, well I guess yesterdays bad idle was a one off. Perhaps a very cold motor. Anyway bad idle usually comes from the carburetor so lets leave that one for now. You need to do a proper spark test. The other test you can do in the mean time if you don't have the spark tester is to run the motor and pull each spark plug boot, one at a time and see if it stays running or dies, indicating that it is only running on one cylinder.