1997 20hp Misfire cyclinder #1

[aaasnapper]

I have had an issue with misfire on #1 piston.
I had checked out all components (using DVA meter) and replaced power pack, charge coil and ignition coils. (mainly becuase the issue was not resolved)

The engine idles fine and is fine at high revs.

The misfire only seems to occur after the engine has warmed up and when the engine has gone from higher revs back to idle and then as you try to increase the revs the misfire occurs at a certian rpm then it takes off and is fine. However, backing off on the rpms will make it misfire again.

 

[jimdd810]

Re: 1997 20hp Misfire cyclinder #1

You have one issue that is common in 2 cylinder engines. They will skip or jump when you go from higher rpms to idle. It is a balance issue. 2 cylinders idle pretty rough to begin with.

Another issue might be fuel related. I would do a compression check first, while doing that I would inspect the plugs to make sure the cylinders are burning correctly.

Your problem could be with both cylinders.

Let us know what you find/

 

[Joe Reeves]

Re: 1997 20hp Misfire cyclinder #1

What exactly do you mean by misfire? When you attempt to increase throttle. does the engine hesitate, act like it's about to die out, spit back thru the carburetor (which sounds like a mild backfire), what? try to describe the effect.

 

[aaasnapper]

Re: 1997 20hp Misfire cyclinder #1

Ok,

When I attempt to accelerate the engine does hesitate. Just guessing on the rpm range, it would be probably about 2000-2500 rpm where it does this.
I do not believe it spits back through the carberattor.
Once I launch from the boat ramp i can start the engine fine head out to my fishing ground which is a about 5 minutes away. (engine runs fine).
Stop the engine, and then restart to shift position and thats when the problems seem to start. Upon accelerating in the certain rev range the motor seems to hesitate. If I leave the engine for a while it would be fine ussually.

I know I was missing a spark on cycliner #1 as the plug was black when I pulled it out. After replacing all the parts mentioned above, it has improved the situation but has not fixed it.

 

[Cofe]

Re: 1997 20hp Misfire cyclinder #1

I have had similar problems with a motor, and found the coils were not grounded properly. Check the washers on the coil bolts. I found that paint on one of the washers was not letting the coil ground well when the motor warmed up. As the motor warmed up the bolt would expand and cause the ground fault.

Here is a pick of the proper washers. #4 washers are cardboard, and #11 is the grounding lock washer.

 

[jimdd810]

Re: 1997 20hp Misfire cyclinder #1

I think your low speed jet may be the culprit. Check the washers ond grounds on the coils. Then it may be time to over haul your carb. This sounds like a fuel issue to me.

 

[boobie]

Re: 1997 20hp Misfire cyclinder #1

It's possible you have something wrong with your timer base wiring. As the base rotates you could have a circuit in it opening up.

 

[Joe Reeves]

Re: 1997 20hp Misfire cyclinder #1

A black spark plug, especially a black fluffy one, indicates weak ignition/spark.

Do a basic trouble shooting procedure. Check compression.... what are the individual cylinder readings.

Do a spark test. With the spark plugs removed, the spark should/must jump a 7/16" gap with a strong blue lightning like flame... a real SNAP! Does it? Note... a spark test using the spark plugs is a waste of time, use a tester and the 7/16" gap!

On that model, a slightly out of adjustment slow speed needle valve can result in weird happenings, adjust it as follows.

(Carburetor Adjustment - Single S/S Adjustable Needle Valve)
(J. Reeves)

Initial setting is: Slow speed = seat gently, then open 1-1/2 turns.

Start engine and set the rpms to where it just stays running. In segments of 1/8 turns, start to turn the S/S needle valve in. Wait a few seconds for the engine to respond. As you turn the valve in, the rpms will increase. Lower the rpms again to where the engine will just stay running.

Eventually you'll hit the point where the engine wants to die out or it will spit back (sounds like a mild backfire). At that point, back out the valve 1/4 turn. Within that 1/4 turn, you'll find the smoothest slow speed setting.

Note 1: As a final double check setting of the slow speed valve(s), if the engine has more than one carburetor, do not attempt to gradually adjust all of the valves/carburetors at the same time. Do one at a time until you hit the above response (die out or spit back), then go on to the next valve/carburetor. It may be necessary to back out "all" of the slow speed adjustable needle valves 1/8 turn before doing this final adjustment due to the fact that one of the valves might be initially set ever so slightly lean.

Note 2: If the engine should be a three (3) cylinder engine with three (3) carburetors, start the adjustment sequence with the center carburetor.

When you have finished the above adjustment, you will have no reason to move them again unless the carburetor fouls/gums up from sitting, in which case you would be required to remove, clean, and rebuild the carburetor anyway.

 

[aaasnapper]

Re: 1997 20hp Misfire cyclinder #1

Replaced the fibre washer underneath ignition coils- No change
Checked for spark using spark tester- Bright blue spark with a good crack
Checked compression and is fine on both.
Finally Adjusted slow idle- right between sweet spot of choking and dieing. no change.

Goinf off logic I would say it is an iginition problem. The only thing I can now trace it back to is a small gouge that exists on one of the magnets within the fly wheel.

The gouge which is 1mm deep and tapers back to 0mm across a length of 5mm or so was caused by the charge coil impacting with the magnet. A mechanic who checked it out said both charge coil and magnet were fine. I have since changed Charged coil and noticed it ran better.

However, before I go out and replace a fly wheel (expenive) is it possible that the small gouge in the magnet would cause the above mentioned effect?