'86 8hp misfires when warm

[iwombat]

It takes a long time to get this to happen, but if I run this engine for about 1/2 hour it will begin to misfire. Sometimes it goes away, then comes back. I isolated it down to cylinder #1, then switched coils. It stayed at cylinder #1. I'm guessing the power pack is on the way out, but before I go and buy one I'm fishing for other options.

I don't have a very reliable way to test this either since it comes and goes pretty much at will. Tracking it down to #1 takes about an hour of monkeying around.

 

[tashasdaddy]

Re: '86 8hp misfires when warm

sure sounds like your on the right track.

 

[Xcusme]

Re: '86 8hp misfires when warm

Well, you do have options. If you suspect a thermal issue with the power pack, heat it with a good hair dryer to hasten the dropped cylinder condition. If cooling it with dry ice or electronic freeze spray makes things right, suspect the pack. Another option is the timer base. I doubt it would be the stator, both cylinders would be affected. I know you checked the wiring plug for corrosion...right?

 

[iwombat]

Re: '86 8hp misfires when warm

Replaced the plug and wire with a spare I had from another motor. I'll try the hair dryer bit tomorrow.

It's behaving like it's firing the #1 plug out of time causing the motor to fight itself. If I remove the #1 plug it just chugs along on one cylinder fine. I may try marking both TDCs and hitting it with a timing light on #1 to see if it's firing on #2s time.

 

[tashasdaddy]

Re: '86 8hp misfires when warm

there have been several different post with different motors doing just that, firing or 2 cylinders at a time, all were resolved with a new powerpack.

 

[iwombat]

Re: '86 8hp misfires when warm

Hair dryer to warm the powerpack reproduces the problem in a couple of minutes.

An ice pack on the powerpack eliminates it in about as much time.



That powerpack is looking extremely suspicious right now. I'll replace it tonight.



Thanks for the tip.

 

[iwombat]

Re: '86 8hp misfires when warm

New powerpack on, it's been chugging away for the last 2 hours now with no problems.

 

[Xcusme]

Re: '86 8hp misfires when warm

Hair dryer to warm the powerpack reproduces the problem in a couple of minutes.

An ice pack on the powerpack eliminates it in about as much time.



That powerpack is looking extremely suspicious right now. I'll replace it tonight.



Thanks for the tip.

Yup, I kinda thought that's where it was leading....Glad you got it sorted out.

 

[tashasdaddy]

Re: '86 8hp misfires when warm

thought so. congrats.

 

[iwombat]

Re: '86 8hp misfires when warm

That was my hunch too. I just needed a way to prove it before replacing parts.

thanks again