sovereign misfire

[jabo]

I went to brave the cold thurs night with my 97 18 hp twin kohler.after clearing 1st driveway went to refuel.thats when i noticed a misfire when idling down.thought maybe snow was causing miss.cleaned off snow-still misses.pulled plug wire off r/s bank and noticed big drop in rpms.pulled left bank plug wire off and seemed to run better,put back on miss is worse.pulled plugs and checked ok-just replaced 10/03.is this a known concern? i know someone who went with a hotter plug but only on left side-did not try r/s bank yet and said was improved.i figured i would throw this out to the forum and see what comes up.thanks in advance.

[HubbardRA]

Sounds like the left side plug has gone bad. On most of these two cylinder engines both plugs are fired at the same time, by one coil since one is on compression and the other is on exhaust. If one plug fouls, then the engine will run very badly because this also effects the firing of the other plug. Putting in a new set of plugs, or at least a new one in the left side should cure the problem.

[roma3112]

guys along this line, i have the same basic tractor/engine any benefit to replacing (when needed) the standard champion plug with say a Bosch platinum?

[papamerkle]

I had same problem with champion plugs. I use Autolite spark plugs. All My small motors run Autolite plugs. Champion start making there plug overseas in the 90's. The Bosch and NGK spark plugs are too pricey for me. In the past I had more problems when gas sitting around for more than 1 or 2 months. I use Staybil year round. Keeping air filter clean is important for any plug life.

[HubbardRA]

You can use any make of plug. The big problem is making sure that you have the correct heat range. I have run into this problem many times when modifying engines.

[jabo]

I know certain engines like certain plugs-ex.gm cars like ac/delco,ford-motorcraft etc.what works best with the simplicity line? Expanding on Romas comment,what about a platinum type plug? Last thought,must I stay with the same heat range?

[Tim_S]

I have heard on several occasions about getting a hotter plug. I think I need to do this on my 16hp twin as the plugs are a little black and the engine is tight. Is there a cross reference or number chart that anyone is aware of that would enable me to know what a hotter plug is and how much hotter? I know I could always ask at the auto parts counter but it would be useful information to me especially as I am fixing quite a few tractors on the side and will be doing more engine work to have the ability to look at a plug and right away determine if its the right one inserted? I suppose that it wouldnt be of much use also unless it was a cross reference across manufacturers. One more stupid question..........if you are getting the same voltage across the electrode and the gap is the same how do the plugs differ? The only notable difference I can tell is the distance in which the plug goes into the cylinder head possibly a winding inside?? Beats me.