k 301 skiping and backfiring

[Brendan.B 0]

Hey guys first post wondering if u could help me...just bought my second horse a c121. It runs good for about 15/20 mins. Then it starts skipping and back firing at high idle. Or under a load. I did new point/condensor/plug/airfilter/fuel fiter...and the coil looks new so i didnt touch it. Gonna try the coil from my electro 12 on it tommrow to see if that helps...other than that were else to look? Thank u

[WH nut 553]

Make sure the coil is wired correctly, Neg to points and condenser

[Brendan.B 0]

Yea i just looked the negative is going to points and condensor...ive never expirienced this. It runs so well otherwise

[WH nut 553]

Have you tried the coil yet?

[Ed Kennell 35,904]

When was it decarboned last ?

[Ed Kennell 35,904]

       Pardon my manners Brendan.

[rmaynard 14,922]

  Have you tried tweaking the carburetor adjustments? 

I am having the same problem with my B-100. I have done the routine stuff like carburetor cleaned/adjust, points, condenser, etc., but the problem remains. Silly thing is that it just started to do this during this last snow. I was forced to use some gas that has ethanol in it, and not my regular e-free gas. So I think I may have some contaminants in the fuel. If that is not it, I am going to have to pull the head, de-carbon and check the valves.

[Fordiesel69 221]

Carbon on cylinder will not cause this symptom.  Rather it will cause a detonation knock / ping depending on how you interperate the sound, and also depending on the wear on the connecting rod.  Or it can cause dieseling when shuting off.

 

Try pulling the choke out when this occurs again.  If you can keep the engine running much better, by applying partial choke, then you have a fuel supply problem

 

If not then you have an ignition problem

[Fordiesel69 221]

Don't forget to pull the gas shutoff out of the tank.  Inspect the screen for blockage.

[Ed Kennell 35,904]

I agree you need a good fuel supply and good fire at the plug. These basics are fairly easy to check and cheap to fix.   But,The fact that this machine runs good for 15-20 minutes and then backfires, indicates to me the problem is temperature related.   Could be a coil breakdown with increased temp.  But I have had a C-101 and a C-160 that showed this same problem and was resolved by removing the head   and cleaning the combustion chamber of all carbon and adjusting the valves.  I could see some carbon on the low pressure side of the intake valve and I believe this was a result of the carbon glowing after running for a short time and causing early ignition on the intake stroke before the intake valve was fully closed.

 

                                            

[Brendan.B 0]

I dont no the last time it was decarboned...i baught it about a month ago and have plowed with it three times. The symptoms apeard the last two times. Unfortunetly i worked to late today....and have to work in the morning. Im gonna try the coil that i know is good/ check the carbon build up tommrow afternoon. Ill get back to ya. Thank you...i never expierienced this with the other 12 horse

[illinilefttackle 399]

Brendan-just my 2 cents- but take it slow-I agree try the coil- but hold off pulling the head-put a little "Sea Foam" in the tank-warm it up-then richen up your high speed screw- try it, drive around a little and give the Sea Foam a chance to work. Then-if no cigar- Pull the head off-Good Luck-Al

[Brendan.B 0]

So i pulled the head...there was quiet a bit of build up. Cleaned it new gasket and put the other coil on for the hell of it. Ive run it over a half hour now and seams to be okay...ill no better this week i guess. More snow wednesday! Couldnt really work it hard today though its a little muddy

[rmaynard 14,922]

I would be interested to see if the problem returns if you put the old coil back on. It would be nice to know what solved the problem, carbon or coil.

[Ed Kennell 35,904]

 Stick that coil back in to see if it's bad.  Be sure to run it till it's hot.

[Ed Kennell 35,904]

Did you try that old coil yet Branden ? We all learn by knowing what solves a particular problem.

[Brendan.B 0]

I have but not long enuff for conformation. For a while we were getting a couple of storms a week, however, thankfully the snow has calmed down. I am leaning toward the coil myself. On another note. I wasnt sure if heat itself could ruin a coil? I did replace a bad muffler that could have blown exhaust at it?...not sure...I will get back as soon as I no! Thank you

[WH nut 553]

Heat will kill a coil and a bad muffler would be a bad thing on a coil.

[tunahead72 2,346]

Hi Brendan, and

 

It sounds like you've found your problem, but while you're at it, make sure you have good air circulation around the engine -- cooling fins clean, sheet metal covers all in place, no mouse nests in the blower housing, that sort of thing.

 

And if it starts acting up again, you may have a fuel problem -- make sure you have fresh fuel in the tank, carb is reasonably clean and properly adjusted.  You might consider replacing the fuel line, especially if you're using ethanol gas that's been sitting for a long time.