K301 Backfires and more

[Wheel Horse Guy]

Hi all, I have a K301 12hp that I bought 4 years. The guy I got it from said it was a shortblock from Kohler. It ran great for 3 years until it threw a rod. I took it apart and found that when the conecting rod broke it also broke off one of the wieghts on the cam. I found a used cam with the exact numbers on it and I got a used crank and connecting rod. I put it back together and it started right up but backfires when going from full throttle to idle. I put a new carb on but no change. I also noticed now at full throttle it looks like a steady flame comming out of the muffler. This is my first time working on a small engine. I do have the manual for K series engines. Do I have somethine wrong?
Robert

 

[Rivets]

I'm thinking one of two things may be causing the problem. Valve timing off or fuel mixture too rich. Here's a manual which may help you. Not to be a smart ____, but are you sure the used parts are correct?

http://www.mymowerparts.com/pdf/Koh...al-K91-K141-K161-K181-K241-K301-K321-K341.pdf

 

[Wheel Horse Guy]

Yes, I think the timing is correct because it will start on the first pull of the rope. The cam has the exact numbers on it as the damaged one. I could not find any numbers on my damaged crank. The replacement crank looked the same accept mine has a nut to secure the flywheel and the replacement has a bolt. It backfired with two different carbs so I thought that would rule out that. Am I wrong in my assumptions? The muffler is something I had laying around, it is 6" and is just straight through, could that cause these problems? I do not think you are a smart_____.
Robert

 

[Rivets]

When using used parts you have to be very careful, very easy to get taken. Numbers on the parts don't mean they are the same part number. I'm concerned with the crankshaft, bolt vs. nut. Did you check following, angle of the crankpin to the timing mark, angle of the crankpin to the flywheel keyway, angle of the keyway to the timing mark. All three must be exact. The same is true with the camshaft, angle of the timing mark to both cam lobes. If the carbs are not adjusted right they can cause backfires. A straight pipe muffler may be the culprit, as you are not getting enough back pressure on the exhaust valve. Any or all of these could be causing the problem. You have a lot of things to check.

 

[cashman]

You didn't say weather the K301 had battery or magneto ignition? If it has battery ignition, it's best to use a timing light to set the ignition timing. Also the valve lash (cold) could be off a little? As far as the bolt vs the nut on the flywheel, Kohler made a change in the 1980's to all the crankshafts and dropped the external threads (nut) for internal threads (bolt). You could check the flywheel key slot on the old crankshaft to see if it is in the correct position on the new crankshaft.

 

[bertsmobile1]

You didn't say weather the K301 had battery or magneto ignition? If it has battery ignition, it's best to use a timing light to set the ignition timing. Also the valve lash (cold) could be off a little? As far as the bolt vs the nut on the flywheel, Kohler made a change in the 1980's to all the crankshafts and dropped the external threads (nut) for internal threads (bolt). You could check the flywheel key slot on the old crankshaft to see if it is in the correct position on the new crankshaft.

Double check the valve timing then do it again just to be sure,
rotate the engine and note where the piston is comparred to where the valves are at.
The exhaust should open very close to BDC the inlet should open just before the exhaust closes after TDC
Most side valve motors will run ( sort of ) with the cam a couple of teeth out either way they are very forgiving engines .
At idle there should be no flames coming out the open exhaust port. At full speed you should see about 1/2" to 1" flame at the open exhaust port which should be blue/white in colour.
Any longer and your timing is way off and as the spark is controlled by the flywheel key with a tiny adjustment via the points gap, then the cam is the No 1 suspect.
A yellow flame at the open exhaust means the engine is running too rich.
Try to avoid running the engine without a muffler on for any length of time as the exhaust valave runs at forging ( bright red ) heat and the oxygen in the air which comes into contact with it between openings will burn the valve then you will have to lap them in again.

 

[Wheel Horse Guy]

Rivets, can I just compare the cams and cranks to each other by eye or could they be only thousands of an inch difference?
I did adjust both carbs. I will get another muffler.
Cashman, it is battery ignition. How do I check the timing with a timing light? I have only used a timing light on a V8
engine where there is a timing mark on the harmonic balancer. Would it start on the first pull if out of time?
I did adjust the valves but will check them again.
Bertsmoble1, I will check the valves again and again. There is no flame at idle and it purrs like a kitten. At full speed there is about a 1/2" to 1"
blue flame coming out of the muffler. I have not run it without a muffler at all.
Very good information coming from everyone, thanks.
Robert

 

[bertsmobile1]

OK
I obviousy did not read your post carefully enough.
There should never ever be flames coming out of the muffler.
What I said is what is allowable with neither muffler nor header pipe on.
Flames from the muffler without a lot of missing will usually be a main jet way to big
Same as Rivets.
Has to be late timing or way too rich mixture

 

[Polaraco]

I'm thinking one of two things may be causing the problem. Valve timing off or fuel mixture too rich. Here's a manual which may help you. Not to be a smart ____, but are you sure the used parts are correct?

http://www.mymowerparts.com/pdf/Koh...al-K91-K141-K161-K181-K241-K301-K321-K341.pdf

OK
I obviousy did not read your post carefully enough.
There should never ever be flames coming out of the muffler.
What I said is what is allowable with neither muffler nor header pipe on.
Flames from the muffler without a lot of missing will usually be a main jet way to big
Same as Rivets.
Has to be late timing or way too rich mixture

A gas engine is a gas engine

I have to agree with these guys. It has to be too much fuel, especially at higher speeds. The fact it's blue is sort of a good thing, but not good. It means you are burning off the excess fuel, good combustion, but I can bet it's not good for the engine. You can burn exhaust valves or seats that way. They're not made for that much heat.

Check the carb over. It almost sounds like the float (If equipped) is sticking open a tiny bit. Those carbs are pretty simple. They're no Edelbrock or Holley

 

[cashman]

The ignition timing procedure is illustrated in the Kohler K series manuals. There is a timing sight hole in the blower housing on the carb side. Hook up any automotive style timing light as you would on a V-8. Remove the cover for the points and adjust the ignition gap until the timing marks on the flywheel are centered in the sight hole while pointing the timing light at the sight hole. It's very simple to do and you'll end up with the ignition timing right on if done correctly. Then replace the points cover after you've dialed in the ignition timing. Just setting the points at .020" might get you in somewhat correct time. The single cylinder Kohlers are not maybe as sensitive as the twins on the ignition timing but all of them will run and start better if the ignition timing is correct. I've also ran into the same problems when someone has replaced the Kohler ignition coil with a cheap automotive style coil?