I'm still looking for the solution

B&D posted, Single carb supplying an odd fire engine will always run one cylinder leaner than the other. It's the nature of the beast.

For 6 years now I been looking for the solution. Why is it the nature of the beast?

Later today, I plan to do another compression test and leak down test.

I got a tack that I can replace the battery. Yesterday, while the tractor was running at different speeds I measured left and right head temps at the same place and exhaust temps.

The exhaust temps were within 2 degrees of each other, while at all speeds up to 2600 RPM's, the left cylinder runs 50 degrees cooler than the right. The left cylinder makes small amounts of carbon on top of piston and head. Right cylinder runs clean. The tip of the plug stays clean after switching to the next hotter plug 6 years ago. So how can the exhaust temps be the same, while one head is 50 degrees cooler?

I have eliminated spark plug and ignition coils (ign modules) as the problem. Hydraulic valve lifters. All new filters. Starts and runs just fine. Engine doesn't use a drop of oil. All cooling fins are clean.

I bought the engine with 400 hrs on it. Currently have 1600 hrs. Engine runs strong. I would love to find the solution.

If you google air cooled engines with one cylinder running hotter you will find I'm not alone. No one seems to know why. NATURE OF THE BEAST.

What engine ?

If an air cooled onan you have to have the rubber seal in place around the oil filter to the shroud or else you will loose a valve seat on that cylinder.

Hello Geo-TH,In,

After 1200 hours or running I'll take a wild guess and say: THAT IS NORMAL! No two combustion cycles, on the same cylinder, produce the same H.P. Way to many variables! When you got two cylinders, that doubles the variation, and so on. Only way to get all the cylinders close, is to fuel them and tune them individually, as in fuel injection. I said close, not the same,

Guido.

If there are cooling fins on the engine flywheel blowing air across the cylinder heads, one cylinder head could be receiving more airflow than the other causing a higher operating temp inside one of the cylinders. Carbon is sometimes an indication of excess fuel or incomplete combustion going on in a combustion chamber. Lots of variables in engine design possible.

What engine do you have that you are testing this theory on? B/D was more than likely referring to a JD 2 cyl. tractor which because of it's side by side design and seperate 180° journals for rods, draws two gulps of fuel/air only 180° apart and then rotates 540° and does it again. Because of relatively low rpm (950-1200)at wot and half that in normal use, the column of air (theoretically) slams to a stop for part of that 540° of crank rotation and then two big cylinders both want to take a gulp only half a turn from each other. What he's saying is the second one is not going to get quite as much. RPM will have an affect on this. When you hear the "put" sound from one of these, you are actually hearing two firing strokes so close together it sounds like one. Since the two are so close together, the tractor doesn't know but what it is one big power stroke with the larger forces of the first cylinder just added to the slightly lesser one of second cylinder. You still get the benefit of both. They changed to two throat carbs in '53 on most but not all of them to help solve the problem. I don't claim to speak for B/D but I still believe he was talking about these engines.

Guido, The engine is a 20 hp kohler. I was successful in doing a compression test, even though many say can't be done because there is a decompression valve. Well, it can be done. The cylinder making carbon has 180 psi. The good cylinder that is burning cleanly, 165.

The boys at a lawn mower service, the place where I buy parts, they sell new mowers and has been in business for 30 years. The service manager said right away, bad head gasket. How could I have used an engine with a bad head gasket use it for 1200 hrs, for 6 years? The cylinder is pumping 180 and bad head gasket?

I borrowed a leak-down tester from a friend. Someone has abused one gauge. I get reading all over the place. I gave up and called it a day.

Here is an idea I came up with today. I Need to confirm first. What if the lean cylinder actually has a burnt intake valve? On compression storke, some air is going backward in the intake manifold. If a little of the air goes backward in the carb, it's picking up more fuel. So when the other cylinder in on intake, it's getting too rich of a mix. I also discovered the V-twin the pistons are not 180 out, perhaps closer to 120 out.

The service manager said the only good way to remove the carbon in the left cylinder is to remove the head. I may just do that in the spring, after the snow is gone. The service manager said it will cost me $200 if I pull the heads and they replace the valves, plane the head. I may just do that. He claims he's seem Kohlers with 6-8000 hrs if properly maintained.

If it "Starts and runs just fine. Engine doesn't use a drop of oil. All cooling fins are clean."

What is the problem? Are you trying to fix what is not broke?

I am guessing its the same engine as last time on that Termite. 20 hp Kohler Command.

I can think of at least 2 factors that would make cylinder temperatures different.

1. Slight difference in intake runner length from the carburetor. Usually there is a different curve into one cylinder than the other too.Lots of the later 2 cylinder engines are two barrel with different jets in each barrel to compensate for this.

2. different air deliverly from the flywheel fan. Some engines have an extra vane in the cover to direct air toward the hotter cylinder to try to compensate for this. I saw a Briggs Vanguard like that today.

Hello Geo-TH,In,

Now you are possibly on to something. Just make sure the cylinder you are pressurizing is in the proper position. Having the cylinders not 180 apart is one consideration when pressurizing. Hydraulic Lifters that leaks down after the engine has been off for awhile, will change compression results Also the compression test should be make on a hot engine, and wide open throttle, and same amount of engine revolutions. Keep at it...........


Guido.

Yes, kohler on terramite. The problem is the left cylinder is running extremely rich, plug is black since I stopped using E20 over the winter. I think there is an excessive carbon build up in they cylinder, because it has 180# compression compared to 165 in the cylinder burning cleanly. Intake manifold is the same length for each cylinder.

Leak down tester has a damaged gauge. Plan to get a new one today. There is a problem, just not sure what it is. I can say what it isn't. Therefore it has to be either a valve or head gasket. I thinking if the intake valve of the lean cylinder is leaking just a little, causing the air to flow backwards in the carb, producing too much fuel mix for the rich cylinder. Need to comfirm first.

I recently came across a used carb off an 18 hp kohler command. I took it apart yesterday. Cleaned it. May install it. Thinking it has smaller jets, may lean engine. If nothing else, just eliminate another possibility.

Good chance the heads are coming off soon, after the snow is gone. Kohler recommends removing heads to decarbon the engine.

To remove carbon from the cylinders slowly pour water down the intake while running at moderate rpm. Don't pour enough to kill engine. In fact when FAA is trying to determine why engine stopped causing airplane accident, first thing they do is pull a spark plug. If it is real clean they know it was water contamination. If spark plug normal it was something else.

Geo-TH,Just a thought about something you could try.Make a restrictor plate to go under the intake between the manifold and the block.With a smaller hole than the intake has,to reduce the flow of fuel mix to the right side.Maybe 1/2 the size of the intake port Also that may increase the fuel mix a little on the left side.The left side may have some carbon under the valve face,causing some leakage.You might try putting some water in a spray bottle and mist the whole bottle or two of water down the carb throat while running 1/2 throttle or more. This should clean the carbon off of the piston and valves.

George, you could be looking at a "problem" that is built into that engine. Among the variables that can cause discrepancies:
1) Valve to seat sealing.
2) Difference in the leakdown rates of hydraulic lifters.
3) Length of overall valve train. Pushrod, valve stem length, etc. as well as the mass of each individual valve train.
4) Differences in the finish of each cylinder wall.
5) Difference in the piston ring sealing. Items like the actual tension of the ring to the cylinder.
6) mixture swirl patterns in the intake manifold. Could cause some mixture to de-atomize.
7) Difference in valve timing from one cylinder to the other. Caused by "imprecise" cam grind.
8) Gasket alignment between manifold and head.
9) Difference in finish in the cooling fins on each head.
10) Interior finish and routing of cooling air within the shrouding.


I could go on like this all day, but...
I suggest that the problem you are chasing is in the basic design. After all, this is not a precision built piece of machinery. Somewhere, compromises were made that resulted in a potential stackup of tolerances responsible for the condition that you are observing. Apparently, even the people that service those engines have no idea why this condition exists - only that they have to remove and de-carbon the heads periodically. The answer may well be that it really is the nature of the beast!