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Hot cold?


Well-known member
I was just wondering, I have a 6 cyl continental and it runs good but was wondering why cylinders 1 3 5 run where the exhaust pipes get hot when running for about 30 seconds and cylinders 2 4 6 run to where the exhaust pipes are still cold. I mean no heat on the pipes at all and the other side is hot to where you can't touch it. I am completely lost on it. The cylinders all have good compression and spark. The cold side also has alot of unburnt fuel that comes out of it, the inside of the pipes are wet. I have been told my carb need to be rebuilt but it's not even the right carb, it's a carb off of an a 65 so it's to small for the engine anyway. I would think that it would make the engine run hot because of the lack of fuel from a small carb. I was just curious if anybody has seen where cylinders run hot on one side of the engine but not the other. And if anybody has a ma3 carb they would like to sale or know where I can get one for a decent price. Thanks again for any more help.
It sounds like you have bad plugs on that side or bad wires or bad magneto. It's odd that it is just on that side. If it's pouring out fuel and the exhaust isn't hot it sounds like you are not getting spark or it's sparking at the wrong time.

I think someone said you have the plug wires on incorrectly on that side. If that's true the plugs even though good will fire when the valves are open, thus not burning the fuel in the cylinder. I'd start there. I can't belive it's running good on 3 cylinders. Let us know what you find.
It's an aircraft engine, a c-125 continental. It has a little bit of fuel that drips out of the number 6 cylinder but that's it. Even the air that comes out of the exhaust of those cylinders has no heat. I could see if it was just one cylinder but it's way strange that its all three on one side and it runs good. It starts to choke out at around 2000 rpm but I think it's just lack of fuel from the small carb thats on it. I am still looking for a carb that fits it.
what am i checking the intake for? it poped once and then it has been fine ever since, but I would like to know what I am checking it for because both side feed from the same port.
The wires are ran like they are supposed too. The number on the mag cap goes to the cylinder number. Left mag goes to the bottom plugs and the right to the top.
Let me tell you your problem. That motor has an intake runner that feeds three cylinders correct?? If so you have an intake leak. If you are leaking fuel and popping there is a problem. The plug wires are not crossed or it would hardly run,probably not at all on 3 cylinders. At idle it sucks air and the pipes will not be hot. When you rev it up the fuel will overtake the air leak and they will get hot. It is easier for the vaccum of the piston to suck air into the cylinder around the intake,than it is to suck fuel from the carb. FIX YOUR INTAKE LEAKS and you will not have a problem. When you get at 2000 it is like a blow torch. With more oxygen comes more heat . It might start breaking down because the cylinder head temp is getting hot. You should have a leak down test done because an intake leak makes it run lean continued usewill cause it to burn a piston.
That might be the problem, but if it was to run lean with the intake leaking, it should run hot not cold, right? I will check that out hopefully thats the problem. The fuel that is not been burned is coming out of the number 6 cylinder exhaust pipe, it's not much but you can stick your finger in the pipe and it feels wet, and you can smell it in the pipe. Thanks for any more help.
At an idle the pipe will be cold because the motor is sucking air not fuel. It needs fuel to burn to get hot. At high rpm it will pull some fuel to it and run. But it will be a lean mixture. The piston and cylinder temperature gets hot. That is why it pops. Now you have a cylinder leaking fuel or oil. You may have burned that cylinder or piston because of the lean/hot condition. It also causes valve seats to drop. I have to leave so I am turning this off now. I am interested to see what you find. If you have any more questions I can read them tomorrow.
sometimes when a engine backfires the sudden back pressure will expand intake connections be it hoses or flanges and cause a vacuum leak and change the air/fuel ratio
I know the pistons and valves are still good, I have never taken the boat out with this engine, it has only ran on the trailer for 4-5 times at no more then 2 minutes at a time. The compression tests on the cylinders are all above 90 and they don't leak at all. I bought the engine without a carb on it and was told by an aircraft mechanic that I could run it with my small stromberg carb from my a 65 to see if it would fire and run. I need a bigger carb but I didn't want to buy one until I seen the engine fire, now that I know it will run I am trying to find an ma3. I think that the intake next to the engine was leaking and I might have fixed the problem. But if it's not, is it possible for all three cylinders to suck air from one of the rubber clamps between the intake and the elbow or does it have to be before the intake splits three ways? I had one rubber on the middle cylinder that seemed to be a little loose on the clamp. I will try a new intake gasket and some new rubbers and hope it works. Again if any body has an ma3 they would like to sale please let me know, there is zero airboat parts kicking around my neck of the woods and I am having a hard time finding a carb that will fit it. The only carbs I can find are ma 4's and 4.5's. Thanks again for the help.