Backfire

[DeeJee]

I mounted my Kohler Magnum on go kart a day or so ago, and had to remove the stock exhaust, as it was side mounted in the wrong spot, just behind the seat. I replaced the muffler with straight pipes, and am going to use bisquit mufflers on the twin pipes. I was working on throttle linkage yesterday, started it, and the backingfiring through exhaust is ear shattering. There is, at times, fire belching from them especially when I rev up. I can adjust air/fuel mixture some, and help it a little, but cannot get rid of the problem. And there is a occasional pop through the carb, but very slight. I suspect that no back pressure, straight pipes, and Kohler's engine design is a lot of the problem. I might help the situation by putting elbows on the one inch pipes, then the muffler. This would help the situation some by adding back pressure, and directing the exhaust toward the back of the kart. I am not a carb man, but had to clean the carb when I first started. I set the air/fuel mixture by seating the needles, then backing off the required turns. I can change the engine sound with minute adjustments on the needles, so do not think I am off too much.
Suggestions?

 

[BirdFanatic]

I mounted my Kohler Magnum on go kart a day or so ago, and had to remove the stock exhaust, as it was side mounted in the wrong spot, just behind the seat. I replaced the muffler with straight pipes, and am going to use bisquit mufflers on the twin pipes. I was working on throttle linkage yesterday, started it, and the backingfiring through exhaust is ear shattering. There is, at times, fire belching from them especially when I rev up. I can adjust air/fuel mixture some, and help it a little, but cannot get rid of the problem. And there is a occasional pop through the carb, but very slight. I suspect that no back pressure, straight pipes, and Kohler's engine design is a lot of the problem. I might help the situation by putting elbows on the one inch pipes, then the muffler. This would help the situation some by adding back pressure, and directing the exhaust toward the back of the kart. I am not a carb man, but had to clean the carb when I first started. I set the air/fuel mixture by seating the needles, then backing off the required turns. I can change the engine sound with minute adjustments on the needles, so do not think I am off too much.
Suggestions?

HAve you tried Exhaust valve lash

 

[firemanjim]

Kinda sounds like excessive fuel.....

 

[Poboy kartman]

....And Bird makes a good point.....too tight a valve lash will keep the exhaust valve from closing completely....allowing unburned fuel charge to enter the exhaust pipe during the compression cycle.....

 

[DeeJee]

It was running good until I removed the muffler. Valve adjustment would be my first guess, but how could that happen overnight, and to both cylinder's? There is no doubt about excessive fuel, the flame shooting out of exhaust confirms that. But, I wqould guess that it might also be po ssible that Kohler designed the system to have a certain amount of back pressure to aid in the combustion, and by removing the muffler, this even combustion was removed. Is this plausible?

 

[justinlogue5_0]

I am gonna say it has nothing to do with the muffler or back pressure and strictly fuel or valve adjustment. I say this because almost every Kohler I have used (including the current one on my Dixie Chopper mower) will make the exhaust glow red if you run it at night. During the day and with a muffler keeping the flame inside, you don't notice it. It doesn't hurt anything on my set up so I just haven't bothered to check valve lash and fix the issue.

 

[Desertduler]

When you have hot exhaust gases coming out of the exhaust that is mostly unburned from the engine say from when the throttle is chopped oxygen will mix with the hot gases and the charge will explode, this is common with a short open exhaust system.

 

[Desertduler]

The same thing can occur with a exhaust system that has a leak in it, oxygen can be drawn in through the leak and mix with the exhaust gases and explode also. Remember the simplest thing, what did you change and or do that made this happen?

 

[DeeJee]

Thanks to all for your comments. I suppose a exhaust leak is entirely possible. I welded a one inch black pipe to flanges I made, and used a wire welder. It was a tight fit, and in fact I had to use cap screws instead of the origional bolts. Plus I did not use new gaskets, so there might be some leak there. I started it up a few minutes ago, and was getting vapor out the exhaust before t fired off. If push comes to shove, I will pull the shrouds and then the heads. It is a pain in the postier.

 

[firemanjim]

For giggles, put the stock exhaust back on and see if it still acts the same......

 

[Desertduler]

If you want to find the exhaust leak, shoot a little ATF in the carburetor with the engine running and then hold a rag over the exhaust exit an you might find it.

 

[chancer]

You already got some good advice, but as you originally said Kohler design may have something to do with it. I have a Kohler on my lawn tractor and that thing back fires super loud every time it shuts off. I searched the lawn tractor forums and everybody just blames it on Kohler engines. There was even a bulletin from Kohler explaining exactly how to turn off your tractor. I know it sounds like you may have a couple other issues but keep in mind Rumor has it Kohlers like to back fire when shut off.

 

[BirdFanatic]

You already got some good advice, but as you originally said Kohler design may have something to do with it. I have a Kohler on my lawn tractor and that thing back fires super loud every time it shuts off. I searched the lawn tractor forums and everybody just blames it on Kohler engines. There was even a bulletin from Kohler explaining exactly how to turn off your tractor. I know it sounds like you may have a couple other issues but keep in mind Rumor has it Kohlers like to back fire when shut off.

Un like my gx390 that likes to back fire on throttle up

 

[Scout]

When you have hot exhaust gases coming out of the exhaust that is mostly unburned from the engine say from when the throttle is chopped oxygen will mix with the hot gases and the charge will explode, this is common with a short open exhaust system.

I'm going to agree. When I did the intake and exhaust on my 212, I had flames from the exhaust when I let off the throttle. I bumped up the carb jet size and it doesn't do it anymore.

Did you do anything to the intake? Without a matching intake, you may find that it doesn't run as well as it should.

 

[Louie The Lot Lizard]

A friend has a big Toro commercial rig he uses on his palatial estate. Each and every time he shuts down the big Kohler V-Twin it fires one off, sounds like a 20 ga. shotgun, and this is THROUGH THE MUFFLER.

 

[BirdFanatic]

Yea have to admit has a kohler vanguard v twin 16hp and it backfired when shutting off not so loud because it had a original exhaust that restricted the sound .

 

[DeeJee]

I kept fine tuning the fuel jet, and helped it a lot. Kohler says that back pressure is important. I have mufflers ordered, should be here midweek, so will see what happens then. And I did nothing to the intake. It is possible that I need a carb kit, new jets, etc. When I cleaned the carb, it was pretty grungy. The spark plugs look okay, but with a spark tester, they burn closer to yellow than blue. New plugs might help. A hotter plug might improve combustion. I now belive it is a combination ot things, starting with the straight pipes and no mufflers.
Thanks to all for the input.

 

[Desertduler]

Back pressure in a four cycle engine is a bad thing for performance, any burnt exhaust gases that are left un scavenged in the combustion chamber after the exhaust valve closes just takes up volume that a fresh air fuel mixture could have not had it been there and it will dilute the combustion charge resulting in power loss. A hotter spark plug does not burn the air fuel mixture more complete it has to do with heat dissipation from the spark plug into the cooling system.

 

[Desertduler]

Another way I like to explain combustion dilution which may sound silly but true goes like this, lets take a 10lb cannon ball that with 2.5 lbs of powder will shoot the ball a known distance, then take a 10lb cannon ball and try to shoot it the same distance with 2.25 lbs of fresh powder and then add .25 of burnt powder to the charge and see how far the ball flies.

 

[JMINDY]

A friend has a big Toro commercial rig he uses on his palatial estate. Each and every time he shuts down the big Kohler V-Twin it fires one off, sounds like a 20 ga. shotgun, and this is THROUGH THE MUFFLER.

I have a Troy Built mower with Kohler motor, does the same thing every time! It's a spare mower that I hardly ever use, so I don't usually remember... always gets me.