FE 350 Still backfiring

[torey3]

2006 fe 350 still backifiring. Changed the spark plug, it only has 30 hours and it had already has carbon deposits. The cart backfires when rolling back into the throttle. I have been playing with the throttle linkage. I am not sure that I know what the butterfly is on the carb, can anyone clarify? There is a screw that a plate on the carb linkage can rest on, is that where the butterfly is? If so, the butterfly is closing up to that screw as close as it will get so I think it is closing all the way, is there any way to tell for sure? Could it be running lean since backing off the governer and getting more gas/speed? I am driving myself crazy!!!
Thanks

[torey3]

Any help on this one???

[scottyb]

The butterfly is a throttle plate that is circular and fits in the throat of the carburetor.... the throttle linkage you are messing with is connected to it. it opens and closes like a valve. hope this helps

[invalidsession]

The first thing I would be looking for is an air leak. Check all of your air intake plumbing for cracks etc. Next (engine running)spray some WD40 / carb cleaner etc around the area, paying special attention to the intake manifold. Any leak will then manifest itself as a change of note in the engine. Secondly, your spark plug can tell its own story as to what may be happening; a light tan/white would indicate a lean condition whereas a dark sooty appearance would show a rich condition. Ideally, a nice medium brown is what you want to see since this indicates an even fuel / air ratio burn.
Did this "backfire" occur after any work was done ? Is the engine standard or modified in any way ? Any clues will help the kind folks here point you in the right direction and get your cart running properly again.
Good luck,

Chris.

[torey3]

The backfiring occured very commonly when it was banging off the rev limiter. I have since disconnected the rev limiter and the back fire happens much less. The original owner adjusted the throttle linkage to get more speed. I adjusted the governer above the rear axel, to the point I am getting about as much as I can out of it without over revving. It smells of gas and the spark plug colors suggest that it is running rich. When adjusting the linkage I can see what looks to me to be the butterfly moving on the outside of the carb and it appears to be closing. The idle adjustment screw is not touching the linkage. I have heard people talking about using a "hotter" plug, any one in particular? It is on 08 with 60 hours
Thanks guys.

[crash12888]

Hey Torey, what you are describing is caused by the throttle plate not returning to fully closed when you let off of the pedal.
When you let off of the pedal it does two things, 1st it closes the throttle plate in the carb by way of the linkage, 2nd it kills spark to the coil/plug by way of the "grounding" micro switch, with the throttle open even just a bit coasting or slowing down it is still drawing fuel into the engine but with no fire.
When you push the pedal to go it ignites the fuel in the cylinder and BOOM!

Screw the throttle stop screw out until it doesn't touch the throttle arm and then start the cart in neutral, rev it half throttle a couple of times and then let off of the pedal.
Carefully push the throttle arm toward the stop screw.
If it will rotate more closed then you have your linkage adjusted to tight.
It needs to close completely to eliminate the backfire.

Also you need to adjust you linkage so the "start" micro switch engages just before the throttle starts to open.

Sorry so long but I like to explain how and why things do what they do.

[scottyb]

That is an excellent explatation Crash Even I could understand parts of that

[crash12888]

Jus try'n to stay outa the zone..............

[scottyb]

I hear you...... me? I'm more into golf carts

[torey3]

Originally Posted by crash12888

Hey Torey, what you are describing is caused by the throttle plate not returning to fully closed when you let off of the pedal.
When you let off of the pedal it does two things, 1st it closes the throttle plate in the carb by way of the linkage, 2nd it kills spark to the coil/plug by way of the "grounding" micro switch, with the throttle open even just a bit coasting or slowing down it is still drawing fuel into the engine but with no fire.
When you push the pedal to go it ignites the fuel in the cylinder and BOOM!

Screw the throttle stop screw out until it doesn't touch the throttle arm and then start the cart in neutral, rev it half throttle a couple of times and then let off of the pedal.
Carefully push the throttle arm toward the stop screw.
If it will rotate more closed then you have your linkage adjusted to tight.
It needs to close completely to eliminate the backfire.

Also you need to adjust you linkage so the "start" micro switch engages just before the throttle starts to open.

Sorry so long but I like to explain how and why things do what they do.

Crash,
Did the work this weekend. I took off the air inlet house that feeds the carb and used a compact mirror and flashlight to see the butterfly. I adjusted the linkage so that it is closing and I think the micro switch is set right as well. 2 trips around the block and one back fire, crap. Am I better off having the throttle cable looser than tighter? I also noticed that the micro switch also clicks when the pedal is released; do I need to adjust that to click at a certain time as well? I did a new plug as well.