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Hit & Miss Gas Engine Discussion

Adjustment of Fuel Needle valve


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  #1  
Old 08-01-2007, 10:25:55 PM
actionhac actionhac is offline
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Default Adjustment of Fuel Needle valve

I was running my FM Z 6hp ignitor engine today. It's the first time I have run it with fuel being drawn from the tank and not just the mixer reservoir. This engine is throttle governed.
I can't decide where the fuel needle valve should be set.
One turn out gives me a strong explosion with a slightly sooty exhaust.
1/2-3/4 out, weak explosion, clean exhaust.
Should I set it open only enuff to keep the engine running or will this lean mix be hard on things?
Or should I have the slightly sooty big bangs that might cause carbon and foul things up?
There dosn't seem to be a happy middle ground.

Robert
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  #2  
Old 08-02-2007, 12:11:47 AM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: Adjustment of Fuel Needle valve

If your engine has it's original mixer needle valve, it will have a notch cut in it that will point straight up. Otherwise, set the needle so the smoke just clears.
Andrew
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Old 08-02-2007, 07:37:35 AM
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George Vaughan George Vaughan is offline
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Wink Re: Adjustment of Fuel Needle valve

The "best" position for your needle valve will actually vary somewhat while the engine is running. Starting up and running cold requires a slightly more rich position....as the heat builds you can gradually lean it out until you reach the setting that allows your engine to run best. The Fairbanks engines normally to not use a fuel pump...I have found with mine that the amount of fuel in the base tank has a direct influence on the needle valve setting as well. A completely full tank requires less opening of the needle valve than when the tank is relatively low on fuel. One tip, if you start out the day with a full tank of fuel and plan to run the engine for an extended period of time (at a show for instance) make sure that the fuel tank has some means to allow air inside...if it does not let some air in a vacuum will result and the engine will start running poorly and will drive you nuts trying to figure out why.
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Old 08-08-2007, 01:22:01 PM
actionhac actionhac is offline
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Default Re: Adjustment of Fuel Needle valve

I had my engine out for a run today.
I have come to the conclusion that the needle valve on the mixer must be for inrichening the mix for STARTING and when the engine is warmed up you close it!
The engine runs the best it has ever run with the needle completly closed.
There must be a fixed passage that the fuel goes thru? bypassing the needle?
I'm not sure if this is the way its ment to be but it makes a BIG differance in the way it runs.

Robert
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Old 08-08-2007, 03:01:30 PM
Joe Morris Joe Morris is offline
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Question Re: Adjustment of Fuel Needle valve

Quote:
Originally Posted by actionhac View Post
I was running my FM Z 6hp ignitor engine today. It's the first time I have run it with fuel being drawn from the tank and not just the mixer reservoir. This engine is throttle governed.
I can't decide where the fuel needle valve should be set.
One turn out gives me a strong explosion with a slightly sooty exhaust.
1/2-3/4 out, weak explosion, clean exhaust.
Should I set it open only enuff to keep the engine running or will this lean mix be hard on things?
Or should I have the slightly sooty big bangs that might cause carbon and foul things up?
There dosn't seem to be a happy middle ground.

Robert
It sounds like to me that you may have a replacement needle valve on the tank side. and the threads are too long and bottoming out before the point of the needle reaches the seat. I have seen this happen a few times. There is no reasonable explanation for the engine running with the needle closed. and the reason is that one turn causes a lot of black smoke is probably the fact that the valve is already open some when the valve is supposed to be closed. Joe Morris
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Old 08-09-2007, 06:50:04 AM
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Gene Fisher Gene Fisher is offline
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Default Re: Adjustment of Fuel Needle valve

When the threads are worn on a needle valve it will be impossible to adjust it to run right. No air can enter any carb except into the air intake on any engine. It will make the mixture wrong and the engine will not run right. Put some grease on the threads and see the difference.
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