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Hit & Miss Gas Engine Discussion

Any "Trick" to diagnosing fuel problem?


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  #1  
Old 12-30-2007, 12:25:09 AM
DerekC DerekC is offline
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Default Any "Trick" to diagnosing fuel problem?

1924 FM "Z" 3HP, spark-plug engine.

It runs fine on the "Start" side fuel in the fuel-mixer reservoir, but it's not feeding from the main fuel tank.

A few details...

Brand NEW Fuel-Tank, clean
Brand NEW check-valve
Clean NEW gasoline

I have tested the line in several ways, blowing air through, both by mouth and with compressed-air from a blow-gun. I also flowed fluid through it. The check-valve holds as well going back toward the tank.

When the engine failed to run on the main tank, I tried priming the line, still didn't work.
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Old 12-30-2007, 12:37:25 AM
Kevin O. Pulver Kevin O. Pulver is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

I'm not sure I understand.
The check valve will hold fuel when you blow on it.
But the engine is not getting fuel.
Is the check valve letting fuel pass toward the engine?
Do we have good "suction" from the piston going past TDC on intake stroke?
The intake valve is not stuck or too heavy a spring on it?
I had a weak EXHAUST spring on a 12HP Herc, and the engine wouldn't draw fuel because it was easier to pull the exhaust open than to pull the intake open. Never overlook the obvious. Tell us if this is helpful or not. We'll help you get to the bottom of it. This engine isn't computerized it can only stump one for so long! Kevin
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Old 12-30-2007, 12:42:01 AM
Kevin O. Pulver Kevin O. Pulver is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

Derek,
I'm not familiar with Zs much. It's hit and miss correct?
You should be able to hear the intake make a short and quick "snort" sound when you roll it through intake stroke. Are the valves BOTH seated well?
If you have compression, then we assume they are. How about your valve timing/cam timing? Are you certain they are correct. You say it runs when you prime it, so we will assume all these are OK. That makes me wonder if somehow the check valve is stuck. It holds fuel, but will it admit fuel?
Kevin
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Old 12-30-2007, 12:47:05 AM
DerekC DerekC is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

Thanks Kevin.

That is a concern to me, is it generating suction through the main metering? I don't think it is, but I don't know if or why not? I'm not sure if fuel is being drawn up or not?

I thought about installing some sort of clear-plastic line to see if fuel IS flowing into the line.

P.S.: The exhaust valve spring and keeper is "New" as well and as I said, the engine runs just fine on the start-side.
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Old 12-30-2007, 12:54:30 AM
DerekC DerekC is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

Actually, it's a throttle-governed engine.

It starts easily and runs well from the start-side reservoir, but will not start or even transition-over while already running from the start-side.
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Old 12-30-2007, 01:56:47 AM
Ironman Ironman is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

One thing you may want to look into is to be sure that the check ball does not seat against the intake fuel tubing. I have seen several cases where someone installed a new check valve assembly and fuel line on their engine, and then had the same problem you are having. What was happening was that the suction of the engine caused the check ball to rise up and actually seat itself against the fuel line itself, which kept it from being able to suck any fuel. The cure to this is to cut or file a slot on the bottom of the fuel line before installing the check valve assembly. This will allow fuel to be drawn even if the check ball does seat against the fuel line. It's something you might want to try........
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Old 12-30-2007, 02:10:30 AM
Kevin O. Pulver Kevin O. Pulver is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

Ironman has a good point.
If you're brave you could suck on the carb side of fuel line and feel what is happening. Or you could use the clear line as you said. That NEW check valve may be working TOO WELL. I've seen some homemade ones that had a couple hack-sawed grooves in it to prevent what Ironman mentions.
Kevin
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Old 12-30-2007, 02:12:09 AM
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Ron Haskell Ron Haskell is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

Hi Derek. Bring it over tomorrow, we will get it running. Ron
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Old 12-30-2007, 03:33:16 AM
Andrew Mackey Andrew Mackey is offline
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Exclamation Re: Any "Trick" to diagnosing fuel problem?

Check also the main fuel valve and the fuel line itself. It is possible that it has debris in it between the fuel line and the actual orifice that is mounted in the mixer, after the check. Make sure that the fuel orifice is open. A lot of times debris gets past the check, but lodges in the line before the fuel adjuster. Did you have a fuel issue before installing the new items? this may have been the problem before you started! Try this: remove the fuel adjuster needle valve. Put a finger over the needle valve mount hole and turn the engine thru the intake stroke. Remove your finger. Is there gas there? If not, then there is a blockage. There should be a gasket between the valve and the mixer body as well. If this gasket is shot or missing, the fuel draw will be reduced, leading to too a lean mixture.
Andrew
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Old 12-30-2007, 07:40:40 AM
Ed Radtke Ed Radtke is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

You did close the start needle before opening the main needle,right? O K,just checking.
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Old 12-30-2007, 08:03:57 AM
Leonard Keifer Leonard Keifer is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

"If you're brave you could suck on the carb side of fuel line"

Should go without saying, but Ill say it anyway: Do NOT suck on the fuel line by mouth. If you're going to do this use some kind of rubber bulb (you could probalby adapt an old turkey baster, better not use the wife's new one!).
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Old 12-30-2007, 08:16:04 AM
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Eric M. Eric M. is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

My bet is that the blockage is somewhere in the needle valve. If the line flows one way and the check holds, that's not a likely place to look.
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Old 12-30-2007, 10:21:08 AM
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Default Re: Any "Trick" to diagnosing fuel problem?

Check the spring on the intake air compensating valve- Too weak & it won't suck the distance from main tank.
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Old 12-30-2007, 10:26:34 AM
J.B. Castagnos J.B. Castagnos is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

Doesn't this engine have the disc on the carb inlet? This is to create a vacuum on the fuel line. Is the spring stong enough on the disc, the fuel is there for the start side, has to be lifted from the tank for the run side.
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Old 12-30-2007, 10:29:21 AM
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Elden DuRand Elden DuRand is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

Quote:
Originally Posted by Bob Naske View Post
Check the spring on the intake air compensating valve- Too weak & it won't suck the distance from main tank.
Bob:

I'm with you. The compensating choke (flutter choke) is most likely the problem.

To diagnose it, get the engine running on the starting side then, with a finger closing off about half of the air inlet, slowly open the tank needle about a half turn.

As soon as it starts running rich, close the starting needle and tweak the tank needle 'til it runs right. You might have to cover or uncover the air inlet some to get it right but, it should be able to be adjusted 'til the engine runs right.

Note that this will only work for one speed and load. If you change either, you have to go through the process again.

If it runs when hand choked, fix the flutter choke. Some restriction in the air inlet is necessary to make enough suction to draw fuel from the tank.

If the flutter choke spring tension is exactly right, the engine will run at all speeds and loads without having to adjust the mixture. The only thing that will make you change the needle setting is fuel level in the tank.

Take care - Elden
http://www.oldengine.org/members/durand/
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Old 12-30-2007, 11:56:00 AM
Kevin O. Pulver Kevin O. Pulver is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

Don't worry Leonard,
With this weak new gas you hafta drink a lot more of it to wind up dead.
It won't hurt him to suck on the fuel line.
Kevin
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Old 12-30-2007, 12:50:52 PM
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Gary Pflum Gary Pflum is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

If the fuel line comes off and out of the engine easily like it does on my 5 hp Z, remove it and drain the fuel out of it while you are inspecting it. To test it safely just stick the check valve end in a glass of water. Check it both directions. Lifting fuel up and holding fuel from dropping down. I am sure that you have made sure that the valve is vertical when it is installed in the tank.
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Old 12-30-2007, 07:44:29 PM
DerekC DerekC is offline
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Default Re: Any "Trick" to diagnosing fuel problem?

Well....Thanks to all of you for the great advice you gave...
I NOW have it working!!! This is my first flywheel engine, bought it back in October, and this is the first time I've had it running off the main tank.

The tank that came with the engine was a leaker and the previous owner already bought, but hadn't installed a NEW replacement tank. Until today, I've just been running it off the start-side reservoir.

The problem seems to have been the check-valve after all, with the check-ball jambing into the end of the fuel-line. To diagnose I applied a suction-pump to the mixer-valve (needle-removed, end plugged) and it wouldn't draw fuel. I know I tested for flow when I made up the line a month back, but the check-ball problem must have been an intermittent.

I used a hack-saw to cut a slot in the end of the fuel line, cleaned up any burrs, reassembled, primed the line with the suction-pump (just to test and help get it over the hump) and IT WORKED!!!

Ran it on gasoline in the main tank. When I was satisfied it worked, I decided to drain the tank and refill it with Coleman Camp Fuel to try running the engine on something other than gasoline. That worked too!!!

Thanks again to all of you for your Great Advice and offers of help.

DC
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