[elankford]

My tractor seems to be overheating, and it has been suggested it is running lean. Before it began running rough, it simply started running fast after 30 minutes. Now it runs rough at lower speeds, and surges. Before it got worse, I had suspected a fuel line leak, and all lines have now been replaced. I got a vacuum tester, and the crankcase impulse line simply pulsates, with no net vacuum. I suspect this is normal. The fuel pump suction side pulls about 2.6 inHg. My vacuum tester pulls fuel freely through the fuel line, with no bubbles. Despite all that, my new fuel filter now fills no more than about 1/8", or barely a drop in the bottom. A year ago, it stayed about half full, and one day 3 months ago, it stayed nearly full. Now, I have no idea how any fuel has gotten into the carburetor at all. Apparently not enough has, though, because it runs pretty roughly, and surges. Why is it doing this? I tried using a shop vac to blow into the tank filler neck, and pressurize the fuel tank. With the engine running, the fuel filter still did not fill any higher. Tilting the filter to a near vertical while running should have purged the air, but it did nothing. I do not know what is wrong here. I suppose I need to check the fuel pump output pressure, too, but it looks like my vacuum tester does not test pressure. I can see how high it can pump up a piece of fuel line tubing. Let's see...3 psi is about 84" of gasoline height.

Any suggestions?

 

[scubaprokid]

Ed,

Minimum vacuum at both slow and fast idle is 2.6 inHg. Looks like you at at the minimum. You can also perform a pump minimum flow test by disconnecting the fuel filter outlet hose. Hold the filter in a graduated container and crank the engine for 30 seconds. Minimum fuel flow is 4 oz/30 sec. If you are checking pressure of the pump, it should read 1.7 PSI minimum at both slow and fast idle. Crankcase vacuum checked with a Manometer at the oil dipstick hole should read minimum: 10 inH2O (B43G) and 13 inH2O (P218G).

You state it is overheating: I am sure you have checked and cleaned all the cooling fins and the flywheel fan is clean. Have you also checked your muffler for restrictions or a plugged condition?

Please keep us updated on what you find.

 

[khe]

Try loosening the fuel tank cap and see if it runs better. If it does, the cap vet could be plugged.

 

[elankford]

Great suggestions, Tim. The pump flow was great, but I discovered sediment that looked like rust particles. I cranked and ran out a pint several times until clean. Incidentally, to drain the output line after testing, I raised it, and gasoline quickly siphoned back into the tank, even though I recently replaced the pick up filter with integral check valve. Hmm, no checking. Anyway, on reconnecting the lines, the fuel pump very quickly primed the line and filled the filter full. Within a minute of running, the engine ran smoother, and surging ceased. Now I need to figure out how to tune it with the air cleaner still on. How do I get to that screw?

Kevin, even pressurizing the fuel tank made no difference.

I do not think I have the answer...unless the rust particles were preventing effective pump function, and disconnecting the line and allowing high flow without any back pressure dislodged the offending particles, and this finally fully removed them. Maybe that is the explanation. Any particles that managed to leave the pump in the past would have drifted back into the pump from the filter on shut down.

This place is great!

 

[scubaprokid]

Ed,

Glad to hear you are back up and running. Interesting to hear about the pick-up filters with integral check valve. I am assuming you replaced both main & reserve. Sounds like you still have some crud in the tank though, which could be plugging your new filters. I have heard horror stories of people finding items ranging from old metal gas caps, screw drivers, children’s toys, etc.. in these tanks.

Good luck on getting to the carb. screws. I always remove the air filter housing.

 

[elankford]

I removed the tank last fall, when I replaced the pick up lines and filter. When I dumped the tank, I did not see sediment. I wonder if the rust sediment had collected in the fuel pump. I have replaced the fuel filter twice, and have not seen particulates either time. Yes, I have now replaced all the fuel line, including that in the tank.

 

[elankford]

The problem persists, with the engine running pretty well for about 20 minutes, and then there is a noticeable spontaneous increase of engine speed. It now begins to have some speed variation after 20 minutes, whereas it used to be fast and steady after the first 30 minutes. As soon as the speed starts to vary, I turn it off. I watch the fuel filter level as I run, and it tends to vary, but generally stays very low now. Adjusting the carburetor jet seems to do nothing to change how the engine runs, at a low to moderate idle speed. This is a sure sign of a fouled carburetor, right? It actually idles fairly well, and not what I would expect with a clogged carburetor. How can it, if the low speed jet is not functioning?

 

[mickstan]

The fuel pump vacuum line on the engine can get brittle after all these years. I would pull the engine, remove the tin, remove the flywheel and give it a good cleaning. Then replace the vacuum tube and the fuel pump. Just my 2 cents.

 

[ducks13]

Ed,
I'd ignore the fuel filter level, it just doesn't mean anything in my experience. You have good fuel flow, that is all you need.

The idle mixture screw only makes a difference at an idle. Is that what you are calling the carb jet?

Carb don't usually clog or unclog after 20 minutes operation.

When you have the engine running at full throttle try slowly pulling out the choke and see if it increases the engine speed, if not then it is not runnning lean.

 

[ereed011]

I posted this because my cousin was having trouble with his even after a carb rebuild.
http://www.wfmachines.com/discus/messages/17/34491.html?1250898640

 

[elankford]

My fuel pump meets specs, so I do not see how a replacement can improve that.

John, maybe I have 2 problems. The idle not changing with the idle mixture screw turned from closure to 2 turns out cannot be good. Maybe I have a governor problem, too, or a cracked cam changing dimensions when it gets hot.

Can I disassemble and reassemble the carburetor and clean and adjust it without replacing the gaskets? The kit is $102 from Cummins.

 

[mickstan]

You can get lucky! Just be careful during dis-assembly. And try your local NAPA dealer for a rebuild kit. Tell them what engine you have and the spec number from the tag, and they should be able to fix you up. They can even get you the fuel pump.

 

[ducks13]

You can really clean the carb on the tractor by just taking the top off, there is not much in these carbs. take out the idle mixture scresw and then clean all the passages in the bowl and throttle body with aersol carb cleaner and then blow it out with compresssed air. Check the float level and put it back together. If the bowl gasket breaks you will have to repair or replace it, be carefull taking it apart.

 

[elankford]

I did that. It now surges a little bit at all speeds, but runs fairly smoothly. What is new is that on starting with the throttle low, the motor races to about WOT briefly and then slows to the appropriate speed for the throttle setting. What does this indicate? Float valve stuck open?

 

[lodogg2221]

Governor bad is what causes racing...

On the fuel filter issue, it is completely normal for it not to be full.
This engine has a fuel pump and does not need a full filter to fill the fuel bowl in the carb.

Mine has at times appeared empty, all variations of full, and completely full. None of those levels affected performance one bit.

Of course thats just my experience with Onans and fuel filter levels after just 22 years of using them...

 

[leisure67]

My 318 had the exact symptoms you are describing. I replaced all the gaskets from the bottom of the intake manifold to the top of the carb. Also had to replace the intake manifold itself because it was separating. It was very obvious why the engine was surging after inspecting these worn out parts.
My fuel filter usually has very little gas in it as well which made me believe it was a fuel delivery issue. Disconnecting the fuel line at the out side of the fuel filter & cranking the engine ruled that out.
Good luck with yours Ed.