starving for gasoline

banjoblast · May 31, 2015

My JD D is missing at full load, I think the engine is starving for fuel. I have all the passages clean and it flows a decent amount of fuel out the bottom of the bowl without it running. With the tractor running at idle it will run some fuel out of the bottom however at full load I can open the valve at the bottom of the bowl and nothing comes out. So at full load it will run good power for 3 or 4 seconds and then it will stumble and miss and then it will pick up and run okay for a few seconds. I have a proven carb on it (one that runs good on another D I have) and no matter what the needle setting are, it will not smooth out and pull steady. The cam I have in it is ground to (in my opinion) hold the intake valve open too long (but what do I know). Any theories out there?

535353m · May 31, 2015

my tractor did the same,it had a restriction at the bottom of the fuel tank. Might need a low pressure fuel pump.bigger lines.

banjoblast · May 31, 2015

Thanks, I cleaned the tank and it'll flow a reasonable stream out the bottom of the bowl when the tractor is off. That makes me think the tank and lines are okay. What low pressure pump would you recommend? I'm thinking that will be the best solution.

535353m · May 31, 2015

Napa has ok quality 5-6 lb pumps

RandyB(MI) · May 31, 2015

What do you mean by "full load" and if actually under full load (pulling), how are you opening the drain? Wide open throttle lever still just uses tiny idle ports and 1/4 throttle plate opening. Doesn't add up. If this carb works correctly on another "D" then not only is it not the carb, but also doesn't need a pressure pump. My guess is that you are running an automotive filter on the one with the problem. These filters are made to flow under pressure, and won't flow from gravity feed sufficiently . Just the mods to the engine aren't going to make that much diff. in fuel useage .

banjoblast · May 31, 2015

The tractor has a sediment bowl. I took it off and drilled out the passages a little bit. I don't use an inline filter. I pull the engine down to 900 RPM (on the dyno), throttle full open and it just starts to cycle between missing and running okay. It will cycle between missing and running at 800, 700, 600. I open the petcock under load.....and nothing, not a drop comes out. I shut the tractor off and it will flow what I think is a normal stream out of the bowl. Makes me want to howl. (why don't those two words rhyme?)

RandyB(MI) · May 31, 2015

I can't imagine why it doesn't do the same on the other tractor on same dyno. Sounds like a China made needle and seat with too small a hole in it or wrong length needle (I've seen both before) not letting enough fuel in but it should do it on both tractors. Let us know what you finally find out. RB

banjoblast · Jun 1, 2015

The carb was rebuilt by a reputable rebuilder and worked perfect on my other D.....won me lots of ribbons.....with not a problem. My other D has the stock camshaft but it is advanced one tooth to get the intake valve closed quicker....no chance of the piston pushing any compression back up the intake at lugging speeds. The present problem tractor has the intake valve held open well into the piston stroke coming into the compression stroke so that makes me wonder if that would make any difference. I need to research the carb bowl positive or negative pressure at full power. As I think about when I was playing around with it, at full power with the petcock open and my finger gently on the opening, it seemed to pulse with positive and negative pressure in the bowl. I'll have to check that again.

timmy curl · Jun 1, 2015

Missing under a load is often spark plugs, wouldn't hurt to try another set.

RandyB(MI) · Jun 1, 2015

Those bowls are vented internally and work fine that way,BUT! I have seen people put external vent tube on them. You may want to try that. Does it do the same thing without air filter connected?? If pressure in bowl wa keeping fuel from entering , then when you open drain it should relieve that and fuel should come in to bowl instantly again. Put a hose barb in place of the drain and clear plastic tubing long enough to run straight up and tape it to hood side and watch the fuel level from cold start to starvation.

banjoblast · Jun 1, 2015

I bought an inline pump and am in the process of installing it. I bought spark plugs also. And a sack of rubber bands to hold my fingers crossed till I try these suggestions.
I'll post the results.

41106 · Jun 2, 2015

I second the comment on plugs.....exactly what mine was doing and I went through everything else first just to find bad plugs. Good luck.

banjoblast · Jun 7, 2015

I got the in line booster pump installed in the gas line, and it didn't do much if any good. So I checked the distributer and it was looking worn out. So I next held the wires away from the plugs and watched the spark and noted the missing spark when the motor missed a few beats but only on the number 2 cylinder. Ran out of time, so I'll put a known good running distributor on next. I'll bet it will smooth out, may not have been the gas supply after all.

banjoblast · Jun 8, 2015

And the winner of the mystery solving is: Plugs. I changed out the #2 plug and that smoothed it out and it pulls steady on the dyno. Like you said, a lot of farting around for a spark plug. But I got a fuel pump installed and I don't have to worry about the empty carb bowl.

starving for gasoline

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