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D4 pony carb doesn't respond to adjustment after refurbishment

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10 months 3 weeks ago #250937 by neil
Hi all, I cleaned out this carb (the bowl cross-passage and the emulsion tube included), fitted new gaskets and a new float valve and main jet. Set it up on my test stand pony and I can get it to idle, and can also get it to run at rated rpm for just a short while before it starts dying off. I adjusted the float to 1 1/16 which gives a high-ish fuel level in the bowl. The choking off after a couple of seconds of rated rpm sounds like it's starving so I need to deal with that, but what I also found was that adjusting the main jet seemed to have no effect on the running of the carb. This leads me to think that it is running on an alternate supply of gas. Can't quite remember what that alternate supply is called right now. I did replace the jet and I wonder if it's actually the wrong jet for that carb. I noticed that winding the jet screw in and out was very easy, as if it was not actually lifting the jet against the spring (it has the horizontal adjuster). I verified that the right angle toggle is engaged with the jet and I could see it adjusting when I had the top off the bowl.
Any thoughts on what I've missed? All gaskets are new including the bowl to throttle body gasket.
 

Cheers,
Neil

Pittsford, NY

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10 months 3 weeks ago #250939 by trainzkid88
is it a nice fit in the thread? might be drawing air some where.

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10 months 3 weeks ago #250940 by kittyman1
-what does sparkplug look like? (new one helps hugely)
-is it running lean? engine getting overly hot? not taking load?

-need to insure fuel supply is steady and adequate...

-otherwise my guess is passages still not clean enough...etc....
-or maybe not even fuel related? spark timing...etc...
-keep searching

always dropping GOLD, all you have to do is just pick it UP !

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10 months 3 weeks ago - 10 months 3 weeks ago #250942 by Dandy Dave
Is the Carb bowl vent plugged? That will drive you nuts if it is. Usually will make the carburetor flood over but not always, or right away.

1940 Cat 12 Grader 6M17
1956 Cat D2-5U
1956 Cat D6- 9U 23721
Copake, NY.
Last edit: 10 months 3 weeks ago by Dandy Dave.
The following user(s) said Thank You: kittyman1

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10 months 3 weeks ago #250948 by neil
Thank you gentlemen, I'll recheck all these things. For reference, I first ran the pony with its original carb and it ran as expected - idle, accelerate, rated. Suspecting the problem being with the fuel bowl area, I swapped only the fuel bowl, and it gave teh same symptoms as when it was on its original throttle body and installed on my buddy's HT4. I will check the bowl venting arrangement. It's different to my 3J which has a breather - the HT4 carb does not have a visible external breather. It has a big stud in the bowl base where the drain plug usually goes - not clear why, possible the previous owner lost the plug and found a "will-fit". If the bowl is not venting properly, I could see problems with either a vacuum developing in there causing starvation, or drawing too much fuel in under vacuum causing flooding. Will investigate. Anyone happen to know what the "proper" venting arrangement is on these later model carbs without a side vent?

Cheers,
Neil

Pittsford, NY

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10 months 3 weeks ago - 10 months 3 weeks ago #250960 by Old Magnet
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Last edit: 10 months 3 weeks ago by Old Magnet.

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10 months 3 weeks ago #250966 by neil
Turns out that I misdiagnosed the main jet adjuster bracket: it was quite bent and basically didn't move. I corrected that and now it runs but I'm still iffy on the float level. I'll try it under load and see what it does. The test stand is good but I can't load the pony which is what I need next. Idles beautifully

Cheers,
Neil

Pittsford, NY

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10 months 2 weeks ago #250993 by kittyman1
Carb bowl Vent plugged....awesome DandyDave....i forgot about that one....! ? !

always dropping GOLD, all you have to do is just pick it UP !

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9 months 3 weeks ago #251572 by Mike Hudson
Hey Neil glad you are on a roll. I was just fixing to tell you that I am getting by with mine, but it runs really fast if I don’t throttle it down pretty good. I don’t believe the governor is working right or at all on my d2   I’m always on the wrong side to see it operate.  And another thing I cut the gas off every time on it and somehow gas gets in the oil. I have to change oil really often I guess it’s getting in the while I’m running it. Only thing I can think of unless that little petcock isn’t shutting completely off. Pony’s are a hand ful. 

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9 months 3 weeks ago #251591 by neil
Another problem we're having is that the viton-tipped float needle seems to stick. This is a new float valve from MacDonald. Does anyone have a recommendation for a different float valve and seat?

Cheers,
Neil

Pittsford, NY

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