1948 Model B

[Sam from WA]

has anyone ever had a tractor that has all new carb parts, rebuilt magneto, plugs and wires and the tractor still surges?
I have a B that everything is adjusted right, but surges pretty bad. we're thinkin that we have a vaccuum leak somewhere, but the engine was just rebuilt not 10 years ago and probably has 500 hours on it.

 

[F-I-T]

Sam:

Have you checked the governor control rod for the proper length? It easy to do and if someone was trying things to get it stop hunting, they could have taken the length the wrong way.

Engine off, throttle wide open, disconnect the rod at the carburetor. Hold the rod in your right hand and put just enough pressure on it to take out any slack in the internal governor linkage. Hold the carb butterfly open with you left hand and the rod should be 1/2 hole short from making the connection. The half hole provides a preload as you have to pull it against the leaf spring to get it to connect and that takes out all the slack that the bearing sleeve, weights, etc. can have. Check it. You might get lucky.

Frank

 

[GeorgiaHayFarmer]

Sam,

After checking the throttle rod that FIT wrote about, take a close look at your carb. What parts were replaced? You need to make sure you have a clean carb in EVERY passage, correct fuel flow stream from the bottom of the carb bowl when your drain valve is opened for at least 30 seconds, clean fuel, good bushings at the throttle plate shaft(properly installed), no air gaps around the throttle plate when it is closed at or near the idle position, and all idle air passages are clean and at the correct dimensions. If the throttle plate was not replaced, take a look around the outside edges when it is closed or near closed at the top and bottom. See any worn out places on the throttle plate or carb throat near the bushings? It is not only important to have proper fuel flow, but to have correct air flow. Make sure you don't have a clogged air intake filter element, although I don't think that is the problem. On top of the upper bushing at the throttle shaft should have a felt dust seal. Is it there? Is the plug installed at the bottom of the throttle shaft bushing so your not sucking air at that position? Are your spark plugs clean and dry? If you have a fresh set, you could throw some in and elliminate those being fuel fouled, from the equation. How far out are your idle and load needles? Does the problem, clear up somewhat if you turn your idle needle out from say 1 and 1/4 turn to 2 complete turns from fully closed? Don't forget to be gentle with the needles. They can be damage at the tapered end if over tightened. Turn it in till it starts to stop, nothing more, then back out to 1 or 1 1/4 turns from there. This should give you a good place to start from provided everything else checks out ok. Hope this helps you find the problem.

Scott

 

[P Browning]

Sam, if by surging you mean the engine is throttling to remain alive, this indicates that one or more of the IDLE passage way segments remains blocked. The best solvents known to man will not clear rust, and rust is the main cause of carburetor passage way blockage in DLTX series single barrel carburetors. There is a simple test!

Go to the JD-H Restoration Site (below), scan across to ARTRICLES 1, and of the drop-downs thereunder, select CARBURETORS. On the final page of the piece, you will find a no-wrench test of both the IDLE and LOAD sides of the carburetor. Please post back the result of those tests, and we go from there. (PatB)
Restoration Site, JD H

 

[Sam from WA]

The carburetor was completely cleaned this last year when we had it apart and rebuilt. The govenor linkage is all set to specs as well. Would a vaccuum leak possibly cause the engine to surge?

 

[Sam from WA]

The engine surges when under load and at high speed as well

 

[F-I-T]

>>>Would a vacuum leak possibly cause the engine to surge? >>>

Not under load. Nothing for vacuum when an engine is under load and the carburetor throttle plate is open all the way. Surging fuel flow is a probably culprit. Just because a carburetor has been "gone through" is no guarantee that an offending port was checked and properly cleaned.

Ask yourself when it began to surge? Before or after the carb cleaning? Do you have sufficient fuel flow from the carburetor drain (pencil size stream for at least a minute)? Do you have a bird feather sticking in the tank out flow port? Id the mesh screen in the sediment bowl clogged with old varnish that has been released with the introduction of some ethanol? Is the input screen to the carburetor cleaned of goo?

Frank

 

[Sam from WA]

Everything about his tractor is rebuilt and cleaned. The carb had every passage cleaned with a small wire and compressed air. The engine was surging before we rebuilt the carb as the carburetor was worn out, the throttle shaft could wiggle quit a bit in its bushings. There is nothing in the fuel tank other than clean regular unleaded gasoline.

 

[fixit]

Sugestion: Hold carb lever by hand, gov disconected. If surges, it"s starving for fuel, if steady problem would apear to be in gov housing. Thrust brng etc. I have a 49 doing same thing & is in gov. Drives me nuts but not enough to tear into the gov. Good luck.

 

[F-I-T]

I've seen many, many rebuilt carburetors that had a passage missed. The surging in this case, I would bet, is fuel related, as there is no vacuum, WHEN UNDER LOAD, to call a vacuum leak into question. If when under load, it surges, apply the load, disconnect the speed control rod from the governor, and try to hold the speed constant by holding the carburetor butterfly in a fixed position. The same can be done at no load fast idle, but it's easier to rule out vacuum problems when trying this on an engine under partial or full load. Here's where having a dyno spoils you. If it still surges, it's fuel that is not being metered consistantly into and through the carburetor. If you can hold the speed steady, and the governor speed rod is jumping around in your right hand, then look to the governor as causing the surging.

Check that fuel flow out of the bowl, too. Check for a sticky float, float needle, etc.