T-20 won't run at hot

[Wisperson311]

I have a 1950 Harry Ferguson. Starts fine. When it gets full up to temp, it starts lugging and wants to stall. If I hold open the choke it stays alive and will barely stay alive lugging back and forth and lurching/stalling. It has new plugs, I converted the points to electronic, I redid all the throttle linkages, I even took the front engine plate off to check the governor (fly wheel plates (not the balls type), it was fine although way over adjusted, I properly adjusted it.
It has good gas, a vented fuel cap, I cleaned all the gas filters. Its not the manifold intake (I sprayed carb cleaner at the manifold and no throttle change.
I really don't understand what the problem is.
Anyone have some ideas?

 

[joeysmith]

Possibly vapor locking in the fuel line?

 

[Wisperson311]

Possibly vapor locking in the fuel line?

Thank you. That is something I have not made any attempts to check. I forgot to mention that existing coil was mounted horizontally and was an oil filled type and should have been mounting vertically. I replaced that with a new solid filled type. (the electrical system is all 12V)
I will now try to insulate/thermally shield the the fuel line and possibly the carb, and repost in a couple days.

thank you !

 

[lodoc]

Weak mechanical fuel pump can give similar issues. Consider checking fuel pump pressure

 

[Brown David]

Weak mechanical fuel pump can give similar issues. Consider checking fuel pump pressure

Where is the fuel pump on that tractor?

 

[Ron(Ont)]

The only fuel pump is gravity.

 

[Brown David]

The only fuel pump is gravity.

I know that but apparently lodoc doesn't.

 

[Ericp351]

Now now, Mr. Brown. This is the new woke touchy fealy tractor place. Try to be Canadian polite! You all got more lakes to lose? This guy converted, so coil may lack a ballast resistor, overheating. Carb may be very lean, Torch barnd plugs, et cetera. Got to be nicey nicey, lest cancel culture may hit the once Great White North!

 

[Wisperson311]

The coil is a hi-performance type and it does have an internal ballast resistor. I checked the plug wires for corrosion or cracks and they look fine.
The plugs themselves are good quality and gapped correctly. The compression is a bit low at 95 psi (should be 102 to 120 according to the manual), and there's good matching between the 4 cylinders.
The carb is set where recommended, for the idle and the main jet.

It occurs to me if the problem is "vapor lock" ....the carb on the machine now is new and is cast aluminum. I have what I think is the original carb.
I think that is an iron body. If there is some fuel heating issue I wonder if the carb material might be a factor.

I haven't tried yet to insulate the fuel line or insert a heat shield between the carb and the engine. I got some material so that's next

 

[Ericp351]

I prefer coils with the external ballast resister, as cheaper and easier to troubleshoot. More selection also. Ain't sending you shopping. If not already done, highly recommend you confirm fat, blue spark when hot and troublesome. Pull your plug and run on three while grounding, or even use a spare. Non resister and steel core wires best, proven. Original carbs, good floats, simply do not vapor lock, even with todays fuel and hard use. That said , IF vapor lock, substitute fuel vender before change to fuel feed or carb. Did you pull and read plugs as lean? When ever in doubt, fatten mixture screw up to half turn! Good luck with tractor and suffering the RainBow bigrade! Post script, above based on POINTS, more reliable and fast to troubleshoot. Contact (USA?) maker of your kit as to plugs and wires. Very hard to argue for resister plugs, even if bonehead owner demands a fancy stereo system! Last edit, given you info Rmenber, all ignition troubles are ignition. Most fuel troubles, at lest before China carbs, are ignition.

 

[Ron(Ont)]

When it is acting up requiring more choke, try removing the fuel tank cap. If it is plugged it will run lean.

 

[Wisperson311]

I forgot proper name for my model: TO-20. I tried wrapping insulating tape with a radiant reflective outside around the fuel line. Also put a piece on the the carb face next to the engine (although it didn't stay on very long). Engine has the same problem. Gets up to temp ok, then when hot it will run only if the choke is fully closed and then only in lurches (I live on a hill and nothing is flat here. It will pull in 1st gear but only lurching and threatening to stall. I will check the spark (although it's a new hi-performance coil).
While the tractor is lurching, some gas spits out the vent in the gas cap (I took an ordinary gas cap and drilled two holes in it_not while the cap was on the tank))...so I believe the tank is vented (tank happens to be full, so the lurching sloshes the tank..I think that's ok.)

I had the tank off to remove the front gear case months ago.
Is there supposed to be a thermal blanket between the tank and engine? (I didn't see one when I took the tank off)

At his point I think I will rebuild what I think is the original carb, and install that and see what happens.

 

[Ericp351]

No as to the blanket, But, some 20, 30,s, and most 35,s have a metal "wing" around ex man. Refitting to proper carb is way to go, except confirm spark soon. Poor thing lost her gen, then points, than carb.! Deserves a protest! A simple cold , wet rag is easiest way to rule out vapor lock. I overworked my little 20 brush cutting in summer. Vapor lock not a problem if radiatior at all clean, in and out. Have you checked time? They well tolerate a few extra degrees.

 

[Wisperson311]

The tractor runs great in the barn on a level surface. I ran it for over 30 minutes like that, moving throttle from idle to mid rpms and throttle response was excellent, no hesitation. I took it out to go around the barn and that is a slight slope (maybe 8ft vertical for 40 ft length)
Then it started to complain and only run at low throttle and the choke fully closed. Started to complain going uphill, seemed to complain more going down hill. Once it enters the lurch mode...it stays that way until parked in barn on level surface....then it runs but only at low idle and choke all the way closed....although no lurching, coughing, other misfires.

I will check the spark once I get it in that mode again ( I doubt it but its possible, a brand new relatively expensive coil could be bad).
In mean time I will rebuild the original carb.

I wonder if maybe the distributor is bad. It might be the original I don't know. The centrifugal advance weights, seemed ok when I set the timing for the new electronic ignition. This last test makes me think the tractor maybe doesn't like to run on a full tank at load...at least that's relatively easy thing to check.

 

[Brown David]

You've got a fuel supply problem.

 

[Wisperson311]

Thank you BD , that it runs when hot with the choke closed suggests there is not enough fuel getting thru...air is fine( and it doesn't affect this problem whether the air intake is open or hooked to the air filter), so it's the fuel delivery or the carb.

When I had the tank off, I rinsed it out but didn't really clean anything or didn't see anything. The sediment bowl and valve assembly were removed from the tank and cleaned (it wasn't dirty). Maybe I missed something in the tank. I haven't pulled the carb drain plug to see if the gas streams out (don't like the idea with a hot engine) but will do that. If that look fine, then its rebuild the old carb I think

thank you

 

[Jim L WA]

Another thing to check would be that the float isn't making contact and hanging up against the bowl when you go up hill. But If you can rebuild the original carburetor you might be in the clover.