Ford 971 Carb. issues

davh55

Member
Tractor will not start without full ckoke and then have to keep it almost closed to run. It has a Marvel Shebler TRX-813 carburetor that was just cleaned because of the same issue. Have changed float level and all areas and passages seem to be open. Need some thoughts, have not changed carb yet but thinking I may have to. The price of a new one is over $350. Thx. Dave
 
Can you turn main screw in and
tractor dies? If not something is
still dirty. At the bottom of main
needle there is a tiny hole that
leads to 2 other tiny holes in
ridge on bottom of carb. Mine were
packed tight with junk didn't know
they were there. Plenty of fuel
flow?
 
If you buy a new carb there are
folks on here that would love to
have that old one. Myself
included,I have a carb from a 134
engine on my 960. Bigger is
better?! Lol
 

I will take the carb apart and check the small passages again. Seems to be be sealed around intake gaskets, has plenty of vacuum through carb inlet but might spray some carb cleaner around and see. It also seems to have plenty fuel when I cover the inlet then fuel shows up. I'm sure I have probably missed a passage somewhere. Just seems unusual since it will not fire without total covering of inlet. I have both adjustment jets at 1 turn open.
 
If the carb was just cleaned, and worked good for a short while, sounds like fuel contamination.

Look closely at the idle circuit. That is the smallest orifice, most prone to clogging. On that model, the idle mixture screw regulates air bleed, not fuel, so turning it in enrichens the mix, backing it out leans it.

If it won't idle or run top end without choke, either the main is clogged, or set too lean, or fuel is not making it to the bowl.

Is the tank rusty and flaking from the inside? If so, that will foul the carb. Filters will help, but they are too restrictive for gravity systems.

You might be able to dump out the tank, wash it out with E85, but if rusted badly may start it to leaking.
 
I was once involved with a 971 with a similar problem. It would start up and run OK cold, but after it warmed up it acted like it was starving for fuel unless you ran it with the choke half closed. You name it, I tried it, including having the fuel tank boiled, carb professionally rebuilt etc. I was convinced it had something to do with the proximity of the exhaust system to the fuel system 'cause it always ran great in the winter. Someone insisted it was vapor lock, but how can a gravity feed system vapor lock? I rerouted the fuel line as far away from the exhaust components as I could to minimize the possibility of gasoline boiling or vaporizing in the fuel line, but it made no difference.

I cussed that thing for 5 1/2 years, and when I finally quit that job and moved on we still didn't have it resolved. (Though that wasn't the reason I quit that job).

Sorry I can't help. Actually, I liked the tractor. It had SOS, and in the summer we ran it on a 7', dual blade finish mower. You couldn't have asked for a more ideal combination of tractor and mower.
 

I cleaned the carb because it was doing the same thing before I cleaned it. It had rust and contaminants in it but seems to be clear and a good flow from the tank. I am hoping that there is still a passage or blockage in the carb that I have not found. It just seems like a major obstruction since it will not fire till after I hold my hand over the inlet of the carb to get it to fire and still have the choke just barely open. Seems to be restrictive of gas flow, however gas shows up after I hold my hand over inlet of carb. Reset float level with no change. Must be restrictive through main jet. Does any of this make since, carb cleaned up good and blown out by good air pressure. Seems to be open but not 100 percent sure.
 
quote="davh55"](reply to post at 07:25:57 09/17/18) [/quote]

it will not start cold or hot until extreme choking applied. Does not change after engine runs to warm up.
 

Could not find a main jet that screws into main jet inlet just the needle that screws in. Should the Marvel Shebler have a numbered main jet that you could change?
 
When one cleans/rebuilds a carb you need to soak it for a good long time 24 hour is not unheard of. Plus you need to spray out all the passageways with carb cleaner then poke them out with a small piece of wire or as I use a torch tip cleaner tool and blow them out with air and then spray and poke out again and do so 3 or 4 times if not more to be sure
 
(quoted from post at 10:37:34 09/17/18)
Could not find a main jet that screws into main jet inlet just the needle that screws in. Should the Marvel Shebler have a numbered main jet that you could change?
on't be afraid to open it more than one turn.
eUhDKFx.jpg
 
That almost sounds more like a vacuum leak.

When you held your hand over the air inlet, did you get a strong, steady vacuum against your hand?

If weak or pulsating, could be a vacuum leak around the intake gasket, carb mount gasket, or an intake valve not closing. That has a siamese manifold I think, they can burn through internally bringing exhaust back into the intake. If you can get a vacuum gauge, take a look at the vacuum if you can get it to idle. It should be a steady reading of 15-20 in. If low, there is a vacuum leak, if pulsating check the valves, run a compression test.

Here is a fuel circuit of that carb. There may be some difference in the main adjust configuration, but everything else is the same. Try opening the main adjust another turn. There is no numbered main jet, it is fully adjustable.
Carb Circuit
 

It has a strong vacuum pull when I cover the carb inlet with my hand. Your pic shows what I was looking for. I have not taken the internal brass jet like part out behind the adjustment needle. I will check this out and pretty sure that is the issue.

thx. Dave
 
I redid one, the needle that came with the kit had the wrong taper on it, check to make sure they are identical with old.
 

Opened carb back up and found 3 issues. I had set float to high and had to reset. The real problem was the main jet and the 2 passages on top of the bowl just behind the main jet sticking up. The main jet would not come out since someone before me made it impossible to take it out. Do not want to use drill to take it out but may have to. Cleaned them up and made them clear with carb cleaner. Have not fired up yet but will do and respond. My fault completely for not thoroughly completing the job the first time. I do appreciate all the response. Thx. Dave
 

Started right up and continues to run good. Thanks for all the input. I'm embarrassed but learned a valuable lesson, "Why is there never enough time to do it right--but always enough time to do it over?"

PS: Shifts great, hydraulic lift is good, PTO turns while disengaged, and Power assist steering is not great but have little experience with it. Don't know what to expect with one arm loader on the narrow front, which the loader is coming off soon. Have some to learn but looking forward to it!

Thx. Dave
 

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