Gas engine dies when hot, but will keep running with choke pulled out a little bit

[Cedarsnapp]

I have a 1965 MF 135 Deluxe Tractor with Z145 gas engine. I have recently replaced the (vented) gas cap and flushed the fuel tank and fuel filter. The filter stays full of gas. The engine starts right up and runs great but after about 10 minutes it often just dies. If I am quick and pull the choke out just a tiny bit, it will keep running. If I am slow and the engine dies, it starts right up with the choke out a little bit and then continues to run fine as long as the choke is on a little bit.

Any thoughts about this problem and what I can do to fix it?

Thanks, Cedarsnapp

 

[ericm979]

Sounds like a fuel flow problem. The new filter could be restrictive or too small. Or the vented cap is not venting enough.

 

[Cedarsnapp]

Thanks. I'll check the fuel line from the filter down to the carb for any obstructions. The filter itself is getting plenty of fuel to it.

 

[Spanner]

I have a 1965 MF 135 Deluxe Tractor with Z145 gas engine. I have recently replaced the (vented) gas cap and flushed the fuel tank and fuel filter. The filter stays full of gas. The engine starts right up and runs great but after about 10 minutes it often just dies. If I am quick and pull the choke out just a tiny bit, it will keep running. If I am slow and the engine dies, it starts right up with the choke out a little bit and then continues to run fine as long as the choke is on a little bit.

Any thoughts about this problem and what I can do to fix it?

Thanks, Cedarsnapp

Your description fits a mixture problem.

Then you say the engine will die after about 10 mins - So I'm wondering if you have a blockage in the carb at the fuel inlet or float needle valve seat and the carb just runs low on fuel. ?

Can you check the float level?

You seem to have a sufficient flow of fuel to keep the engine running on 'choke' which is a richened mixture.

:wrench:

 

[ericm979]

My reasoning was that there's a flow problem causing an eventual low fuel level in the bowl. That makes the mixture go lean as the fuel has to be pulled up a higher distance to get into the carb's throat. The choke would increase the vacuum in the venturi which would compensate, causing the engine to keep running. If the float level was set low it'd run poorly all the time not just after 10 minutes. I'm assuming a plate type choke that masks part of the intake tract, not an enrichener commonly seen on motorcycles.

Just having fuel visible in the filter doesn't mean that it's flowing enough fuel.

 

[oldpilgrim]

Run it with the gas cap off. See what happens.

 

[Cedarsnapp]

Run it with the gas cap off. See what happens.

I'll try that. Thanks to you both for educating me about this problem.

 

[Cedarsnapp]

Spanner,

Thanks for your thoughts. I know what and where the float bowl is, but I don't know how to check it. Would it fill up again by gravity once I turn off the engine? Do I just quickly remove it or is there a better way to check the level? Thanks.

 

[ericm979]

I would not drive with the gas cap off. You don't want to spash gas out of the tank and onto the engine. Staionary is ok.
In this situation I prefer to run it until it shows symptoms and then loosen the cap. If it's really not venting it'll have a mild vacuum on it. Sometimes you can hear it whoosh (with the engine off). But if it runs poorly and then runs well again right after loosening the cap, you have definitively shown that the tank vent is the problem.

 

[RSKY]

Could it be a restriction in the airflow. Maybe a dirty air filter?

Keep us informed when you find the problem.

 

[ericm979]

Restricted airflow would cause it to run rich, not lean as he's experiencing.

Cedarsnapp, there's a couple ways in theory to check the float level. One is by disassembing the carb and measuring, the other is by using a hose attached to the float bowl to show the level outside the carb. I say in theory because different carb designs often make one of those easier than the other.

But like I said, low float level affects running all the time, not only after 10 minutes. So it's unlikely to be the problem.

The problem started after you changed the fuel filter and flushed the tank. Occam's Razor says that those are probably the causes of the problem. The filter may not be flowing fuel fast enough to keep the float bowl full. Or the tank flushing may have gotten gunk into the inlet.

You can measure flow by removing the feed to the carn and running it into a container. Turn on the gas tap or unblock the fuel line if there's no tap and measure the amount of flow in a minute. Your shop manual may have a spec for that but if it doesn't you can still see if its a good flow or a trickle.

 

[Spanner]

Spanner,

Thanks for your thoughts. I know what and where the float bowl is, but I don't know how to check it. Would it fill up again by gravity once I turn off the engine? Do I just quickly remove it or is there a better way to check the level? Thanks.

I would think (without looking) that YouTube has videos showing this procedure. It has just about everything else for these tractors.
I'm also wondering about air-leaks downstream of the carburetor. Maybe at the inlet manifold? Adding choke would help compensate for air-leaks.

RSKY: The engine is apparently running lean and adding choke keeps it running. A blocked air filter is causing the mixture to be rich, not lean.

(Edit: Posted from P.1 and just seen Erics post above. Similar thinking.)
:wrench:

 

[Spanner]

Some good advice options in this earlier thread:

http://www.tractorbynet.com/forums/massey-ferguson-owning-operating/358097-mf-135-gas-wont-stay.html

:wrench:

 

[s219]

An old timer's trick when your tractor is sputtering as it runs out of gas is to flip the choke on. I used to do that with my riding mower when it was out of gas, and it would buy me enough run time to make it the 400' back to the barn. I'd be inclined to think this is a fuel delivery / fuel starvation problem first, and then maybe think about conditions that could cause lean running second. Seems to me that if it started after you changed the fuel filter and cap, then one of those is at fault. Poor venting through the cap could cause fuel starvation. Wrong filter or filter with a lot of restriction could cause fuel starvation.

 

[Tractorable]

My FJ40 Land Cruiser had a similar problem. It would start and idle just fine but when I went to drive it it would stall and die after going about 100yds. I eventually put a vacuum pump on the fuel line and discovered I could barely suck any fuel through. It got enough fuel to idle but that's it.

Turned out the hard line going into the fuel tank was 90% clogged with weld when a previous owner welded the hard line to the fuel tank flange.

Run your fuel line to a separate fuel container to check for fuel starvation upstream of the carb. Once you eliminate that as a potential issue then move your focus to the carb.

 

[Cedarsnapp]

UPDATE: PROBLEM SOLVED. Thanks so much to everyone for excellent suggestions. I checked the fuel flow after the filter (excellent) and after the line from the fuel filter to the carb (also excellent). I checked all the hoses and carb connections, tightened them and found one hose connection from air cleaner to carb was slightly loose, probably allowing some air to leak. That seemed to help a bit but problem still lingered. Then I cleaned the inside of the carb (squirted some Gumout Carb cleaner down air intake while engine was running and that cleared it up. Now runs great. So probably was partial clog in a carb jet. Carb is a Marvel - Schebler and appears to be very basic.

 

[Spanner]

I like a story with a happy ending. Thanks for update CS.

:wrench: