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.