MF135 - dying after minute of running

Hello all - in need of your expertise.

I ve acquired my grandfather s M135 (Continental gas) that has been sitting for a number of years. The issue I m having is that it dies after running for a few minutes after its warmed up.

It cranks up great every time with no choke even when cold. It runs strong while running even under a load. However, after a few minutes it will rev down and die like its running out of fuel. Give it a minute off and it cranks right back up with no problem but then dies again about a minute and a half later. When it starts to rev down, if you play with the choke you can get a few more seconds out of it, but it will still die. It feels like a fuel starvation issue like its using the fuel out of the bowl and then dying, but I m no expert. It runs for about the same amount of time each time you try. It will die while under way or just sitting stationary idling.

In getting it running again here are the things I ve done:

-service/fluid change
-new plugs and plug wires
-new points/condenser/distributor cap and rotor
-new tank and fuel lines and fuel
-carb clean (and new carb explained below)

I originally put a knock-off replacement carb on it when I first started working on it. It cranked and ran well on the knock-off carb but it would not go up hill. Any time it was on any incline it would rev down and die like it s doing now. It would go up the incline backwards with no issue but any time it was nose up it would die. I was thinking it was a float sticking issue. After removing the new carb several times/confirming float height and movement I gave up on it and went back to the old carb and cleaned it. It ran great for a few days on the old carb and then started this cycle of dying (but it will go up hill while its running).

It still seems like a fuel starvation issue. When it dies, the sediment bowl is full of fuel. Also thought maybe a vacuum issue and removed the fuel cap while running - same result and it still died. As mentioned above, tank is new, valve and sediment bowl cleaned. New fuel lines. I need to confirm there is fuel in the carb bowl when it happens but ran out of light today.

I m obviously missing something and may be chasing the wrong cause entirely. Reading the forums on similar issues but not making any headway. Any guidance you can provide would be appreciated - working 90 seconds at a time is challenging.

Thank you,

Just a thought. You said it starts good cold without the choke. Could it be running to rich?

Let it run until it quits, immediately pull the ignition coil wire from cap and see if you get a good, hot(blue) spark against the block when cranking. If not good then the coil is dying. The condenser could be bad right out of the box too but I would suspect the coil for now. If good spark then I would guess a blockage in the fuel system, ensure a continuous flow from the fuel line to the carb first then check the carb again.

I agree with MF-1 coil or condenser. The cheap Chinese condensers are junk, don't waste your money on one. BTDT

Other posters are right about the Chinese condensers being garbage and often failing
as soon as they warm up, but you also might be onto something with fuel starvation.
Every couple of weeks someone on this forum has a similar problem of their tractor
running only for a minute or so, and it almost always turns out to be some
gunk/crapulence in the fuel tank/tap/lines. Exactly like you thought with the fuel in
the carb bowl - it trickles in while it's shut down enough to fill the bowl and run
for a little bit, but can't keep up for extended periods or when using more fuel
(driving up hill, like you said).

That said, you mention there's a new tank and lines, which really shouldn't be an
issue. Was there a new fuel tap, and it free-flowing? I'd pull the carb drain plug (if
it has one) next time it happens and see if you have a good, healthy stream of fuel
pouring out. An old trick is to thread a barbed fitting into the carb bowl drain, then
run a section of clear fuel line from the fitting in a 'U' shape with the other end
open and elevated above the carb - it makes a sight glass so you can monitor the level
in the carb while it's running.

One of the more irksome sources of this issue is when something's floating around in
the fuel tank: When it's not running, it floats around harmlessly, but when it starts
running and pulling fuel from the tank, it creates a slight whirlpool effect and sucks
it over the inlet blocking flow - kind of like when you pull the plug in a bath tub.

Maybe you already tried this, but did you check the gas cap?

I hadn't considered that bc it seemed to run so well (while its running). But I should pull the plugs to confirm. Thanks.

This post was edited by curt2005 on 01/23/2023 at 10:46 am.

New tank, but still using the old cap. In one of the tries, I pulled the cap off and the result was the same. It still died after about a minute/minute and a half. But i've ordered a new cap bc the current one is bit rough. Thanks.

Good suggestion re: the barb and line. I've wanted to check the bowl when it dies but the drain plug is in a tight spot right at the exhaust so getting to it in the heat of the moment is challenging. Will try this to rule out fuel.

What's in the carb bowl vs the strenght of the spark should tell me alot.

Thanks everyone. Will test those and report back.

Great suggestion, thanks. My attention has been solely fuel related I didn't consider ignition. Given the coil is original, I should have one on hand anyways and will order one along with condensor. Will check the spark strength when it happens to confirm.

Some years back I had a similar issue with my Ford 640. I finally decided to replace the coil. When I tried to take the old
coil off, one of the wires broke when I had barely touched it. It appeared that vibration and corrosion had destroyed most
of the strands of the wire right at the terminal connection. I replaced the wire, and the tractor has been running fine for
years. I'm guessing that the same thing could happen in any wire or switch in the ignition circuit.

You have a lot of good suggestions.

My guess would be fuel. As a quick check
I'd take the air intake pipe off, then
start it, wait for it to start to die, and
give it a shot of carb cleaner. If it
picks up you have a fuel processor.

The elbow going into the carb should have
a screen on it. Might be clogged up. Did
you take the elbow out of the old carb?

I've had good luck with Standard ignition
parts. I think the part numbers are right
for the screw cap distributor.

I agree - going through and replacing the wiring is on my list of things to do given the age. I've already found some terminal connections that were weak. Hopefully checking this and the spark as suggsted above will shed some light. Thanks.

UPDATE - up and running.

Thanks for all the suggestions. I used them all. Looks like the issue was in the fuel valve.

Started out checking the electrical. Put a meter on + side of the coil and used an inline spark detector between the distributor and the plugs. Checking for voltage to the coil and spark across the plugs. Recreated the problem and the voltage never dropped and the spark was strong across all plugs when it would die. Appeared like spark was not the issue but I did find several issues in the electrical to address while checking. In removing the wiring plug from the ignition switch, the B terminal spade brake and stayed in the plug (it had been nearly broken all the way across for some time). The voltage regulator also had several terminals that were in rough shape. I eneded up putting a new coil, regulator, ignition switch and rewiring the whole tractor (which was on the list anyways) and making new battery cables as the old were not in great shape. All the electrical back together, fired it up and it did the same thing.

So on to the fuel side I added a nipple to the float bowl drain like DanielW suggest and add some clear tubing to watch the level in the bowl. Fired it up and a moment before it died the fuel in the sight tube dropped and was sucked back into the bowl but then immediately returned to the sight tube once the engine died. Checked the sediment bowl again which was clean. Pulled the bowl. Looking in the inlet there appeared to be something clogging the inlet. Pulled the tank and removed the fuel valve. The top side (tank side) of the vale was filled with metal shavings and gray sludge the same color as the new tank. This was a brand new tank so I'm assuming this is from overspray and crap from manufacturing. My fault for assuming it was clean.

So, pull the valve assembly apart and gave everyting a good cleaning. Ran some fresh fuel through the tank with the valvel still out in hopes of getting any remaining trash out. Put everything back together, added a filter down stream from the valve. Fired it up on the first try and ran it around the property for about 25 minutes - never a sputter.

So looking like this issue is resolved. More projects to do (new voltage reg needs adjusting, lights, etc.) but feels great to get this resolved with everyone's help.

Thanks again.