MF 135 Runs beautifully for 30 to 45 minutes

   / MF 135 Runs beautifully for 30 to 45 minutes #1  

Waggawill

New member
Joined
Sep 28, 2023
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8
Tractor
MF-135 4cyl petrol
Hi all,

I have a MF 135 with a standard motor co 4 cylinder petrol engine, it has given good service and is well looked after.

My problem is that it has developed a starts and runs perfectly for 30 to 45 mins then like someone turned on a switch it starts to misfire and splutters and if left will stop

What I have done thus fare to rectify.

  • Carby kit (cleaned and checked)
  • New distributer Plugs & Leads (Including Coil)
  • Had a rattle up the front so new timing chain, governor cup and weights (this removed the rattle and the governor response improved)
  • I have changed all the oil, engine, gearbox / transmission
  • Reset tappets 010 & 012 so many times.
  • Flushed the tank, cleaned the bowl filter and replaced the cork gasket.
  • Using 95 Octane ULP with a little valve save added.
  • Compression test 145psi all 4 cylinders.
  • Oil pressure 60psi
  • General running temperature anywhere from 10deg C up to 38deg C (Welcome to Australia), inland location mostly dry with low humidity.
  • Ignition timing set at 10deg TDC via flywheel hole, I have not retarded at all.
It has me stumped, all the local mechanics require a laptop to conduct their trade, no real help there.
Any help or advice will be welcome. Thanks in advance,

Bill..
 

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   / MF 135 Runs beautifully for 30 to 45 minutes #2  
One potential cause for a fail after 30 minutes can be a blocked fuel tank vent, preventing more fuel to be sucked down to the engine.

Try removing the fuel cap when it does this. If vacuum makes the cap hard to remove, you've found the problem.

And welcome aboard!
 
   / MF 135 Runs beautifully for 30 to 45 minutes #3  
I'm not a fan of replacing parts before tests prove old one is bad but I make exception for condensers. If the tractor had a tune up including condenser recently I'd give odds the new condenser was bad from factory (many are these days). To confirm or eliminate fuel as cause try a couple things. Have a container to catch gas and wrench that fits carburetor drain handy when engine begins stuttering. Park tractor and let it sputter to a stop then pull drain. If stream isn't strong and/or slows you have a stoppage upstream. If that checks out remove air intake hose and run engine without it. Have starting fluid with straw handy and spray into carb when engine begins to stutter. If rpms pick up and can be maintained with start fluid there's blockage in float valve or jet. Swap in a known to be good coil. If ballast is in line temporarily bypass with jumper when engine falters. "Hot wire" from battery to coil to see if there's a break in wire leading to coil.
 
   / MF 135 Runs beautifully for 30 to 45 minutes #4  
see if it depends on the throttle setting (fuel rate is a problem) or if it temperature dependent (lux capacitor creating spark gets hot, clearence changes so no spark signal is generated. This is a gap issue on the flywheel on some motors.
 
   / MF 135 Runs beautifully for 30 to 45 minutes #5  
When it sputters and dies, are you able to start it again right away?

I didn’t see in your list of things that you have done that you replaced the fuel filter. If you have not already put a new fuel filter in, you should do that.
 
   / MF 135 Runs beautifully for 30 to 45 minutes #6  
When it sputters and dies have you tried pulling out the choke to see if it runs differently? When it starts sputtering and running rough take a can of something aerosol that is flammable (carb cleaner works well) and spray around the intake manifold. If there is a crack in the manifold it willsuck the liquid in for a second and run fine. I am going to guess you either have an intake manifold gasket that is sucking air as the manifold will start to pull away when it warms up, or you have a crack in the manifold which usually takes about 30-45 minutes to warm up enough to find.
 
   / MF 135 Runs beautifully for 30 to 45 minutes #7  
Typical behavior of a failing ignition coil, check you spark when it happens. Is it blue or yellow? Many good fuel systems have taken the blame and been screwed up because of bad ignition.
 
   / MF 135 Runs beautifully for 30 to 45 minutes #8  
Typical behavior of a failing ignition coil, check you spark when it happens. Is it blue or yellow? Many good fuel systems have taken the blame and been screwed up because of bad ignition.
Note ......what he said. Ignition coils don't last forever and they do strange things when failing.
 
   / MF 135 Runs beautifully for 30 to 45 minutes
  • Thread Starter
#9  
One potential cause for a fail after 30 minutes can be a blocked fuel tank vent, preventing more fuel to be sucked down to the engine.

Try removing the fuel cap when it does this. If vacuum makes the cap hard to remove, you've found the problem.

And welcome aboard!
Thanks for the reply California, yep one of the first things I did fuel vent is operational. I even did a fuel temperature check before and after 30min no issue found.
 
   / MF 135 Runs beautifully for 30 to 45 minutes
  • Thread Starter
#10  
I'm not a fan of replacing parts before tests prove old one is bad but I make exception for condensers. If the tractor had a tune up including condenser recently I'd give odds the new condenser was bad from factory (many are these days). To confirm or eliminate fuel as cause try a couple things. Have a container to catch gas and wrench that fits carburetor drain handy when engine begins stuttering. Park tractor and let it sputter to a stop then pull drain. If stream isn't strong and/or slows you have a stoppage upstream. If that checks out remove air intake hose and run engine without it. Have starting fluid with straw handy and spray into carb when engine begins to stutter. If rpms pick up and can be maintained with start fluid there's blockage in float valve or jet. Swap in a known to be good coil. If ballast is in line temporarily bypass with jumper when engine falters. "Hot wire" from battery to coil to see if there's a break in wire leading to coil.
Cheers jaxs: can and will try this, good hints thank you.
 
 
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