MF 135 misses at high rpm

kermkep · Feb 5, 2016

I have a 1974 Mf135 3 cyl. Perkins gas. It runs great below 1500 rpm. Above there it sometimes misses and backfires to the point it will die. Maybe next time I start it , it will run fine.
Problem is intermittant. I've tuned it up and have gone thru the carb. I'm clear out of ideas and patience. Any ideas would be
appreciated. Thanks

blue water massey · Feb 5, 2016

make sure you have a good supply of fuel flow
to check take out the plug on the bottom of carb or remove fuel line and let the fuel flow for at
least 5 mins
should have a steady supply the entir time it's running
if not check ful filter/s cinked lines or a fuel cap vent that might not be working creating a
vacum in the tank
also look to see if te fuel line runs anywhere it might get hot causing a vapor lock
should that check out you may have a bad condenser or he coil maybe going bad
if you changed the condenser and its still doing now I'd look at the coil after checking fuel
flow
new condensers lately are a crap shoot if you get a good one out of the box
seen and heard of to many new ones that were trash from the get go
others may have other ideas to check

2tractors · Feb 6, 2016

Pull choke and see if it helps if so fuel problem. Crank it up after dark and check for arcing plug wires.Check air intake and fuel cap vent.

David G · Feb 6, 2016

if it does this at 1500 under no load I doubt it is a fuel issue, check for valve clearance, good electrical system, point gap or timing too advanced.

It take very little fuel to make RPM under no load.

Under load, different story.

Tony in Mass. · Feb 6, 2016

The cards are stacked against it. First it is missing a cylinder. Second, it- like a 1980's Oldsmobile, is a diesel engine converted to burn gas. Both ideas have come and gone for a reason.
Like David mentioned, I timed mine by ear, twisted the dist while wide open till it was ready to fly apart, but, it still has to idle down, start and stop sorta normal- so you need to find that sweet spot.
Mine was a lawn mower, and after trying to use it for jobs needing more torque, it is back to being a lawn mower again, but does a good job at it!

Phil Tibbetts · Feb 8, 2016

I had a MF20 turf 3cyl gasser and it ran real smooth. I think it should run good if tuned and everything is set correctly. IMO

kermkep · Feb 26, 2016

After changing the condenser, coil, and fuel line it seems to have corrected the problem. I had tried a
used condenser and coil that I had but had no success. Finally got new parts all at the same time so I
don't know for sure what fixed the problem. Thanks to everyone for their suggestions.

ptfarmer · Feb 26, 2016

Condenser's go bad a lot more often than coils do. Even a new condenser right out of the box can be bad.

MF 135 misses at high rpm

kermkep

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blue water massey

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2tractors

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David G

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Tony in Mass.

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Phil Tibbetts

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kermkep

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ptfarmer

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