M274a5 engine running issues

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bms07
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M274a5 engine running issues

Post by bms07 » Sun Mar 10, 2019 7:31 pm

I got this mule and it already had engine work done to it. It has new pistons and jugs. They are letter matching. It has generator heads. When I first started it. It would idle smooth and run good to about half throttle. Above half throttle it run like crap. It would back fire bad. Took mag off and had John Emery test it. Nothing wrong with it. Bought new carb and put it back together. No more back firing. But now above half throttle its slow to pick up rpm. Has no power. Next checked compression. I have 160 psi on one side and 163 psi on the other side. I was a little worried on compression being so high. Bought new compression gauge same result. So I decided to take motor out and disassemble. That's when I found out pistons and cylinders are letter matching. Checked crank to cam timing. Did not find anything wrong. Put in 4 new lifters and put it all back together. So it has new spark plugs, carb, fuel pump and governor. Checked timing with magneto synchronizer. Set it between 18 and 24 degrees at hand cranking. Starts right up and runs smooth. push on gas petal revs right up to about half throttle and it seems to struggle to get wide open. And rpm fluctuates at wide open. Take for test drive. Half throttle or below its great. Above that has no power. So I'm at a lost with what's wrong with it. Could there be issues with the new carb? Any suggestions?
Thanks Brad
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muleman7
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Re: M274a5 engine running issues

Post by muleman7 » Sun Mar 10, 2019 7:59 pm

You need Compression, Fuel and Ignition to run.

You had the Mag checked and installed a new Carb [This eliminates the Carb inlet screen clogged]

New Cyl-Pistons matched and Genset Heads giving you 160psi.

I use a timing light to set engine to 18 degrees BTDC running above 800 RPMs. I have a 14" length of metal stranded automotive ignition wire. The end into the spark plug is stripped to 3/4" and doubled over then pushed into the spark plug unit it bottoms then held into the spark plug with a distributor boot over the threads. The other end is stripped to 1-1/2" and folded over the spring end of the military ignition cable. I attach the inductance pick up clip for my timing light to the automotive ignition lead.

Check the following to verify you are not starving for fuel at Mid to High RPMs.

1-Fuel Tank Filter
2-Sediment Bowl Filter [Pull filter and if gas tank is full you should have a steady stream of fuel pouring from the top indicating your tank filter is OK]
3-Fuel Lines
4-Fuel Pump [if you have the AC Flat Top Pump I have Rebuild Kits. You do not pull the base of the pump to rebuild]
Last edited by muleman7 on Mon Mar 11, 2019 10:09 am, edited 1 time in total.
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Chuck W.
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Re: M274a5 engine running issues

Post by Chuck W. » Mon Mar 11, 2019 9:24 am

I'm with Charles on this, sounds like a plugged in-tank fuel filter/lines/pump problem.

bms07
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Re: M274a5 engine running issues

Post by bms07 » Mon Mar 11, 2019 3:58 pm

I will diagnose fuel lines. Thanks
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M274A5 with 106mm

tga
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Re: M274a5 engine running issues

Post by tga » Sun Mar 17, 2019 6:19 am

My guess is a Sticking valve...use marvel mystery oil at 3 times the suggested mixing ratio in a gallon of gas. Usually clears them up, be sure to run marvel at the prescribed mix ratio after that. No lead gas equals sticking valves due to lack of lubrication especially after sitting for some time.

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