Page 1 of 1

M274a5 engine running issues

Posted: Sun Mar 10, 2019 7:31 pm
by bms07
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

Re: M274a5 engine running issues

Posted: Sun Mar 10, 2019 7:59 pm
by muleman7
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]

Re: M274a5 engine running issues

Posted: Mon Mar 11, 2019 9:24 am
by Chuck W.
I'm with Charles on this, sounds like a plugged in-tank fuel filter/lines/pump problem.

Re: M274a5 engine running issues

Posted: Mon Mar 11, 2019 3:58 pm
by bms07
I will diagnose fuel lines. Thanks

Re: M274a5 engine running issues

Posted: Sun Mar 17, 2019 6:19 am
by tga
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.

Re: M274a5 engine running issues

Posted: Tue Aug 06, 2019 1:44 pm
by Mulebuck12
I dont want to get off subject but my mule was running great then started it one morning an it was pumping oil out of port on the front of engine just below fuel pump it has a valve threaded into it any one know why this is happening

Re: M274a5 engine running issues

Posted: Wed Aug 07, 2019 7:32 am
by Chuck W.

Re: M274a5 engine running issues

Posted: Sat Aug 10, 2019 8:11 am
by muleman7
I agree with Chuck W the pumping of oil out of the outlet vent valve can be caused by the front cam bearing spinning. His post has the link to my post on replacing the cam shaft assy without pulling the engine.

I use Rislone engine oil additive others use Marvel Mystery Oil added to the engine oil both will do an excellent job of keeping the inside of the engine clean and the hydraulic lifters working properly.

I use SeaFoam in the gas tank to keep any moisture in suspension and the fuel system clean. I only use Non-Ethanol fuel mixed with Sta-Bil 2oz per 5 gals. It works with all small engines 2cyl or 4cyl

I use Rotella T1 30wt oil as it meets the Mil-L-2104 standard that is stamped on the oil stick.


Rislone Engine Treatment


Rislone with ZDDP for added protection especially when installing a new Cam. Also use a cam lube for new installs.


Re: M274a5 engine running issues

Posted: Sat Aug 10, 2019 12:03 pm
by markrdje
Charles; What do you think of adding lead substitute to the gas?For the old jeeps it was beneficial for the valves.

Re: M274a5 engine running issues

Posted: Sat Aug 10, 2019 4:04 pm
by muleman7
Great Question I will answer with links to Web Articles.

Lead added to fuel is: tetraethyl lead, or TEL.

The mule heads have valve seat inserts I do not know if they are hardened but guess they are harder than the old style "soft" seats.

Lead was mainly used as an octane booster needed in the higher compression engines to prevent engine knock by raising the Ignition Temp of compressed fuels.

From one of the articles higher compression engines require higher octane fuels and when constantly run hard the valves MAY benefit from a lead additive.

Upper cylinder lubrication can be obtained from Rislone or Marvel Mystery Oil or other additives your choice.

The Mule engine with the copper head spacer is 6.4 to 1 compression and the Genset engine is 6.9 to 1 compression. They are seldom run hard or under constant heavy loads.

I have rebuilt many mule engines and have not come across any valve seat degradation. The exhaust seat will come loose [fall out] leaving the exhaust valve open when mice [rats] build a nest on top of the head and cylinder starving it of cooling air.

"1. Using Lead Free Fuel in Older Vehicles - Mechanical Implications
While lead is added to gasoline for the purpose of raising octane number and therefore allowing higher compression and more efficient engines, it also has other effects on engine operation. Lead salts are formed by the combustion of lead additives and are deposited on the walls of the combustion chamber. These deposits serve as lubricants between valves and valve seats; at the same time, these deposits can corrode exhaust valves, foul spark plugs, increase emissions of unburned hydrocarbons and degrade lubricating oil in the crankcase."

Above statement is taken from the link below. ... ns.d4e.pdf ... -gasoline/ ... ou-need-it ... your-fuel/

Re: M274a5 engine running issues

Posted: Sat Aug 10, 2019 7:33 pm
by markrdje
So it sounds like to me that putting lead additive to the mule would be a bad idea.It don't sound so good either for the 151 jeeps

Re: M274a5 engine running issues

Posted: Sun Aug 11, 2019 8:44 pm
by savagebrother
Royal Purple ROY01030 SAE30 synthetic Oil ??? have you guys seen this???
it will smooth out and quiet your motor like you would never think.
my motor runs great but sometimes when it would set more than a couple of weeks without starting a lifter would stick until it warmed up
with royal purple nothing sticks it starts so easy and with the warm weather i don't even have to use the choke when starting.
you wont need to change oil with colder weather.