M37 no power, good idle

[copperline]

I have a 52 M37. The previous owner left it sitting for a long time and when i got it it had badly contaminated fuel. I have replaced or cleaned every part from tank to carb. I have also replaced the points with petronix electronic ignition. I have also replaced the coil and checked timing (2 BTDC)

The truck starts right up and idles really well but seems to not have much power behind it. It stalled going up a hill. Just doesnt feel right. Lots of hesitation above idle. I have no idea what to look at next.

Any help would me immensely appreciated.

 

[NDT]

From tank TO carb or INCLUDING carb? What vacuum readings are you seeking at various rpms? Does pulling out the choke partially help?

 

[copperline]

From tank TO carb or INCLUDING carb? What vacuum readings are you seeking at various rpms? Does pulling out the choke partially help?

I have not tested the vacuum yet but when I do pull off a vaccum line the engine really gets bad. Ill check vacuum today. And yes I rebuilt the carb. Only think i haven't done is replace the plugs but I did clean them very well. They looked pretty good.

 

[OutpostM37]

With this vehicle sitting so long, it is time for a compression test, leak back test. Things that come to mind are:
Sticky valves
Sticky rings
rust/dirt in the carburetor jets
weak fuel pump, diaphragm leaking
Keep us posted on what you find.

 

[Bulldogger]

Sure the fuel lines are clear and pumps can handle full load/flow?

Distributor not advancing? I assume the M37 dizzy has flyweights, or is it vacuum advance? easy to have those little springs rust or the vacuum advance seize or leak. Hard to see a vacuum leak at the advance, but you could disconnect or crimp the vacuum advance, if it has it, and listen for engine pitch change.

Since I don't know much about the M37 power plant, I'll stop with my less-than-knowledgeable advice and wish you luck!

BDGR

 

[milstencil]

Did you replace the filter in the tank. Known to decompose and contaminate the fuel.
Fire wall fuel filter? Also known to rust and put fine particles into fuel.
You should have a see thru filter at the carb to see if you have anything in the fuel.
Rick

 

[Ferroequinologist]

I had a similar issue. Rebuilt carb, no power idled great. Accelerator pump piston got damaged somehow when I put it back together. Redid it and all good. I would also agree to check in tank filter if it has one, my 54 didn't. Might also be a pinched or plugged line not letting enough fuel through.

 

[copperline]

I checked the vacuum and i have 17" which seems exactly correct. What I noticed today is when i slowly accelerate its pretty good but when i push fast on the gas it craps out. I did clean all of the filters, tank, firewall and inline. I did also blow out the lines. I am confident its no longer contamination.

Any other thoughts?

 

[hndrsonj]

I'd re-read post #7. I also had that problem with a rebuilt carb. I finally installed one from Midwest Military and it runs great!

 

[Roller]

I checked the vacuum and i have 17" which seems exactly correct. What I noticed today is when i slowly accelerate its pretty good but when i push fast on the gas it craps out. I did clean all of the filters, tank, firewall and inline. I did also blow out the lines. I am confident its no longer contaminatio

As stated above I think the accelerater piston is not working properly, worn throttle body or bad seal.

Frank

 

[OutpostM37]

As stated above I think the accelerater piston is not working properly, worn throttle body or bad seal.

Frank

Suggest that when you get the old girl running good, you use some Marvel Mystery oil in the gas tank. Roughly an once per gallon of gas. This will help the leather of the accelerator pump work and stay alive. The gas nowadays with the alcohol in it, gives old carburetors fits.

 

[tguinn]

I restored a 1949 Dodge Powerwagon a few years ago that probably has the same carb. After rebuilding the carb, had the same problem. Turns out the spring for the accelerator pump is the wrong spring tension, had to reuse the old one. Also, if you put in an electronic ignition module in the distributor, the timing may need advanced a bit.
Tim

 

[copperline]

I took the carb apart (for what seems like the 20th time) and put the old piston in. It seems to have helped some but the problem is certainly still there. New gaskets too. If I slowly press the accelerator down its great but if I push it down quickly its just pops and sputters and will slowly catch up. Going up a hill is where the problem really shows itself. Just has very little power under load, especially in the low RPM's

I did advance the timing a little bit with the new electronic ignition. I'm at about 2 to 4 BTDC.

I did close the idle mixture screw a bit to see if that might help. I didnt sense any difference really.

The truck starts up quick even when cold and doesnt want any choke at all. Its amazing how quickly she starts up.

This problem is driving me nuts.

 

[jeffhuey1n]

I had the problem you described many years ago. I had a 1967 Toyota Land Cruiser. It idled fine, filters were all good. I finally chased the problem to a blown head gasket. The gap on the head gasket only became problematic when I was pulling a load or climbing a hill. Changed out the head gasket, problem went away.

 

[tguinn]

You can use the new piston, just use the old spring, the tension on the new ones are too stiff. Every vehicle i put a pertronix in had to have the timing advanced to make run right.

 

[Johnbyrdgates]

I took the carb apart (for what seems like the 20th time) and put the old piston in. It seems to have helped some but the problem is certainly still there. New gaskets too. If I slowly press the accelerator down its great but if I push it down quickly its just pops and sputters and will slowly catch up. Going up a hill is where the problem really shows itself. Just has very little power under load, especially in the low RPM's

I did advance the timing a little bit with the new electronic ignition. I'm at about 2 to 4 BTDC.

I did close the idle mixture screw a bit to see if that might help. I didnt sense any difference really.

The truck starts up quick even when cold and doesnt want any choke at all. Its amazing how quickly she starts up.

This problem is driving me nuts.

My ‘53 M37 with original engine and 38000 miles on it exhibited similar loss of power under load. Compression was good and no fuel contamination issues. Drove me crazy for over a year. I decided to rebuild the engine since I was restoring the body and had everything off the frame anyway. When I got to the camshaft, the lobe driving the fuel pump foot had a 3/16” groove worn in it so the pump could no longer actuate fully. I researched motor oils and discovered that with the advent of catalytic converters in the 70’s motor oils had zinc and phosphorous removed from them which causes wear on flathead engines.

 

[John Mc]

My ‘53 M37 with original engine and 38000 miles on it exhibited similar loss of power under load. Compression was good and no fuel contamination issues. Drove me crazy for over a year. I decided to rebuild the engine since I was restoring the body and had everything off the frame anyway. When I got to the camshaft, the lobe driving the fuel pump foot had a 3/16” groove worn in it so the pump could no longer actuate fully. I researched motor oils and discovered that with the advent of catalytic converters in the 70’s motor oils had zinc and phosphorous removed from them which causes wear on flathead engines.

Try Amsoil Z-Rod 10W-30 oil. Specially formulaed for older engines that need the zinc.

 

[OutpostM37]

Occasionally the auto parts store puts Valvoline racing oil on sale for $6/qt. I use the 30wt valvoline racing. This oil has the high zinc and phosphorus compounds needed for older engines. Attached is the Mobile 1 guide to oils and their respective additive levels. Safe levels of zinc for older engines is considered to be ≈1000-1200 ppm.