No Power Under Load

[xd2200]

My M37 is essentially all stock. When going down the road it has no power - I have trouble starting off and it will only reach about 30MPH. When I rev the engine in the yard it seems to work fine. I have installed new plugs. Also, I have checked the compression, fuel pump pressure, vacuum, points, condenser coil, distributor cap and plug wires. At this point I am thinking that the gas has gone bad. I only put about 100-200 miles per year on my truck so a portion of the gas is probably old ( I do use stabilizer.) Before I drain the gas (and figure out how to dispose of it) does anyone have any other thoughts as to what the gremlin might be?

[m37paul]

You did not mention timing. I use ethanol-free gas in my truck and Gibson tractors. Standing for 6 months does not seem to be a problem. Good luck, Paul

[RMS]

I would suspect timing is too advanced. with the long stroke and dwell @ tdc of it is easy to give it too much advance causing it to fight its self. book says 2deg btdc. 4deg is lots 6deg is too much.

[rickf]

Modern gas, even with stabilizer, is only good for 6-9 months before it starts to go bad. After a year even with stabilizer you will find it has turned dark orange and will burn sort of like kerosene. Since it is a royal pain to drain the tank I would first check the initial timing and also check the timing advance as you rev the engine to be sure it is advancing as it should. If the timing is on and working then get rid of the gas and try fresh, non ethanol gas if you can get it. Since we are going into winter I am assuming you may be done for the season so put very little in there and use about double the stabilizer. Use the Marine Stabil. It will not hurt to use the extra. It will not guarantee fresh gas next summer but it may prevent what little is in there fron contaminating the new stuff you put in in the spring.

[just me]

Gibson Tractors. I used to have Gibson Tractors. 3 different A's and a D Super on 24's with a steering wheel.

[NAM VET]

I am no expert on these trucks, but like the above poster suggests, I would check your timing. I recently had a pre-ignition "rattle" soon after a professional rebuild of my motor and all things attached to it, including a Pertronix. But In a few hundred miles, the timing had slipped, to too much advance. It would start and run, but at low RPM load had a pronounced rattle. Maybe the way the gears of the oil pump and distributor mesh wants to turn it to advance. Anyway, taped two 6 volt batteries together, then soldered wires in series to their terminals, and had then a 24 V source of power for my inductive timing light. Of course, I did use a spark plug wire for a place for my timing light's inductive pick up. Made sure my idle rpm was correct at about 525 rpm, and found it was something like 12 degrees advanced. In order to correct it to 4 degrees BTDC, had to get under and move the dizzy first with the "coarse" adjustment just a little, then use the fine adjustment to correctly set. It is not easy to get a socket or wrench on either fastener, and hold the dizzy in place with one hand, while idling, so I just snugged it down with the motor off, and kept checking the timing until I had it correct, and then tightened it up. By the way, I used an ARP stainless bullet nose stud for the fine adjustment "bolt", so if you have to remove the fine bolt for some reason, I suggest the same stud. Can't cross thread it. Both nuts or bolts are 7/16 socket or wrench. It is a tight space and wrenches and extensions tend to hit the dizzy body inhibiting a good lock on the fine bolt or in my case, nut. If you don't have pre-ignition knock sounds, then perhaps your timing is too late. Anyway let us know what you find. Since an expert had just rebuilt my dizzy I was sure the weights were working fine.


As for draining the tank, my '52 truck has a tank drain petcock, but it leaked a bit, and I was afraid to tighten it more and break it off, so ran the tank as low as possible, then backed the rear up on ramps, loosened it enough to have a fast drip into a large plastic container, and it still had about four gallons of fresh gas in it. Replaced the petcock with an NPT with sealant.

I hate working around gas, my brother in law was badly burned and nearly died as a teen when a gas tank exploded, leaving him pretty scarred. Plus, I had a fuel leak in my Triumph TR8 long ago, and when that leak was ignited by the pilot lite of a garage hot water heater, it burned out the garage, and nearly my home. I never work on any fuel things on any vehicle in my garage now. If you drain your tank it is a real issue what to do with the gas too.

Good luck and report back when you get it running right.

NV

[Kaegi]

I would check dwell first then timing. one possibility is the float in carb isn't opening enough under load. modern gas makes them sticky if truck sits. I dont think its old gas. flatheads are designed to run on 70 octane or lower fuel. And they will run good on terrible fuel. much better than an over head valve engine would

[xd2200]

UPDATE
1. I have drained the old gas and put in new - this did not help. As suggested, next I will check the timing. The manual says 2 degrees BTDC and to make a chalk mark on the pulley. When I look down at the pulley (from the engine side) I see the markings on the pulley. Would "before" be on the left side of the DC mark?

2. I was also was also wondering if perhaps the carburetor accelerator pump could be the culprit?

[ashyers]

When the pulley is turning the 4deg mark will precede the TDC mark when passing the timing pointer. The accel pump is for transients, if the motor's not pulling a constant load I'd look elsewhere at this point.

How's the engine behaving?

Is it smooth with no ability to take load, missing, surging? Will it rev to the governed setting w/ no load?

What were the compression readings?

This may help with the diagnosis.

Andy

[xd2200]

Engine revs up nicely under no load - slight miss at idle. When I try to drive it down the road it stumbles badly and will not rev up.

[Kaegi]

I still think possibly the float isn't opening far enough. or if it was rebuilt then this problem started it could be set too low.
on the ignition do you have or know someone with a dwell meter? timing doesnt mean too much if dwell is way off

[xd2200]

I will check the float later today.
I have a dwell meter but not sure how I would hook it up with the 24v waterproof ignition.

[Kaegi]

forgot about the wiring. there is an adapter kit for working on M series vehicles. i think good investment if owning one. can diagnose charging and ignition systems with it. I dont recall them costing much. 75? someone here must have the kit part number

[ashyers]

If you give it a bit of choke will it take load? If so I'd chase fuel.

As far as the float, set it "wet" and use the hand pump on the fuel pump to fill the bowl and bowl drain as required. We had a carb in here that was "rebuilt" by a vendor and the float was set so low the bowl drained under load causing all kinds of drama.

I've also been driven nuts by bad condensers lately. Seems that new means suspect. One lasted 15minutes! The vehicle behaved like it ran out of gas...

Andy

[Halfdunn]

Alright Gents, I too have a issue with little or no power as I perceive it as stated in the earlier threads above.

I have connected the proper timing light adapter to the #1 plug, marked the belt pulley with chalk at the DC mark and 2 deg after TDC mark, but cannot adjust the distributor enough to bring it into the proper range. Before adjustment attempt, it showed being in the 10 deg BTDC area. After loosening the hold down bolt on the distributor, I can only get the timing into the 5 deg BTDC range. There is no adjustment knob on the timing light in case of a question like some lights provided in past years. Is there another bolt to loosen the distributor adjustment other than the one visible from the top looking down on the unit?


Could it be possible that the distributor is off by one or two gear teeth in the drive or is it correct or out 180 deg? I have referenced the TM for the M-37 engine timing procedures and seem to be following step by step. I do have a timing pointer above the pulley and it looks to be attached to the engine straight and not bent or damaged in any case.


Any help?