Backfiring and not running without choke almost closed

[grimlock97]

I have been tinkering with the m37, trying to get it running again, about a week ago, I was finally able to get it fired up for the first time, the coil was bad, the primary resistance was spot on but the secondary was non existent, it ran and it sounded pretty good, but it was still flooding the intake, at that point it would not run without the choke almost closed, so to remedy the flooding issue, I ordered a fuel pump rebuild kit (seemed like the diaphragm was busted and pumping gas into the intake from the vacuum side of the pump, I rebuilt the pump, re-installed it, it pumps great, so while I was waiting on those parts, I cleaned the carburetor for the 5th time and put new gaskets on, I got the carb back on today and fired it up, it will not run without me fethering the throttle unless the choke is almost closed, also, the exhaust sounds different, kind of hollow sounding, hard to explain, also whenever it gets warmed up just a little bc I can't keep it running very long, its harder to start then when cold, a little ether gets it going, new plugs, new wires, new points, new condenser, new coil, 24v still, new choke cable, new / rebuilt fuel pump, new gaskets on and in carb, what gives? any help appreciated.

 

[rchalmers3]

Sounds like you have a bunch of new parts, just need to get them working in concert!

My suggestion, in order of operation is to:

1) Put a dwell meter on the points and set the points accordingly. Sometimes setting the points gap without confirming the dwell does not make for a good running engine.

2) Set the timing to spec

3) Adjust idle mixture and speed to spec

4) Any troubles with the above steps will require diagnosis and remedy of any issues you uncover.

Rick

 

[steelandcanvas]

Not being familiar with M37 engines, but could the distributor be 180* out?

 

[grimlock97]

I don't think the dizzy is 180 out, it hasn't been removed at all, it ran great once I put the good coil in there, though with the choke on, the timing has been set to 2 degrees past tdc on cylinder #1, I confirmed all that while trying to diagnose the weak spark no start issue, there is only one screw on the carb which is the idle mixture and I have got the engine running and adjusted it all the way in then half a turn out, and even further and the motor doesn't skip a beat or change pitch or anything, like it does nothing. can the dwell, make it to where you have to push the pedal all the way down to get the beast to start after its warm, I can get it started but have to have the choke just right to let it idle, then I have to fether the pedal constantly to keep it running if I mess with the choke at all, I set the points gap to .20 when I set them, it really acts like a vacuum leak or dirty carburetor, but its fresh fuel in a recently red koted tank that was dipped, then a new fuel pump and very clean carb. I can get the dwell meter on there if you think that's the way to go, it's rough idle before dying if I push the choke all the way in with my foot off the pedal, it hasn't backfired since it has warmed up

 

[73m819]

LOOK for a VACUUM leak

 

[grimlock97]

I have been, I can hear hissing out of the vacuum wipers, but surely that's not the leak, is it? It has a new base gasket, and all new gaskets on the carb, other than a known exhaust leak I didn't really find one, unless i'm missing somewhere, the vacuum part on the fuel pump is all new with new gaskets and I took it back off to check it, but it dang sure acts like a vacuum leak.

 

[foxtrk2]

just as a hint I had similar problem with my 37 turned out to be cracks in distributor cap had used after market one and when screwed plug wires down to specks they cracked the cap had to find nos cap and ran great ever after foxtrk 2

 

[G-Force]

It could be a fuel restriction or not enough fuel getting to the carb. Are you sure the timing is supposed to be 2 degrees after tdc? That doesn't sound right. Also, does it have a mechanical advance (weights under the plate the points mount on). These could be stuck in the retracted position so they don't let it advance. Pull the distributor cap and see if you can turn the rotor and does it snap back to its original position. If it has vacuum advance ( highly unlikely) maybe the diaphragm is bad. Just thinking online here.....

 

[bchauvette]

In my humble opinion and with a lot of experience in other than military vehicles I would check fuel pump output by simply disconnecting the fuel line at the carb and turning it over and watch the fuel flow into a container. Flooding may be a bad float and needle valve assembly in the carb. Having to run with choke on indicates restricted flow in the carb. Have the carb professionally rebuilt. Make sure They h ave an acid soak/agitate device to completely clean out the carb.

 

[Ferroequinologist]

I took my wiper motors off, and forgot to plug the lines. It acts the same way yours does. I would fix the vacuum leak(s).

 

[grimlock97]

It could be a fuel restriction or not enough fuel getting to the carb. Are you sure the timing is supposed to be 2 degrees after tdc? That doesn't sound right. Also, does it have a mechanical advance (weights under the plate the points mount on). These could be stuck in the retracted position so they don't let it advance. Pull the distributor cap and see if you can turn the rotor and does it snap back to its original position. If it has vacuum advance ( highly unlikely) maybe the diaphragm is bad. Just thinking online here.....

Timing per the TM is 2 degrees after TDC, i will check the weights, i know they can get sticky, i'll look into it. Thanks

 

[grimlock97]

In my humble opinion and with a lot of experience in other than military vehicles I would check fuel pump output by simply disconnecting the fuel line at the carb and turning it over and watch the fuel flow into a container. Flooding may be a bad float and needle valve assembly in the carb. Having to run with choke on indicates restricted flow in the carb. Have the carb professionally rebuilt. Make sure They h ave an acid soak/agitate device to completely clean out the carb.

Thanks for the suggestions, the fuel pump is putting out a good stream of fuel, the carburetor was professionaly rebuilt last year, and it is very clean, almost looks new, and i have cleaned it a couple of times just to make sure, i have ruled out the needle valve and float, but the float level could possibly be set too high, the gasket between the bowl and top of the carb is wet. thanks again, just need a lot more tinkering i guess.

 

[zout]

With all that fuel in the intake (hopefully you have done this) make sure you have changed the oil and filter - nothing worse than fuel thinning out motor oil and filter saturated.

 

[grimlock97]

With all that fuel in the intake (hopefully you have done this) make sure you have changed the oil and filter - nothing worse than fuel thinning out motor oil and filter saturated.

Oh yeah, I have changed it twice, that's one reason I need to get everything right, I'm tired of changing fresh oil. I haven't had gas in there since the fuel pump was rebuilt though

 

[T. Highway]

The TM callout for timing spec is wrong. This has been discussed many times on the G741 site.

I would set timing to 4 degrees BTDC with a timing light and then fine tune it from there.

I would also check your float height and make sure that it is NO lower than 5/64" below the top edge when the needle closes.

I hope this helps,

Bert

 

[DLJ]

Check vacuum line going to wipers ,had a similar problem. Simple enough to pull the hoses to check. Needing choke to run is usually vacuum.

 

[grimlock97]

Check vacuum line going to wipers ,had a similar problem. Simple enough to pull the hoses to check. Needing choke to run is usually vacuum.

Yeah, idk why but I just feel like it's vacuum related a little, I disconnected the wiper vacuum from the fuel pump today and plugged it at the pump since both wipers were leaking and it ran without the choke but only if I kept my foot on the gas, after it warmed up it seemed like I had to feather the gas, tomorrow when I get to fool with it some more, one of the base gasket bolts was loose, not very loose but it wasn't hard to turn with a wrench either, so i'm tightening that down then i'm going to try it again, if it's still not running at that time i'll spray some carb cleaner around the base, if it's not that i'm pulling the carb again and going to try to set the float for the 3rd time. thanks for all the help, i'm pretty close to giving up bc I'm sinking more and more money into her and can't enjoy driving her at all, but I do love wrenching!

 

[Ferroequinologist]

I took my wiper motors off, and forgot to plug the lines. It acts the same way yours does. I would fix the vacuum leak(s).

You must have missed my earlier post....

 

[73m819]

I said in post 5 that you need to check for a vacuum leak, another 4 or 5 members said "LOOK FOR A VACUUM LEAK" and where to look for it.

Finding and fixing a vacuum leak is cheap. if it was the float, it would NOT run with the choke closed.

 

[grimlock97]

I said in post 5 that you need to check for a vacuum leak, another 4 or 5 members said "LOOK FOR A VACUUM LEAK" and where to look for it.

Finding and fixing a vacuum leak is cheap. if it was the float, it would NOT run with the choke closed.

Yes, thank you, I posted in post 6 that I have been looking for a vacuum leak but cannot find one, where else could I possibly check, the carb is making a loud hissing noise, the wiper motors are disconnected at the fuel pump and it is blocked off there, so no vacuum leak at the pump, unless it's on the intake side, but that is threaded tight, the carburetor has a new base gasket and is tightened up, there is no vacuum advance, can anyone think of another location to look for a leak?