What would cause a M37 to sputter while running?

[carolinamv]

My M37 runs great , drives good, idles good, well kinda. It sounds like when its idling that it sputters every few seconds from the exhaust. But the idle sounds good except the sputter that's inside the idle noise. Drives down the road fine, just does that it idle.

I replaced the spark plugs (nice blue arc), coil, put cleaner gas in the tank (not perfect but its cleaner fuel that was in the tank) , should I have the carb rebuilt?

[just me]

Live with it. The design of the intake is inefficient as all get out. If anything is the least bit out, it will do that sput every few seconds. There is most likely enough wear in the throttle shaft, erosion in passages, little bits in the corners of the jets that you won't be able to tune it out. Unless you have the tools to pull and replace the emulsion tube, Main vent tube (Special tools required), jets and bleeds, you won't get it totally clean. A little loss of compression in one cylinder will cause it. A valve not perfect can cause it. A vacuum leak.
You can go nuts chasing it. I can tune it out for a month or two and then it comes back. During the upcoming overhaul, I will be changing the intake and exhaust system and using brand new carbs. If it still does it afterwards, I'll live with it.
Oh, and I forgot that worn distributor advance weights, stuck advance plate, worn cam lobes or worn shaft/bushings in the distributor will also do it.

[carolinamv]

Yeah I ruled out a vacuum leak also, I was thinking condenser maybe, or dirty carb. its a restored truck but it sat for a number of years before I got it a few years ago.

[just me]

Depends on just how "restored" it is. But after sitting for a time, I would strongly suspect gunk in the passages of the carb. Or a worn out distributor.
As to the restored reference,
There is the normal "Restored" from sellers. It has a coat of paint on it.
The "Restored" by an average mechanic. It has a coat of paint and a tune up. Oil levels checked.
"Restored" by a body man. Tin is perfect, paint is perfect. Blew the dust off the mechanicals.
Then Fully "Restored". Every part was disassembled until no two parts touched. Every item brought back to factory specifications or better. The carb, distributor, engine, driveline, electrical, body, EVERYTHING is as new. This is VERY RARE.
There is another subset of Fully "Restored" where weaknesses in the original are upgraded for useability. Even rarer. (And this one tends to expose new weaknesses and this can cascade until you end up with a resto-rod that looks like an original, but is really a new vehicle. Like a Legacy.)

[carolinamv]

Its fully restored, nut and bolt, about 10 years ago or so. High level, body,motor,etc. then it sat for a time, then the guy I got it from really didn't drive it and it sat more.

When I start it , it takes it about 5 min for it to start doing that.

[CSCameron]

My civilian 230 motor did the same thing initially. Not rebuilt like yours though, it did sit for 20 years. I did rebuild the carb. It has gotten better over time by running it. Not sure if yours might do the same after running it for a while? At this point I'm not worried about it.

[carolinamv]

I start it in the garage every day and let it run for about 15-20 min over the past few days.

I don't drive it a lot, but I'm going to drive it this weekend if its nice out. But it seems when I do that still doesn't do much to it .

[carolinamv]

I checked my timing today and idle screw , it was pretty far advanced, we set it correctly , still a big of sputter even with the idle set a touch higher.

I installed a new condenser for NAPA today, I also noticed some of my plug wires that go into the top of my distrib were loose and only barely hand tight.

[Kaegi]

I agree maybe it needs to be driven. clean out the cob webs. set points with a dwell meter then check timing. Like was mentioned could be some very small problem in the carb as well. Just running it in the driveway will not burn the carbon out of the combustion chambers either. gotta go wind it up for 1/2 and hour on the road. go scare some Toyotas off the road. ;/)

[carolinamv]

Very true, I will drive it more. I hope loose plug wires and the condenser might have done the trick .