Posted by DDD [108.162.221.57] on Monday, January 04, 2016 at 09:04:45 :
Hapy new year all!
hoping for some guidance on the poor running condition of my M37 engine
(BTW. I posted this on the M37 site as well. I am hoping to expand the question here to the collective flathead crowd, as I believe at this time the issue I am seeing is flathead engine, and not M37 specific.. but will see)
Some background info ..The truck is a 63 M37. I have done a lot of work to this truck, but for the
sake of the issue at hand, Ill keep it to the fuel and electrical.
FUEL system: I have replaced the entire fuel system, from tank to carb. Tank was flushed and relined. Brand new stainless steel in tank fuel filter and and pickup installed in tank..All brand new armoured fuel lines installed. All vent lines installed. NOS fuel pump. NOS carb, both from VPW. In other words, ALL NEW
Electrical:
Replaced the wiring with a brand new set of shielded wires. new plugs. New distro cap, inner. I decided to install a set of pertronics ignition to eliminate the points and condenser. Retained the original in distributor coil however. All vent lines to keep the coil cool and vented installed.
OK.. so the problem:
I start the truck from dead winter cold.. with a slight choke, starts up. Immediately runs perfect. No popping or missing. As it begins to warm up, the
engine begins to stumble, or miss. Like a burnt valve or something. Ocational, once every few seconds or more.
as it warms, the “missing” or poping comes closer and closer intervals. Completely warm the truck continues this poping and missing and puffing at the exhaust pipe.
I checked the timing and set to TDC. Checked all plugs. Set to 0.025". No fouling or oil on any plugs.
A bit blackened and sooty like running rich.
Did a compression check. All between 105-95. Not greatest but its uniform
\So whats causing this?
I let it cool overnight. Start up the truck. Once again, the same dance. From dead cold start, runs smooth as silk, but that’s only for a a minute or so, perhaps longer, and then the occational miss begins again.
So I try an experiment. I pull out the choke. As expected, it begins to stall on me.
Idle goes low. Wants to die. Just before she quits on me I push the
Choke back in. No more choke. As soon as I do the truck runs nice.!! But ONLY for a few seconds.
Still. It runs nice! No popping of missing! WTH! I keep thinking I
Got more carb issues then. Cant be engine internals like valves if it returns to a great running engine for a few seconds!
anyone shed light on this?
It was suggested on the M37 site that I perhaps have vacuum issues, perhaps in the form of bad gaskets or loose fit around the manifolds and or carb. I tightened everything. And used carb cleaner to see if I can raise the RPMs with a shot of cleaner.. nothing.. so it appears, as first glance, that I dont have a vacuum leak around the intake or carb body.
Anyone wish to comment?
Valve issues? I cant see how, unless after warm up the valve clearance tightens and causes this condition to occur?
Carb issues?
Float level? Will too much gas in the float cause this condition?
Exhaust leak at the muffler?
Or is this electrical? Did I get a bum set of reproduction wires?
I cant imagine as the truck runs smooth from a dead start for a minute.. no grounding of the wires?
Or coil? Could the coil be bad? I mean once warm, could it act up and perform like this?
But again, how does choking the engine make a bad coil return to normal?
Is the carb getting warmed up as the truck warms up causing something to happen in the bowl?
Float setting? I adjusted it countless times now, and to be honest, I can get only minimal changes to the float level before the needle don’t want to open at all..
I am open to any and all suggestions where to look next.
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