M38 running poorly - possible ventline problem

[Shooby]

HELLO,

This is my first time using this forum. I really appriciate any help anyone can provide. I have a 1951, m38 with a Cartor W-O carb and a regular fuel pumb, not the big fuel/vaccum pump. Still have the 24 volt electrical system.

The problem is that I am experiencing chugging at slower speeds, when RPMS increase the problem goes away.

I noticed that the ventline to the distibutor broke off (the one next to the harnes filter). I reconected it and the problem went away. Now, three weeks later, the problem is back only the ventline is intact. I figured that something must have gotten plugged in the ventline. I replaced the tubing and fittings with new. I used steel break line instead of copper. I hope this is okay, there seems to be plenty of play in the line for distributor adjustments?

Now for a little background on my ventlines. The ventline in question goes from my intake manifold to the distributor (the one next to the harness filter). Note sure if this is correct location for this type of application? The other ventline (next to the engine block) on the distributor is not connected to any thing. I have a CJ 3a style cross over tube so no place to go with the ventline?

Not sure if this is a ventline problem or perhaps I just need a good tune
up - replace points, condensor and rotor??

FYI - This jeep has been in the family for over 45 years and has ran very well with this set-up.

Any idea's?

Thanks,
Shooby

PS - how does the vacuum advance work on this vehicle?

[wesk]

Shooby,

The vent line to the military distributor is only there to vent the distributor housing of harmful electrical fumes and it does help keep the coil cool in hot weather. It's other line should go to the cross over tube but you can run it to your air cleaner as well. The main concern with this line is that it was originally meant to run from the dual fuel/vacuum pump to the "T" fitting for the vacuum wiper hose and at that "T" fitting there is suppose to be a small restrictor in the line for the tube to the distributor so that the vacuum to the distributor housing vent is restricted to about 1/5 of the available vacuum. Do not pull straight vacuum off the intake for this vent system.

There is no vacuum advance on the military distributor. There is a centrifugal advance (often referred to as the governor) that is simply a movable advance plate under the points that is operated by a pair of counter weights and springs. If this advance system sticks you will experience the chugging or lugging at low RPMs. To check it remove the distributor caps and grasp the rotor and try to turn it each way. It should move freely in one direction about 10 degrees and then when released the springs should move it back to where it was. If it can't be moved then that is your problem and you'll need to remove the distributor and remove the contacts and their plate to get to the mechanism and free it up and lube it.

A loose set of points or a set of very worn points that hardly open when the high point of the cam hits their rubbing block can cause a similar set of symptons. So if the centrifugal advance is working freely check the points for loose hold down screws and check their gap when on the high point of the cam for .020 gap.

Finally if none of this appears to be the problem then move on to your fuel system. Especially starting with the carb accelerator pump.

[Shooby]

Thanks Wes! You have been a huge help. This site is a great resource...thanks for being available to us non gear heads!

I will check the points, govenor etc to make sure it is all working properly.

Why does the jeep run worse (chuggng is far more substantial) when the ventline is not connected to the distributor as it sounds like it doesn't really have anything to do with performance?

So in my application, would it be best to NOT run the vent line to the manifold or should I simply restrict the vacuum to 1/5th the original volume? Any suggestions on where to get the restrictor or what I could use in place of it? Can you post a picture of what the restrictor looks like if it's not to much trouble?

Technically it sounds like the jeep should run fine with out the distributor ventlines?

Thanks again Wes!

Shooby