'40 engine "stumbles"

[mike42]

This just started a couple weeks ago. Starts up no problem and engine runs great, but after starting out and driving a bit the engines stumbles once in awhile. Not all the time but just once in awhile. Rebuilt carb and rebuilt coil and condenser.

I've seen a thread on here before about this but can't find it. Could this be the float ?

Thx......Mike

[Brian]

Mike, have you checked the plugs?

[mike42]

Yes new autolites

[Ken/Alabama]

Check the ignition switch for burned and pitted contact plate and brush. Also make sure the rotor isn't cracked . I had this happen a couple years back ,found a very fine crack in the rotor and after it got hot it would start missing under a load.

[ken ct]

Originally Posted by mike42

Yes new autolites

Wheew, that could be almost any thing. Could be carb,dist do not try and find the problem in both at the same time.Somewhat depends on what parts and who put these units together and where the parts were gotten. This is a tough one.We need more info on what was done. ken ct.

[mike42]

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Bought rebuilt carb last Summer from C & G, Skip Haney just did the coil and new NAPA Condenser. Installed new Autolites in May. Car was running just fine until 2 weeks ago and then....bang ! It started to stumble all of a sudden before the new coil rebuild and condenser. I was thinking someone on The Barn said awhile back it might be a carb float valve sticking ?? It is just a slight hesitation for a micro second and then keeps on purring. It happens when cold and happens when warmed up. Maybe it is a rotor !

[G.M.]

Typical sticky valve symptoms. Get a quart of Marvel Mystery Oil. Drizzle a little down both side of the carb while the engine is running. Put a half of the bottle in the fuel tank and go for a drive, in about 7 miles the slight miss will disappear. Put about a pint in with every tank of gas, Before doing this take the car down to below 10 MPH in high gear and step on the gas pedal. It will give several bucks as it picks up speed. Try it again after the treatment and the car pulls out smoothly with no bucking. If you have dual exhausts you will hear a boom, boom, bip, after treatment it's just boom, boom, boom. G.M.

[mike42]

Well you're not going to believe this, but I started the thread here to discuss and for the last two days......NO PROBLEM ! What the hell......had it out yesterday and today and she purred ! I'll try the MMO though.

Thx guys

Mike

[russcc]

Bad gas ?

[Rebel Sympathy]

Let's see...... This is August. Maybe it was trying to vapor lock just a tad? Could be.......

Mike

[L78CHEVELLE]

I had this same problem on one of my '40 Fords. Not bad enough to dwell on the situation but it happened cold or hot. My problem did go away and the only change I made was switching from Shell gasoline to Speedway gasoline high test fuel. Never came back and I have never gone back to Shell fuel.

[mike42]

Guys.......

In Michigan we have what is called recreational fuel. No ethanol in the blend at all. It costs more but this is a hobby and hobbies cost money. It very well may have been vapor lock though, even though I kicked on the electric pump. I forgot about that !

L78 I too had Shell probs and switched to mobile before going to the Marathon recreational fuel.

Do you think MMO really works or just in our minds ?

Thx guys....I'll let you know if prob returns.

Mike

[G.M.]

MMO WORKS I have seen instant results hundreds of times. I also use it in my diesels. My wife's diesel was getting a little sluggish and I added some to the fuel tank and she complained, asked what I did to her car because it was spinning wheels when she started out. Do the simple low speed pull out test I described, add the MMO and try the test again and you will see the results. G.M.

[mike42]

Will do..thx GM