1972 350 Surging Under Load When Stopped and at Operating Temperature

The previous owner said the wires are new, I think that's true. Per a previous comment I posted, I ran the motor in the dark last night to check for any arching, and I could actually see each plug wire firing. Again, not sure if that's supposed to be the case, maybe these wires are total crap.. but I looked at each plug, and I could see the faint flashing on each one, so I think fire is getting to each cylinder

And, for everyone: the problem definitely only happens when the car is up to full operating temp. It runs great for the first ten minutes of driving or so, then it starts getting bad.

 

That sounds like the coil.


It runs great for the first ten minutes
Question Does It run bad at hot idle only. how does she do at running speed..

Im thinking Power valve stuck..

 

For the heck of it spray some carb cleaner in the vent tube.

with a tiny hook tool you can hold up the float though the vent and run the carb dry. Gets more cleaner to the PV

 

so you say no vacuum leaks ..... thats good

question ......when your car surges .....how does your exhaust look .? darker than usual ??

check that PCV valve

 

It runs pretty badly both at idle and running speed. When I give it gas, it kind of cuts out as it gets up to speed. When I'm cruising at 50mph, for example, it's hard to tell if it's still running rough just because of the noise.

With the carb, I ran a bunch of gumout through it yesterday, but didn't seem to help. That being said, I'll wait to see what you say about it running badly both at idle and acceleration. It's mostly noticeable at stops where it's cutting out and pulling the car forward even with brakes applied at the same pressure.

 

The exhaust actually looks completely normal all the time, even when it's running rough. I haven't found any strange-colored exhaust, and it doesn't seem to emit much visible exhaust in general.

 

oh I assumed just at idle .....fuel issue or ignition left

when it surges look down into the carb with the engine running and look for gas dribbling /flooding
also we assumed you have checked that your spark plug wires are not crossed and you have checked your spark plug condition and gap is correct

 

How does she run at 12-1500 RPM in neutral??? Warm motor

runs good for 10 minutes ( stone cold motor) the carb is choke mode ( fast idle) for about that length of time.

I'm thinking the corn-gas got to your carb. Sounds like its in your idle circuit...... Might be time for a rebuild.

 

I'll take a look down the carb when I can get it warmed up. Raining like crazy today, we'll see if I can get it warmed up.

Wires aren't crossed, I verified that earlier today. I did ask earlier on, not sure if it made it through - the rotor spins clockwise in the '72 350, correct?

I haven't checked the plugs, but I will do that today and tell you what I find.

I'm thinking you're right - to me, it sounds like something in the carb or that coil like you mentioned. I've never rebuilt a carb, so this might be a perfect learning experience. Incidentally, do you know what the float level is supposed to be set at for this carb? I want to verify that when I get in there.

 

diagnosing from a distance ain't easy ....

stick with the basics first

and yes rotor spins clockwise

 

All Buick 350s have the 18436572 firing order, and all distributors, points and hei for all year Buick 350s spin clockwise. Odd cylinders on drivers bank, #1 is drivers front, Even cylinders on the other bank, #2 at front. Your plug wires should not be doing that. Change the coil and see if it stops glowing. If not, change the wires too and keep the new coil on there.

 

Float level measurement should come with the kit..

Since your carb is in basic working order should be no problem for a simple reseal.. Re bushing you will be into it a bit more..

 

Thank you! I thought that was a little strange. Again, to clarify, it's only in the dark I can see it, and it's not arching or anything, but sounds like it's still not supposed to be doing that at all?

 

Check the point&dwell,,, plug gap and what plugs are they.

Stick with all the simple stuff first.

 

X2, I'd say that's your smoking/glowing gun right there, you shouldn't see ANYTHING from the plug wires

 

Thanks, guys. . . I'll go through the electronic aspect, then if that's not working, I'll give the fuel pump a try for $25, then look at carb if that doesn't do it. I'll keep everyone posted!

 

Make sure your gas tank vent isn't plugged before you go and spend $$ on a new pump.

Drive the car until it starts surging, pull over, put car in park and go to the back of car and remove gas cap. If you hear air sucking in the tank when you remove it will confirm the vent is plugged.

Without a vent the fuel pump has a hard time suctioning fuel against the vacuum that has formed after driving a while. So it might not even be related to the engine being warmed up.

If this is the problem, a quick and easy fix would be to simply get a vented cap that will fit your car. GL

 

Another idea I'll try - Thanks!