surging while cruising

[Lancelot72]

Hey all,

I'm having a problem with my car surging while at highway cruising speeds.  I think it's anything above 40mph or so.  I have read other posts about surging and haven't really found anything describing what I have.  It's not threatening to die or cut out.  It sounds great at idle.  It does have a bad hesitation when accelerating from idle, but I don't know if that's a different issue or part of the same.  It's a 351C 2v with a rebuilt 2 brl Carb that the PO installed within the last year.

I have tried spraying a modest amount of carb cleaner around the vacuum lines to see if the engine would react but it never did.  I'm a novice at engines and could really use some advice on what to try next.

Thanks,

Lance

 

[Jeff73Mach1]

I would start with a fresh fuel filter. You may want to check the pump for pressure and volume output, but a couple cranks with the coil disconnected and the line from the carb running into a can while briefly cranking will give you confirmation that the fuel pump is pumping a reasonable amount.

Vacuum leaks can cause surges by changing the vacuum advance. A vacuum gauge on the engine will tell you a lot. If you haven't used one try this guide. It is a cheap and very versatile tool

https://www.onallcylinders.com/2015/05/08/quick-tech-how-to-read-a-vacuum-gauge-to-pinpoint-engine-problems/

 

[TheRktmn]

Check that your vacuum advance is hooked and working.

 

[clevelandcoupe]

I am remembering (dating myself again) an issue back in the early eighties, that the fuel tank surge canisters had issues that caused surging. Of coarse, if all the factory emission control devices are still attached. Or possibly the tank venting or lack there of.

Just a few thoughts.....

Thanks, Jay

 

[Don C]

Two key statements, rebuilt carburetor and installed by previous owner. One or both are the likely cause, especially if the previous owner also rebuilt the carburetor.

 

[73' mach 1]

Probably a stretch but is this an auto or manual? If everything else above checks out is it possible the TC is starting to go?

 

[Lancelot72]

Thanks for all the replies.  You guys have given me enough ideas on what to check next that I should be busy for a while.  I'll keep you informed on what I find.

 

[Lancelot72]

Probably a stretch but is this an auto or manual? If everything else above checks out is it possible the TC is starting to go?

It is the FMX Auto trans.  The PO had the transmission rebuilt within the last year also.

 

[Lancelot72]

I just noticed there is an empty vacuum port on top if the vacuum advance valve.  Can anyone tell me if this should be plugged or if it should be connected somewhere else?

http://www.lancelotsworkshop.com/images/forum/geraldine/20200221_110758b.jpg[/img]

 

[TheRktmn]

That was a temperature controlled advance (actually ******) used as part of the emissions setup. It really isn't necessary unless you are in an emissions required area. Just make sure that the outer port you are using works and is connected to a ported, not full, vacuum source.

 

[jpaz]

I would also recommend that you get rid of that glass fuel filter. They are very unsafe, easy to break and cause a fire.

 

[red351]

Sounds like the carb needs a little jetting up.

 

[Lancelot72]

I would also recommend that you get rid of that glass fuel filter. They are very unsafe, easy to break and cause a fire.

Thanks Jpaz.  I have read that and it is on the list of things to do.  Hopefully, In about a month we will be starting the big tear down for paint and the engine will be coming out at that time.  I will make sure it is gone when the engine goes back in.

 

[Ron Tanzi]

I would also recommend that you get rid of that glass fuel filter. They are very unsafe, easy to break and cause a fire.

Agree the glass filters suck and do a poor filtration job. 

Ron

 

[Ron Tanzi]

If the engine has never been torn down I would be concerned about timing chain wear especially @ the cam sprocket which if factory has nylon coated teeth. The nylon teeth break down with age making the chain very loose. This could be the cause of your surging issue. When I removed the timing cover of my 1972 351C 2V 25 years ago the timing chain was loose to the point that I could remove the chain with gears still in place. This was the original engine and had 103 K miles on it. I know the history for a fact being that my parents bought the car new. You could check for chain slack by rotating the crankshaft forward and backward while watching the distributor rotor and calculating the number of degrees of rotation that are required to move the rotor. The other option is to remove the fuel pump which allows access to one side of the chain. At that point you can assess the chain wear.

Best, Ron

 

[Lancelot72]

I found that there was a vacuum port running from the front side of the intake manifold but the hose attached to it was stuck onto a hex shaped  end of a bolt on the carburetor.  That had to be a really good seal, lets put a hexagon in a round hole and hope none of the air gets by. :-/    I was thinking this might be the vacuum hose that should have been attached to the vacuum advance port.  So I reattached it there.  When I took it for a test drive the car was running like crap.  so I pulled over and put the hose back where it was.  She went back to normal.  I have since capped off the port on the intake manifold and the vacuum advance port in the pick above.  I also removed and capped off all of the vacuum hoses going to the AC/Heater.  Hopefully I will get time to take her for a test drive and see if there is any difference.  Maybe someone can tell me if the port on top of the vacuum advance is supposed to be connected to the port coming out of the front passengers side of the intake manifold.  The engine is a 351c 2v.

Thanks, Lance

 

[TheRktmn]

72 351C vacuum diagram: