Engine surging

[Steffan]

I just came back from a local car show and as I was cruising along about 55-60 mph it felt like the engine was surging. I have had the carb rebuilt and torn apart 3 times. As you drive along you can feel a slight surge, not a miss in the engine. As well it still has a hesitation when accelerating from a stop. The accelerator pump appears to be giving a good shot of fuel. As soon as you get over the hesitation the car runs up to 100 mph like a scared rabbit.

Another issue is the shift points. It shifts from low at about 30-35 mph and from second to drive at about 60-65 mph. This is under full throttle. I thought the shift points would be higher, maybe 45 mph from low to second and around 70-75 mph for second to drive.

I am thinking of changing to an after market carb, maybe the Edelbrock Street Avenger.

Any suggestions?

[Dakota Boy]

Ttoo much timing/advacne might cause the surging. This happened on my own car.

Shift points on an automatic trans...... vacuum modulator. Pull off the vacuum line and if there is trans. fluid in the line, the modulator is junk.

Shift points can be adjusted a little bit by turning the tiny screw inside the modulator; accessed thru the hole where the vacuum line attaches. counterclockwise will make it shift earlier.

[jopizz]

Squarebirds don't have a vacuum modulator. They began in '61.

[Guest]

As far as engine timing goes get hold of a good quality vacuum guage and use the following web site, it will also give you an insite into other issues you may have

http://www.secondchancegarage.com/public/186.cfm

Richard

[Astrowing]

Also check your vacuum advance unit to make sure it is working correctly, it would cause timing to be erratic. Also, distributor itself may be causing erratic timing issues.

[simplyconnected]

Check timing chain slop:

Start at 6° BTDC. With a socket and long breaker bar, slowly crank your damper pulley back and forth while feeling the distributor rotor. Look at your timing marks and see how many degrees the crank turns before the distributor starts to move. 'Timing set slop' is where stop light hesitation and surging comes from.

If your engine is 'up in years' (like me), consider replacing your timing set.

I always urge folks to 'degree your cam/crank'. It doesn't take long, it requires no additional parts, and the degree wheel may be downloaded from the net. After finding 'true zero', advance your cam 4° to bring the torque curve closer to street efficiency (instead of Interstate Highway efficiency). - Dave

[Steffan]

The engine has been completely rebuilt.
The timing has been set using a vacuum gauge to get maximum vacuum and then backing off a bit to allow for the advance. While under acceleration there is no hesitation or surge. The accelerator pump is giving a good shot of fuel.
There is a carb rebuilder about an hour away but I would hate to pay another 250.00 just to have the same problem. Also I have been looking into Pony Carbs on the Internet, anyone know if they are any good with their rebuilds?

[Howard Prout]

The engine has been completely rebuilt.
The timing has been set using a vacuum gauge to get maximum vacuum and then backing off a bit to allow for the advance. While under acceleration there is no hesitation or surge. The accelerator pump is giving a good shot of fuel.
There is a carb rebuilder about an hour away but I would hate to pay another 250.00 just to have the same problem. Also I have been looking into Pony Carbs on the Internet, anyone know if they are any good with their rebuilds?

Have you checked out your fuel pump? Any chance it was caused by a vapour lock?

[tbird430]

Have you checked your fuel filter and/or has the fuel tank "sock" been checked?

[simplyconnected]

...As soon as you get over the hesitation the car runs up to 100 mph like a scared rabbit...

This doesn't sound like fuel starvation.
What did you get when you rotated the crank?
If your engine is 'freshly overhauled', it shouldn't have ANY hesitation from a light.

[jopizz]

I've had a similar problem in the past and it turned out to be the no. 7 & 8 spark plug wires being right next to one another. They should be as far apart as possible.

[byersmtrco]

Check for vacuum leaks.
The vac/adv in the dist is a likely culprit.

When my 65 did that it was my pre-warning that the
brake booster was about to go.

[scumdog]

Too much timing advance is my guess.

Back it off a few degrees and take the car out and see if you notice any change.

[FINSRIN]

Good advice in those postings. If carb has a lot of miles and was rebuilt. Depending on thoroughness of rebuilder, could be slop in primary throttle bar running through/across carb. Will change mixture ratio driving on primaries as raw air enters via throttle bar hole as bar moves within hole. When secondary opens the surging is reduced because of lower vacuum sucking raw air in plus any leakage is lower percentage of total air entering motor. Secondary had less use and seal was good. I was bitten by that one years ago.

Bill