68 hesitation when accelerating from a stop when warm

[Tomlx50]

Hello my 68 autostick starting having a problem with accelerating from a stop when warm it will hesitate real bad. I have to let off the gas or it will stall. 
Timing good, changed spark plugs and wire,
Checked points gap and then replaced points and condenser.
This is driving me crazy at first it's fine then after a few min of driving it starts to do it.

[tmea]

There are two things I would recommend checking. First, your centrifugal and vacuum advance on your distributor. Easy to check if you have a timing light. Second is the accelerator pump on your carburetor. If you have the OME carb it will be on the r/s side of the engine and easily accessible. Remove the cover plate and check the diaphragm inside. It maybe torn. If neither of those are the problem I'd get a can of starter spray and check for vacuum leaks. Start at the cylinder head intake joints and work your way up to the carburetor. If you notice a change in rpm when you spray in a given joint you have a vacuum leak there. A good thing to fix right away as these leaks cause your engine to run very lean and very hot.

Tom

[72VWBeet]

I have the same issue with my 72. when I accelerate at a green light, it feels like its choking, I let my foot out and step on it again and runs fine.  My mechanic is taking a look at that now among a few other things, but he thinks it needs a new carb.  I trust him, he owns a Import car repair shop and has a 67 beetle convertible which he restored himself completely to show car level.  The car is silver with dark red leather low backs and a dark red convertible top. This car is nothing less than beautiful and perfect.

[tmea]

72VWbeet:

I'd save your money by checking your point gap and timing first. You can do it your self. The directions are in the owners manual and it is a simple procedure. The problems that usually cause your symptom are:

- Point gap/dwell angle incorrect
- Incorrect timing (these two things go together) set your point gap first then timing.
- Accelerator pump setting.

Tom

[Albie 2]

I am new to this site and it seems to be a good place to find information. As for the problem of acceleration stalling. I have read that the problem could be the fuel that we have to use. It is usually 10% ethanol. This causes problems as it actually needs more air to burn correctly. The idle valve which you can access on the side of the carb is I believe is a 45 or 50. By going to a larger size (50 or 55) the problem can be alleviated. This is a relatively inexpensive piece so it won't break the bank to try it.

[sb001]

First, your centrifugal and vacuum advance on your distributor. Easy to check if you have a timing light.

How do you check the vacuum advance on a SVDA/ DVDA with just a timing light? I would think you would need more than just the light to check the vacuum advance accuracy- you would need a vacuum gauge that can measure in-Hg or mm-Hg. There is no other real way to determine at what point the vacuum advance stops and centrifugal advance takes over.
But I do agree that it sounds like the vacuum advance is acting up, since it kicks in right at acceleration from a stop- either hooked up wrong, has a leak, or the canister is bad. Vacuum advance on my 69 autostick (but 1600 SP engine) is 8-12 degrees @ 240 mm-Hg-- this is why my crank pulley has a 10 degree BTDC mark. I would need a vacuum pump hooked up to the canister that I can manually introduce 240mm-Hg of vacuum and then take a reading on the pulley and see if it's at 10 degrees BTDC. Since a vacuum leak at the carb can cause issues with the vacuum advance signal, I would also suggest the spray test around the carb, intake etc see if the RPMs increase anywhere. Also, what distributor are you running?

[tmea]

To check the function of the centrifugal advance, with timing light connected and vacuum advance line disconnected and plugged you can check the function of centrifugal advance by merely keeping the timing light on while increasing RPM by pushing the accel arm. You can do the same after re-connecting the vacuum line to test the function of the vacuum advance. If you have a dwell/rpm meter you can measure more accurately. With the two (cent and vacuum) combined you should get a max advance of around 34 degrees. For my car I always adjust the timing for maximum advance (34 degrees) at 3,000 rpm. IMO this is far more important than setting the timing at the prescribed setting at 900rpm.

Tom

[sb001]

But what is vacuum advance at WOT? Is it still around 10 degrees?

According to Old Volks Home, the advance specs on my Bosch AE distributor are:

Advance/Retard Range: Vacuum: 8-12deg Adv; Centrifugal: 13-16deg @ 2200rpm, 25-28deg @ 3900rpm

So wouldn't this mean that I'd be getting close to 40 degrees total advance if I am still getting 10 degrees of vacuum advance combined with the 28 degrees of mechanical advance at 3900 RPM (WOT)? That seems awfully high!

[tmea]

No, your vacuum signal decreases at WOT so in your case at 3900 RPM your vacuum advance would be minimal. Almost all of your advance at WOT comes from centrifugal advance. At highway speeds you need 28 to 32 degrees of advance.