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Sat Nov 07, 2009 11:36 am

My 74 bug , all stock, that i have owned for almost 20 years has a problem. It is for the most part un-drivable. It idles fine, It accelerates fine with one exception. The initial touch of the gas peddle causes the engine to drop rpm & stall. Sometime i can feather press the peddle to get more rpm from idle then acceleration becomes normal. My local Vw Mechanic, a great guy, has attempted to solve the problem but i am afraid he is at his wits end.
Things we have done so far:
replaced carb
cleaned & sealed gas tank
replace all fuel lines
new coil, points & all tune up items.
This was all before the start of summer as i drive my 73 vert in the summer ;)
I am trying to get the 74 ready to drive again this winter but the problem persist.
Could this be a problem with the distributer , in particular the vacuum advance?
Any ideas or suggestions? Thanks everyone.
P.S. This has somewhat been a problem for the life of this car with me. Only recently has the hesitation worsened to the point it is not drivable.
Thanks

Sat Nov 07, 2009 1:07 pm

George Evans wrote:
Could this be a problem with the distributer , in particular the vacuum advance?

Yes, if the vacuum advance is not working. Could be the centrifugal part is seized up too. I've had seen both happen before. In a 74, that would be an SVDA, that's what you have right? You can verify the vacuum advance with the distributor cap off by sucking on the advance hose and watching the breaker plate move, and the centrifugal by doing the wrist-twist on the rotor and seeing how well the shaft rotates and springs back, and then verify both with the engine running using a timing light. Which replacement carb did you put on there? Have you verified that the accelerator pump is spraying good and right as you open the throttle?

Make sure no vacuum leaks on the manifold where they meet the head or at the rubber boots.

-Andy

Sat Nov 07, 2009 1:13 pm

It doe's have a single vacuum line to the canister. Believe me when i say everything else has been gown over adjusted & or replaced more than once.

Sat Nov 07, 2009 2:10 pm

Yeah, check the advance out. And the accelerator pump - it's not unknown to have issues with a new carb, and even be the same issue with the old carb!

A smooth acceleration off idle on dual ports can be touchy. If you've read my thread on all the little tweaks and things they did the carburetors over the years, and the fact that many carbs had a specific distributor inteneded to match up with them, you can see that if things go wrong driviability suffers. I messed around for years on my DP baja trying to get a good off-idle throttle (before I realized how unsuitable the 009 I had on there was) It was after I started working at the VW repair shop and discovering that the best running bugs were ones that were still original with all the parts working right that I decided the 009 I had in there might be to blame. At one point about 15 years ago I tried a couple of different vacuum distributors and although it wasn't the right one, found one that ran.... well, better than the 009, and took a long road trip with it. But halfway though that trip, it started running like crap again. Checked it out and found the centrifugal portion was seizing up when the engine was hot. So threw in the 009 I had in the trunk and continued on, living with darn flat spot. ](*,)

But it's one of those things you kind of get used to, double-pumping the gas pedal when taking off from a stop. A few months ago I took a BOCAR 34PICT-3 and modded it by putting a drilling through the venturi up top like on the 28PICT carbs so that it produced a vacuum signal similar to the mid-60s carbs, and used it with my 1966-7 "K" distirbutor. At first it ran quite good, but that carb is known for being something of a piece of junk. And over time it got worse and worse, but it was gradual and I adapted. It was only after watching my brother try to drive it once day that I realized how bad it had gotten, and went back and got rid of that carb and put on my trusty old adapted 30PICT-1 I was using previously. It's funny when your foot is used to compensate for such things and then the car suddenly runs well enough that you don't have to....

But I'm rambling again. Hope you figure something out!

-Andy

Sat Nov 07, 2009 4:00 pm

Rule out one thing at a time I say.....

I have a little vacuum pump that I use to see if the distributor can not only will hold a vacuum, but will advance the timing some when applied.

Is the dwell angle correct on the points? Verify they are correct and move on.

Then hook up the timing light to it and reve it up and down to see if there is something going on around the "stall speed". Set the timing to be about 28º BTDC at about 3500 RPMs or until there is no more centrifical advance to be had with the vacuum hose off the can.

I am not a big fan of the replacement carbs myself, I prefer to send my german solex carb down to keifernet to have it rebuilt. If you still have yours, I would send it down to him and have that one rebuilt. Is the one you have on there still a 34PICT3? Is the ported vacuum for the distributor hooked up to the correct carb port?

If you don't, it is time to rebuild the carb that you have paying careful attention to the passages and blowing them out with compressed air. When you are doing that, read up on how to adjust and point the accelertor pump so that it is doing its job correctly.

Are the heat risers working correctly?

Make sure you do not have platinum plugs in this thing. They don't work well for you.

Sat Nov 07, 2009 4:17 pm

Thanks everyone for the great abvice. I have been down this road & have done the these thing & more except the distributer.
Sending the original dizzy for rebuild is an option. What do you guys think of aircooled.net's single vacuum dizzy for $140?

Sat Nov 07, 2009 4:19 pm

Test yours first and see if that really is the problem.

The aircooled one is a fine unit though.