Bigger Jets and Bad Spots

[Justin1958]

Bug is running really sweetly except for the off the line hesitation that I hear so many complaints about. Timing, points/dwell, and valves are all spot on. 30/31 carb has been adjusted. Accelerator pump stroke lengthened but that didn't make any difference. Would upping the main jet size help?

Meanwhile, I got caught in the rain a week ago and the car was defaced by nature as it was covered with all these iridescent silvery spots that have been very difficult to remove.

I had used a polish sealer that I have been happy with for years, but this is the first time a vintage car of mine has gotten wet. I have tried all sorts of compounds and polishes. Finally settled on a wash with vinegar, Meguires ultimate compound, more vinegar, Nu Finish, more vinegar, and a final swipe and buff with Turtle Wax Ice. It is then only ALMOST as nice as the Formula 113 wax that started all these problems.

[jamin12369]

Let me be the first to ask "Which Dizzy do you have?"

[baldessariclan]

What sort of distributor are you using? Good vacuum advance usually completely eliminates “off the line” hesitation issues.
_________________
1971 Standard Beetle — fairly stock / driver

baldessariclan -- often in error, never in doubt...

[Justin1958]

113905205P. It is the correct distributor for a '68 Autostick bug, and it is a freshly renewed one that included a good vac advance can from a respected Samba vendor of distributors.

I should have included this info earlier. The advance is connected to a port on the lower right of the 30/31 carb. I was advised, and this was confirmed by others, that this gave a better "signal" that was more closer to the carb that originally came with this setup. BTW, the engine is a mystery. It had been replaced by the dealer many years ago and has no number.

Thank you,
Justin

[baldessariclan]

Justin,

I'm not familiar with the correct carb and distributor setup for a 1968 Autostick, so hopefully somebody more knowledgeable will chime in on this.

What I do know is that if the 1968 Autostick carb and distributor combination operates similarly to the later 34PICT-3 carbs paired with DVDA distributors, your vacuum advance signal should be such that there is none at idle, and then a large boost in vacuum just as you crack open the throttle (thus giving the advance to make that extra power you need when starting from a standstill).

The advance vacuum port in these 34PICT-3 carburetors lies right underneath the edge of the throttle plate when it is at idle, which completely blocks the port (= no vacuum signal at idle). When the throttle plate is cracked slightly open, all the air rushing through the small gap between the throttle plate and carb wall creates very low pressure (venturi effect), and a corresponding strong vacuum signal at that port. As the throttle plate opens wider, the air speed through gap (and related vacuum signal) both drop off. So that vacuum signal is mainly good for giving you a lot of advance when starting from a stopped position, and also when cruising at highway speed with low engine loading.

Once again though, I'm not sure which models of 30/31 carbs operated similarly to the later 34 series carbs with regards to vacuum signal. I think the earlier carb models were designed to operate with a SVA (single vacuum-only advance) distributor, which relies on a completely different vacuum porting / signal system, and won't work properly with the later DVDA type distributors.
_________________
1971 Standard Beetle — fairly stock / driver

baldessariclan -- often in error, never in doubt...

[sb001]

[baldessariclan]

Here's some helpful schematic illustrations I found in the photo gallery a while back (pics courtesy of Juanito84) -- They give a good basic understanding of how the vacuum advance systems work on SVA vs. SVDA/DVDA type carburetors.


SVA type carb vacuum advance signal at closed-throttle / idle (low RPM's, no load):

SVA type carb vacuum advance signal at partially-open throttle / accelerating from stop (low RPM's, high load):

SVA type carb vacuum advance signal at full-open throttle, low speed accelerating (low RPM's, high load):

SVA type carb vacuum advance signal at full-open throttle, high speed accelerating (high RPM's, high load):

SVA type carb vacuum advance signal at partially-open throttle, high speed cruising (high RPM's, low load):

Note that for the SVA distributors, the vacuum advance system completely covers for all engine speed and loading spark advance requirements.





SVDA/DVDA type carb vacuum advance signal at closed-throttle / idle (low RPM's, no load):

SVDA/DVDA type carb vacuum advance signal at partially-open throttle / accelerating from stop (low RPM's, high load) --or-- partially-open throttle, high speed cruising (high RPM's, low load):

SVDA/DVDA type carb vacuum advance signal at full-open throttle, low speed accelerating (low RPM's, high load) --or-- full-open throttle, high speed accelerating (high RPM's, high load):

For the SVDA/DVDA distributors, there is also a mechanical (centrifugal) spark advance that kicks in progressively as the engine RPM's get higher -- it reacts to ("senses") only engine speed, though.
The vacuum advance system covers for the engine loading requirements.
The total spark advance comes from both the mechanical and vacuum systems (they are additive) for this carburetor & distributor combination.
_________________
1971 Standard Beetle — fairly stock / driver

baldessariclan -- often in error, never in doubt...

[baldessariclan]

So anyway, my suspicion is that you might have a SVA-type carburetor incorrectly coupled with a SVDA-type distributor, as sb001 noted above...
_________________
1971 Standard Beetle — fairly stock / driver

baldessariclan -- often in error, never in doubt...

[mark tucker]

eye wood put a magna spark dist in it and tune it for your app. as for the spots....I used some swap meet special wax/protectant stuff on mine, looked awesome, so I did the wifes montaro....2 months lator both card clear coat(mine with peral) were dead/dieing/ AFU. stay away from non major company products.

[sb001]

[baldessariclan]

[ashman40]

[Justin1958]

Wow, great way to tell the story. I am using the angled port in the rear, D in your illustration. When I first got the car the distributor AND the autostick solenoid were both connected to the usual port on the left. The elderly woman who owned the car had it serviced religiously at a VW specialist and I doubt she would have been one to drive the car with the delicate hesitation it has now. There were a host of other things wrong with it when I got it so I can't isolate the effects of that vacuum line hook-up.
Justin

[sb001]

[sb001]

OK ashman, I experimented a bit with the H30/31 this evening:

This first pic shows the typical left-side vacuum advance port "A", and you can see the "pipe" from it extending into the venturi:

Note that there do not seem to be ANY other drillings connected to this- it's just a tube that extends straight into the upper part of the venturi. I sprayed some carb cleaner through it and that is the only place it came out. I assume this port is for use with an SVA distributor, although unlike the illustrations above it apparently does not borrow additional vacuum from just above the throttle plate.

(On a side note you can also barely see the drilling for the autostick port "C" in that photo, in the upper right where the throat narrows-- it extends straight out to that port.)

This next pic shows the area beneath the throttle plate (with the "D" port visible just above the base flange):

The main drilling you see there in the rim of the carb throat is the vacuum retard drilling, it goes through the carb throat wall into that open tube, where it goes up and connects to the retard port "B" on the back of the carb. (That open bottom of the tube is of course sealed when you mount the carb to the intake with a gasket.)

The circuit for the "D" port extends at that downward angle into that "channel" that goes around the edge of the carb base. On the other end of that channel there is another drilling, where the circuit goes up and comes out just above the throttle plate. The picture below shows this drilling circled in red, along with the vacuum path for port "D":

So... when you have the carb mounted on the intake the gasket covers that channel and seals it airtight.

Again this drilling is on the opposite side of the carb throat from the "A" port circuit and does not appear to be connected to it in any way. Just to be sure, I sprayed some carb cleaner up into this circuit from the bottom opening into the channel, and it only came out that drilling directly above the throttle plate. So apparently "A" and "D" are two completely independent vacuum advance paths, with A coming from the upper venturi and D coming from lower just above the throttle plate.

Hope this helps
_________________
I'm the humblest guy on this board.

1969 autostick sedan, family owned since new
1600 SP engine
Solex 30 PICT 3 carburetor
Bosch 113905205AE autostick distributor

[ashman40]

Really appreciate the effort to confirm the vacuum ports. I am satisfied that on H30/31 carbs...

port "A" is for the SVA vacuum advance
port "B" is for vacuum retard (intake vacuum)
port "C" is for the autostick
port "D" is for SVDA/DVDA vacuum advance

THANKS!
_________________
AshMan40
---------------------------
'67 Beetle #1 {project car that never made it to the road }
'75 Beetle 1200LS (RHD Japan model) {junked due to frame rot}
'67 Beetle #2 {2019 project car - Wish me luck!}

[Justin1958]

This is fascinating. I wish I had a printer that could do a clear job worthy of this info. I will keep up my hunt for the correct carb and until then I will just deal with the hesitation. It is a remarkable car and I love driving it in good times and bad.

Thank you for the research that went into these posts.
Justin

[baldessariclan]

[sb001]