Tuning help needed - volume control screw problem

[BugNerd]

Howdy,

I’ve read everything on here that I could, as well as Rob and Dave’s and Limebug and others to tune up my engine, and I’m running into stumbling on acceleration.

Here are the basics:
SVDA distributor (confirmed with a pump that the canister holds vacuum and advances timing)
Points gapped to .016
Choke set properly at full warm up and wide open throttle plate
Static timed to 7.5° BTDC and then timed at idle to same with vacuum line plugged
Got it running and idling at 850/900 with the bypass screw (big one on left side of carb)
Volume control screw 2.5 turns out
Accelerator pump dialed in for full squirt right now (but I had it at half squirt and no squirt and the issue was the same)

On acceleration, it bogs badly, with bucking hesitation when pulling away from a stop sign. I’ve been farting around with this thing to no success and need some expertise here.

*** The one clue that may help you more experienced folks help me is that there is absolutely no change in idle or running when I (gently) bottom out the volume control screw or screw it out nearly all the way. What could that mean? Might that be my issue? How would I fix that? ***

Thanks for any thoughts you might have in this. I welcome anything and everything at this point because I’m stumbling more than my engine is.
_________________
Tucker

1969 Beetle, 1776cc, manual conversion (done by PO), Bosch 034 SVDA, 34Pict-3, 2.5" drop spindles w/disc brakes, DIY 4” narrowed beam w/Airkewld adjusters, 205/65R15 out back and 175/55R15 up front on EMPI GT-8s.

1974 Kombi Safare Custom Camper NUGGET that needs everything

My YouTube build videos: School St. Garage.

Sold with sadness:
'73 VW Bug
'79 VW Bus

Sold with joy:
'99 VW Beetle TDI (all I miss are the mpgs)

[anthax]

First, make sure you don't have any intake leaks anywhere.

Second, take the carb completely apart and clean with carb cleaner and compressed air. Reassemble and test.

[Q-Dog]

What carburetor are you using?
_________________
Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[BugNerd]

No leaks anywhere. Sprayed starter fluid at various meeting points of different parts. No change in idle/revs.

I’m running a Bocar 34Pict3.

I cleaned and rebuilt it a year ago but the engine wasn’t running or driving at the time, so the rebuild has very few miles on it. I didn’t do a carb dip though. So I’m assuming if it needs a dip and cleaning there’s a clogged passageway somewhere connected to the volume control screw?
_________________
Tucker

1969 Beetle, 1776cc, manual conversion (done by PO), Bosch 034 SVDA, 34Pict-3, 2.5" drop spindles w/disc brakes, DIY 4” narrowed beam w/Airkewld adjusters, 205/65R15 out back and 175/55R15 up front on EMPI GT-8s.

1974 Kombi Safare Custom Camper NUGGET that needs everything

My YouTube build videos: School St. Garage.

Sold with sadness:
'73 VW Bug
'79 VW Bus

Sold with joy:
'99 VW Beetle TDI (all I miss are the mpgs)

[Q-Dog]

I would use a timing light to verify the vacuum advance is actually advancing when you rev it up.
_________________
Brian

'69 Dune Buggy
'69 Beetle Convertible
'70 Beetle

[Danwvw]

Dual Port engines can be really bad about bogging on taking off especially when the stock warm air to the carburetor is removed and an aftermarket header that is too big for the engine is used. Anything that makes the engine slow to warm up like an external oil cooler that does not help matters. The 1585cc, 1641cc, 1679cc and 1.8L type 1 builds like mine below don't really need external oil cooling when the engine compartment is properly sealed because a Stock VW DogHouse fan system is actually very much improved over the earlier type 1 engine's cooling. Aftermarket fan housings that do not completely copy the original doghouse fan shroud design don't cool as well and often the cooling flaps are removed and that causes the engine to not stay at or above operating temperature around town and this too will cause bogging.
Next is the SVDA I take it that is what they sell for them now but it's really not the right distributor. Try to find a Bosch 205-AN or something with a good Vac canaster, (Retard doesn't matter. I would not connect it).
A good 034 SVDA distributor should work with the right vac canister for a PICT-34 if you have a good vacuum signal,
Also, I suspect the Accelerator PUmp circuit may be leaking back somewhere causing a delay in fuel at the nozzle.
_________________
1960 Beetle And 1679cc DP W-100 & Dual Zeniths!

[kangaboy]

Time it correctly. Full advance @ 30-32°.
_________________
-74 Standard - "CaliBug" 2084T, MS3X w/FI and Crank Fire
-76 Westy - "Gandalf"
-18 GTI SE

[BugNerd]

[BugNerd]

[BugNerd]

[FreeBug]

[Zed999]

[oprn]

+2 on making sure the thermostat, flaps and intake heat are all working properly. These engines will run too cold around town without even if you think it's warmed up.

Check your valve adjustment too and do a compression test. A leaky intake valve could give this kind of grief.

[Q-Dog]

[Frank Bassman]

if the carb sat with gas for a year you now have clogged passages. Pay special attention to the idle passages, your issue is there most likely.


Check that the points' pivot shaft is not bouncing up and down too...


-Frank

[lelef]

Does the intake heater system works properly?
I had icing problems in the past also in summer,put a hand on the runners just under the carb if they are really cold should be an icing problem

[VW_Jimbo]

I think you should dip the carb and rebuild. Also, double check your vacuum hose connections and hoses. Hoses sometimes collaspe under vacuum leading to sorts of issues and chasing your tail.

When was the last time you change the fuel filter. Maybe it is fuel starvation at high demand. Sometimes that leads to a clogged tank screen.
_________________
Jimbo

There is never enough time to do it right the first time, but all the time necessary the second time!

[mikedjames]

As well as making sure the throttle closes totally,
I would also check for the butterfly plate not having worn the side of the carburettor choke - it either leaves a gap at throttle closed, or it hangs up on a ledge it cut itself, a touch off throttle closed.
Sometimes this is coupled with an air leak round the throttle spindle, the whole assembly moves around, so a blip on the throttle may cause the idle to change completely as the butterfly plate either hangs up or closes properly.


All of these mean that the volume screw does less than it should because there is an uncontrolled path for air to flow through the carburettor.

You can re bush the spindle to stop the air leak and the tendency of a wobbly butterfly plate to cut into the carburettor body, sand down a small step if there is one, and loosen the screws clamping the throttle plate and move it around until it closes properly.
_________________
Ancient vehicles and vessels

1974 VW T2 : Devon Eurovette camper with 1641 DP T1 engine, Progressive carb, full flow oil cooler, EDIS crank timed ignition.
Engine 1: 40k miles (rocker shaft clip fell off), Engine 2: 30k miles (rebuild, dropped valve). Engine 3: a JK Preservation Parts "new" engine, aluminium case: 26k miles: new top end.
Gearbox rebuild 2021 by Bears.

1979 Westerly GK24 24 foot racer/cruiser yacht Forethought of Gosport.
1973 wooden Pacer sailing dinghy

[BugNerd]

Thanks for the feedback, folks.

I bought carb dip and will be getting a rebuild kit from Wolfsburg West on the way home tomorrow. When it’s apart, I’ll do a closer inspection of the choke and the vacuum ports et al to see if the carb is even worthy of the rebuild (it had sat for 14 years before I gave it a “brake cleaner and wire brush” cleaning—not dipped—as part of my effort to get the engine running). My past experience with Motorcraft carbs has not been terribly helpful on this little guy.

I’ll also check filters and anything else mentioned above. You all have given me a great list of things to check that I hadn’t known to look for.

I’ll report back later in the week if I’ve made progressed or learned something new.
_________________
Tucker

1969 Beetle, 1776cc, manual conversion (done by PO), Bosch 034 SVDA, 34Pict-3, 2.5" drop spindles w/disc brakes, DIY 4” narrowed beam w/Airkewld adjusters, 205/65R15 out back and 175/55R15 up front on EMPI GT-8s.

1974 Kombi Safare Custom Camper NUGGET that needs everything

My YouTube build videos: School St. Garage.

Sold with sadness:
'73 VW Bug
'79 VW Bus

Sold with joy:
'99 VW Beetle TDI (all I miss are the mpgs)

[Danwvw]

The biggest reason a 1600 DP with the PICT-34 carb will crap out on takeoff, is not having enough back pressure on the exhaust. Too big of exhaust the 1 and 1/2" headers cause them to bog on takeoff, dual carbs are needed to run them. A 1 3/8" Header would be better.
_________________
1960 Beetle And 1679cc DP W-100 & Dual Zeniths!