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Sun May 06, 2012 11:30 am

I am trying to sort a few, potentially related, issues.

First- I have a very noticeable flat spot just off idle, both under load and with no load on the engine. The flat spot is noticeable enough that the car will buck if the throttle is opened too quickly off idle. The car runs reasonably smooth at any other throttle angle/opening. Idle is smooth as well.

Second- I have a hot starting issue. It takes several seconds of cranking the engine before the engine will start. I have not been able to determine whether pumping the gas pedal helps or not. The car starts immediately when the engine is cold.

Specs are as folows:
-71 Squareback
-The engine was rebuilt approx 4,000 miles ago. Stock build, no major modifications
-The car has a SVDA 034 distributor with electronic ignition (presumably from hotspark.com)
-Dual 34 PICT carbs. Carbs have been synced at idle and at ~3000 rpm
-Timing is set at 30 degrees BTDC @ ~3500 rpm with the vacuum disconnected.
-Total advance is ~40 degrees BTDC with the vacuum hose connected.

Please let me know if I have left out any vital information. Any help will be greatly appreciated. Thanks in advance!

Sun May 06, 2012 12:14 pm

The sizes of All the jetting in your carburetors?

Sun May 06, 2012 5:48 pm

Mike Fisher wrote: The sizes of All the jetting in your carburetors?

I spoke with the previous owner... he said "It has the smallest fuel jets available for the two carbs but the air correction jets are not interchangable so I drilled them out to obtain about 12-1 ratio". I am essentially starting at ground zero, or worse actually because I can't trust the actual sizes of drilled jets.

Upon first inspection I discovered that these are actually Solex 32/34PSI.2 carbs, not PICT carbs.

So I tore the carb apart to see what is in there, or at least what size the jets were before the drilling.

Jets are as follows:
Idle: 50
Main: 120
Air Corrector: 130 (but potentially larger because the PO drilled them)
Venturis: 22Can someone give me jetting suggestions for a stock 1600 engine with dual 32/34PSI.2 carbs? By the way I live in St Louis Missouri, essentially at sea level?

Sun May 06, 2012 6:15 pm

John at www.aircooled.net will give you free advice and sell you parts if he thinks you need them. Read his VW Carburetor Tech Articles first.

Sun May 06, 2012 6:31 pm

The air correction jets are probably opened up to 180, which should be close with the main jets (still slightly rich). You'll have to verify the size using some jet drills to be sure. Ideally, you'd like to see somewhere between 180 and 240.

Your timing is probably off though. From the numbers you gave above, you should be somewhere between 5 and 10 degrees BTDC, with a total advance (with the hose on) of 30 to 32 degrees. The 30 degrees with the hose off, probably has you getting off the line about 10 degrees retarded, which is why it's falling on it's face in the flat spot. Something to keep in mind, you want the total advance no more that 32 degrees, at 3200 rpms. And these engines love all the advance you can give them, right up to the point where they'll grenade. :o This is the main reason for limiting the total to 32 degrees max.

Sun May 06, 2012 10:18 pm

Bobnotch wrote: Your timing is probably off though. From the numbers you gave above, you should be somewhere between 5 and 10 degrees BTDC, with a total advance (with the hose on) of 30 to 32 degrees. The 30 degrees with the hose off, probably has you getting off the line about 10 degrees retarded, which is why it's falling on it's face in the flat spot. Something to keep in mind, you want the total advance no more that 32 degrees, at 3200 rpms. And these engines love all the advance you can give them, right up to the point where they'll grenade. :o This is the main reason for limiting the total to 32 degrees max.

When performing the initial timing I followed these instructions: http://www.hot-spark.com/Installing-SVDA-034.pdf Granted I did not install or purchase this distributor initially, I only inherited this setup from the previous owner so I can't be sure of the distributor's origin.

Are you suggesting that I time the engine to 30-32 degrees with the vacuum hose connected? Wouldn't this effectively turn the timing back 10 degrees from where it is now and put me 10 more degrees retard at idle? Maybe I am misunderstanding the logic?

Would it be better to just run the engine with the vacuum hose plugged and totally disconnected from the distributor?

Tue May 08, 2012 8:37 pm

At the advice of the guys at AC.net I retarded the timing by 2 degrees (to 28 degrees @ ~3500+ RPM with the vacuum can disconnected and plugged). Overall the vehicle seemed to accelerate a bit smoother, but the top end (top speed) was completely gone. It did not noticeably help the flat spot. The hard start wasn't much better either.

Time for a rejet maybe?

One tech suggested bumping up to 27 venturis and rejeting from there

Another tech suggested the following jets:
Idle - 55
Main - 125 or 130
Air Corr: 130 (a new undrilled 130)
Venturi: 22Anyone have experience jetting dual 32/34 PSI.2 carbs on a stock 1600 engine?

Wed May 09, 2012 7:58 am

Bobnotch wrote: The air correction jets are probably opened up to 180, which should be close with the main jets (still slightly rich). You'll have to verify the size using some jet drills to be sure. Ideally, you'd like to see somewhere between 180 and 240.

Your timing is probably off though. From the numbers you gave above, you should be somewhere between 5 and 10 degrees BTDC, with a total advance (with the hose on) of 30 to 32 degrees. The 30 degrees with the hose off, probably has you getting off the line about 10 degrees retarded, which is why it's falling on it's face in the flat spot. Something to keep in mind, you want the total advance no more that 32 degrees, at 3200 rpms. And these engines love all the advance you can give them, right up to the point where they'll grenade. :o This is the main reason for limiting the total to 32 degrees max.

Bob says you want 180-240, so I wouldn't be buying 130's. He's also telling you to buy some jet drills to verify what you already have in there. Buy the jet drills and report back your findings Here to Bobnotch! :wink:

Wed May 09, 2012 8:02 am

depending on the carb version (there's a bazillion different PDSIT models) they will have the wrong vacuum signal for that distributor

Wed May 09, 2012 1:16 pm

Slow 1200 wrote: depending on the carb version (there's a bazillion different PDSIT models) they will have the wrong vacuum signal for that distributor

My carbs say are marked as Borsol 32/34PDSI.2 is this enough to tell if the "vacuum signal" is correct.

From the hot spark website: "If your engine is running...an aftermarket carburetor setup without an available vacuum source, the vacuum-advance mechanism may not advance fully. However, the distributor's centrifugal-advance mechanism will provide the same advance curve as a properly set-up 009 centrifugal-advance distributor, simply by capping off the vacuum port."

Could I just be experiencing an overall lean condition PLUS the normal 009 flat spot?

Wed May 09, 2012 1:34 pm

Mike Fisher wrote: Bob says you want 180-240, so I wouldn't be buying 130's. He's also telling you to buy some jet drills to verify what you already have in there. Buy the jet drills and report back your findings Here to Bobnotch! :wink:

do you have a good source for jet drills? are weber jet drills the same size as solex jet drills? are both just standard MM sizes?

Wed May 09, 2012 1:52 pm

Quote: is this enough to tell if the "vacuum signal" is correct

buy a vacuum gauge ($10) and see if there is a vacuum signal off idle.

I had a poor vacuum signal on mine until I plugged the hole in the venturi.
If you look at the vacuum tube going into the carb and follow it straight through into the throat of the carb, does it have a hole there? Mine did and it made the vacuum signal weak, as soon as I plugged it we got a good vacuum signal.

Quote: are weber jet drills the same size as solex jet drills? are both just standard MM sizes?

Yes, in a pinch you can use the shank of micro drills(hobby shops) to check the jet sizes as well, you'll need calipers to check the diameter of the drills though.

my thread where we were playing with the jetting on the PDSITs
http://www.thesamba.com/vw/forum/viewtopic.php?t=474164&postdays=0&postorder=asc&start=0

Wed May 09, 2012 4:26 pm

And a little searching of the forum brought this up.

The early dual carbed cars (up thru 65) used 23mm vents, 135 mains, 185 correction, versus the later "new" 130 main, 240 correction, using g45 pilot jet(early and late). From Aug 66 on, the left carb got a 24mm vent, 132.5main jet, 150 air correction jet. And if you're having a flat spot, then change the g45 to g50 pilot jets. This info came out of the Blue Bentley, which is from the VW workshop manual.