30 PICT-3 Bucking at 2000 rpm with 034 SVDA on 1641

KILLERWATT · Last edited by KILLERWATT on Sun Oct 19, 2014 8:12 am; edited 2 times in total

Freshly built, dual port, 1641 with a Engle 100 cam, a 30 PICT-3 and 034 SVDA distributor in a bus. It pulls hard but has a hesitation and starts bucking around 2000-3000 rpm.

I've timed the SVDA at 30 btd with the hose plugged at 3500. With the hose connected it's at 8 btd at 900 rpm and 44 btd at full advance. I've up'ed the fuel pressure to 3lbs.

I tried a 127 main and then went to a 130 main it helped but the problem is still there.

Brian · Posted: Fri Oct 17, 2014 10:12 am Post subject:

Do you have the "Shepard's hook" going on with the vacuum line?
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KILLERWATT · Posted: Fri Oct 17, 2014 10:18 am Post subject:

Brian · Posted: Fri Oct 17, 2014 11:49 am Post subject:

I don't run vacuum advances, but I know you need to have a hook.
Here is one that's setup correctly:

Image may have been reduced in size. Click image to view fullscreen.

And here is one that is incorrectly put in:

The goal is to not let fluid fall into the canister.
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KILLERWATT · Posted: Fri Oct 17, 2014 5:48 pm Post subject:

Can I go bigger than 130 on the main?

Frank Bassman · Posted: Fri Oct 17, 2014 8:33 pm Post subject:

I may be wrong, but I think your distributor is not a match for your 30 Pict-3.

http://www.thesamba.com/vw/forum/viewtopic.php?t=443358

If you've got a spare centrifugal-only distributor I'd slap it on and see if there is improvement.(Only for the time being. Vacuum/Centrifugal distributor types give better driveability in my opinion.) Provided your plugs are reasonably clean, a funky advance signal mismatch looks like it could be giving you your symptoms.

Sure it's not a 34-Pict 3?

Going larger on your main may just end up fouling your plugs. There's something else going on and incorrect timing advance may be it.

Brian · Posted: Fri Oct 17, 2014 9:44 pm Post subject:

I'm rocking a 34-3 with a 019, it isnt smooth but gets me to 60 in under 20.

That 34 will be fine with a 30 because 1600 doesn't differ too much from a 1641
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[email protected] · Posted: Sat Oct 18, 2014 6:01 am Post subject:

The improvement with the main jet is going in the right direction. You probably need more fuel in the idle circuit, and possibly the main circuit. I've run 34 picts with a similar combo with idle jets as big as 70, and main jets as big as 135. VW set their carbs to run on completely stock engines. Even the lesser back pressure of a header on a completely stock engine can require more fuel. It's been a while since I've played with any 30 size carbs, but if your version has the solenoid in the idle circuit, that can be swapped out for a standard jet. Buy a few stock idle jets in the classifieds, and get a pin vise drill bit set, and open a few up to 55, 60, 65, 70. You can also get a few main jets to open up if you have the proper drill bits, or acess to a jet ream/gauges.

Edit: You could also drive the Bus at a steady speed/rpm when the hesitation occurs for about 10-15 seconds, then immediately turn off the ignition, and coast off the side of the road to pull one of the plugs to look at. If the porcelain is ghost white with verly little carbon around the edge, that would tell you you need more fuel. Remember to get a plug wrench that has foam or something to pull out the plug with the socket once loose. I usually take an extra plug to swap for the one pulled, so I can let the pulled one cool down to get a closer look back at the shop. And take some gloves to handle hot stuff, and a container to put the hot plug in if you decide to swap it with another one, so you don't melt any interior items.

KILLERWATT · Posted: Mon Oct 20, 2014 10:34 am Post subject:

Still doing it with a 135 but seems to be coming in later like 2500 rpm now.

I bought the biggest jet our VW parts store had 137.5 hopefully this gets it.

danielsan · Posted: Mon Oct 20, 2014 1:26 pm Post subject:

What frank bassman said -- bad carb / distributor combo. You need 34 pict for an SVDA or a vacuum only for a 30 pict 3. Aircooled.net used to make an svda for 30/31 s but hasn't had them in stock for a long time.

[email protected] · Posted: Mon Oct 20, 2014 3:08 pm Post subject:

Try going back to the 130 main, and increasing the idle jet size. If your stumble is below 3000 rpm, it's in the idle circuit. If your idle jet is too small, you could go to a 140 main, and it would make little difference below 3000 rpm.

KILLERWATT · Posted: Mon Oct 20, 2014 3:38 pm Post subject:

I thought for sure I had a 55 idle in there; ended up being only a 50 upon further inspection. Tried a 55 and it only did it between 2000-2500rpm. Put a 60 idle and went to a shop and got a 140 main.

No stumble at all now. I'm going to try leaning out the main like you said. Folks were telling me the idle wasn't a factor after 2000rpm but my findings are that it definitely is up to 2500.

Luft kühl · Posted: Mon Oct 20, 2014 4:11 pm Post subject:

It has already been mentioned twice that your carb and distributor are mismatched, and will not work together.

If you choose to ignore this advice, your engine will never run properly, no matter what combination of jets you use.

KILLERWATT · Posted: Mon Oct 20, 2014 6:07 pm Post subject:

Luft kühl · Posted: Mon Oct 20, 2014 7:19 pm Post subject:

The 30 mm carbs 30 pict-1 , 30 pict-2 , and 30 pict-3 were used on single port engines (66-70). These carbs have the proper vacuum signal for SVA "vacuum only" type distributors.

SVDA distributors are used with the 34 mm carbs on dual port engines (1971 and later).

The "vacuum only" distributor that matches your 30 pict-3 is #113-905-205T.

Or, since your engine is a dual port, you also have the choice of getting a 34 pict-3 (or 4) to match your SVDA distributor.

[email protected] · Posted: Mon Oct 20, 2014 9:33 pm Post subject:

Slow 1200 · Samba Member Joined: July 02, 2004 Posts: 2105

Afaik The only 30-pict3 that will work with a svda is one from an autostick beetle, what's the number on the carb?

glutamodo · Posted: Tue Oct 21, 2014 10:59 am Post subject:

I don't care if you put it on a bigger engine with a cam, that's not going to change the internal vacuum plumbing of the carb.

This is the thread from many years ago, where I went into this in detail:

http://www.thesamba.com/vw/forum/viewtopic.php?t=185095

The modification state number on the 1970 30PICT-3s is stamped on the bowl. Subsequent 30PICT-3s (for the 1200 engine) were stamped on the left side of the base flange, which was the normal location from mid66-onward.

KILLERWATT · Posted: Sun Oct 26, 2014 5:24 pm Post subject:

Plugged the vacuum port and borrowed a 009 from a buddy. I went on a camping trip where I drove the bus on the highway for 2 hours each way, about 240 miles.

It still hesitates at 2500 and then clears up a 3000rpm. Gas mileage sucked with the 140 main on the way up so I went back to a 130. It didn't make a difference either way.

I've read where people say they run a 30 pict with a 1641; but I'm moving on to a 34 pict

KILLERWATT · Posted: Thu Nov 06, 2014 12:18 am Post subject:

Junked the 30-3 pict, I installed a 34 pict. I ran it with the 009 and then the SVDA; it still hesitates at 2500rpm in 3rd and 4th gear.


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30 PICT-3 Bucking at 2000 rpm with 034 SVDA on 1641
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