1974 super beetle dual carb troubles

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benkozak19
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1974 super beetle dual carb troubles

Post by benkozak19 » Sun Sep 15, 2013 3:49 pm

hi I have a 74 super with an 1835 in it and I cant get it jetted right...it has a engle 110 cam, stock valves, electronic igniton all running with some empi dual 34's. ive tried bigger mains but my plugs fouled out so I went smaller with no affect. ive been told im asking these little carbs to do quite a bit but also that I should be able to make it work out better than it is. it drives great down the highway but once I putt around town its starts popping and sputtering. if anyone has some insight or has this same stup and knows some jet sizes that work well let me know please! oh and ive quadruple checked timing, valve clearances, and plug gaps I just cant get them to stop fouling!

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Marc
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Re: 1974 super beetle dual carb troubles

Post by Marc » Sun Sep 15, 2013 5:41 pm

I loves me the Weber 34ICTs on a mild motor, great mileage/driveability and nearly the power you get with 40mm "Kadron" Solexes...the EMPI 34s are supposedly a clone of the 34ICTs, but I can't attest to how faithfully they were copied. The Webers typically come with a 130-135 main, a 50-52 idle, and a 160 air correction in an F78 emulsion tube, with a 1.75mm float valve (the carb was developed for use as a single on the Bedford van in Britain).
Duals on a stock/near-stock 1600 ACVW need bigger idles (55-60), bigger mains (135-150), and ideally F3 or F6 emulsion tubes. The float valve should ideally also be reduced to 1.25-1.50, but that's not super-important if it's working right. Same goes for fuel pressure, ideally it's not over ~2½ psi, but healthy float valves can handle two or three times that much without leaking by. If you're running a stock pump, I doubt that pressure is the issue.
I don't know if EMPI bothered to prejet their copies for the ACVW or if they just sent a couple of Webers to China with instructions to "make these, and cheap"...but the above numbers should give you some idea of the ballpark you need to be in. The idle circuit influences the mixture for all but the top 20% or so of the RPM range, so getting it right is vital. I'd guess your 1835 to want 60s. Having the "wrong" emulsion tubes primarily affects mid-range transitions; changing the diameter of the tube and the number/location of the air bleed holes in it fine-tunes the behavior of the carb primarily below wide-open throttle. Changing the main jet size affects the entire RPM range while the air correction jet has a progressive effect, mattering less at low speeds than at high (rule-of-of thumb is that a step change on the A/C is worth about 1/3 of a step on the main, at high RPM...so if you're just-right at steady-state in the midrange and lean up top, you might try reducing the A/C by a couple steps and the main by one. You can also use the "lean-best-idle" method to gauge whether your jets are the right size: http://www.redlineweber.com/html/Tech/3 ... unning.htm
As with any carbs, all bets are off if the float levels are wrong or the float valves are leaking by, and it is extremely important that you get the mechanical synchronization of the linkage spot-on - both carbs should hit shut and wide-open simultaneously. Sometimes you'll find that one carb gets a wider range of travel for the same movement of the cable - it needs to have its leverage reduced by slotting the linkage arm, or simply bending the lever on the throttle shaft "out" to increase the distance between the shaft and the linkage ball. Conversely, a carb that doesn't have enough travel needs its lever bent in towards the shaft to shorten its effective length and yield more degrees of rotation for the same linear motion of the linkage. Until the linkage is perfectly synchronized, all other tweaks are pissin' into the wind.

benkozak19
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Re: 1974 super beetle dual carb troubles

Post by benkozak19 » Sun Sep 15, 2013 10:19 pm

you are my ******* hero I gotta wait till im back in the town where its at next weekend and ill check to make sure fuel isn't leaking through from too much pressure then ill check everything over and start ordering parts!

surfwagon
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Re: 1974 super beetle dual carb troubles

Post by surfwagon » Sun Nov 24, 2013 9:16 pm

I am enjoying good results :D with my baby weber 34 ICT carbs on my stock rebuilt vanagon 2.0 type iv
FWIW ----- idles 60 , main 160 , F 6 emulsion tubes and 185 airs in humid Hawaii at sea level
David
but I am going to switch and try out some dual 40 IDF's in the near future. :)

benkozak19
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Re: 1974 super beetle dual carb troubles

Post by benkozak19 » Fri Jul 15, 2016 8:24 pm

4 years later...pulled my beetle out of the graveyard fresh gas, 135 mains, Air Correction 1.60, .50 pump, and 60 idles and she shoots flames...running at 3psi i want to drive my bug but it doesnt want me to drive it...its too rich with linkages disconnected too, could it be my float level? If you have any idea what i should do please comment!

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Piledriver
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Re: 1974 super beetle dual carb troubles

Post by Piledriver » Fri Jul 15, 2016 10:48 pm

Make sure the fuel float valves are shutting off, could have dried crud buildup making them stick... fuel pressure is the driver of the biggest "untunably rich" issue on Webers or their children, but not the only possibility.

All Webers and derivatives have a tendency to randomly pee fuel internally over ~2.5 PSI, makes tuning them seem impossible... pinch off the to-pump fuel line and see if it clears up.
I, for one, regularly embrace our new robot overlords, as I am the guy fixing the robots...

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gtmdriver
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Re: 1974 super beetle dual carb troubles

Post by gtmdriver » Sat Jul 16, 2016 1:03 pm

The original fitment for a Weber 34 ICT was as a single carb on a Bedford CF van so it's not surprising that it needs recalibrating for twin use on a VW Beetle.

The emulsion tube is nowhere near what is required.

I ran with these settings on my otherwise standard 1600 TP

Main Idle Air Emulsion
150 55 170 F3 or F6

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