I've read countless posts on adjustments, jets, linkages, etc but I'm new to all of this. Got the car in December 2015, and was told the following: 2.3l, scat c-25 cam. It has the stock non-vacuum distributor w/points, dual weber 40's, ?hex-bar linkage, bursch muffler/no headers. Came w/50 idle jets, 190 ac, 125 mains, f7 e-tubes. I live at elevation 3700'. Have tried f-11 e-tubes, went to 45 idles, ran good at 3500 rpm+, constant pop at lower rpm or flat throttle. Have tried many combos of mains, ac, idles, e-tubes but still pops considerably at flat throttle. Don't have ability to check air-fuel ratio (yet). I'm running out of bourbon-please help (with carbs, have line on more bourbon).

sorry brother I just ran out of my last bottle of Stagg ;-)
usually popping at idle is an air leak....throttle shafts on the carbs are probably worn....
wiggle them and see if any play....can be other things too

But- does she got the jack?

One of the things I found is many times people think they have a carb problem and it is really something else. Like an ignition problem or air leak. I just found out on another car of mine that I had a dying coil, when I swear it felt like it was running out of gas on the high end.

It does sound like you could have an air leak somewhere.

At idle, it runs great, after warmup, 900-950 rpm. The popping from the carbs is more at a constant pedal; not under acceleration. Then, on de-accel, it backfires lightly. Stand on the pedal and it will run strong all the way to 5500/6000 rpm; just pops out the carbs at a steady pedal.

You havent mentioned the synchronization between the carbs.
Do you have a tool to measure it?

It is critical to do it at Idle with the linkage disconnected, then hook it up and measure again at low throttle and higher RPMs.
The linkages are prone to vary in synch with throttle position if not setup just right.

A cable linkage from tangerine racing is a set it & forget it solution.

Removed, disassembled & cleaned carbs. Installed, synced carbs prior to hooking up linkage. Set idle mixture at 2 turns out, then checked sync. Reconnected linkage, then synced at 2500rpm. At that point, had 50 idle jets, 125 m, 190 ac, f7 e-tubes. Running very rich, idle mixture was at 1/4 turn out for best idle. Switched to 45 idles, f11 e-tubes, set mixture at 1 3/4 - 2 turns all around, ran great, idled great, popped at cruise. I've tried different combinations of main, air & e-tubes, but still pops from carbs when at a steady pedal at most rpm ranges and a light backfire from exhaust at deaccel. Seems to pop more with f11 tubes, runs better with f7, 125 or 130 mains, 190 ac. ???

How do you know it was rich with the 50 idles and f7 emulsion tubes?
I suggest bigger idles and f11s.

I agree.

Try 55 idles, F11 tubes and mains 130-140 with 200 air correctors for base setting a 2.3L Then adjust/try slightly larger/smaller mains & airs for your altitude.

Tah-dah! That is why they came with EFI.

And that is why the OE EFI was such a great set-up, & part of the reason I chose 914 over the various other used 914-6, 912, Fiat 124, MGB, TR$/^, etc. options back in 1975! I'd already had enough of the carb follies - especially multi-carbs & synchronizing them, with my prior cars, those of my buddies, folks & uncle!

Carbs on 914s are generally the cheap & lazy way out of an engine rebuild/refit, for those not willing to learn about EFI.

IMHO, go find the original EFI & reinstall it (if it can be tuned to your set-up), so you 'll have same or better performance, without all of the hassles of re-jetting, floats stuck, synchronizing, etc., etc. Otherwise, there are aftermarket EFI systems out there which Raby, FAT Performance, etc. uses with great success on built T-IV's like yours.

Good Luck!
Tom
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You just told him to put the stock EFI back onto a 2.3L motor with a carb cam.
Good luck with that.

It seems to me that your idle and main jets are too small. I have Dellorto 40's on a 2056 with 34 vents, 60 idle jets, 132 main jets and 180 air. Popping at cruise would seem like it is running lean or has an air leak. Have you pulled a spark plugs to look at the color?

http://www.aircooled.net/vw-carburetors-jetting-102/


If nothing else you EFI guys are persistent.

Oh, and I will bet $100 that my effectively stock 2056 engine with dual webers will drive circles around any stock EFI car you want to try.

"Appeared" to be running rich with the 50's as the plugs were black, smoking slightly with a very strong fuel smell. When adjusting the idle mix by ear & watching the tach, had to screw the mix screws almost completely in. Changed to 45's, F11, 125m,190ac and the idle mix was good at 1 3/4 turns, but popped out carbs. Switched to 140 mains, engine bogged from initial throttle like too much fuel. Changed to 195 ac, then 200ac, no help. Thought the f7 might help at lower rpm so switched to F7, 125m, 190 ac; didn't bog down, ran good but still popped.

What size main venturis?

My favorite topic.

Air bypass screws fully in on all throats before you started?
What size venturi?

Lastly, you are only 1/4 turn out on the idle screws? Seems way too small.

Based on my experience, the idles are too small. I ran 65 with a 34 mm Vent @ close to sea level using drla 45's.

Carlos

Check also that the idle screws that act on the levers are no more than 1/2 turn in moving the levers off the stops. If you wind them in too far you'll expose the progression holes and get similar symptoms.
As Chris said what size are your venturi's? Minimum 28mm, max 32mm required.

Venturies are 32's, air bypass are in all the way. I'll check for an air leak somewhere. I agree, it sounds like a lean condition. Then when I try to make it richer, it dies at initial throttle. I'll check with the PO and see if he had these problems.

Also make sure the jets that came in the carbs aren't already reamed to a larger size.

I'm going to guess you need to consider the following:
1. larger mains, go up to a 150 and see what that does
2. linkage adjustment problem, if you have a cross bar with drop links, make sure the drop links are exactly the same length and they are both on the idle stop at the exact same position
3. exhaust leak or leaky muffler could cause the popping on decel

Here's my carb tuning procedure from a March 03 post:

Assumptions: the carbs have the optimum jet and venturi package (good luck on this one), the float level in the carbs is correct, the cams are correctly timed, the valves are properly adjusted, the ignition timing is dead on, you have the proper spark plugs for your engine, the linkage is good, the fuel is good, the engine is good.

Remember that the mixture and air bypass adjustment screws are precision needle valves, not head gaskets. Use your fingers to tighten them, not your fist.
Start and warm up the engine.
Make sure the two drop links for the throttle linkage are exactly the same length, and disconnected. You can use a 8mm thin igntion wrench to snap them off.
Turn the mixture screws all the way in and then 5 half turns out.
Turn the air bypass screws all the way in.
Turn the idle speed screws out til it just touches, and then in 5 half turns (both sides).
Put on your hearing protection and start the car.
Use your STE and find the barrel that pulls the most. We'll call this one baseline.
Balance the barrel in the other carb that pulls the most with the idle speed screw. (if you have a Uni-syn, give it to someone you don't like and purchase a STE airflow meter)
Go back to the other carb, with the baseline barrel. You will have one all the way in, then use the air bypass screws and balance the other two barrels.
Go to the other carb and do the same thing.
Snug the jamb nuts on the air bypass screws.
All six barrels should pull the same amount of air at this point, if not repeat air adjustment proceedure.
Snap the throttle linkage drop links back on the carbs. If the idle changes then you need to barely adjust the linkage mounts so snapping the drop links on, doesn't change the side to side idle balance.
Use the hand throttle or a vice grip and rag to lock the linkage between 1400 and 1800 rpm.
Start back at the baseline barrel and adjust the mixture screw in or out, to get the smoothest running and highest rpm, then turn it in 1/4 turn.
Do the same with the five other mixture screws.
If you have to turn the mixture screws more than two turns either way, you've got the wrong jets.
Recheck side to side and individual air balance, adjust as needed.
Road test the car.
If you get snapping and poping out the intake, it's generally a lean condition.
If you get heavy exhaust fumes, or pboofing out the exhaust it's probably too rich.
If you get a flat spot or popping out the intake at between 2800 and 3200 rpm, you probably need larger idle jets.

That's a rough, five minute draft of my carb tuning proceedure, hope it helps!

If it goes good it should take about 45 minutes, if not about three years.

PK

You said you took the carbs apart and cleaned them. Did you put kits in them? Are you setting them up for the first time? If you are setting them up for the first time it would help if they were freshly rebuilt and the float levels were set correctly.

Seems odd that you could have a rich condition with 50 idle jets especially on a 2.3. A 60 or a 65 idle jet would be my guess for that size engine. I am at 2500 ft of elevation and run a 60 idle on a 2056.

When trying to find a vacuum leak I have had good luck using a spray bottle with water in it. Flood the areas around the base of the carbs and around the base of the manifolds and listen for a brief rpm change. Carb cleaner strips paint and makes a big mess...water does the same thing.

I have also seen the air bypass and mixture screws swapped, and while they will interchange, the functions do not

Unfortunately work calls and I will be unable to work on the car until Saturday. I'm not beyond missing some item you've all suggested so I will recheck all that I can Saturday. Thanks for the input/suggestions and I'll get back later. Jim