Dual Weber IDF 40s, Carb Rookie question... Options

[malcolm2]

Hello everyone. I will preface by saying that this is an engine from a 914. (IMG:style_emoticons/default/piratenanner.gif)

But it is in my VW Bus. Just now getting it moving down the road. Everything is new.

Carbs are new and I am a carb rookie, as well. Bought them from Aircooled.net and had them cleaned and set-up for the bus. My 914 has L-Jet FI, this group has taught me enough about that system to be dangerous.

So here is my question for the carb experts. What should the Pump Valve spray look like? It seems erratic and drippy. It kicks in 1st as I open the throttle, not a spray but pore, really. I will say that I see that in all 4.

[Superhawk996]

Still sounding a bit like it’s bogging a little when throttle begins to open before it picks up RPMs. You are on 28mm venturis so should be better than that.

I think you’re getting a bit distracted by fuel pressure. To be honest, carbs don’t care much and will run in a wide range of pressure between 1-4 psi. Don’t believe me. Try this - run your fuel pump till bowls are full - then disconnect and plug the fuel line. You’ll be amazed how long it will idle / and do light transitions before the bowls run low and start running really poorly.

You’re expecting a 0-15 psi gauge to be accurate in the 1-3 psi range. I think you’re probably seeing gauge “sticktion” at those low pressures where the needle temporarily sticks from internal gauge friction with just barely enough pressure to even begin to move the gauge. As someone said earlier you want a gauge that is about 0-5 psi to have an accurate indication.

Depending on the range that the regulator is designed for it may be that the “sticktion” is in the regulator if that was designed for 0-15 psi. Edit: just looked at your JEG’s link - you should be peachy!

Bottom line - I suspect you’re chasing your tail on fuel pressure.

Barrels to barrel airflow is pretty good. Edit: after watching a 2nd time - I’d say that one cylinder is 6 vs all the others at 6.5. Might bring that one up to 6.5 with air bypass. Then recheck idle mix.

Are you sure your idle mix is tuned properly for best lean idle? I know you said you’re about one turn out which is probably about right but you should be getting an idle speed drop if you open or close the idle mix from that setting if you’re at best lean idle. Is that the case?

What is your idle speed set at? The tach is not the best indicator if true idle speed. I use a digital engine multimeter to set idle speed. Idle sounds sort of low. Once you have best lean idle set, you should only be using the carb linkage, idle screw to tweek the idle speed. After you tweek that, you need to go back and recheck best lean idle mix - it’s an iterative loop.

Also what distributor set up are you using? You may not be getting enough advance early enough.

Final edit - I just compared 1st video to latest. Defiantly improving. Good job. (IMG:style_emoticons/default/smilie_pokal.gif) Keep tweaking it and once you have the idle speed and mix finessed - go back and recheck carb to carb sync and how equally your linkages are moving. You’re getting there

[malcolm2]

Are you sure your idle mix is tuned properly for best lean idle? I know you said you’re about one turn out which is probably about right but you should be getting an idle speed drop if you open or close the idle mix from that setting if you’re at best lean idle. Is that the case?

What is your idle speed set at? The tach is not the best indicator if true idle speed. I use a digital engine multimeter to set idle speed. Idle sounds sort of low. Once you have best lean idle set, you should only be using the carb linkage, idle screw to tweek the idle speed. After you tweek that, you need to go back and recheck best lean idle mix - it’s an iterative loop.

Also what distributor set up are you using? You may not be getting enough advance early enough.

Here is the LBI method I was using, per http://www.redlineweber.com/html/Tech/idf_...nt_controls.htm

DO YOU SEE ANYTHING ELSE I SHOULD DO, OR DO DIFFERENTLY??

Linkage removed
Speed Screw 1/2 turn in after touching
Bypass screws closed
Mixture screws out 1 turn

Engine runs poorly as expected.
1. turn IN mix screw until the engine runs worse... i would turn each screw about 1/4, then move to the next one, and so on. 2nd time around (1/4 at a time), as I got to the 3rd barrel, the engine would run worse.
2. turn OUT mix screw until the engine runs better. Again 1/4 turn at a time, til I got no reaction. Turn them back IN until they are BEST.

Then I set the Speed screw to 950 to 1000rpm. I have an analog meter.... one lead on batt- one lead on coil-. using the V8 scale and doubling it. I am sure you remember those old timers.

I placed the snail on the front barrel of one side then the other. adjusted the High flow barrel down to the low flow barrel with the speed screw. then adjust both back to 950 -1000, matching flow using the snail.

From there, i went to the bypass screws. checking flow front barrel to back barrel and adjusting the LOW flow up to the high flow. Leaving the high flow CLOSED. Then again, matching the right to left carb's flow to the idle rpm with the speed screw.

I have a new pertronix SVDA disty with a P3 module in it. I dismantled it, and cleaned and lubed it after arrival.... another AC.net item.

[Superhawk996]

Linkage removed
Speed Screw 1/2 turn in after touching
Bypass screws closed
Mixture screws out 1 turn

Generally I think you’re on the right path and doing reasonable things. You don’t mention readjusting mixtures after resetting idle speed. Idle mix affects idle speed and vice versa. Same again after setting an air bypass - recheck mix all the way around again after that. Everything affects everything else.

I might go only 1/4 turn on the initial idle speed screw just to ensure that transition port is fully closed when you are adjusting mixture initially.

And probably just slow down on the idle mix screw adjustment - there is always some time delay between turning the screw and observing the effect when it finally gets to the engine.

Maybe smaller 1/8 turn changes as you get closer. It really is a multiple iteration process between mixture, idle speed, air bypass. Each change affects the others. Agree with Rhodyguy that small changes have big effects as you get closer and closer.

Check ignition advance and make sure you’re starting to begin a good advance by 1500 rpm. As noted on NGK chart retarded timing (not enough advance) can manifest as running rich. Basically just verify SVDA is working properly.

And finally, it isn’t unheard of to have to go down an idle jet size. Too big of a jet really jacks up the speed & mixture effects of the needle mix screw adjustments. .