Type 4 / dual IDFs tuning issues

[Culito]

Hey y'all, here's the specs:

Type 4 2.0L
Dual IDFs setup by aircooled.net:
Vents 28
Emulsion F11
Idle 50
Main 115
Air 175
Dist: 74 bus DVDA using only advance side, ported vac signal from left carb, timed 30deg. max advance (vac line unhooked and plugged at carb while timing it).
I've been told the curve on this dist. is pretty much like a 009 with extra advance at part throttle.
It's in a heavy bus with a pretty open exhaust.

Problem:
Idle to about 2000 rpm is great. Pulls good, even power. Over that, it kind of falls on its face and pops out of carbs (kind of a "chiff" sound a few times) unless I stomp it, then it goes. Sounds like it's leaning out. 3000-3500 rpm it clears out and cruises fine.

I gave them a tiny bit more on the acc pumps with no change.

I'm wondering about the distributor. Not the right curve? Not enough advance at part throttle? Too much advance?
Or is it leaning out?

Any suggestions welcome.

Thanks!
_________________
Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug

[udidwht]

For 2.0....

28 vents

47.5 idle jets

120 main jets

200 air corrector

F11 tubes

Fuel pressure - 3.5 max

Float height 10-11mm (carb top gasket in place ball NOT depressed)

Float drop - 28 - 32mm


Also hook up a vacuum gauge to your hose running to the carb and verify what (if any) vacuum you're getting. IDF's generally either get 0 or small-moderate signal. You should also check the vacuum advance on the distributor using a hand pump/w gauge. Look to see when the vac advance starts moving and no longer advances. Right those #'s down for reference. Shoot for ~ 14:0 at LBI
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Headflow Masters New AMC 42x36mm heads w/Porsche swivel adjusters
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73 Web Cam w/Web solids
Dual 40mm IDF Webers - LM-2 - 47.5 idles/125 mains/190 air corr./F11 tubes/28mm Vents - Float height 10.45mm/Drop 32mm
Bosch SVDA w/Pertronix module (7.5 initial 28 total @ 3400rpm)
Bosch W8CC plugs
Pertronix Flamethrower 40K coil
S&S 4-1 w/Walker QP 17862
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[Culito]

Thanks!
Specs for the 205S distributor:

Advance/Retard Range: Vacuum: 8.5-11deg Adv @ 7.9 In. Hg; Centrifugal: 8-13deg @ 1600 rpm, 20.5-24.5 @ 3400 rpm

I'll do some more investigation re: vacuum signals. Can that be modified on the IDFs?
_________________
Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug

[udidwht]

[Culito]

Thanks.
It idles beautifully so I don't know if I want to mess with those - unless it affects the whole stack.
_________________
Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug

[udidwht]

[Culito]

Noted!

I just did a quick and dirty check of the vacuum with a Harbor Freight gauge, and just revving it up in the driveway I get almost 6-7mm Hg. Not bad!
_________________
Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug

[udidwht]

[Culito]

[oprn]

Measure your vacuum signal on the road at normal cruising speed and plan your advance around that number. The value you get in the driveway is of no use in real life.

Been there, done that.

[Alstrup]

The anti pulse valve does not increase vacum. It smoothes the pulses out so you get a chance to see the peaks of the vacum. It - may - have a small effect on the vacum can too, I´m not sure. I never use this solution anymore.
Yes, if you want to dial it in best possible you should get a measurement on the road. There can easily be a 10-15% variation from backyard reving to real cruise.

T

[Culito]

I get that the valve doesn't increase vacuum.
I think I actually have an absolute air pressure logger left over from my physics lab days. I might hook that up and take a drive. It's a bus so every thing is waaay back there.

It was suggested that I first and foremost check sync at the affected RPM, so that's my first plan.

The days are getting shorter and colder, so that might be a while, however.

Thanks all.
_________________
Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug

[Culito]

Y'all want data?


Link


20 second section of drive:

I'm seeing a lot of pulsation (as expected) just off idle which will need to be conditioned either with an anti-pulse or small reservoir. I'm also wondering if a tee between the two carbs might even out the signal.

So, I'm seeing 102 kPa atmospheric pressure, and that's what the sensor is reading at idle or closed throttle.
At peak vac, I'm reading around 75kPa, a difference of ~28kPa which roughly equals 8 in Hg. Right in range, it seems.

I'm guessing with the pulsations, however, the vac can is essentially taking the average of the min and max of the individual pulses over time, so it's not getting the full effect of the vacuum signal.
I might have to set this up again after trying a small res., pulse valve, or tee'd signal.

So there's that!
_________________
Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug

[Alstrup]

[Culito]

[oprn]

At what point in the drive did you see your 28 kPa? I must confess to having a hard time following that video!

The 102 kPa tells me you are not too far above sea level, the highest I can get is 93 to 94 kPa.

Yes my engine pulses so bad on a 1 cylinder vacuum signal that the electronics could not make any sense out of it. Adding a volume chamber does wonders for smoothing it out. On electronic systems I would say it's mandatory. This is what I used. An 8 OZ model aircraft fuel tank with all 4 cylinder signals going in and one to the sensor. If you are using the stock distributor vacuum pot it may have enough volume on it's own without any additional added.

[Culito]

Actually I was pissed at myself for accidentally leaving the camera on timelapse mode!
The lowest reading I got was around 75kPa (28kPa below my pressure here.)

I am right around sea level.

I think I have a vacuum setup in mind similar to that.
Cold weather's moving in though, might be next year for that project.
_________________
Copyright CJ Industries, Inc.
'64 standard w/2.0L type 4
'62 bug

[andk5591]

Would STRONGLY suggest reaching out to John at Aircooled.net since he set up your carbs.....I have found him to be one of the best resources for IDFs.
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[Alstrup]

[oprn]