So I'm tossing up whether to buy a wideband air fuel gauge kit.
I recently installed some new carbs and I can't figure out which way to go with my jetting. I'm finding it hard to know whether to go richer or
leaner with my jetting and accel pump.
So I figure that once everything is setup that I prob won't have a need for it all and therefore I'm struggling to justify the cost (especially
considering I've got other costs coming up).
Units I'm looking at:
http://wbo2.com/2j/default.htm
http://www.wide-band.com/product-p/apsx_d2n.htm
I'm keen to get any input on this, or if you're in Bris and have a unit I can borrow let me know
What carbies have you fitted to what size engine.
35 PDSIT with 30mm vents and 160 main to a 1640cc engine
Ive got 45, 50 and 55 idle jets to play with
Forget the 45. 50 or 55 would be closer to the mark. I would use the 55 if you are unsure. Do you have a vacuum advance distributor?
Depending on the symptoms are you getting, determines what you will need to change.
The idle jets are only active on light throttle (cruise) and up to around 2500 rpm. After that, it's the combination of main,
air correction jet and emulsion tubes that provide a smooth transition from the idle to the main. Dave
thanks dave. Currently got the 50s in but was also playing with the 55s. Yes Ive got a SVDA plumbed to the left carb with an anti-pulse valve. timed
to 30deg with vacuum disconnected.
carb sync is fine and idling around 850rpm. mixture screws set around 2.5 turns out and respond well to adjustment.
symptoms im getting are a 'fluttering' around 1500rpm as i accelerate normally away from stop. there's also a hesitation as i squeeze the throttle
from steady cruise. above 2500rpm generally feels ok but hard to pick up with all the uncertainty down low. also doesn't like to cruise on 60kph in
4th
i figure the accelerator pump has a fair amount to do with the stumbling but not sure which way to go. Ive already set at 0.8cc/pump which has the nut
nearly all the way off the rod. Ive tried going richer but seems to be about as bad
With the engine idling, turn the idle mixture screw in slowly until the engine starts to drop in speed and then turn back out 1/2 turn.
Try taking a couple of degrees out of the timing to 28 BTDC @ 3500 rpm (vacuum disconnected). You could also try adding another couple of degrees to
32 BTDC @ 3500.
Then change to the 55 idles with the same as above.
After 2500 rpm the main jets are working.
Pity you are so far away, as an A/F meter takes a lot of the guess work out of the equation. Dave
How comes you times the SVDA to 30deg BTDC? I would of thought it would be the same as for original vac/mech dizzy and you time that to 7.5BTDC at
850rpm with the vac line to the carb blocked off.
As it's pretty easy to change the timing then maybe try this first and see of the flat spot is any better. True that a stumble at 1500rpm is the
transistion point of idel to main circuit and fully on main circuit by 2500rpm but too little or much ignition advance will also cause the engine to
hesitate.
I used to have 34ICTs on a 1641 and ended up on 55's after a few issues with the 50's they were on. I also changed the tubes from F6 to F9 IIRC.
Could have been the other way around but a simple way of finding the right tube is that the fuel level in the tube drops as the revs rise. So wherever
you get a flat spot you use a tube this more holes in that area of the tube to enrich the mixture. Took me lots of faffing around and even changing
spring rates in my 009 to get her driving smoothly 
What size venturi were you running?
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| Originally
posted by psimitar How comes you times the SVDA to 30deg BTDC? I would of thought it would be the same as for original vac/mech dizzy and you time that to 7.5BTDC at 850rpm with the vac line to the carb blocked off. As it's pretty easy to change the timing then maybe try this first and see of the flat spot is any better. True that a stumble at 1500rpm is the transistion point of idel to main circuit and fully on main circuit by 2500rpm but too little or much ignition advance will also cause the engine to hesitate. I used to have 34ICTs on a 1641 and ended up on 55's after a few issues with the 50's they were on. I also changed the tubes from F6 to F9 IIRC. Could have been the other way around but a simple way of finding the right tube is that the fuel level in the tube drops as the revs rise. So wherever you get a flat spot you use a tube this more holes in that area of the tube to enrich the mixture. Took me lots of faffing around and even changing spring rates in my 009 to get her driving smoothly |
Psimitar... 30 deg at full advance
So the original question was around wideband. Anyone with input on this?
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Im using one of these https://www.innovatemotorsports.com/xcart/product.php?productid=16328
348.60 from Adaptronic http://www.adaptronic.com.au/product-category/accessories/innovative-motorspo...
steve - did you have any issues with cable lengths? I'm just not sure if these kits provide enough cable to account for rear mounted engines
I have the same as Steve, in No8 Beetle. It came with about 2.5m of cable...enough for my application. It's very handy.
I mounted my unit in front of the gear stick and O2 sensor goes into the dump which isnt too far away from the rear axle, if its working on Greg's car it must have enough cable