Itinerant Air-Cooled

Well, this is my 1st post here, though I visited the forum numerous times.
My situation is this: I have converted my 2 liter aircooled Vanagon to use the 32-34 PDSIT system (CIS, DVDA and all). I've jetted the carbs to be in line with the setup used in Britain: 137.5 mains and 140 air correction with 55 pilot)
In order to get the on-off reference hose to balance at no rpm change, I am at 5 turns out in the mixture screw. This is almost equivalent to having no mixture screw at all (as it is backed out completely from its orifice). I've tried using 155 air correction but found it struggling after 50 mph [not totally sure it was not drowning in fuel, perhaps?] ...and could never reach the no-rpm change balance -no matter the turns out.
Any insights as to why my 5 turns are needed to pass the On/Off test?

Is this five turn measurement on the CIS mix or the dual carb mixes?

Welcome!
Robbie

The 5 turns are for each carb body (both at 5 turns out). The CIS mixture screw is set properly according to Colins procedure.
When you back out the mixture screw to 2.5 turns (as initial setting) the tip is flush with the inner wall of the venturi. When you back them out another 2.5 tunrs (now at 5) -the tip does not even poke into the orifice: it is fully extracted from the orifice. At this point I and at a balance point using the ON/Off technique with the "reference hose".
Am I jetted incorrectly?
The vehicle starts great, has decent pickup and gets almost 20 mpg on the highway (55 - 60 mph). Gets 15 - 18 around town.

CT68Westy wrote: ↑

Sun Dec 13, 2020 6:29 pm

The 5 turns are for each carb body (both at 5 turns out). The CIS mixture screw is set properly according to Colins procedure.
When you back out the mixture screw to 2.5 turns (as initial setting) the tip is flush with the inner wall of the venturi. When you back them out another 2.5 tunrs (now at 5) -the tip does not even poke into the orifice: it is fully extracted from the orifice. At this point I and at a balance point using the ON/Off technique with the "reference hose".
Am I jetted incorrectly?
The vehicle starts great, has decent pickup and gets almost 20 mpg on the highway (55 - 60 mph). Gets 15 - 18 around town.

I would let go of the mixture reference hose method in this case. Your reality, 20 mpg, good power, trumps everything else.

I would ask, where is your mixture reference hose getting its vacuum from?
Colin

Yes, if your experience is satisfactory, I wouldn't mess with it too much. How do the plugs look after a good amount of city driving?

My reference hose setup is T-eed right into the line which comes off the right carb's secondary port from the intake manifold elbow. I plug this hose when not in use for tuning (no leaks).
This hose is working fine for the CIS mixture adjustment (rich-UP rpm/lean-DOWN rpm)
I checked my plugs just a few weeks ago and they are a tawny-brown/tan color.
My focus is on if my jetting would affect the On/Off balance: if I jet larger, would the number of turns on the 2 mixture screws go back to 2-3 turns out range.
Thanks for your input and feedback on my post thus far.

Potentially, but the pilot jet (in the solenoid tip) has a vast majority of influence over speeds that low. Finding good condition solenoids THAT FIT is quite difficult these days. There are four designs that I know of, and none are cross-compatible. Both are available in 6v and 12v versions, also in 4+ jet sizes, for a total of 32 part numbers if I'm not mistaken……