TheSamba.com :: View topic - "finger on

Wed Nov 18, 2009 11:17 pm

Tried adjusting the carbs on my '77 2L bus (34PDSIT2/3) according to directions given by Amskeptic (to whom I'm indebted for, at least, providing direction).

Problem is, though I believe there're no air leaks in the system, when I try the 'finger on - finger off' method of getting the mixture right, no matter what I do, putting my finger on the hose and taking it off affects the idle not in the slightest (as far as I can discern). Amazing?

I screwed both mixture screws in in turn until the engine stalled (before they 'bottomed out' I believe) and then screwed them out a couple of turns.

I get the idea both screws should be balanced and slightly lean - but how do I get an idea of the mixture when the method described above doesn't work?

I haven't got a carb balancer to sync the airflow into the top of the carbs so had to miss a few steps in the instructions. I believe they're still good and balanced from a service the bus had several months ago.

There's a slight popping from the exhaust (too lean at the mixture screws? at the central mixture screw?) when going down hills in low gear.

I have to admit I'm attempting this with only a very slight understanding of what is happening inside the carbs.

Any suggestions?

Wed Nov 18, 2009 11:23 pm

can you feel any vacuum on the reference hose?

I think if you are too far out with your mixture the reference hose loses effect, but i might be wrong - someone correct me?

when my exhaust ws popping i was too lean, like a turn or two. took a few days of driving down hills/decelerating in gear popping then richening it to get the popping to go away.

you'll get it, keep trying

Wed Nov 18, 2009 11:33 pm

There's a definite vacuum on the reference hose. I don't have a vacuum retard.

Thu Nov 19, 2009 8:22 am

i had the same problem. use a vacuum gauge to tune it in. If the needle of the vac gauge is floating back and forth more than 2-3 psi it’s rich. If it’s steady but occasionally drops a little, it’s too lean. If it’s totally steady you’re close to the right setting. then go to the finger on-off method from there. but it should be pretty close........and if those carbs are not synced........ good luck, it will take you forever to get it right.

dave

Sat Nov 21, 2009 9:27 pm

Replaced a scruffy piece of hose on the central idle circuit and while I was at it, took off the mixture reference hose to have a look at it. Found it almost impossible to blow through it (despite having felt a vacuum on the line with the engine running earlier). Pushed a wire down the tube, came to a blockage, got it out and found a screw.

Can't believe it got in there by accident. Think the vw shop I last took it to put it in there after they replaced the heads. They did mention I needed to get a kit for the carbs.

What do you reckon it was for?