pict 34 fast idle adjustment tech

[The13bats]

I have been messing with tuning my vw trike which is a 1600 dual port pict 34 3 with svda distributor, my OCD really got questioning the fast idle adjustment, if one looks around the net there are a couple ways stated as correct to adjust it, one says turn the screw in until it just touches the lowest step on the choke cam then 1/4 turn more you are done, the other way says use note paper as a gauge when the screw touches the paper remove paper turn 1/2 and its good, all sites say this afjustment is very important, and what its doing is setting the butterfly open .004, about the thickness of note paper.
so ive always done that and ive always had the least bit of hesitations off idle, so today i had the carb off and it sure seems the butterfly is closed snug no .004 do i used a note paper gauge between the butterfly and throttle bore and set the idle screw this way which was more turns in than the recommended way, in my preliminary tests it now has much better throttle response off idle zero hesitation,
so, im no pict 34 guru, just wanting to learn them, this fast idle adjustment is only in play at idle and i would think coming off idle
an no, im not using the fast idle screw to adjust curb idle the large bypass screw is for that.
basically what im questioning is the recommended adjustment procedure doesnt give me .004 butterfly opening.

[Bruce2]

How thick is a piece of paper?

[SCOTTRODS]

I'd say that using a proper feeler gauge would make more sense, and would be an absolutely repeatable version of the setting. Paper is not a gauge and should never be used as such. If you need .004" of clearance, adjust to the clearance you need. Pi gauges or feelers make better sense, whether using them directly on th butterfly (not recommended by me at least) or by finding the correct feeler gauge to set the choke step adjustment to, allowing the .004" you are looking for.

[The13bats]

the paper did measure .004 and i wasnt splitting hairs or trying to say that paper is a replacement for a real feeler gauge, even though several self appointed vw guru sites say use paper between the fast idle screw and choke cam, my questions got lost because of paper so lets forget paper for the moment.

what i did i do not believe is correct and opens the butterfly too much, that being said when i follow any instructions how to adjust fadt idle screw it doesnt seem to ooen the butterfly at all.

so i will word this a different way, all the write ups i have ever read on adjusting the fast idle screw regardless of how the get there want the end result to be .004 opening of the butterfly, so tell me ask this where can that .004 be found to measure? ( with a correct gauge of course ) after replies to that question ill go on.

[Bruce2]

... if one looks around the net there are a couple ways stated as correct to adjust it, one says turn the screw in until it just touches the lowest step on the choke cam then 1/4 turn more you are done, ...

This is the way VW says to do it. I've always done it that way and the engine always runs great.
Have you tried setting it that way, then measuring the gap between the throttle plate and bore?

[Bruce2]

34 PICT tip:
In the Bentley, the sealing washer between the inlet valve and the carb top is supposed to be ½mm thick. All of the aftermarket rebuild kits available supply a thicker sealing washer (~1.3-1.5mm). This thicker washer will cause the float level to be lower. This causes leaner running. Either use the original thin washer or slowly sand the aftermarket one on sandpaper on a flat plate until it's the right thickness.

[The13bats]

i made a reply, now its gone, will repost it later

[kreemoweet]

Anything you read that claims the purpose of the adjustment in question (note: there is NO "fast idle adjustment" on a 34PICT-3, the screw in
question is called the "throttle plate adjustment" screw) is to set some gap or other at the butterfly, is bogus information. There is no such specification. The purpose is to make sure there is no vacuum leakage to the spark advance port just above the throttle, and to ensure the
throttle plate does not slam into the bore wall when it closes under spring tension. There is an alternative, and preferred, method of making
that adjustment in a service bulletin to the VW Workshop Manual I have (for Type 2's but it's the same carb): attach vac gauge to advance nipple,
start engine and idle at normal operating temp, turn screw in until gauge shows reading, turn screw out until gauge vac drops to 0, and then out 1/4 turn more. Adjust other screws to get proper idle speed and mixture (CO content).

This new procedure makes a lot of sense to me, because I find it's often not that easy to tell exactly when the adjustment screw hits the
fast idle cam and starts to open the butterfly, because the screw thread is very snug in the bracket. The screw was capped at the factory
to discourage owners and uninformed mechanics from messing with it, and is not regarded as a normal tune-up adjustment.

[The13bats]

Im not a "normal" gear head, and while i want to suggest you crawl the net and tell the countless posts calling "the screw" the fast idle screw, even rob and dave do, ill leave that dog to rest,
I too from my OCD never liked the idea of adjusting "the screw" the way that basically every post out there says to for the very reason you mentioned and when i made my other post that isnt here i had mentioned that i contacted a buddy who knows about vehicles than anyone ive ever met, he said to be brief that the adjust procedures and the idea of getting some critical .004 was bs,
makes one wonder why you are the first i have seen post a way to adjust "the screw" ( especially since its a service bulletin ) that to me at least has a smell of logical merit and i cant wait to try it, i knew there had to be a better way,

I never bought into the .004 giving just enough flow because even with the butterfly closed fully a 34 has a nice hole in the plate always giving some flow, the idea the adjustment is to just keep the buttlerfly from being the stop makes sense,

hopefully i can try this later or tomorrow ,

cheers
b

[kreemoweet]

There's an .004 in. spec given in the Type 2 Bentley manual for the 34 PDSIT-2/3 carbs on dual-carbed Type 4 engines, which of course has nothing to do with the 34 PICT carbs. A little geometric analysis of the procedure given in the Bentley for adjusting throttle valve on 34 PICT carb will show
that the gap will be FAR less than .004 in.

Here's a link to the alternate procedure I mentioned: https://www.thesamba.com/vw/archives/ma ... s/WB25.jpg

[The13bats]

thanks kreem,

life, feeling poorly and chores have taken precedence but im hoping later this afternoon early evening when the balmy heat index isnt over 100 i can try this vaccum gauge setting, i want to see how close i am doing it the way i did it, not how everyone else says it much be done,

my heater belt hasnt made it here yet so that will have to wait

[The13bats]

Kreem,
grind on this for a moment, i fired up the trike running great, made sure it was up to temp, i hook my vac gauge to the timing port by pulling the hose off the dizzy and sticking it on the gauge,

i start slowly turning the fast idle screw in, ( yeah i know you had a different name for the screw )
i see no movement on my gauge, if i blip the throttle gauge jumps, so i keep turning its now increasing idle rpm by the time the gauge moves that screw is way too far in,
so i back it up past where it effects idle and at the point i know the screw not the butterfly is the stop,

i go for a ride for a couple hours and it runs sweet, really perfect,
so no issues, my ocd asks me what gives, bad vac gauge or?

after looking at the shop memo you posted that memo stated that was to correct a couple issues i didnt have, so in my case since i dont have the shop memo issues im good with just knowing the screw is my stop not the butterfly,

many thanks for your help on this.