PDSIT - throttle plate mixture screw orifice

[rustbus]

Hey Guys!

My first post - i've been "lurking" for a year or two now -

question, if you dont mind. thought I would post it here as colin has helped me in the past with my pdsit's (whether he knows it i dunno)

check these pics. when I bottom out the mixture screws on any of my 4 rebuilt carbs, they all protrude a different amount....which is correct? is there a right or wrong? does it matter? obviously when i back them out 3 turns for a starting point they end up in wildly different positions. will this get all sorted in the tuning procedure?

can i compensate for this? should I? I think i should, as these orifices are little and a little goes a long way with mixtures...right?

Thanks for any tips guys!

[RSorak 71Westy]

IMHO you're worrying about trivial things. When the screws are backed out the same amount, they are the same diff off the seat so should flow about the same. What youre seeing is the diff in seat heights. This screw only adjusts the idle mixture while the engine is idling, and has little to no effect while actually driving down the road.

[rustbus]

thats cool, good to know. i dont like it much when i get carried away with the silly little stuff...I do it a lot some times and it can be a huge waste of time!

thanks for the advice, now i can install these in peace (of mind)

[Amskeptic]

thats cool, good to know. i dont like it much when i get carried away with the silly little stuff...I do it a lot some times and it can be a huge waste of time!

thanks for the advice, now i can install these in peace (of mind)

I am not of the opinion that yours was a "trivial" question in the slightest.
If anything, it shows an alert attention to detail that will serve you well.

RSorak, however, is spot on with his reply as to the physics of fuel flow, the seated positions may differ, but the flow rates are determined by the distance created by the thread pitch as you turn the screws out.

That said, the differences in your photographs are evidence that someone has been hauling those screws closed with a vengeance. This CAN distort the bore of the throttle body on the PDSIT carbs. I recommend that you grease the rubber o-rings on the mixture screws so they move easily and you can then tell instantly when they seat. Usually, if a new or dry o-ring is fighting you as you try to seat and count back the mixture screws, you won't be able to tell when seating has occurred as easily . . . that is when people mangle these poor things.
Colin

[rustbus]

hey thanks Amskept, (short for amskeptic) yeah, i do see your point about attention to detail. but sometimes, i swear, when i get 'under the influence' and I can just stare and clean and polish these little parts endlessly. i would think i could find something better to do with my time. but whatever. i like this stuf