Hey all, I'm about to rebuild a carby to go onto my Baja. I just noticed that it has a small pop rivet in the main butterfly.
Is there meant to be a hole there?
Should I remove the rivet or just leave it?





Answers ASAP cause I want to get this done this arvo.

Thanks


Smiley

my 34 pict got a small hole like that in the auto choke butterly at top...

the throttle butterfly (from memory) had a dimple that was small and round but not a full hole again from memory. whether thats any relevance to the other carbs.

maybe theres more info in these old training vids:

:S??

http://www.youtube.com/watch?v=XOxxS1EMphU 

maybe the last person to rebuild it put the auto choke butterfly in the main throttle butterflies position (perhaps original butterfly damaged or misplaced??)...

and used a pop rivet to fill in the autochoke hole to replicate the original throttle butterfly.

all air bypass from the sealed throttle butteryfly should come from the idle jet.

If my memory seves me correctly this is one of the tricks that people do to overcome the "flat spot" that is experienced when you fit a 009 dizzy to a engine with a 34pict carby. among other things.


Cheers
Brendan

It may have been modified to run with a 009 distributer?

see here http://www.aircooledtech.com/34pict3_modification/

My car has a 009 on it. Should I solder the hole up?


Smiley

how did it run before?
even if you removed it they prob drilled the hole out to get the rivet to fit?

If you're gonna run a 009 either leave it or silver solder the hole up.

It is indeed a method of curing the dreaded flat spot when using the 34pict/009 distributor. I had a massive flat spot just off idle on my 1776 using the above combo. Soldered up the hole and smoothed it and bingo! No flat spot.

Its got something to do with the position of the idle port which is near the hole. Filling the hole changes the flow of the port, as set out in several techincal articles on the subject. The modification causes the engine to run rich on idle, but soon after you open the throttle you go off the idle port and the thing runs as designed to do. I have noticed no difference in consumption or any ill effects after 2 years running this system.

regards

Old Hutcho

Cool, thanks for the tips gents.

Do I have to use silver solder, or is electrical solder sufficient?



Smiley

Definately silver solder, way to big and under too extreme conditions for electrical solder to hold out.

It's about a 4mm hole from the factory, they take a 1/8" rivet loosely.

Unusual to see a carb that still has stock studs and no helicoils.

Please don't solder the hole up - the rivet does just fine - if it is a closed end style rivet - I use stainless rivets - if it ain't, there is a chance that the head of the pin, which gets left in the rivet, can come loose and go into the engine and leave the butterfly with a smaller hole anyway.
The hole was part of the attempt by VW to comply with the new clean air laws, back then. The butterfly adjustment was backed fully off and the dizzy had both advance and retard vacuum (the retard hose should be removed and the take-off on the carb blocked off). Tuning then reverts to the previously standard method of adjusting the butterfly for initial idle speed as well as the big screw for bypass idle fine tuning and the smaller one - or was it the other way around? - (which was supposed to be a firm factory setting) for mixture control.
I suppose, if the current rego checks included testing clean-air provisions, that all of this, including drilling out the rivet would need to be presented as standard, at rego test time.
You usually see a 009 in there, replacing the dual vacuum job - I personally detest 009s - think that they belong on constant rev industrial or full blown racing cars - think that they are just a lazy, compromise option for a road car - they are only just a little better than a dizzy with the advance mechanism disabled totally - as in some cars with 100% LPG fitted. The early Kombi "Blue Screamer" - .031, I think, is much better - as well as any of the 356/912, early Alfas, Volvo and several others which I forget.
It is possible that clean air checks 'may' be part of the new rego checks criteria being currently (March 2011) considered - later 1600s would struggle to pass without all of the old clean air junk reinstalled (including the much later dual heater exchange manifold/muffler).
My approach has been to install a Fish, which has better efficiencies in exhaust quality/fuel consumption/power, depending upon how you choose to have it tuned on a particular day.

A "clean-air" rego check would be a far more effective method of chasing the old bangers off our roads, than that $2000 rebate process of recent times.

Leave the rivet there - much easier to remove, if forced to, one day. Don't throw ANY of that old 'clean air' stuff away - keep it in a box at the back of the shed.