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Published on Jan 1, 2012
This is to show you the steps on how to modify your Solex 34 Pict 3 carb. The soldering and drilling of the Jets can apply to any carburetor! Heres a tool to resize your jets. This tool will make it very easy. http://classicandspeedparts.com/index...
You don't really need this one, but if your a perfectionist here's a link http://www.chircoestore.com/catalog/p... This mod is actually a pretty good way to get a large engine build on the road, especially if you ran out of money for those super expensive dual carbs! You will find that it will have tons of torque throughout the rpm range.
Explanation of Why it Works: The hose is to keep your fuel bowl as close to atmospheric pressure as possible. Other wise the fuel will not flow in to the throttle air stream because of the negative air pressure in the fuel bowl that's created by the breather tube that ends at the center of the air stream (Above the choke), which is a negative air stream area. Because the fuel in the bowl is at a negative pressure, the fuel is actually pulling away from your jets giving you a stumble, bog and a surging feeling when driving with out a venturi in your carb. The venturi normally creates a larger negative air pressure at the throttle plate that over powers the vacuum that's in the fuel bowl, which causes fuel to get sucked into the air stream. It basically works like an airplane wing but round. So by decreasing the vacuum in the bowl it makes it easier for the fuel to get sucked in by your jets and into the throttle air stream area. I hope this helps!!!....What?.... LMAO If you run a thinner hose form the vent tube all the way through and exit the air cleaner you should eliminate any remaining stumbles. I know it works better because I already tried it and determined that this approach works best.
If you jet the 34 PICT 3 carb right you should end up with a normal carb with no hesitations.
NOTE: The following jets are for a 1904cc to 1915cc engine! But you can use this data as a base or at least to be close for an initial startup of a larger engine and then fine tune your jets. Idle jet is 62mm..... 65mm runs rich, 57mm runs ok but lost power below 3000rpm. Main jet is 165mm.... 150mm runs ok but runs lean and hot Air jet is 60mm......... 70mm and higher increases the hesitation problem but an engine with more ccs may be able to run with a larger air jet. Aux jet is 42mm........ right next to the idle jet at 11 o'clock. This is for high rpms only, close to 5k. So if you plan to rev the shit out of your engine you might want to change this to 42mm or bigger, but will work fine with the stock jet. My advise is leave it stock. Fine tune your Idle jet, main jet, and air jet. If you do increase the size of this jet your Idle jet will need to be a lot bigger!!!!