<VV> Changing Jets

[Grant Young]

From: Ralphsebrell <ralphsebrell at aol.com>
To: virtualvairs at corvair.org
Subject: <VV> Main jet size
Has any of you drilled out or changed out the main jet to a larger size? Like 60? For all 4 carbs, or just the 2 primaries? I'm interested in this for a 1969 de smoged 140.
Ralph 1969/140/4sp

Hi Ralph. There is a lot of anecdotal and a little actual data out there on the best jet size combination for a 140. I must have tried a dozen or more combinations on my last 140, but decided the earlier model combination of .051"/.049" was the best all around for performance and economy. I wouldn't recommend more than .053"/.051", and it will cost you 3-5 mpg under the same driving style compared to stock in your engine. I don't recommend drilling them out as it will affect the fuel flow characteristics and they might all be different. I have all sizes from .045" to .070" if you want to experiment.

As far as removing them, it is always best to soak them with some carb cleaner before attempting a removal and then use a large screw driver that you sharply tap into the slot in the jet and then try turning it while pushing down with all your might. If you have a long enough bit to fit into a drill, that also often works well. The tapping seems to often break the bond between jet and bowl, as does the shock from a drill. Be prepared, however, because there are some that will not come out with way. In that case I have has the best success starting with a small bit such as 1/8" and drilling through it. This will often create enough heat and vibration to free it up If not, work up in 1/16" increments trying it after each. If the jet breaks, you can drill it out with a slightly larger bit, but don't go over 1/4" :-). You should also chase the threads and clean out all the passages well after drilling to make sure nothing winds up in your new jet.

Grant