Mpls Funk

Hi all,

I am getting closer to completing my first carb re-build, many thanks to you all.

How do I know what size jets I should have in it? the previous owner was racing it...I'm not. He had 67 in the primary and 76 in the secondary. The car is a 1970 350/350 with this Holley 4150 (650 cfm) double pumper (ultimately I'm going to put the original Qjet on, but that's my next project...I am practicing rebuilding with the Holley!).

Anyway - I just got to thinking, before I button this back up, should I just put those jets back in, or should I change them for some reason?

Also - a (very good) video that I'm watching about how to re-build it shows jet extensions in his carb...why would someone use jet extensions?

Thanks!

7t9l82

unless there was a drivability problem due to the set up i would leave it alone. racing or not shouldn't be much of a factor, the engine needs what it needs. my guess if a guy was racing it is probably tuned pretty well, just clean the carb and put it back. oh and rebuilding a Holley will teach you exactly nothing about rebuilding a Quadrajet. it is a much more complex carb.

7t9l82

jet extensions are used to keep the jet submerged in fuel during heavy acceleration. nothing that will hurt on a street engine. just more evidence whoever set the carb up knew something about what he was doing. my suggestion is don't screw it up by trying to "fix" it.

PAmotorman

get the LIST number off of the front choke housing and go to the holley website and see what jets came in the carb stock

427Hotrod

Go on Holley's website....they have a listing of all the carbs and what was in them in the way of jets. power valves and squirters. Go by the LIST number stamped on the choke housing.

http://documents.holley.com/techlibr...al_listing.pdf



JIM

doorgunner

Those are the size jets that came with my 600CFM Holley that is on my '93 350SBC. Does the car smell/idle rich?

I would think, being a rookie, that the 1970 and earlier engine would need even larger jets, but the Holley does have the power valve which adds 20-30% more fuel on hard accelleration...BUT LIKE THE OTHER MEMBERS SAID---DON'T MESS WITH IT UNTIL YOU SEE HOW THE CAR RUNS WITH THE CARB AS IS. It is not that hard to change the Holley jets or the power valve even with the carb on the engine....10 minutes at the most.

My project car 1970 350 SBC had an Edelbrock 600CFM carb with .080 primary and .100 secondary jets in it from the previous owner...and it idles on the rich side. I reduced the primary jets to .068 and the secondary jets to .075, but the car would barely idle and had very little power---so I went with .072 and .082 jets, but it doesn't have the power that the .080 and .100 jets gave it (even though I definitely don't need that much power).....now the spark plugs look very clean. I think .085 and .095 would be perfect for street/highway driving. With the .100 secondary jets it sounds like the hood is going to be sucked into the intake when the secondary kicks in....LOL!

427Hotrod

There is a LOT more to the fuel curve than just the jet size. It's easily possible to have larger jets paired with a larger air bleed and run fine.

Start with what it was built with..it will be very close if the metering blocks are the correct ones for it. I've fixed many a swap meet carb that was considered junk by removing all the mods and putting it back to stock. The Holley is very easy to modify...but most of it isn't necessary.

JIM

Mpls Funk

I looked up my list number and in fact these are the jet sizes that it came with. so I left them alone and put it back together.

On to the next challenge!