carburetor jets

[sg1747]

What is the recommended jet size on the primary and secondary for a 4053?

[firez]

I run 68s and 72s in my 68 Z28. I think a lot of guys step them up to 72s and 76s but I find them to rich.I find each car is a little different in what they like.

[70 Forest Green Zee]

I think Eric Jackson would be the guy to ask.

[Mr.Nickey Nova]

They came with 68's and 76's from the factory,but some change out the 68's for 72's which is what i did.

[L78steve]

The 68s I find to lean .The 70s will cover the stumble but the 72s work the best .

[sg1747]

then what do you use in the rear.

[VintageMusclecar]

72 primary 76 secondary should work just fine. If the engine is stock (or close to it), stay with the 6.5 PV in the front and an 8.5 in the back.

Eric

[Chevy454]

Funny you mention the pv, Eric...I was just fixing to ask if pv selection was more critical on a 302 than a comparable bbc?

[Keith Tedford]

Stock, other than headers, I always ran #73 primaries and #76 secondaries with the stock power valves in our 4346 carb on our L78 and L72 engines. Our 427 came from the factory with #68 primary jets and there was definite lean surge and 60 mph. They worked fine with this setup. If nothing else, it is a good starting point for fine tuning. The engines ran/run clean with long plug life. Sort of duplicating what Eric said, but the combination does work.

[VintageMusclecar]

Rob;

Good question. The OE PV specs on the 4053 (and 4346) carbs flies in the face of "conventional wisdom" that states you should run a PV that's rated at 1/2 of what engine idle vacuum is. Since most 302's idle around 9-11", that would call for a 4.5 to 5.5 PV. However...stick a 4.5 PPV in a 4053 on a basically stock 302 and watch a mysterious off-idle hesitation appear...been down that road previously with numerous customers who tried it themselves.

For consideration: The only differences between a 4053 and a 4346 carb are the vented pri. bowl and an 8.5 PPV on the 4346 instead of the non-vented front bowl and 6.5 PPV used on the 4053.

I would be interested to know what your L72 idle vacuum is, and what PV you're running up front (blocked rear, correct?).

Keith;

I've found that on a stock 302 with manifolds, a 70 primary jet seems to be enough to eliminate the lean cruise issue, and 72's are well-documented for best performance. Any time I build a carb for a 302/L72/L78 with headers, it automatically gets 72's in the front.