Ukraine Train

I am in the process of rebuilding my engine and will be rebuilding my carb shortly. The problem is I have no clue about tuning (though I did get some Holley books) and don't know with what parts to start off with so that I'm not burning up time and money on parts that are way off. The carb is a 4160 750cfm. My engine only needs like a 600cfm but the carb came with the car. My cam specs are: 218/228 duration at .050" lift, .492/.492 lift. It will be 9.4-10:1 CR (not sure which yet as I haven't decided on heads) and won't see more than 5500rpm.

According to this book, and as long as the old owner didn't screw with the carb, then it has #122-72 main jets, 134-21 secondary main jet (plate?), 134-131 primary metering block, 134-21 secondary metering block, 125-65 primary power valve, .025 primary discharge nozzle size, and a 'plain' colored secondary nozzle spring.

What parts would you recommend that I start out with for my combo? TIA

82camaro

Try it the way it is.

F-BIRD'88

I'll second that. No tuning should be required.

82camaro

Some tuning "may" be required. But you aren't going to know until you try it.

Damon

Yep, run it like it came out of the box first. It'll probably run pretty good. Make sure you adjust the idle mixture screws to achieve a good idle and drive it around a little.

My next piece of advice is a "usually works" kinda suggestion. The #72 main jets are often a smidge rich for a street driven small block. Not horrendously so, but many times you'll get a little more throttle response and better mileage by going down 4 jet sizes to a #68. Every engine wants something a little different.

But like everyone said, run it like it came out of the box first, then start tuning from there.

Skip Fix

If its the 3310 vacuum secondarey 750 it should be close out of the box on jetting.

Power valve tuning depending on idle vacuum. Power valve should be at least 2 numbers below idle vacuum.

Vaccum secondary spring tinkering can be helpful too, to quick and it bogs. That carb should have a medium "plain" spring in it.

Ukraine Train

it's a 4160 carb.

one thing i forgot to mention is that i kept having an off-idle bog problem with this carb. i'll be using the same cam before and after the rebuild so the only difference will be the compression ratio. i'm not sure if the bog was just due to the carb being tired or if there was an incorrect part in there.

F-BIRD'88

Check the accelerator pump linkage. There should be no slack in the linkage when at idle. fuel should shoot out the discharge nozzles as soon as you move the throttle.
Be sure the spring in the linkage is not tightened all the way down.
Remove the accelerator discharge nozzles and screw. There should be a check valve under the screw. If its missing you'll get a bog off idle cause the accelerator pump fuel discharge will lag.

Flip the carb over and see where the throttle blades are.
see how much of the transfer slot is exposed at idle.
if more tha .030" increase the secondary idle stop to allow more air through the secondary side at idle.
You can also run more intial timing advance with the larger than stock cam. both these will allow you to return the primary throttle
plates back to the proper idle position.
If, at idle the primary throttle blades are either not open enough
(covering the transisiton slots) or too far open ( more than .030") then you'll get poor off idle response.

Ukraine Train

Thanks for everyone's help. The next thing I can't figure out is which rebuild kit to get, ie. Trick Kit, Quick Kit, etc...

The number on the choke tower is 80508

Skip Fix

Playing with different squirter sizes on the acelerator pump and erven different cams(they screw on to the throttle shaft, can get rid of an off idle bog.

My 85 Bronco 351 had a factory Holley with a bog that was cured with a smaller squirter, so bigger isn't always the fix.

I'm not familiar withg that carb # I'll have to look it up in my Holley catalog.
The best rebuild kit has power valve needles and seats and all the gaskets, not sure what it's called.

Ukraine Train

ok i tore into the carb tonight. turns out the previous owner did some work to it. it now has secondary jets instead of just a metering plate. the primary jets are 68s and the secondaries are 76s. also, the accelarator pump was setup weird. attached to the bowl was a thin red rubber diaphragm instead of the typical check ball thing that i've read about. i'm not sure what the deal is with that, i'll call holley tech support in the morning

thanks for everyone's input by the way

Skip Fix

Some Holleys use a rubber diapragm as the one way valve in place of a check ball.

Sounds like some weird jetting. Ususally add about 8 jet sizes in place of a power valve. In the secondaries fuel goes away fron the power valve on acceleration so they usually aren't used.

five7kid

iTrader: (14)

or ?

4 isn't a bad starting place for primary-secondary jetting. If it really needs more fuel under power, then jet up the secondaries.

The reason secondaries don't (typically) have a power valve is the secondaries aren't in play in cruise situations - when the power valve would be closed. No VS carb will have a secondary PV

What PV is in there now? Too low a PV # can also cause off-idle "stumble", I'll call it ("bog" is associated with nailing it to WOT, and can last a split second to several seconds). In "normal" driving, a quick hesitation coming off idle is typically a mis-matched power valve.

Ukraine Train

the power valve is a 6.5"

are you saying the secondary jets should be about 4 numbers higher than the primary? sorry i'm new at this lol

do accelerator pumps come in different flavors? the old one i took out had a black diaphragm and the new one was turquoise

five7kid

iTrader: (14)

6.5 would seem adequate. Only way to know for sure is to get some cruise vacuum readings.

Yes, secondaries 4 sizes larger than primaries - for starters. That's assuming the primaries are jetted properly.

Diaphragm color shouldn't make any difference, to the best of my knowledge. There are two basic sizes, 30cc and 50cc.

Unless the sizes are color-coded. Anybody ever hear of that?

Skip Fix

The actual accelerator pump diaphragms the green ones are acohol compatible, black ones plain gas.

Ukraine Train

well today i tried some tuning. i pulled my plugs and they were extremely fouled so i put in 65 primary jets, went for an easy drive and then checked the number 1 and 2 plugs. 1 was dark tan, a 64 would be ideal for it. 2, though, was still very fouled so i pulled 3 and 4 and 4 was dark tan and 3 was very fouled. i have a dual plane intake so what's happening is the cylinders that correspond to one side of the intake are running richer than the other side. so i ordered a pair of 60, 58, and 56 jets and will get them tomorrow. i will try a 64 on the leaner side and will use the ones that i ordered to get the other side right.

also, i'm pulling 15" of vacuum at idle and 21" at cruise but giving it a slight amount of gas will make it drop to about 8" so i think the 6.5" power valve is ok

Ukraine Train

I just thought of something else. I'm running spark plugs which are two heat ranges colder than stock. My compression (10:1) is a half point higher than stock and I'm running 16° initial timing, which is about 10 more than stock. Is it possible that my plugs are just too cold for the setup and that results in the fouled plugs? I'm concerned that I will lean out the jets enough to get the plugs tan but because the plugs are so cold I'll be running lean.