I have a rebuilt 4160. Should I convert the secondary side to 4150 style? Is secondary fuel control important for the RX7?

Also what jets should I start out with? I've got a kit on its way with 64-81 jets.

My motor is a TII 4 port, S5 TII rotors 9.0:1 everything else is s4. And I've got a big streetport and street exhaust porting.

 

secondary fuel control will be important, no idea about 4150 vs 4160 i don't know holleys very well.

if you're non turbo, i'd disable the secondaries, and this will let you tune up to 30-50% throttle. on an NA, i'd start with the biggest jet you have, and then start leaning it out. ideally it'll be too rich to run, and then as you lean it out it'll be better and better until it starts bucking, or its too lean.

once you know where too lean and too rich is, it'll be fairly clear what jets you want. at low RPM and load, you want it to be on the lean side, so go until it bucks, and then richen it up until it stops and you're done. if you had a wideband you'd be shooting for 14.7 +/- about .5.

once that's done, hook up the secondaries, and do it again. @full power you want to stay a little richer, so find the spot where it stops gaining power and then go a little richer. for example, if max power happens @13.2, you want to be 13:1 or even 12.8, impact on seat of the pants power should be teeny, but you'll have a little safety margin just in case.

 

4160 has no metering plate on secondary side, no jets. All it is is holes in a plate, preset by factory non adjustable. 4150 has a secondary metering plate with jets. Its a cheap swap though 4150 parts go right on..so Ill probably end up converting it.

Wideband is also high up on my list of parts i need to get still. Im not gonna tune without it, itll make it way easier.

Thanks a lot for the advice dude. Ill post my results..when the engine and everything is in

 

IMO you don't need a wideband with a carb, but only if you have a logical tuning process. you have to tune idle, then the primaries, then the secondaries, you have to find out what parts of the carb do what.

if you don't you'll just be lost.

the advantage of tuning without a wideband is that it actually makes you pay attention to what the engine wants.

 

Having run both 4150 and 4160 types on the carbs ive built, I can tell you for a vac secondary the metering plate is fine. Google the quick fuel "jet plate" if you want exchangeable jets.

The metering plate design was to keep the carb compact, and is not very effective at low rpm metering at all, relying totally on the IFR's and AB's for low speed AFR.

However, the Vac secondaries arent going to open until the airspeed and vac are ideal (assuming the spring on the diaphragm is ideal), so low speed metering will be done by the primary block. So theres really no reason for a 4160 to be converted to 4150 unless its mech secondaries, or you need a power valve on the secondary side. The 4160 doesnt have a tunable idle circuit on the secondary side either, so that metering block would have idle screws that would do nothing at all. Lol


whats the ID# on the airhorn of the carb you have? jetting advice cant really be given without knowing the carb size, or what the pressed in AB's are...

 

Start with a Racing Beat carburetor. They don't just sell repackaged Holleys, they alter the internal passages, some severely.

I didn't have one apart, but I did note that some of the air bleeds were opened up to almost the size of the drillings that they were pressed into. Others who have opened them up mentioned alterations to the emulsion well drillings and the PVCRs.

 

I know I was able to get a 4160 to perform very well. All modifications were made using devcon to modify air bleeds as well as the size of the openings on the secondary metering plate. I deleted the vacuum secondary activation by using a mechanical secondary base plate and blocking the vacuum passages with lead shot.

When life gives you lemons...

 

I'm not made of money I'm not buying the Racing Beat kit I'd go EFI if I had that much.. And I already have the Carb and manifold and other stuff are on they're way.

Why modify the air bleeds though? To fix what problems? I think I'm just gonna buy the conversion kit to convert the secondary side to 4150 style. And why is everyone deleting the vacuum secondaries? I mean its really not hard to hook up properly. And mine is a 600 cfm version..

 

Thanks for the advice man I just saw your post. So I won't convert to 4150 style.

You meam the Holley part number? Its a 600 cfm version.

 

The modified air bleeds will make slight idle mixture changes so it does not foul plugs. Modifying primary high speed air bleeds changes the transition from idle to mains. High speed secondary makes the transition from primary to secondary smoother since it does not have a 2nd accelerator pump. Only reason mine was modified to mechanical was that it was for a drag racing application.

Just my 2 cents worth of hands on working experience with the subject.

 

Yeah thanks man I'm gonna read up on working my carb over to better suit my application.

 

I have and read my Holley book front to back I'm fully prepared for this now. But I also read that Holley does not recommend modifying air bleeds at all.. although it is quite common. Also idle mixture changes can be made by drilling holes in the throttle plates and the stop screw for secondaries can be adjusted to provide extra air at idle so both of those mods eliminate the need to modify the air bleeds. I also read extensively on PVCR modifications and tuning so that should be pretty easy to figure out.

 

yep, its pretty simple. start with idle. then off idle/part throttle cruise, and you may want to disable the secondaries, as you see what the engine likes, and then hook up the secondaries and then see what it likes.

 

Yep ill do that exactly like you said

 

Make sure you dont totally close the secondaries when tuning! This exaggerates the already terribad cornering stalls the holley is subject to, and can mess up your primary jetting! The idle circuit and low speed air bleeds wont do anything at all if that blade is totally shut, and thus cuts your idle and low speed fuel supply in HALF.

Tune WITH an 8.5" hg power valve!

if you CAN, try to retain your vac secondaries. A 600 cfm will stall hard below 3.5k rpm with no secondary squirter.

If you remove your metering block you will see 2 jets on the fuel side, and a large valve with a 1" nut head on it on the other side. This is the power valve! Make sure its at least an 8.5 (assuming your car has decent vacuum 15-18 inches@idle) The two passages on either side of it, each having 2 holes in them that run from top to bottom parallel to each other are the emulsion wells.

After youve figured out what AB's you want (do this after finding an initial jetting) you will "tune" these wells for the rotary. Its very basic on a standard cast holley, as there is only 2 different emulsion restrictions. The one at the higher point of the well affects mid low-mid range AFR (acts like a jet, adding fuel to the air in the booster) and the lowest one affects pretty much WOT and high rpm.


Racing beat shuts the low rpm port altogether, and enlarges the holy hell out of the high rpm. Youll find out why

Also dont drill holes in your throttle blades lol. It *shouldnt* be needed with that youre working with..

 

I have it apart right now. Its got #66 jets in it right now. 34R-9716B metering plate
I took out the power valve but it has no part number on it. It is the "picture window" type with just a circular gasket. It has a 6 an e and a 5 on it..so is it a 6.5" then?

 

Use a 6.5 power valve, don't waste any money changing to 4150, add at least a 1/4" open spacer, buy the quick fuel adjustable vac secondary diaphragm and get a universal dashpot to prevent stalling when you let go of the throttle.

 

Also, utilize the timed vac port on the front metering block to run your vac advance.

 

The reason Holley does not recommend messing with air bleeds... They are referring to people who bought then specifically calibrated for their application. All Holley setups for rotary's are custom builds. Not even the ones from Racing Beat as those are calibrated and modified in house.

 

Okay yeah Im not gonna bother changing the secondary side to 4150. And I already bought an open spacer its on its way. I will look into the quick fuel diaphragm I was just gonna buy the Holley spring kit for it. Ok that vac port right above the idle screw right? So just tee the disty vac advance together and hook up to there?

 

yeppers