All double pumpers are 4150's. The 4160 lacks the secondary metering block, and has a metering plate in it's place. The 650 is a little too big for your build in my opinion. A well tuned vacuum sec. 600 will give you a little stronger acceleration as the secondaries will "come in" when they're needed, not "instantly" when the go pedal is mashed. You can "fix" the 650 to help the fuel curve, but you're really only wasting fuel bumping up the accelerator pump volume doing this. If you're not concerned about fuel consumption, then go ahead and go this route. The 800 ? Don't waste your time, it's far too big for a 302. Fuel gets delivered to the venturis via the vacuum "pull" created in the throttle bores, the 800's bores will not deliver the "pull" on 302 that a smaller carb will and thus will not get the fuel into the venturis in the volume needed to feed the motor.
Those numbers he quoted must be the squirters, not the jets. Holley doesn't make jets that small. 28's if they were made would be far too small to feed a 650. My 250 cfm 2 bbls came with 58's
Some good tuning guides on this page: http://www.bob2000.com/carb.htm Look up your part number here for Holley directions: http://holley.com/TechService/Instructions.asp?query=&page=2 Look under "Carb Numerical Listing" for a complete setup for your carb from the Holley factory. Jet sizes, squirters, power valves, etc. http://holley.com/TechService/Library.asp They are simple to tune. Read and learn what to do. SPark
I uh... realized that shortly after he posted the full specs. Which would be why I was like they seem small, but they are within 10 of each other and supposedly that is what matters most for keeping the primary and secondary in step with each other. I don't have Holley's catalog sitting in my head, so I figured he was either reading it wrong, or someone put some tiny suckers on their. But, hey thanks for clarifying. So if he's got the 28cc squirter being powered by the 18cc cam (which means only 18cc's of fuel are being pushed out of the accelerator, even if it's the 30cc pump) then he is not delivering enough fuel. Put on the right pump cams, and I bet that sucker comes to life.
Didn't read everything here but a few quick generalizations. More manifold vacuum is ALWAYS better and that's where you should start tuning before screwing around with the carb in greater detail. Get a vac gauge and max it out with proper initial timing/vac advance numbers. I usually adjust initial as high as I can get it without starter kickback and/or pinging and give it a tiny bit more from the vac advance pots adjustment range. It's going to be a balancing act. Talk to anyone here or elsewhere that runs heavy initial timing numbers and see what their opinion is vs anything even remotely near stock numbers. Cams and single planes LOVE heavy timing and I usually run anywhere from 20-25 degrees of initial with quicker than average centrifugal sweeps to end up at around 40-42 degrees total. IMO.. 36-38 degrees is for "good enough for me" sissy's.. or those running WELL over 7,000 rpm(although there are some factory stock guys running upwards of 45* @ 9,000-10,000 rpm)..newer fast burn heads and/or aluminum heads. It's been proven for years on dyno's, dragstrips, and street races that these little low compression motors need more than that to broaden the torque spread AND make max power. Also.. running manifold vac advance in conjunction with heavy initial lead will clean up the idle(although NOX will go through the roof) and make for excellent throttle response due to very high manifold vacuum readings too. Front to rear jet spread for carbs without rear PV's is usually in the range of 6-8 jet sizes to compensate for the lack of rear PV. If you're running best at 2.5 turns out?(which enrichens it).. you either have the transition slot incorrectly exposed?(should be around .030-.040 showing when the idle speed screw has been set).. the IFR is too small(HIGHLY unlikely that's the case on this particular motor).. or the timing is too far advanced(also unlikely as most people are usually far too conservative on base timing settings.. but.. heavy vacuum advance from the pot can cause some issues with lean out on occasion and is worth mentioning if you run full manifold vacuum(most don't do that either). If the front plates are having to be shut tighter than recommended(resulting in failure to expose the proper amount of transition slot) to keep the idle speed down?.. tighten up the rear blades to allow more front opening. It's a balancing act between the two and the front side's transition exposure is the biggest concern that affects mixture quality and drivability. Short gears help considerably.. but a wide ratio style 3 speed still leaves you with less total gear multiplication in 1st and can make a DP carb fall on its face on lower torque small-blocks(severely affects rpm rise for the carb to come up and stay up on the boosters). Then you shift to 2nd and repeat the process all over again. As seems to be the case here. A 4 or 5 speed swap would all but eliminate much of these issues.. but I certainly understand having to work with what you've got for now. You have major holes in the fuel curve under hard throttle and 28 shooter on the front side is WAAYYY too small for a single plane manifold regardless of the most aggressive pump cam being used. A smaller shooter just prolongs the pump-shot and often makes for ruptured or leaky diaphragms over time, is all. Think.. "stretched out balloon" as it constantly battles against its return spring as the big pump cam tries to abruptly force all that fuel out through that small shooter. Personally.. I'd be starting at around 32-34 for the primary shooter size and adjusting cam size from that baseline. That will fill in the hole and get rid of the stumble. Typically.. you cam the shooter all the way to the point that it starts to flatten out and/or go rich enough to puff black smoke.. and then pull back a shooter size and or cam size to lean it back out. If it keeps responding to cam size/larger initial pump shot?.. you still need more shooter size and must rinse and repeat to find optimum size. Getting it right will wake a motor right up on initial tip in and abrupt WOT transitions. Because of the length for your first and second gears(again.. relating to the motors rpm rise rate).. you'll likely need to balance shooter size and pump cam aggressiveness to keep the pump shot going a bit longer than usual to fill in the holes created under heavier throttle transitions as the booster signal falls off. I believe baddad touched on that briefly and he's dead on target there. IMO.. you'll need to learn how to drive this carb based on what the drivetrain and torque output will allow for rpm rise rate just to keep it up on the boosters and do away with some of the holes created during far too abrupt throttle transitions. IOW.. probably no more than half throttle from a standstill.. then roll into the secondary's as the car picks up speed and comes up on the cam and fatter part of the torque curve. Either that?.. or dumb it all down and swap over to a VS setup so you can just mash and go. Unless you have an AFR monitor telling you what the motor wants.. you should NEVER try to tune a carb by throwing all sort of changes to the various circuits. Separate them all up and work each one individually such as idle circuits, accelerator pump/s, main jets, power enrichment(PV), etc. I even go so far as to try and tune the primary side separate of the secondary's by either running a very stiff spring on the secondary side of a VS carb to keep them shut.. or staying under the required throttle percentage to avoid opening up the secondary's on a DP style carb. Takes some time and miles to properly read the plugs.. but helps you dial in the front side before you start getting wilder on the secondary's and at WOT. Bout all I got time for right now and hopefully there's something in all this that can help you along in the tuning process. Good luck with it all
Lots of good info there. Thanks a lot. I just got my hands on a vac secondary holley 600 so I might try and " dumb things down" and go with that carb to save myself a few headaches. Thanks for all the help, tips, and advice guys!
The VS 600 will greatly simplifiy things, about all this carb will need is a lighter secondary spring to allow the secondaries to come in far sooner than what the factory spring lets em open at. I use either of the two lightest springs in the assortment for a 302. You can buy the spring assortment at most of the big chain parts houses.
