Ok, my dual carbs (http://www.v8buick.com/showthread.php?s=&threadid=9734) are on their way as is my Offy dual quad manifold. I've never tuned these Carter Competition Series 750's (AFB's) before so I'll be starting with a blank sheet. Info is not abundant on the net and I'll be buying a book on Carter carbs which will help. My 401 is stock internally and features stock exhaust manifolds. Everything I have learned so far tells me that putting 1500cfm on an essentially stock motor (even a 401) is a crazy thing to do but I just have to do it. Even if just for the looks. Although I am expecting some performance increase. I am not worried about fuel economy (I drive a car that weighs nearly 5,000lbs - it's a bit late to be concerned about fuel economy). Even though the engine is fit (compression is good in all cylinders, plugs colour is the same on all plugs, doesn't use any oil at all 220 RWHP) I don't think it would be a good idea to spin it over 5,000rpm. I don't expect a massive increase in power but I do expect some. The carbs ran fine before they where removed and have been sitting for about a year before I bought them. They where taken off a tunnel-rammed big block Chev. I expect that when I floor it I will be pouring more gas in there than can ever be used by my stock motor but how will it run? I have no experience with dual carbs and can't wait to dive right in. I do however have some experience with over carbed engines. One day when a freind's car refused to leave my house under it's own steam We installed a spare 725cfm Holley onto his 253 cubic inch V8 just to get him home. I expected it to run like a dog but much to my (and my friend's surprise) it ran fine. Gave that little motor a heap of extra power as well but of course he used a large (by his standards - not mine) amount of gas in the process. Actually took me a while to get it back off him he liked it so much. Like I said before, I'm not terribly worried about using too much gas but I am hoping that it will start, drive around and perform ok when I choose to floor it. However, if it turns out to be a bad performer I'll rip it all off and wait until I do some head work and buy some TA short headers and a cam. Which I am sure will make all the world of difference. What can I do to ensure that I get it to run the best it can given my current configuration? I will be running a HEI converted distributor from Dave's small body HEIs so there should be enough spark. I expect that going to smaller jets might help. I plan to run both carbs at the same time as I have heard (and this has been confirmed by folks on this board) that the Offy doesn't have good fuel distribution running on just one carb using a progressive linkage to open the second carb at say, half throttle. The one linkage will open both carbs the same amount in my planned set-up. I know that the setup I have now (modified 800 Q-jet on a 66 spreadbore manifold) is about as good as a stock nailhead needs but...dual carbs are so cool I've just got to see if I can get them to run. So, any hints or tips, advice or encouragement will be most welcome. BTW, I expect at least one of you to call me crazy but hey, I'm having fun with my Buick so I can't be all that crazy...can I? P.S. Going fast in a large car is a lot of fun.
Iz you crazeeee? Bill?!!!? Dual quads on your Electra?ou: Ok Bill, first lets back away from the racing fuel exhaust fumes just for a few moments.ha ha Not that it wasn't there already (need for speed) but I just had to figure the High Performance bug would bite you hard after your first visit to the United States, AND getting to race one of the guys bad Buicks.:Brow: Seriously though I hope this works out well for you, as you know I've got a 401 car also but sold my Super Wildcat two four set-up because I thought it would be to much fuel and a pain (for me anyway) to set-up correctly.So I'm interested in this too. Rejetting as you mentioned, I'm sure will greatly help the application, and I wish you best of luck, AND I wanna see pictures of the finished project. I just know we've got some good men on this board to help ya. We gotta take car of our friend from "down under". Go for it Bill. P.S. Attaching parting shot,dual quads thumbs up picture for you:TU: Fritz
Thanks John. I know I can always count on support from you and yes BobC has a little to do with it. After racing his F.I. BBB I have not been the same. That is one wild Stealth Sleeper that can drive 1,000 miles, pull an 11second quarter and drive 1,000 miles back home. Nice air cleaner. I have a ribbed dual carb scoop that will match perfectly with the ribbed valve covers and valley pan which I bought for 10 bucks at a swap meet that has been waiting for this project (I knew it would come in handy one day).
All I can say is the intake and carbs look nice.. To bad they're still sittin in a box... Bring on the weekend, maybe I'll get some email? Perhaps they're still all drooling over the dvd.. :spank:
Bill, I bought that Carter book and its not all that great (compared to Roe's QJet book). No info at all on tuning a 2x4 setup there. Edelbrock AFB owners manual might be best info if you can find one 'down-under'. There's only one manual to cover all Edelbrock AFB part numbers. On carb sizing - I've heard/read somewhere, can't find it now, but anyway the gist was to go with the same capacity per-carb as a single 4-V, so a pair of 750s may be OK. The important thing to keep in mind is that the secondaries are vacuum operated. So they won't open and guzzle gas unless the engine demands it. The air valve is under the secondary venturis, and it opens against counterweight. As IgnitionMan pointed out, Vince at Offy is knowledgeable and helpful for setup and tuning tips, but the phone bill will be worse than the gasoline bill!
What'd you think of the distributor? Stock carbs are set to use only one carb, rear one, as the idle circuit carb, and those aftermarket ones may just be too big. I just delivered another Nailhead dist to a fellow not far from here, doing the same thing to his 425 you are doing, single 4 to 2x4, on dead stock 4bbl engine, in his 1937 Buick. He will be running the stock carbs, of which he says he has three sets of carbs, so it should prove easier than what you are in for. I've not seen aftermarket carbs work progressive, only full-on, and have seen them need a lot of work to get right. One thing will probably be the idle fuel oriface size. Lets see what comes about with the setup, and go from there.
Okay Bill & Fellas... I took some shots about an hour ago for Bill (unknowingly p ) and thought I'd make 'em available to everyone to see and make fun of the gas he's gonna guzzle.. :gt: :spank: Dave, the dist is in the mail at the moment.. I have no idea where the post office has it.. lol Should arrive by next week, if not sooner.. Bill, I got the measurements you wanted as well.. Check the email box.. Click Here For Images Have Fun Guys!
The distributor is currently flying over the pacific. It should arrive shortly. I can't wait Dave and I will give you a full report as soon as I install it. I have also posted this thread over at the Yahoo NailheadBuick group and have had some interesting responses. For example, It's been suggested that I disconenct the secondaries on both carbs and run off the 4 primaries. Or I could disconnect the secondaries from the rear carb and use one entire carb and the primaries from the second giving me 6 barrels. All interesting stuff. I suppose I will just throw them on and see what happens. I'd like to hear from anyone who has an offy installed on their Nailhead and what it took to get it to run right.
Bill, I think the 6bbl is an easier option here as one set of rear barrels aren't opening up beyond 45deg.. Me thinks someone fidgited with the linkage for some reason... That carb is the rear one in the photos. Dave, I may be calling you on Sunday.. Might not wanna answer the phone.. LoL ou:
The biggest problem will be attempting to get both carbs leaned out enough to be effective. Tunnel ram systems run rich jetting, as they have very large undercarb plenums, and that kills signal to the various circiuots in the carb. The fuel has to be drawn into the inlet system, and if the signal is weak, there has to be an easier way to get the fuel into the void, and that's making the carbs richer. Since you are running in effect, two rear carbs, with idle circuits on both capable of running one engine apiece, you will probably need to restrict the idle orifaces, main jets and needles, springs, etc. Squirter should need to be closed down as well. You also cannot go to a progressive linkage setup, like the stock 2x4 used, because the front carb will have idle and transition circuits in them. Congrats, welcome to "Jetting 1001". To change the idle jet oriface, remove the carb tops, primary booster venturii. there is a tube in each one, out the bottom, with a restriction drilled into it, this is the idle fuel jet, smaller leand it out, etc. record the stock hole size, solder it closed, drill smaller for lean. You will need the smallest drill index available, and a hand pin drill holder, don't use a drill motor or Dremel tool to drill these holes. The idle jet oriface handles fuel available to the idle system, and the amount of tuel treated with the idle air screws, AND the first 1/8th throttle or so from off-idle speed, so changing the oriface changes two distinct functions. Accelerator pump squirters will probably need to be closed down as well, same procedure, pay attention to the output angle the stock hole has, it aims the fuel injected to a certain area in the venturi. Main jets and needles/springs are available in kits, and you'll probably need two sets to do the carbs right. Jet as nescessary, but don't believe the charts sent with the kits, they can mislead. If the engine feels good but just soggy all through the rev range, lets say too rich, and the chart tells you to change the mains AND needles, sometimes the chart will be wrong, as a simple main jet only change would fix it. I'd say since the engine wasn't a 2x4 to begin with, even a stock 2x4 carb set would need to be leaned out a touch from its original configuration, so...you will be changing lots of stuff. You may end up richer than a stock 2x4 setup, but that would be simply to match the air flow into the engine from the larger carbs. Try it the way it is first, go from there. It'll be fun.
Thanks Dave, . I'll print it out and get a set of carb drills and a hand pin drill holder and armed with this info and the Carter manual I think there's a fair chance that I'll probably be able to get these to work. In any case I'll really enjoy the experience and if I can't...well...at least I had some fun trying. I've emailed the original owner to try and determine what state of tune the engine was that these carbs were removed from. Came off a 'Big Block Chev' can mean many different things. I just hope they didn't come off a full race motor.
