Running 3 x 2 barrel Holley 650's, list # 6245 annular discharge on my 327 CI (331) small Chev, Reasonably stout street engine with tight comp, largish roller stick and worked set of Brodix Track 1's, about 550 HP. I am trying to trouble shoot early with this set up and looking for some guidance from experienced Holley guys. I am not running a progressive linkage system yet and have 3 idle circuits, seems like 2 to many. How can I minimize the front and rear carb idle circuits as per the 2 GC Rochester's to give me clean of idle cruise circuit driving? Have a Richmond trans behind this engine with close ratio gear set. Input welcome, cheers Wayne
WOW ,thats almost 2000 cfm on 331 cubic inch.I am amazed. I can't help you but you have my attention.
WOW you like abuse don't you! Find some used Holley's from a tri power Corvette or 6 pack 440 yes you will pay a lot but you will have a decent chance to make it run daily!
almost impossible to do since you have to disable the air circuits in the carb ( transfer slot , idle air bleeds ) and it will effect the way the carb performs as it helps to transition over to the main wells as they are connected . better off looking for the right carb or get a holley book ( Dave Emanuel) and do some heavy reading and experimentaion . you could try cutting the fuel off at the idle fuel screws and closing down the throttle plates on all three and use the center one for fuel adjustment but the air leak might be large from the end carbs and the center fuel screws might not allow enough fuel adjustment plus the mix might be too lean on the ends . Holley used to sell the blocks with out Idle passages seperately , might be worth the phone call to the states to see if they are still made
As ^, close off the outer carb idle circuits (turn in the screws) adjust the linkage so the end carbs are fully closed with some play to allow the center carb to idle the engine. It probably won't idle under 1K-1100 rpm. Never say never..... If it Stumbles or bog you will have to work out the power valves, you should have 2.5 or 3.5 in all to start. Of course jetting will depend on sparkplug readings, unless you have a computer and wide-band o2 sensors.
Just to play the devil's advocate, why wouldn't you want an idle circuit on each carb? Looks to me like it would give more even fuel distribution than just running an idle circuit on the center carb. Sounds to me like you're probably going to have more trouble with getting the right vacuum signal to the carbs, running carbs that big and opening them all at the same time. Your going to lose a lot of vacuum when carbs open up right off idle. I think I would try smaller carbs and progressive linkage if you want any kind of off idle performance.
I would work on a progressive linkage then shut down the 2 outer carbs as far as I could then dial in the linkage for best performance.
Ford Tri-Power also had idle circuits on all carbs. You adjust them the same way you would if you were running a simple 1850 4 barrel. Only six to adjust instead of two. Set all the needles to 1-1/2 turns out from closed. Start the car and turn each in one at a time 1/4 turn. Keep doing that until the idle quality worsens. Then turn them open just enough to clean up the idle. All needles should be the same number of turns out. You can also use a vacuum gauge and shoot for highest vacuum but I never did with my Tri-Power. Poor performance off idle is another issue. With three carbs at 1:1 you will have tip-in problems like crazy. You would need to synchronize all of the carbs like a set of SUs or motorcycle carbs before you could even investigate your pump shot or whatever. Without progressive linkage you will just have a big, wet mess on your hands with those carbs on that engine. Better to block off the outer two (or the center one) with a solid gasket, disconnect the fuel and linkage and leave them there static for looks until you get some proper linkage hooked up.
I am leed to believe that a 650 2 barrel is in fact closer to 350 cfm in 4 barrel terminology due to the signal that the 2 barrels receive, this being true 900 to 1000 4 barrel cfm would appear to be close at WOT? I thought that I would sort this combo out in anticipation of running mechanical stack injection on this engine. thanks for your input.
[ Larry, I am applying the same think as the Rochester Tri power sets that have a designated primary/ secondary carb set. I would be happy to set a progressive linkage to phase in front and rear carbs as engine requirements dictated more fuel as air speed increases. I am trying to limit the available fuel at idle. Had these on a 460 Ford as is with no mods and they were quite acceptable on the larger displacement. Thanks for your input.
Rick, this engine is unlikely to want to idle under 1200 rpm's I don't have base lines for jetting and power valves at present, still tweaking the Magneto to make the engine happy, running 12.8 to 1 pistons in a 65 cc chamber, thanks for your input
Block off both end carbs, and if your engine is any good you will need aluminum plates under the carbs, ( mine sucked holes in the gaskets ). Make it good to run on one carb, completely sorted then add the others. Gary
Where did you find 3 of them? I work with them and know what you've got, they are on the rare side over here. Did you replace your throttle blades? For street you can't have holes in them - hell'uva vacuum leak, won't idle down. I could write a small book on what to do, but the first thing is the throttle blades.
Ok so they ran fine on the 460 ford So now lets look at what is different between the two other than cubic inches Now how about the intakes what do you have on the small block could it be that it has more air speed than the big block had.
Saltflats, the 460 has comp & cam, the manifold is a Wieand Tunnel, we were trying for gas millage as the two 1050's were savage on a road trip! Still went plenty hard to, those carbs are bad boy 2 barrels for sure!
OJ, bought these brand new some years ago, didn't Think much of them till I started wanting traditional looks with real horsepower, I will try & post the picture of my engine as it sits now, I've massaged these carbs to look not like Holleys but there is only so much you can do!The carbs have about 40 hours street driving on them, are you saying to dress the leeding edges of the throttle blades? Cheers Wayne
90 % of all drivability problems with multi carbs are related to the distributor; vacuum advance, mechanical advance and initial timing.
Best leave the blades edges alone, they have a special bevel to them. I have never seen them 'brand new', look at the throttle blades, are there holes machined in them?, like about .080? Those holes are in there for the circletrack guys - that is what that carb is intended for - the hole is intended to prevent a stumble by extending the transfer slot range. To get them to idle you can't have that hole in there, especially in 3 sets of them. With those carbs and if your engine breathes well (good headers etc) it will idle easily at 850ish rpm, at 1200rpm it isn't idling and it is trying to draw from the main wells and overly rich. Are there throttle body gaskets available for them down there? That is the gasket that goes between the throttle body and the throttle plate. We have to make them from 850 throttlebody gaskets and they just don't suit me right.
OJ, brand spankers straight out of the box! No air bleeds on these throttle plates. That's why I was not sure as to your direction. Right now 1000 is as low as the engine will run, the magneto is fresh but the set up may,need a little more leed & back the total advance down some. just bought full gasket sets here, tried Summit, man they were as helpful as a hip pocket in a T shirt! interesting times ahead I feel!
Maybe we are speaking about different carbs, I don't see a Holley 6245 and going per your description as 650cfm annular 2bbl I assumed you mean a Holley 6425, Here's afew pics of one, is it like yours? The race inlet and adapter are extra, but this is a Holley 0-6425 model 2300 650cfm annular discharge carb, you can see the holes in the throttle blades.
I had to drill the holes in mine per Holley. (that was years ago) You want to start out with the idle circuits closed on the end carbs and work with the center carb. Some set ups you may need to open the end carb idle screws, very little in order to smooth out the engine and prevent tip in hesitation. (it also depends on the power valves you ar using).
Nice List 6425's. Is there a way to Convert to ALCOHOL ....as in someone makes a metering plate for the old style tube plates.... I would like to have a pair set up for the blower on Alcohol.
No, they take current Holley-style metering blocks, they don't have 'metering plates'. Alcohol metering blocks are available from AED; Quickfuel; Bo Laws to name a few. You'll need a couple other changes as well, get rid of those velocity stacks for starters.
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