Here is the kind of great information for which I love this forum so very much, so thanks in advance for your help.
When I was the caretaker of 5s287, my Holley 715 was SPOT on. It was that way when I bought the car from Brett. That car was a tad stronger than stock, and had what I thought was a slightly more aggressive solid cam than a stock hipo camshaft. My 66 GT350 was supercharged, so it had a mechanical secondary Holley. My 67 Gt350 had a perfectly set up Le Mans carb also. I have good luck with them so far.
Today, my black 65' K code is the project at hand. The engine has a .030 over bore, with correct TRW pistons, aluminum heads (painted black) with 53cc combustion chambers. I had the combustion chambers cut to that size so as to be about 10.5 to 1 as to compression ratio. Intake ports are matched to an original 66' Shelby dual plane intake manifold. Competition Cams Nostalgia Plus series 271s solid cam, (more aggressive than a Hipo cam, and with modern tight lash of .012 hot) and roller tipped rockers. They fit under the standard hipo valve covers after I modified one of the baffles . Standard Hipo distributor with Petronix components, probably 14 degrees initial timing and another 20 mechanical advance for 34-36 total. No pinging. Jim Cowle's beautiful coated Try Y Headers, T style Cobra oil pan and an Arvinode exhaust. I would like for them to exit on the side like a 65 GT350, but being a factory GT I needed to exit the rear valance. Car is light. Again, aluminum heads, edelbrock painted black aluminum water pump, standard GT non-pony interior, (no console etc.) 66' package tray, no spare inside car, aluminum cragar reproductions, aluminum water pump, radio delete, I pulled the heater, fan, heater core, etc. Detroit locker with 3.89's. Car runs very strong. Wheel hop initially was terrible, so I went with the Maier Racing springs that cured my traction problems. These springs are probably about equal in weight to standard Hipo springs plus Shelby traction bars (or a bit less) as they are 4 1/2 leaf springs vs. 4 leaf factory springs. Problem solved. ( as an aside, the original Shelby traction bars on my 5s287 really DID work! That car just kind of squatted and jumped up. I had 235 60's in back and that helped also). This car makes lots of power. More than did 5s287 did under my care. I am guessing about 360 horses at the flywheel. Maybe a tad more, but I think that is close.
Back to my carb problem.....My reproduction 3259 Carb was purchased new, recently, by me at Branda. Confirmed primary idle transfer slots exposed a small "square". Engine making 12"(varied a bit from 11-13") or so of vacuum at idle. Idle set at about 750-800 RPMs... Had stock 68 & 78 jetting. Seemed to have a lean bog from a stop and every time gears were shifted when full throttle applied. With the 68 primaries, I had the idle mixture screws turned out 1 1/2 to 1 3/4 turns or so. I bumped up the primary jets to 70's from 68's. That seemed to help reduce the bog some. Now, best vacuum is about 1/2 turn out on the idle mixture screws, as the 70's are allowing more fuel. I bought a Holley Vacuum quick change spring kit, and an Accelerator Pump Cam kit. Currently has the stock white cam in position one. Next we changed the stock 25 Squirter nozzle to a 28, and changed to a white (lightest) vacuum secondary spring from the stock yellow spring. Other than the slight hesitation at throttle application, car ran great and pulled hard. VERY.
We thought we might have a vacuum leak given the variations as to idle vacuum. We checked, none found. We pulled the carb to check a couple of things and to use a slightly thicker carb baseplate gasket between it and the intake manifold which we preferred to the thin paper one we were using. We tried 69's as primary jets, as with the 70's installed, and we could bottom the mixture screw on the driver's side and it would still run. Car did not run better, and now we could bottom both idle mixture screws and the car would continue to run. Car had backfired once as we were working on it (it never has in other situations) and I suspected we blew the power valve, which is a failure condition that would allow the engine to continue to run with the idle mixture screws bottomed out. Power valve was the stock 8.5. We tried a 6.5, as depending on which set of Holley instructions you follow, either can be called for. Of course a 6.5 delays the secondary fuel delivery, and the car clearly ran worse. We went back to the stock 8.5 valve, and back to the 70 jets. Adjusted mixture screws again to about 1/2 turn out. Peak vacuum at idle now approaches 15", which is very good given this cam with just under .5" of lift. Car runs great, but still has a slight hesitation on throttle application, but less than before. I have been checking to see that our accelerator pump lever is adjusted properly also.
Our plan is to now maybe A) try a different color accelerator pump cam?, and or maybe B) a slightly bigger squirter from the 28 we are now using. Going from a 25 to a 28 was a definite improvement before. Any other ideas? It seemed to run better when we increased the pump squirter before, so we thought we might try another bump up maybe from a 28 to a 30?
Also, The engine will now idle with the idle screws bottomed. It is my understanding that this is caused by either 1) an idle that is so high as to over ride the idle circuit or 2) a blown power valve or 3) improperly set float levels or 4) improperly adjusted butterflies vs.the transfer slots. Front float level is set at 1/2" from the factory and that is my understanding to be correct. So I don't know what is causing this condition. We did not pull the rear float bowl and check the rear float adjustment. The secondaries do seem to be closed entirely at idle, and appear to be as they should be. No visible signs of fuel dribbling in.
So that is question 2, what could be causing the mixture screws to bottom and the engine still idle?
Many thanks!
Brad