I have read all of the post related to setting up a 2gc tripower and still have questions.... First I am running a 65 383 Chrysler, 9.5:1 comp, aluminum heads (2.14/1.81 valves 310cfm intake/ 230 exhaust @ .600), hyd roller cam specs are: 274/282 advertised, 220/226 @ .050, .488/.488 lift, 112 LSA, 108 intake centerline I am running the Weiand WPD39 intake, 3 2gc's.... outboard carbs idle circuits are plugged, throttle blades have been reworked and completely sealed when closed, power valves have been plugged, trimmed 3 coils off the accelerator pump springs for the outboards and set my floats to 3/4" and jetted to #55's. The center carb is jetted to #56's, 3/4" float level, and stock accelerator pump. I am running the chokes till I can find the right plugs for them. My timing is set @ 34 deg total timing all in by 2800 rpm, 14 initial and 20 mechanical at dist with no vacuum advance installed. I have gotten the engine to idle nicely @ 750-800rpm and the plugs look good, not to lean or rich and if I drive the car easy without engaging the outboards im good. My problem is that its still a pig off the line and borderline fouls the plugs out when I get on it from a stop. My linkage is set up so that the center runs the engine until half throttle then the outboards come in. Is this an outboard carb timing issue? It feels like I am getting way to much fuel from the outboards, is this a simple adjustment I have overlooked? Anyone have a pointers to give me? I have read good things about the Rochesters but I am leaning on going back to the Holley 6BBL set up I have and for me its easier to tune as I am already familiar with the Holley2300's but I really like the look of the 2gc's.
Everything timing wise sounds to be pretty close to optimum. However, if you are not getting any pinging on acceleration when you rev past 2800 your jetting is probably rich generally. I would say that 2800 is a 4-500 low to be all in. When you say the plugs nearly foul when you get on it from a stop, let's think about what is occurring mechanically. With the secondaries set to begin at half throttle that means they open twice as fast as the primary. That means the the accelerator pumps are getting a very energetic squeeze.Lots of fuel and little moving air. I'm not sure what shortening the spring in the accelerator pumps is supposed to do, I assume it is to reduce the size of the shot. It may still be too much. The next thing to do would be to disconnect the accelerator pump linkage to see if there is an improvement in hard acceleration from a stop. The second thing I question is the plugging of the power valves. The engine needs that enrichment at low vacuum/wide open/high rpm operation, that's where things start melting. Power valve are an on or off deal, they open the power circuit when vacuum drops below about in/Hg. There is a spring that forces open the power valve and vacuum works against the spring to allow the main jets to work instead. Perhaps that is where an adjust meant can be made, to change the spring pressure by shorting a coil or two which will cause power valve to Not Open until vacuum drops to 3-4 or5 in/HG. The enrichment that circuit provides is dependent on passage sizing and shouldn't be changed without a wide-band air/fuel meter and the appropriate drill set. All three carb should have the same power circuits. The main jets in the secondaries may need to be different than in the primary to optimize air/fuel ratios when secondaries are operating at small or partial opening. but all three need to work the same at wide open (mostly power circuit). The conditions you are suffering now are most probably caused by large shots of fuel while there is little intake airflow until the engine can stumble thru that to higher RPM and more air flow when the main jets can begin to work. I suggest that you invest in wide band air/fuel meter, a tach, and a vacuum gauge that you install on a small panel that can be set on the seat beside you or hang on the dash to monitor the interrelationship of those 3 parameters to your varying driving conditions. You will soon see and understand what changes need to be made to the carbs. As an aside, back in the mid 60's while campaigning a tri-power 348 in a drag car, we suffered much the same problems as you have. It would stumble then catch up as the air/fuel got back in balance then often the tires would break loose we'd get beat. Our solution was to disconnect the accelerated pumps. Then we would go very lean and fall on its face when we jumped on it. We next put choke tops on the secondaries, however we didn't use any linkage. We made sure the choke butterflies opened and closed smooth and easily. They naturally want to fall open with out linkage attached. I attached various sized washers to the short arm off the choke shaft to counterbalance the butterflies to the closed position until the secondaries sucked them open. After a bit of trial and error we found a nickel was just about right to ease the secondaries into operation. Then when at the line, revving to 4000 I was still only on the primary carb until I dumped the clutch and stabbed the gas. Now there was no showboating or stumble, just smooth acceleration as the choke butterflies gradually opened to let the carbs metering circuits begin to do their job. We won lots of races while the others stumbled and broke loose. You may want to keep those choke tops. This is almost exactly how the Quadrajet operates, where the secondaries' top throttle plate (choke) opens by suction(vacuum) and simultaneously opens a metering rod to proportionally enrich the A/F depending on how open the butterfly is. I hope these comments will help steer you to a solution. Best Regards and Good Luck with all your endeavors, KB.
Well I have made some progress with the tune. I swapped out the advance springs a few times and got the mechanical advance on the distributor where this particular cam/ engine likes it. A nice gradual curve that's all in by 3300rpm vs the aggressive curve I had in there before and I set the initial at 12 deg again with total at 32 I also changed out the spring rates in the accelerator pumps on the out board carbs and readjusted the progressive linkage so that the outboards start opening up at around 60% primary linkage movement. This has helped with the bogging when I floor it to WOT but it's still sluggish and hesatates unless I gradually get into a WOT situation. I am going to keep running the Rochester's and tune them till I can't get anymore out of them and then decide if I am going to swap them out for the Holleys. I am a big fan of the 2300 carbs and you really can't beat the vacuum advance of the secondary's in relation to the engines needs vs the mechanical linkage. Posted using the Full Custom H.A.M.B. App!
Think I've got it figured out, I ran a total of 33 deg and ditched the accelerator pumps on the outboards. The engine runs great now, no lean conditions at all and the engine is very responsive when I tap the throttle. Posted using the Full Custom H.A.M.B. App!
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