Thank you. I have read much on that site also, but I thought restricting the main air bleed made it start sooner.
Big Block Tunnel Ram 660s Questions
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I thought the same til I really started reading and comprehending what does what. I know the typical gets thrown out the window every now and then. But the larger air bleeds carry more fuel thru the emulsion stack, at least that’s what I’ve found on my end. And I am by no means an expert.
Rat Bastid
Dunamis Metron
This comes up all the time. A bigger MAB will START the mains earlier. A smaller MAB will delay the start of the mains.
At low air flows the MAB is subject to very little pressure differential. So changing the MAB works the opposite of what most think.
If you want to delay the start of the mains, use a smaller MAB. It will be richer at higher air flows though.
IMO, most carbs have far too much MAB.
Thank you. So, I think my main issue is the stumble at about 2700-3000 regardless if under load (driving) or in park. Slowly opening the throttle, you can watch in the carbs and see it when it starts to stumble. Maybe I need to video what I am seeing. This is why I thought there may be a loss of signal on the carbs. Stab throttle from a rolling drive to WOT, it falls on its face, then recovers and pulls until I lift. Stab to 3/4 throttle and doesn't stumble at all. This seems like accelerator pump shot. These are 50cc center squirters. I changed one brown accelerator pump cam to upside down. This will give a large quick shot from one carb and a longer shot from the other. I can't drive the car due to winter, but it seemed to respond a bit when I was moving the car. Could I be losing signal on the boosters and making the air lazy when going to WOT? It seemed better when I had a much more restrictive air filter set up.
From the diagram above, restricting the MAB with a wire, should reduce the emulsion and possible straighten out the booster fuel during this erratic time, or am I thinking about this all wrong. I was reading what Tuner had to say about over emulsion and it seems it could possibly be as described. Am I way off here?
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That's not a bad idea. A data logger would be better and it will show you a lot more than you would think possible.
Here's a hint: The fuel from the Transfer Slot reacts much quicker to throttle movement than the pump shot.
I dont have access to a data logger. I am now thinking more about the emulsion issues caused by no transfer slot exposure. I changed everything back to as removed except the exposed transfer slot. Just to be back to square one. One change at a time. I measured all if the bleeds, see attached pics.
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Why? You can block the primary boosters with plasticine and then drive and tune on just the trasfer slot.
I was referring to the fact that the throttle blades were covering the transfer slots completely at idle. This would open exposure to the transfer slot late and expose the transfer slot to atmosphere while idling. I now have a square exposed. I am now concerned with idle speed once back together.
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When you run cams with lots of overlap you create an environment in the cylinder that's lean so it needs lots of initial timing so to counter that you can richen the idle mixture so that it runs more on the lighter fractions of the fuel and that will help dampen the reversion. Then you can less initial and lower the idle rpm.
Hey that's not the primary metering block that's on my 660s. And my blocks have a threaded port for ported vacuum.
They are the same. 5913 and 4224. Mine have a threaded hole for ported vacuum but it doesn't go anywhere. Not fully drilled to the port. Just drilled and tapped on the surface. Maybe yours was drilled, maybe you don't have vacuum advance...
Actually don't have the carbs mounted on anything and never have. Tried to work some 1850s and ended up with new 450s. My carbs have Ford secondary blocks from a 427 mid to hi rise intake. But decided not to run them as I'd read everywhere they are race carbs and not streetable and that's not what I want in my street car. Good luck. Following along.
Well, mine is 100% street right now. Car starts awesome and gets good mileage 12mpg average. I drove it to Mopars in the Park, 6hrs each way. Just need to tune the stumble going to WOT. Otherwise they are amazing
I think Quick Fuel sells metering blocks with all the restrictions changeable. You could try a power valve circuit.
Yes they do and I have used front metering blocks I could use, but as strange as it might sound, I don't want to change the carbs too far from what they are. If changing to front metering blocks, power valves, rear metering blocks, jets, ground secondary cams, etc. It seems I would be better off just getting carbs designed that way instead of turning them into something they aren't. No reinventing the wheel. I just want to tune out the stumble. I have no issues drilling and tapping bleed ports and making different size jets, if I knew more about the circuits. But beyond that, I would like to keep as stock as possible
I agree. I just figured since you have all the restriction sizes you can start by setting the block up as it is now and then start some stumble elimination changes one at a time!!!
inthe9s
New Member
Your idle speed is high because you are advancing the timing at idle by using the vacuum advance with manifold vacuum! Try this- set your idle speedscrews to expose the transfer slot(s) so they are square as they say, put themon the engine and fire it up and let it warm up, then measure your idle speed. Now pull that vacuum advance hose off and plug the hose temporarily, Your idle will go down.
Sorry for the lack of update here. I tried the square transfer slot setting with vacuum advance disconnected. It still idled at 3000. So, I turned it down to the appropriate idle speed. In discussions, it was determined that the fast mechanical ramp plus the manifold vacuum was too much. I removed the vacuum entirely. Just mechanical advance. 18⁰ ar idle and 36⁰ all in at 2200. I also added a 0.136 air bleed to each carb. All problems gone and got 11mpg on a 7hr cruise. It works amazing.
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