Yanking hard at idle???
Those are the cam specs. I can get it to idle 800ish, but the timing advance at that point (no vacuum) is approx. 30 degrees, which is crazy. I verified with a vacuum gauge and I had like 17hg there.
If I drop it down to 20 degrees with the vacuum disconnected, it gets choppy and drops significantly when put into gear. That's why I've been running manifold vacuum, to get me some advance in the canister.
I'll richen it up with the bleeds a little bit more and see where that gets me.
So here's the thing, and it fooled me too. Advancing the timing makes the rpm go up and run leaner, or seem to.
The catch? Its in NEUTRAL. The engine only needs to overcome the internal friction.
Putting it into Drive is like slipping the clutch; it not full load but its more than zero!
So now the question is why is this not working out with your combo?
Anything above 14" Hg should is pulling real hard on the idle circuit. Pay attention to the vac when put in Drive - that's what's important.
I'm going to assume you have a Holley 4150/60 type carb on there based on the mention of 'bleeds'.
So this is what A/J is talking about. On this type of carb, the fuel at idle comes out of two locations. Both are exposed to manifold vacuum.
Transfer slot.
Idle Port.
The transfer slot is also an air bleed. The portion of it above the throttle blade draws in air, and the portion below the blade blows out fuel mixed with air.
This makes the throttle blade's position at idle critical to both idle and off-idle performance.
Generally, the amount of transition slot showing below the primary throttle blades at idle must be between .020" and .040"
Take them outside that range and everything else gets messed up.
With the carb off the engine, count how many turns in the 'idle speed screw' it takes to open the primary blades to .020" and .040"
Write that down. Then you'll never have to take it off again to figure out whether its in the ballpark or not.
Now this assumes everything else is normal. Some guys over on RFS forum have posted finding some real crummy quality on new carbs, everything from metal shavings to emulsion bleeds not drilled. So at least occassionally there are issues that can't be seen from the outside.
My engine is not that different than yours and its idling just under 800 rpm (N), 740 rpm (D) with 17* initial using a Holley 750 cfm list 3310 frankencarb, and also was using '650' VS. With slightly more compression and better lobe seperation on your engine, it should require about the same timing as mine, probably less, certainly not a lot more.
I think I wrote this before but if not:
To carry load at idle the engine needs to be richer, and to fire that richer mixture so the maximum pressure is developed around 20* past TDC the timing needs to be around 10 to 20* Before TDC.
The closer you get it, the less rpm drop there will be when shifting into Drive.
Typical pre-emissions engines had idle AFRs in the 13:1 range. Only to reduce emissions did they move it up to 14.2:1. As mentioned in Chrysler's master tech booklets, this was a trade off on fuel economy at idle. Yup. That's right. Leaner at idle did not save fuel. RPMs had to be increased, taking more fuel - but hopefully less misfires. This combined with reduced initial timing put more heat in the chamber and also kept idle speed from getting too high (timing so late that pressure built up later than would be most efficient).
edit: bah. A/J had you covered - for some reason that post didn't show for me until now, or i wouldn't have typed all that.:rolleyes: LOL. :thumbsup:
