mopowers
Well-Known Member
^^^THIS^^^
How long does that take? 1 minute? Even I, me, the old beat up arthritic guy, can do that in a couple of minutes.
Wow, it must be beer thirty. That was a total brain fart on my part.
^^^THIS^^^
How long does that take? 1 minute? Even I, me, the old beat up arthritic guy, can do that in a couple of minutes.
^^^THIS^^^
How long does that take? 1 minute? Even I, me, the old beat up arthritic guy, can do that in a couple of minutes.
Mechanical advance sticking? Quick way to tell? Easy. Remove the cap and "spring" the rotor against the advance spring, clockwise. it should "snap" back with no delay, nice and free
Vacuum leak? I have no idea.........I'd be checking for that.
Carb float level? Is the carb "puking" fuel, that is visible droplets from the boosters? Usually this results in a "bacon popping sound" as the fuel drops down the carb. Cannot always hear this with a loud engine, or with exhaust leaks. LOOK down the throats when idling
WHAT do the idle screws do? Unscrewing them "more" have any effect? Do they have any effect at all?
Sometimes "really wild cams" do need more air. Holleys generally, have a sort of unobtrusive set screw that effectively adjusts "secondary idle," for lack of a better term. You can set that screw up a little more. to allow some air in the back barrels. This allows the fronts to close back down into the transition slots "Back in" the day, we used to sometimes drill the butterflies
I don't normally advocate connecting the vacuum advance to a manifold source, but in your case (lumpy cam) it might help. It won't cost anything to try it out anyhow.
Also, don't get too hung up on the timing number until you've verified your timing mark with a piston stop. The best selling product in the Mopar Performance catalog was timing tape for a reason.
In neutral, there's no load, so you can keep adding timing and the engine loves it. You can then lean it to match and the engine loves that too. Then you put it gear and it goes - Ugh, the load is killing me. It has no power when set that way.
Try setting the timing around 16 to 18. Then, using your vacuum gage, adjust the fine idle fuel mix for best vacuum. or best rpm if you don't have a vac gage. On an automatic, in theory set fuel mix for best vacuum in gear. In real world, it's easier to set in neutral, then richen it about 1/8 turn and check it in gear.
Since there's a bunch of unknowns in the engine, especially the cam, you'll probably have to experiment with a different initial timing and see which has the least drop in rpm as you go into gear.
I do agree that it if the timing is changing with rpm, that makes it a little more difficult. You can figure this out by with a timing light and tach. Start as low as it the engine will go and the measure timing 100 or 200 rpm. Personally I like to chart the curve out all the way until it starts advancing.
The other issue you may be fighting is the throttle positions. As you open the throttle you not only add air but you feed in more fuel from the idle circuit. How did that happen? Because the throttle blade moves up the transition slot. The idle circuit feeds both the transitition slot and the idle hole. Once the throttle is too far open, there's not enough transition slot left to help the off idle. So it is very important when adjusting idle speed not to let much more or less than .020-.035" of the transition slot showing beneath the primary throttle blades. This is explained with diagrams in Urich and Fisher's Holley Carburetors and Manifolds.
Personally, I've found its worth the time and trouble to take the carb off and set the transition slots so they look square. At the same time, I take note of how many 1/4 turns of the idle speed screw from not touching to .040" of the slots are showing. That way I'll know later on if I'm getting out of range. The purpose of drilling holes in the blades is to get the throttle blades back in position. Cracking the secondary blades a little does about the same thing. This also explained in Urich and Fisher's book.
Recap: Establish what rpm the timing starts to mechanically advance.
Set/check the fuel level as someone else mentioned.
Set the throttle blades so the transistion slots look 'square'
Try adjusting for best POWER at idle using initial timing around 18 degrees, then again say 16 and 20.
PS. You can get by with a light advance spring in the dizzy. It means you have to be willing to tweak the timing back to your initial every time the rpm changes until you get where you want. Advantage is easy starting and one less project. Disadvantage is its another variable to deal with while tuning, and the idle may wander a little more than if it had stronger or shorter spring (or shorter slot).
While you have the carb off, double check that the base gasket matches both the manifold and carb, with lots of overlap, - some manifold/gskt combos expose a small leak at the secondaries.. and when running, with vacuum, opens it more..
I have about 8.5-9 inches of vacuum in neutral, which drops down to about 6-6.5 in gear. If the engine is cold it drops even more. I installed a 4.5 power valve to be safe. With your stock convertor you could be pulling it down even further. Might want to try a bit smaller PV.
Can anyone explain the 'popping' out of the carb as I bring the RPMs up?? Is this caused by a lean condition, or a rich one? Too much overlap?
I always thought engines did this when they didn't have enough timing advance. That's definitely not the case here.
Sounds like its igniting before the intake valve shuts. Almost certainly the immediate cause is timing too advanced.
I'm all for measuring timing rpm relationship before opening up the dizzy. The springs effect the rest of the curve too, so I like to reduce the number of times I have to open up and modify. If your engine likes a quick curve, then filling in the inside end of the slot is the better way to get the initial. Just my preference. There's lots of ways to skin that cat.
Torque converter 'tightness' should have little impact at idle speeds and such low torque. The 'stall speed' goes down with less torque applied.
Power Valve has no impact on idle in most cases. The primary restriction for the fuel is the Idle Feed Restriction. It is usually much smaller than the main jets. When the area of the upstream restrictions are 4 times larger than the IFR it really doesn't matter if upstream flow is increased.
The 'square' transition slot is just an easy starting point. The best opening will vary a little depending on slot width, idle feed and air bleed restrictions, and engine.
Hysteric - Thanks for sharing your experience with that. Very interesting.
I agree with your explanation about the impact of exhaust gas dilution. In addition, my opening paragraph is true even for stock cams. In neutral, power to overcome internal friction, the alternator and the water pump is all that is needed. Lower power conditions allow for leaner mixes, which go hand in hand with more advance for the reason you explained. But it isn't enough power to do anything else. When I was just learning to tinker with cars, I had stock 6 cylinders and its the same deal (except I didn't understand why it would seem better with more and more advance in idle and leaned out, and then lousy when put in gear). Not 'til Shrinker explained it on the old Innovate forum did I really understand.
It's interesting how only a couple people suggested the convertor's to tight...
The only other thing is make sure you have no vacuum leaks around the intake if the heads have been milled or the block decked the intake gasket may not be sealing real good. one easy way to check that is pull the pcv valve out of the valve cover and get a propane cylinder with a torch head on it and some rubber hose put the hose in the valve cover and turn the gas on if the rpm's go up you have a vacuum leak do both sides of the engine just use the oil filler cap or breather hose on the other side. Good Luck