I dont think blue had this problem until he changed carbs for the show?Hmmmm?

I just thought it was the lope of the cam changing the Idle back and forth. making the Vacuum run up and down..there for the timing differance? Huh?

And he was just a little loose in the springs in the dizzy?

 

OK. I'll try to hit on the last several posts since I just got home from a Beach Boys concert (Which was great by the way. Mike Love had everyone dancing in there seats and singing along. Even my wife and me.)

BB: Well, from everything you've described the problem seems to be pointing to the vacuum advance so that's where I'd focus on for now. Do you have a vacuum gauge? See if there's vacuum on the hose when it's idleing.

Yes I do. I have not checked that. But there is a sight surge in manifold vacuum that corresponds to the timing shift. Dizzy is hooked to timed vacuum.

Also, do you still have the original ground strap installed? It's that braided wire with ring-lug connectors.

Yes, it is installed.

Ratsmoker: Maybe there is a vacuum leak in the hose to the advace pot? A vacuum guage like Barry said can tell you a lot of things. If the needle isn't steady there is a leak somewheres.

Nope. There was a funny looking crease in the vacuum line, so I replaced it today. Made no difference.

Beemer Nut: bluesky636, is the vaccum unit like chebby with only a allen wrench to adjust?
I favor and still run the old style advance unit, removeable end nipple to change shims and plunger. I rat packed new ones years ago. You can adjust at what inches to start, full at inches and how many degrees total. Install a vacuum gauge, lower the idle, note when the carb starts vacuum to the dizzy, what's the increase in rpm? Have you adjusted the vacuum unit? Whats your centrifugal curve, same with vacuum ( use a hand vacuum pump)? After you do this it's the carbs turn ot tune. Fun ain't it. Go out and test. Carl........

I don't know. Does a stock Ford distributer have an adjustable vacuum advance? I have to look that one up in the service manual.

Dino @his Dad's: How old is the dizzy in this engine ? If the bushings in the distributor are worn badly, it can make the timing do some weird stuff. DF, @ his Dad's

The dizzy is a brand new remanufactured unit. I think we can rule this one out.

Rapid Russ:I dont think blue had this problem until he changed carbs for the show?Hmmmm?

I just thought it was the lope of the cam changing the Idle back and forth. making the Vacuum run up and down..there for the timing differance? Huh?

And he was just a little loose in the springs in the dizzy?

No. The original Autolite 4100 did it too. I am probably more sensitive to it now because of the new carb. Also, I think the Demon is more sensitive to these things as I am having a heck of a time getting it to run right at idle. Runs way to rich at idle. I need to pull it off, readjust the idle transfer slot and start over. But that is another, though probably related, problem. Someone else suggested the lope of the cam changing the idle and vacuum. I get about 13 +/- 1 inches of manifold vacuum at idle. The flucuations in the vacuum seem to correspond to the fluctuations in the timing. Could this be the problem or is it a fact of life with my cam (see orginal post for cam specs)? Don't know about loose springs in the dizzy. How do I check that?

Well, I think I got everyone. Any other ideas/suggestions? I'm about out of them.

 

Well, to me its only common since with a lopy cam the vacuum is going to very..but its 1;am EST..I get to have 4hrs sleep..before I do it all over again..I'll sleep on it?? Ouchhhh that dam air cleaner stud hurt!! anyway, Tomarrow!!

Russ

 

Yeah, what I'm guessing is the throttle is open too much to make it idle and you're getting ported vacuum to the dizzy every now and then. I'd put a vacuum gauge and see what's coming out of the ported vacuum at idle. If you are getting some then your throttle is open too far. Plus your mixture screws won't have a lot of adjustment at that point. I'm not familiar with that carb. but if the engine is asking for more air, can you crack open the secondary stop? Then you should be able to back off on the idle speed screw and get back into the idle circuit.

Another thing, I've noticed that some of these remanufactured distributors have vacuum units that come on too strong, especially for a truck.

 

I'm beginning to think that my timing/vacuum problems are related to the overly rich idle I am having with the Demon carb. It spits black soot on cold start, and I can't get it lean enough. I think the idle speed screw is all messed up. Next weekend I am going to pull it off, make sure the baseplate is tight, and reset the idle mixture and idle speed screws to factory settings and start all over. The thing runs like gangbusters once it clears its throat(s)!

Well Russ, its now 1:22 AM EST and I am going to bed!

 

i would think that your idles too high which causes the vacum to open and close can you drop it 100rpm or does that just make it too lopey?i had the same sort of problem with my prior jetting. when i stepped up two sizes on the mians it stopped but i had to incress the idle speed due to overrichness which caused it again. i ended up chasing it for months before stepping down on jet size and useing my idles screws to make up for it which makes for VERY hard warm starts and poor milage but it runs great :P. good luck.

 

This might not make sense but i just did this last week on my friends 390. He had a new distributer and a holley carb and It was timed but you could hear something in the idle and it just wasnt right to me. He had his vaccume advance hooked up to the carb like some people do I just swapped it over to the manifold and plugged the carb and the idle smoothed out and it gained a little power. It's almost like the carb was giving it a strange advance. He has a cam just like yours and I may be off but its worth a try for the amount of work involved.

 

Well, tonight I pulled my carburetor and checked the setting of the primary idle transfer slots. With all the twiddling I have been doing on the carb, the slots were 2 to 3 times as long as they are supposed to be. This would account for the high idle and the fact that I could never reach the idle peak/drop when adjusting the mixture screws. The carb is running WAY too rich at idle (it is great off-idle). So I reset the throttle blades which put the idle transfer slots to where they are supposed to be (secondary transfer slots have never been touched and were right on spec) and returned the idle mixture screws to 1.5 turns from full in. I reinstalled everything except ran out of time to hook up the fuel line. I will try and do that tomorrow and if time permits, fire her up and see if I can set the mixture screws properly.

I am beginning to think that the rich mixture/high idle is messing up the vacuum and thus throwing the vacuum advance off (Timing is solid with vacuum advance disconnected and plugged at carb. Idle is smoother also.). I tried hooking up to manifold vacuum as has been suggested but the results were no better.

I also noticed after adjusting the throttle blades/idle transfer slots that while checking out the linkage operation, the choke and fast idle activated which they never did before. Should be interesting when I fire her up again. I'm hoping that this is the cause/cure of all my idle/timing problems. I will let everyone know in the next few days. Thanks for all your suggestions.

 

Bluesky636, the few times that i've helped friends running Demon carbs, the idle was rich and was corrected by reaming the idle air bleeds. This is with tapered clock tool reamers in a pin vice and measuring equal depth per bleed.
Talk with Demon, "they are jerks after they get your money". Old school, can't go too wrong with Holley. And they say it's fun to tune. $.02. Carl....
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