440 vacuum at idle

[jakebondFL]

I am trying to nail down a backfire problem when I floor it from idle. One of the areas I am currently looking at is maybe a vacuum leak. But how much idle vacuum should I be looking at? I have an Edelbrock Torker II single plain manifold, slightly larger cam (.484 lift), and with all my vacuum hoses discoed and plugged I am running 10" Hg at idle (1000 rpm's). The factory service manual from 1971 doesn't list any sort of standard manifold vacuum at idle for a 440. Most sources say that 16" to 22" Hg at idle is the norm, but with a single plane intake and larger lift cam maybe less is the norm??? I dunno. Thinking about replacing intake gaskets to see what that does for me. I have already swapped out carb gaskets. So what I am seeking is maybe a census on what most folks are getting for manifold vacuum at idle on their 440. If 10" Hg at idle is all I am gonna see, maybe I need to start looking elsewhere to fix my backfire problem??

Also, I am running 36 degrees mechanical advance at 2500+ rpms (aboot 12 degrees advance at idle).

[1bluegtx]

Sounds like a carb problem to me.Possibly a vacuum leak.Might try backing the initial advance down a little.The cam in my engine produces an erratic 9" of vacuum at idle.

BRIAN

[Elvad]

Hey Jake its Elvad. 36 degrees is a lot for a pump gas street motor, even if it doesn't ping. Don't forget to try 34 and 32. That may help, otherwise i would look toward an accelerator pump problem. The accelerator pump is only a thin rubber gasket. Look for a steady flow/squirt when you look down the carb(engine off, of course) with no interruption in flow it should be steady stream from idle to WOT with no air or squishy noise. If the car sits a lot, they will dry out. The vacuum reading you have seems about right. Listen for leaks of course, power brakes will go stiff with vac problems. I'm thinkin the accelerator pump(s) dried out. The distributor vacuum advance should only be attached to a manifold vacuum source or not at all(not sure? disconnect it). Seeya, Elvad

[jakebondFL]

I have tried everything timing from 32 on up to 38 @ 2500 + rpms. I have adjusted the accelerator pump arm (I have an Eddy 800 carb), and that didn't do jack. The accelerator pump squirts the way it should. This carburetor was brand new out of the box when it was first installed and barely driven or run since, so I gave up on dinking with the carb. So I hooked up a vacuum gauge and readjusted timing (this time at idle) and adjusted the distributor for best manifold vacuum. Of course the better vacuum readings come at higher RPM's with more advance in timing. Duh, the engine makes more vacuum with increased engine speed (until WOT) So then you adjust the idle back down and then you are back at the same vac reading as when you started but then with more advance in timing. I dunno, this crap makes no sense. Here's the kicker: when I adjusted the timing for best vacuum, my timing ends up to be at 18 degrees advance. No pinging! So I figured I would see how well it works in gear. I tried some power brake loads on the motor and no more cough. None. I put it back in neutral and I try slapping the throttle like a bad step child and I got no cough or backfire whatsoever. The motor just RESPONDS! So I strap in and go for a ride and make some hard pulls on the motor from a standstill and from idling at cruise, this thing pulls like a son of a gun now! I think some larger jets in the carb to fix a small lean spot and this thing will be good to go. I have my vacuum advance hooked up to manifold vacuum, not sure if it is really doing anything for me at this point. So, either 18 degrees advance is what this motor wants (I have read other blogs on the net and 18 or 20 degrees initial doesn't seem to be rare depending on the combination) or my timing tab on my motor is jacked and who knows what the hell I have for intital advance. Whatever, I have learned some things since messing with this mill and the two biggest things I can walk away with now are:
1) The 440 runs like a monster on meth (the way I was told they can run) so I am happy
2) Carburetor fires are fun the first time or two , but not so much after that
3) Fire extinguishers are only good for one shot
I'll post more when I find out more, but ciao for now.

[Elvad]

Timing for best vacuum at idle was a suggestion I was going to make. Hmm, it runs great? I will shut up now. Still one thing, manifold vacuum should be highest with the butterflys closed(at idle) and never go up with rpm (that would be a ported source) Anyhoo, runnin' mint? don't f*** with it. One thing that took me a really long time was to not mess with too many things at once.( I still do it ) You go to the track and pull a 14.5@99mph and you know the car is faster than that so you change the timing, change the float level. change the mixture, change the tire pressure and the next run is a 14.0@100mph. So what helped?? You have no clue 'cause you messed with too many things.Your doing the right thing going slow and being systematic. Do you know anyone who owns a small airplane? A few gallons of 100LoLead AVGAS mixed with a tank of pump gas never hurt anybody just don't say its for a car(no road tax on AVGAS) Bring your blue gas cans to the local small air port and say its for your buddys Piper Cub you just put together. All you need is a tail number like..N440RB.. Or go to you local Sunoco station that sells Cam 2 and for about $45.00 you can fill a 5 gallon can. Glad she's runnin good now.

[jakebondFL]

Thanks for the input, Elvad. As far as I know the vacuum source I am hooked up to is manifold (the driver's side port on the Eddy carb), at least that's what Edelbrock says. Maybe I'm wrong. I'll double check that, though. I don't plan on keeping the Eddy carb on there forever, though. I have an older Holley 3310 that I plan on throwing on there....And no, I don't know anyone who flies private (or can afford to anyway) but I do work around a lot of stuff that uses JP-8, will light your hair on fire, and rattle your fillings loose, though.

[moparite]

Why do you have the vacuum advance hooked up to manifold vacuum? You will get the most vac at closed throttle. This is the opposite of what should be going to the vac advance. I am not familiar with Edelbrock carbs but there should be a port somewhere for the vac advance. You might want to put on the Holley and get it dialed in and then swap it over. I like Holleys myself. They've been making carbs forever and never had a problem with them.