I finally got my new engine going the other night. Broke in the cam and am now trying to get it running. Everything is new and its way out of tune. It seems to idle best at 25+ initial timing. :? The balancer is lined up with TDC.

The setup is: 10.3:1 388, AFR 195, Demon 750DP, Comp XE 274, Crane Gold 1.6 rollers, Edelbrock RPM Air-Gap, Hooker 1 3/4 long tubes. I have a GM HEI distrbutor with Jacobs coil and wires, Accel cap and wires and NGK plugs.

Am I just pouring so mush fuel down it that the timing needs to be advanced to compensate? The cam supposedly likes 16* initial timing so I figured I can run that much initial and no vacuum adanace for now until I recurve the distribtuor. The carb is on there right out of the box. What do you guys figure?

Trevor

 

I'd set the timing for the proper total mechanical, adjust the amount of mechanical so I'd get the proper initial when I have the proper total and it doesn't kick back into the starter, and run the vacuum off manifold for good idle quality.

Most likely, there isn't enough mechanical advance in the distributor to get 34-36 degrees total mechanical and only have 16 degrees initial. That's typical with GM HEI's.

 

How hard is it to adjust the mechanical advance? Just changing out springs? Is it trial and error?

I had someone else recurve my distributor before. IIRC, it was 10* initial and 32* with mechanical. How much vacuum is there at WOT?

 

With mine i set it for total advance of 36* At 3000rpm and let the base fall where it may... around 14-16 degrees on mine. and make up the rest of the timing at idle with the vac addy, out of the manifold vac port like 5-7 said. works well on my vortec motor.

 

If the motor wants 25deg at idle then give it 25degs.

Total timing at high rpm should be 32 to 36deg.
You will have to restrict the amount of mechanical travel
in the mechanical advance. Not just change the springs and weights. (this only changes the rate of advance.)
You want 25deg initial with 36 total. So the mechanical advance has to be restricted to 11degrees of travel.
The advance should be all in by 3000-3500rpm and not advance further.
Vacuum advance has no effect at WOT. It is for part throttle cruising. Like on the hi-way.
A totally separate issue.
Plug the vacuum advance into "ported vacuum" on the carb.

Demon carbs have a idle air adjustment in the center of the carb. Remove the carb stud to adjust it.
May need adjustment to correct the idle speed when the throttles are in the optimum spot at idle
see their internet site for tuning info.

Use a 4.5" power valve with that cam.

Did you check for balancer/ timing tab accuracy (true TDC)? Notorious for being way off.
get a piston stop and check it first.

The extra timing at idle is needed because of the exhaust dilution of the airfuel mix at idle. Slows the fuelburn rate requiring more initial timing at idle.
The increased overlap and duration of the cam u have is what causes the exhaust dilution and rough idle.

 

Not trying to jump in on this post, but that's the same problem I've had since I installed my engine two weeks ago. Don't bother looking at the Demon site for info on the idle/air adjustment because I couldn't find it.

Same thing the shop told me, it just didn't want to start that way with the stock starter.

I'm running the same cam on my 400, and just the same, it seems to want to be timed at around 22-24 degrees initial in order to have anything resembling a semi-smooth idle. I'll be installing a high torque starter tomorrow.

Don't bother connecting a vacuum advance distributor to full manifold vacuum unless you intend not to use it. I've tried it and, for all intensive purposes from what I've seen, it just pulls the vacuum advance to full advance at idle, which really just deletes the vacuum advance altogether, and only the mechanical portion works when rpm is increased further.

More conflicting info....I've been a bit upset at how choppy and lopey the idle is, but others have told me that it should idle smoothly with this cam (XE274H)......No way I can get it to idle smooth. I'm willing to accept it if it's the cam that's causing it and not something else. BTW, my timing mark seems accurate.

Thx for the info F-BIRD'88 - I honestly didn't know about the adjustment under the carb stud....I'll try that myself!

 

Don't know whats "conflicting" about the info. It's true.
don't know what kind of "smooth idle" you're looking for,
but if you want it to idle like a Caddilac, get a stock cam.
Follow my advice and it will idle rock steady at a reasonable speed, won't burn your eyes out, or overheat, barf and spit when you step on the gas.
The idle will have a definate lope, but a steady lope.

Demon Idle Ez

 

Sorry. I think I didn't make it clear. You're not giving me conflicting info at all, but others have. Do I want it to idle like a Caddy?? H*ll no, and I didn't expect it to. Others told me it should idle smooth, and it's not like I've had previous motors with this cam installed so I took there word on it. So I've been looking for ANYTHING else that's causing it to be choppy.

So far as the adjustment under the carb air cleaner stud, even the manual doesn't mention it!! Or their "tuning tips". I did just find the link you attached, and sure enough - I'm supposed to have one of the "Idle eze" adjustments! Of course it's not in the manual, and mentions that it's standard on Speed Demons halfway down the page. I thought the stupid thing was an option I had to buy!

Can't wait to try it out! Great info! That's gotta be the reason it is'nt idling more smoothly! :hail:

 

My demon didn't come with Idle-EZ, i'm pretty sure you have to buy the special baseplate that is equipped with Idle-EZ.

 

From the website:

 

No problem, make your own. get a pepcock from an aquarium store ( pet store). T into the big vacuum source at the base of the carb ( PCV) adjust the opening of the pepcock to allow more or less air in at idle. This will allow you to adjust the idle spped while keeping the throttle blades in the optimum spot for best idle circuit performance. If you really want to be fancy install a inline
paper fuel filter to filter this auxillary idle air.

Be sure to remove the carb and reset the throttle blades first.
This will not replace the need to have the right amount of ignition advance at idle. But will do the same thing as drilling holes in the throttle blades for extra airflow.

 

clever

 

pick up an adjustable vacuum advance kit. they are like 25 bucks.

get your total timing right, and adjust the vacuum advance to give it the proper timing at idle so it'll smooth out.

i've got the XE274 in a 355, and pull better than 15" of vacuum,at dead idle gear..

restrict the vac advance to about 8-10 degrees hook it up manifold, and it'll smooth the idle out. and you won't need a super duper starter.

 

Well, good news on mine I hope....just got home and looked, and I do see a phillips head screw below the air cleaner stud. Hopefully the combination of the idle ease, and being able to advance my timing another 2* for an initial of 22* along with a high torque starter will help things. I'll know more tomorrow.

Trevor Jacek and scottland:

Don't know if this will help, but I called the Demon Tech rep on the phone last week, and he told me to remove all four A/F mixture screws and drill them out with a no. 48 drill bit to get rid of the pig rich choppy idle......

I suppose you end up doing the same thing as the idle-ease screw on the newer ones.

I was hesitant to do that to with mine brand new right out of the box, not to mention it might be a warranty issue....

But I think F-BIRD'88's idea is a spiffy one!

 

Pony Killer -

Is the purpose for doing that to kinda act like a timing retard just for starting? Not trying to be a wise*ss, just asking.

Guess that wouldn't work for mine with a mech. adv dist.....

 

If an engine wants a lot of ignition advance at idle in order to idle properly (and like F-BIRD'88 said, if it wants it, let it have it), the best way to get it is to use manifold vacuum. With the initial timing (set with no vacuum to the vacuum advance) in the 12-16 range, you won't be killing your starter. Then, when it starts up, you'll have the 25 or more degrees it wants to idle. That isn't a "start retard"; that's the way it was done until emissions controls came on the scene.

An adjustable vacuum advance doesn't restrict the amount of vacuum advance directly by the adjustment provided. What it adjusts is the amount of advance for a given vacuum. It's better to fabricate a mechanical "stop" if you want to restrict the total vacuum advance (there was a post about that about a year ago). I've never seen an engine that had too much vacuum advance at idle (they just seem to like it), but too much at part throttle is common - and why they came up with the adjustable vacuum can.

On my 396, I have 18 degrees initial, 40 total w/o vacuum (I wouldn't mind if the initial was slightly lower, but it isn't a big enough issue for me to take the distributor out to change that), and about 45 at idle w/vacuum. It idles much better than it did when I used ported vacuum, and manifold vacuum eliminated an off-idle flat spot when using ported vacuum that didn't want to go away with power valve tuning. And I don't get any part- or full-throttle pinging.