My son and I have built a 383 for our project ZZD but we cannot get the darn thing to idle. I was hoping someone could help us solve the problem.

Specifically the problem is this. When we try to set the idle anywhere below 1100 rpm the idle gets really erratic and lopes along for about 5 seconds then dies. It is so bad that we cannot even get to adjusting the mixture screws at idle because we cannot bring the rpm down low enough for the butterfly in the carb to cover the transition slot enough to draw fuel from the idle circuit.

Here are the basics of the build up

383 cubic inch (350 bored over with 400 crank and rods. Keith black pistons 5cc dome)

Heads are World Products SR's with 1.94 valves, Home ported intake runners are 185cc and compression chamber is 67cc's

Static compression is 11.5 to 1

CompCams XE284H-10 intake Exhaust
Duration at .050 240 246
Lobe lift .338 .340
Lobe separation 110
Gross lift .500 .510

intake is knock off of Air gap

carb 650 speed demon with idle eeze base plate.



That being said is it the Carb that is the problem or is there just too much duration on the cam to get a decent idle??

Please Help. If it is the Cam I am in big trouble cause there is no way I can convince my son to swap it out. He has a friend that runs the same cam and his car idles at about 900rpm.

Thanks
Ric

Rachet,

Start with a vacuum gauge and see what the reading is at idle and at 800 RPM. Please post the results and we will go from there.
Do you have an automatic or stick shift transmission?

Scholman

Vacuum is about 10 in HG at 800 rpm. but it is bouncy.

The Transmission is a stick shift.

Ric

I have the same cam. If you are trying to run vac. advance on your distributor this cam WILL NOT acuate the plunger( on an Accel anyway). I had to mechanically advance the distributor to about 28 btdc for it to idle, but of course it kicks back when you try to start it. My engine is a 355 and it will not idle anything below 1100 without wanting to die. I currently have it set at 18 btdc and it will sort of idle around 900 with some carb tweeking but still kicks back when you try to start it. In my opinion this cam needs a vac. advance for it to idle properly. Don't waste your time with adjustable vac. advance either, all you can adjust is how far the pliunger pulls in, not how hard it is to pull in. Let me know how you engine performs because mine sucks.

Are the boosters pulling over?, There's no reason why you should'nt get this thing to idle well in nuetral of with the proper stall converter. Cams twice that size idle at 1000rpm all day long. Try ignition advance at initial of 16/18, Open the secondary's so you can close the primary's to regain idle control. Then see what happens.

What kind of initial timing is on it????

Did you open the secondarys up at all????

Are you 100 percent sure there is no vacuum leak anyplace????

Keith

__________________
K-Star Automotive
Performance Engines
It's better to have a gun and not need it, then need a gun and not have it.

Ratchet,

With the engine running, place your hand/s over the carburator, allowing just a little air to get by your hand/s. This will cause the engine to run "rich" and if it revs-up then you have a vacuum leak. With the vacuum reading you state in your post I am sure your problem is in the fuel/air ratio area, either too rich or too lean, my money is on the too lean.
Let us know what happens with the restricted air flow test.

Scholman

I don't think the boosters are pulling over.

I don't understand the idea of opening the secondary's to regain idle control. I may have mislead you when I said Speed Demon Carb. The Carb is actually a MIGHTY Demon 650 cfm and it has idle screws at all 4 corners.

Ric

I just went through this with my 383, using the XE274. I had just changed the cam. It would idle at about 1100-1200, but efforts to get it below that caused it to bog and die. I checked the timing at 1100 rpm and it was about 20 degrees. It didn't want to run below that. I finally figured out my timing was coming in too quickly, so I changed to the medium centrifugal springs and it has appeared to solve the problem.

The idea behind opening the secondaries is to get some more idle air through the carb. Your adjustment screws will still work on all 4 corners, probably better. If you get the primaries to far open it effects the pull on the transfer slots causing a rich condition. Opening the secondaries will cure this.

Did you check you initial timing. If you initial timing is not 16 to 18 degrees this will aslo cause problems with the idle on the BG carbs.....

Keith

__________________
K-Star Automotive
Performance Engines
It's better to have a gun and not need it, then need a gun and not have it.

Start engine, loosen distributor and manually advance timing to 28 btdc, adjust carb, whalla, idles fine. It took me months to figure this out but for some reason this cam wants lots of advance at idle. I knw everyone will say that is not the case but if you actually are running this exact cam and have it idling without a vac canister at 900 rpm I would love to know how you did it.

run a vacuum canister, adjust your springs in your distributor, and get a true adjustable vacuum advance (the kind that let you adjust for vacuum signal, not amount of advance). the lean suggestion also holds water, with that cam I'd shoot for about 12:1 ratio at idle

Why 11.5:1 though? I mean I like compression, but that is a bit high- unless of coarse you got a LS1 or an LT1 or damn good aluminum heads.

Simplest way to check for a lean condition is to LEAVE the throttle alone, and bump the accelerator pump one or twice. Try it on the primary side and on the secondary side. It will tell you which circuit is lean.


Is the idleze screwed down? Try that first. (CLockwise to close it off)
Set the primary mixtures at 1t
secondaries at 1/2t

If that doesn't work
pull the carb, and verify your transfer slots on the secondaries at .020. Should look like a box when set right. they are .020 wide.
Be sure the secondaries can close all the way. They may need adjusting, side to side. You will only get them to loosen 1/2 turn MAX
Knock the throttle off the high speed cam, set your idle screw. Do this by unscrewing until it doesn't touch, then go in 1 turn.

Be sure that the secondaries are not getting hung up with the primaries when you give it gas.

The Demons are SUPPOSED to give you more HP, but in my opinion , are tougher to tune. Well, more sensitive.


Don @ 4secondsflat.com puts out a paper specifically for Demon tuning. I think it was $10.000 and he emails it to you, but the info was worth 10x that.



Jeff Parker

It was not the plan the plan was 10.9 or 11 to 1. we even got 5cc dome pistons to get us there. Everything was ready short block was assembled heads ported etc. etc. and then I decided to check the cc's in the chambers. heads were supposed to be 72 cc's but they were reconditioned prior to me purchasing them and yup they were shaved down and the actuall compression chambers measured 67cc's. We decided to put it together anyway and if we ran into a problem with detonation we would just take the heads off and open up the chambers to get back to 72cc's.

We can get sunoco 94 octane here and this cam has a huge amount of overlap and after calculating the running compression ratio vs. the static compression ratio we thought we might have a chance.

Ric

Ok I have heard everywhere from 16 to 28 degrees btdc. Is everyone talking apples or do we have a few oranges mixed in here. When people recommend 16-18 at idle are they talking about 16-18 with the vacuum canister disconnected or connected. I would assume that the 28 degrees you are recommending is with a vacuum canister hooked up pulling in about 18 degrees of crankshaft timing advance at idle. the other 10 degrees is right on the distributor at idle with the mechanical advance not active. that would mean that you only add another 8 to 10 degrees of timing with the mechanical advance as you increase the rpm. That would give a pretty flat advance curve that only ever gets to 36-38 degrees advance?

Ric