Idle Problem On New Engine

[AMXguy]

OK I give up. this is the 3rd engine I've built to the same excact specs and others have been wonderful.

 I have a 440 six pack, six pac cam, 10.1 compression, mopar performance electronic ignition EVERYTHING is brand new and untuned .

 I started it up to break it in and it poped a few times buy took off and right away I put it to 2100 rpm and set the timing to 38 degrees. I ran it for a half hour and all looks perfect, it seems to run a little nervous , not as smooth as it should. vacuum at 2100 is 17 inches. so I bring it down to set the fuel mix and check the initial timing and it wants to die. if I take the timing below 25 or the idle below 1100 it stumbles around and dies.

 If I rev it up hard it responds very nice, run it up to 3000 or so and close the throttle and vacuum climbs to about 22 I think. I can tell how it kicks the started initial is a little high but anything less won't cut it. on break in I checked all the exhaust ports and they ran from 550 to 900 degrees. since it won't idle I messed with the mixture and richer is definetly better but I can't cure it with that, and it won't idle down low enough to know for sure.

 My thoughts are a vacuum leak or could my adjustable rockers be a little loose? I can hear a slight top end noise but not bad. I jetted down one size and went on size less on the power valve just as I did on my last build, could it be too lean? I see no soot in the exhaust tips.  I really really can't imagine a leak but I'm stumped. any and all ideas welcome.

[barracuda7199]

sounds like a vacuum leak thats a big swing in exhaust temps. i would double check the carbs vacuum ports then check the intake gaskets give the bolts a another pull see what that does.

[AMXguy]

I pulled all the easy plugs and #4 was a little dark, #2 was off white and the others were light chocolate, I'm not sure if that means anything or not on a break in.

 I did turn the outboard carbs down to just 1/2 turn open on the idle mix, it seems they're always too rich but is there any chance that could be a problem?

 I used one fiber gasket on top of a new valley pan, everything seemed to fit well. everything is tight. I know the intake could be leaking but I find it hard to imagine as well as it went on.

[Chryco Psycho]

it could be that the vacuum is too low to keep the power valve closed |& is flooding at low RPM or the power valve could just be bad

[AMXguy]

The idle vaccum on the others was around 12 inches, so I put a 5-6 power valve in. all new carbs too.  it did pop back a few times on start up but the new carbs are protected right? if I let it get below 1000 rmp the vacuum drops to zilch, of course the engine is in the process of dying at that point.

 Is the white plug a sign of anything? I've never checked them until I drove a while.

 

[Chryco Psycho]

white plugs are too lean , you need to increase the jetting
you also may needs smaller air bleeds to get it too idle properly , wire can be inseeted into the air bleeds to help it idle

[AMXguy]

But how can you explain only some plugs being white? even though I doubt it could that mean a vacuum leak? I have the jetting excatly the same as my other engine which is a twin, while I know that doesn't mean it's perfect for this engine I can't imagine it being way off.

Since I can't get it to run decent below 1300 rpm I'm wondering how to check for a vauum leak, would the starting fluid method even work at that speed?

[Chryco Psycho]

if you have a dual plane intake & 1-7-4-6 or 3-5-2-8 are all white then one side of the carb is not working correctly

[AMXguy]

No, # 4 is dark brown and #2 is white.

 Maybe I'll pull the distributor and ECU off my Challenger and eliminate them as the problem. I have a feeling it's in the induction side of things but the fact I need 20 degrees of timing to keep it running at all makes me wonder.

[AMXguy]

I swapped dizzy and ECU with my Challenger and no change.

It almost has to be carburation or a vac leak. I did notice when I got it idles down to about 110 which is as low as it would run for a bit there was a little backfiring going on. nothing serious but you could hear blooping out the tailpipe.

 since the carbs are all new and jetted with a proven setting I'm at a loss as to the next move. I'd just hire someone to figure it out but nobody around here is anymore savy than myslef on this kind of set up.

[AMXguy]

OK it seems the problem is a vac leak under the right side of the intake, I'll move this to another thread.