Just an Idle issue!!!!

[Chris Borson]

I have been playing with the idle tune on my rebuilt carb and am still not happy with the fact I have a bit more lope than I thought I would and the exhaust still smells a bit fat to me. Specs are as follows:

 455 Oldsmobile, dish piston, .030 overbore
Heads: "C" heads . OEM with 2.07 intake and 1.88 exhaust
Intake: Edelbrock Torker
Carburetor-number: 17081287

Cam Specs: Comp Hydraulic flat tappet Comp XE274H
.520/.523 lift
230 / 236 @ .050
110 lobe separation

down channel .048
Upper AB .070
Lower AB .070
Idle tube .039
idle air bypass was .090 but just enlarged to .104
73 jets with Cliff's 44 rods

I am getting 12-14 inches of vacuum at 700 rpm in park. I need to run 20 degrees of initial timing to keep it the smoothest. if I go up or down more than 4 degrees it idles more rough. when I did the tip in test rpm dropped when I tipped choke flap and came up a bit when I pulled a vacuum line so it seems bit rich. I tightened APT down to lower rods in jets. Everything else is awesome, nice response, transition, secondary operation. I remember speaking with Cliff about this cam being a turd. Is this my issue? Should I try and lean it out a bit? oh. throttle blade is not uncovering slot, idle screw is one turn after just touching.

Any advice is appreciated!

Thanks,
Chris.

[Frank400]

Cliff will probably tell you so, but I'm quite sure idle down restriction is too small at .048 with such a cam.  I would go at .052 at least, if not .055. 

    That may affect (richen up a bit) your part throttle so you may have to play again with the APT after that.

[Chris Borson]

Thanks Frank. Think APT adjustment is all the way down. If i open the down restriction will it not just get richer?

[carmantx]

Check your primary nozzles during idle to see if you have fuel dripping causing it to be Rich.

[Frank400]

Yes it will get richer which I think it needs with that camshaft.

[77cruiser]

Too lean gives eye burning stinky exhaust. The cam I have in my SBC  gives 12" vac. it's not too stinky, just a bit.

[Cliff Ruggles]

Never a fan of those cams in 455 builds, Pontiac or Olds.  They idle like chit, noticeable reversion, stinky exhaust, and don't make nearly the power as a longer seat timing cam will on a wider LSA.

I tried them when they first cam out, and never went that direction again.  They will require a lot of timing and fuel at idle to make things happy, and still we get gobs of complaints from folks using them about crappy idle quality and noisy valve train.

I've tuned a number of Olds engines with XE grinds in them here and they all act the same way as yours but even with that said I was able to eventually throw enough fuel at them to get rid of the stinky exhaust and make they relatively happy at idle speed........Cliff