Rebuilt Carb

[gikent]

I just installed a Cliff's rebuilt carb that was done a couple of years ago. I am trying to dial it in but have a miss at just off idle up until 1/2 - 3/4 throttle. WOT is great. Idle is fine also. I have tried to adjust the APT throughout a wide range but cannot get it smooth.

[Cliff Ruggles]

Need more info.  Carburetor number, what is was set up for, and what you are using it on?.....Cliff

[gikent]

Cliff, it is a 17057274 rebuilt for and used on a 455, 9.0 compression with XE262 cam. No porting on the 6X heads. Cast Iron intake. 2004r trans with a 3.42 rear.  Stock convertor, Idles with a 11 in vacuum in drive. All this in a 1969 Firebird.

Thanks
Guy

[Frank400]

11 inches of vacuum seems kind of low for such a small camshaft.  Are you sure there isn't a vacuum leak somewhere ?

[gikent]

That was what I was thinking also. I did the propane check and did not get any change in idle speed. I an going to check again this weekend. I will also check the brake booster, but it is new.

Thanks
Guy

[Cliff Ruggles]

Not nearly enough cam for a 455 engine with that much compression.  It's not going to run well, and may have detonation problems.  Seat to seat timing is too short, and LSA too tight.  The long stroke 455 will buck and kick in protest.

I've had two customers recently try to tune 455's that were built with later model 400 heads, just over 9 to 1 compression, and that cam.  Both absolutely HATE it, and can't get them to run well, and all sorts of tuning "issues", etc.

Even with that said, a steady miss could be a plug, plug wire, vacuum leak, incorrectly adjusted valve, or lobe gone off the camshaft......Cliff

[gikent]

All plugs, wires, etc. are new but I will check all these things out this weekend. What cam and lifters would you recommend for a street only combo. I don't mind spending a few more $ to get it right.

[Cliff Ruggles]

At 9 to 1 compression the Crower 60243 or Summit 2802 would be a good choice.  I would run high ratio rockers on them if the heads are set up for them?  At 9.5 to 10 to 1 compression I like the Crower 60919 cam with Rhoad's lifters and high ratio rocker arms.  It's good for at least 1hp per cid, good idle qualities and strong/broad power curve......Cliff

http://www.highperformancepontiac.com/tech/0501pon_kre_aluminum_heads_dyno_results/

[gikent]

Worked on it this weekend. No vacuum leak. But tried a new vacuum gauge and the old one was reading 3" low, so it was about 15" in drive. Also put a gauge on the fuel inlet and it was above 9lbs. Put on a regulator and it runs like a top now. No part throttle missing. Plenty of power for me in a street machine. Thanks ...Guy