Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

carb adjustments

<< < (2/3) > >>

Cliff Ruggles:
For that cam in a 455 with 9.5 to 1 compression, you will need to be on the upper end of recipe #3.  What size idle tubes, idle DCR's, and bypass air are you using now.  What metering rods are teamed up with the 73 main jets?  Which power piston spring?....Cliff

Paul:
Cliff,
 The idle tubes are .38, the idle down channel is .060, the idle DCR's are .093, ( if You are referring to the idle screw holes in the base of the carb ) idle bypass is .90, upper idle air bleed (main body) is.070, lower idle air bleed .070, accelerator discharge holes is .028, main air bleed (main body) .070, primary jets 73, primary metering rods are Your rods #44, fuel inlet seat is .135 (yours) im using the orange power piston spring ( lightest one ) I purchased one of Your rebuild kits when I did the carb. Thank You,

Paul

Cliff Ruggles:
I'd try to tune out the slight off idle stumble with the APT, if you have plenty of idle fuel and full control with the mixture screws.....Cliff

Paul:
Ok thank You. With the above mentioned specs, should I still tune the carb to the high side of recipe 3?

Paul

Cliff Ruggles:
In any and all cases you have to tune the carb for the engine.  The XE284 cam acts pretty big in a 455 engine at 9.5 to 1 compression.   Due to the very fast opening/closing ramps and tight LSA, they also induce a "quirky" idle for lack of better terminology.  I've tuned at least half a dozen 455's here using that cam, and I do NOT like it.  The cam is big enough for the XE line to make decent power, but why should one have to deal with crappy idle quality.  Those cams actually set the valves down so fast they will bounce on the seats, which is why (IMHO) they idle poorly.

In any case, the exact position of the camshaft (ICL), and ignition timing at idle play a huge role here.  In any and all cases, you have to continue to add idle fuel until the engine gets what it wants.  This may include idle bypass air as well to prevent nozzle drip.

The specs that you provided are close, might want to try .039 or even .040" idle tubes, and .110" idle bypass air to see if it helps out some.  DCR's at .060" should be enough......Cliff

Navigation

[0] Message Index

[#] Next page

[*] Previous page