Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor
idle help
73ss:
I installed .039 idle tubes over the weekend. It made a small improvement. Now it responds to pulling off a small vacuum line to where it didn't before.
Question: Did all BB carbs have a .136 bypass or just the smogger units? My original '73 carb is at .136. Do any of you go this big on a BB carb? I'm currently at .125"
To re-cap, I started with 10" vacuum and am now up to 12, 850 rpm, But it still requires lots of timing lead. Its getting there in small steps. I'll have to put my carb tuning skills on hold (Or lack thereof) :D for a while until I get a fuel pressure issue solved. I'll start a new post for that rant.
Kenth:
I have found most if not all 1970-74 Chevy 454 units uses .138" idle bypass air.
73ss:
While trying to get this thing dialed in, I have found that the #2 plug turns black. I had convinced myself that the intake was not sealed properly and causing all of my issues. I pulled it off and took it to the machine shop, They said it was slightly bowed and took a small amount off. While I had it apart, I took the springs off on #2 to check for sticky guides or valves not sealing. I do not have leak down test equipment but the cylinder had what sounded like minimal leakage while filled with compressed air. everything checked out great. I tested the plug wires and they all ohmed out within spec, I decided to replace them anyhow since they are about 7 yrs old. Put it all back together and the same thing. Does not idle well and #2 turns black. Temp readings with a laser temperature gun show that # 2 is running about 250 degrees, the remaining 7 are all high 300's low 400's. I have read on line where the experts say that this is a irrelevant test at idle. The rest of the plugs look ok, some darker than others but #2 is turning black. It doesn't look like oil, the black easily flakes of the plug to where oil will be sticky. The engine hasn't used any oil. Buy comparison, #1 plug is white, looks like it is running lean if anything. Compression test is +- 3 psi across the board. Plugs actually look good after a good 10~15 mile run, but then #2 gets black with idling and in town driving.
I don't claim to be an expert but I've been doing this 25yrs and am stumped. I've never had a motor that has needed this much timing or fuel at idle. Could my intake be junk and just not sealing ? I would think it would suck oil from the bottom side if that were the case. Why would #2 appear to be getting all the fuel? One side of the carb dumping more fuel than the other and it's all running to #2? I have no nozzle drip at all. Any ideas?
Cliff Ruggles:
Did you replace the spark plug or move the one on the troubled cylinder to a different location?
Where is you PCV hooked up?
73ss:
Replaced the plug, PVC is on right valve cover connected to the correct port on front of baseplate. Stock aluminum gen 6 valve covers.
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