Carb adjustment help
- Thread starter Wageslave
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Understood. We are bracing for a blizzard here. That manifold is close to stock and the cam is mild so that is not the problem.
I would start by adjusting yer accelerator pump shot. Is the rod in the middle or the lowest or highest position?
The snow stopped for a little bit before I left for work, so I took a quick trip around the block. I switched the distributor to ported vacuum and did notice a lot better take-off from a stop and my idle dropped from 650 to about 450. My vacuum did not change any though, still about 14.
The rpm drop is because with the advance hooked to manifod vacuum, you had maximum advance at idle.What is your crankshaft timing? I'm not a Chevy guy so I don't know what the initial timing should be for that particular motor. But since the cam and intake are not radical I would start with the proper stock timing and raise the idle rpm to what it should be. I'll bet your vacuum gets better.
Just make sure that the vacuum advance is disconnected and the idle is as low as you can go when you set the timing. On motors where it is particularly hard to set the timing I do this: I pull all the spark plugs and ground the plug wires to the motor. Then I hook my inductive pickup timing light to #1 and set the timing while a friend cranks the motor. That way the motor turns very slowly and there is no advance interference. You get rock solid basic crankshaft timing. Once that is done you can proceed with tuning the motor for best idle and vacuum signal.
Holy crap, vacuum mystery solved. I went to check my secondary opening and accelerator pump and found that my secondary butterfly's are stuck at about 1/4 open. They move just a little when I manually try to move them but not much. I think what happened is when I put the new intake on, I took the carb spacer off that was attatched to the old intake and did not reuse it. So now something is probably hitting the butterflies from underneath.
I guess the carb is coming off this weekend...
I guess the carb is coming off this weekend...
Success...sort of. I got the thing into the garage and rechecked everything. Pulled carb off, as soon as I loosened the passenger rear bolt the secondary freed up. Must have overtorqued it. Changed fuel filter to clear one. Pulled plugs and checked condition, basically looked like new after 4000 miles (not even tan, bright white). Tried to adjust timing with distributor and the vacuum advance can was right against the intake at best vacuum(16-18) so I pulled all the wires and spun it clockwise and put all the plugs back on one position over. Reset the timing to 12 degrees BTDC. Hooked vacuum advance to manifold (not going to chance overheating at idle with thin vortec castings). Changed accelerator pump rod from top hole to middle hole. Reset idle screws to 1.5 turns out (tried 2 turns and it dieseled when I shut it off) and reset the idle to 700 rpm.
I can wing the throttle from idle and she picks right up. As I was tuning it I did hear it ping for the first time, but I currently have some crappy gas that I need to burn out of it before it gets locked down for good. It will back it off to 10 degrees if I hear the slightest hint of pinging on the next tank.
On the upside, it really rips now and will break loose at 15 mph or less if you mash it. Idle is a little better as well. It did have a slight flat spot if you suddenly give it about 50% throttle, but I only got it to happen once and again could be the old gas.
Thank you to everyone for your help. It runs nice enough now to put off my dreams of a dual quad intake with twin TBI's and a Megasquirt 2 to run them all.
I can wing the throttle from idle and she picks right up. As I was tuning it I did hear it ping for the first time, but I currently have some crappy gas that I need to burn out of it before it gets locked down for good. It will back it off to 10 degrees if I hear the slightest hint of pinging on the next tank.
On the upside, it really rips now and will break loose at 15 mph or less if you mash it. Idle is a little better as well. It did have a slight flat spot if you suddenly give it about 50% throttle, but I only got it to happen once and again could be the old gas.
Thank you to everyone for your help. It runs nice enough now to put off my dreams of a dual quad intake with twin TBI's and a Megasquirt 2 to run them all.
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