need carb tuning advice
Thread Starter
Drifting
Joined: Jun 2000
Posts: 1,476
Likes: 1
From: Mt Juliet TN
need carb tuning advice
I still haven't gotten to take this car for a ride after the cam swap
I can't get it to idle. I have the same carb I used before the cam swap the idle worked just fine on it. Heres what I did: I let the car warm up. Set the timing and then set the idle @ 800. But when I blip the throttle the idle jumps to 1200 and won't go back down unless I play with the linkage. I checked for any binding and can't find any. Funny thing is when I disconnect the vacuum cannister the idle seems to work just fine. I know I'm carb tuning challanged but I don't understand why the idle won't stay after you give it gas? I also noticed theres vacuum coming through to the vacuum cannister at idle. Is there supposed to be? any advice would be appreciated.
I just want to take it for a ride
I can't get it to idle. I have the same carb I used before the cam swap the idle worked just fine on it. Heres what I did: I let the car warm up. Set the timing and then set the idle @ 800. But when I blip the throttle the idle jumps to 1200 and won't go back down unless I play with the linkage. I checked for any binding and can't find any. Funny thing is when I disconnect the vacuum cannister the idle seems to work just fine. I know I'm carb tuning challanged but I don't understand why the idle won't stay after you give it gas? I also noticed theres vacuum coming through to the vacuum cannister at idle. Is there supposed to be? any advice would be appreciated. I just want to take it for a ride
Drifting
Joined: Sep 2004
Posts: 1,959
Likes: 1
From: North Bend Ohio
Where do you have that vacuum hooked up? Is it ported or strait manifold vacuum? Manifold vacuum will give you extra advance all the time. Ported advance will only work at RPM above idle. Also, how much larger than stock is this new cam? If it is too big you may be into the transfer slot at idle. Not good.
Hope this helps.
BigBlockk
Later.....
Hope this helps.
BigBlockk
Later.....
Drifting
Joined: Nov 2002
Posts: 1,665
Likes: 1
From: Ontario
The base of the air cleaner could be limiting the top of the accelerator pump lever, causing your idle to sit high. Look on the base of the air cleaner for small dents from the acclerator pump lever. Does this problem happen with no air cleaner on? I had to stack three air cleaner gaskets on top of each other to get enough clearance for my air cleaner.
You say you checked your linkage throttle plates for binding, could be that the holes in the throttle plate for the shaft are worn, check for slop in the primary throttle plate shaft.
Another possibility is you could investigate is how different the engine idles with the vacuum advance disconnected, new cam = different vacuum levels.
Maybe your PCV valve is doing wierd things because of different vacuum levels.
Make sure your mechanical advance isn't sticking.
You say you checked your linkage throttle plates for binding, could be that the holes in the throttle plate for the shaft are worn, check for slop in the primary throttle plate shaft.
Another possibility is you could investigate is how different the engine idles with the vacuum advance disconnected, new cam = different vacuum levels.
Maybe your PCV valve is doing wierd things because of different vacuum levels.
Make sure your mechanical advance isn't sticking.
Thread Starter
Drifting
Joined: Jun 2000
Posts: 1,476
Likes: 1
From: Mt Juliet TN
I haven't got as far as putting an air cleaner on it and the carb is only a year old and worked two weeks ago with the old cam. The port I plugged the vacuum cannister in is at the top of the carb and is at the same place I plugged it in on my old engine. Yes the cam is new and bigger. Old cam 214 duration@50 112 lobe center. New cam 219 duration@50 with 110 lobe center.
I don't understand why I'm getting vacuum from that source at idle. It shouldn't be that way I didn't think. But your right it does work fine with the vacuum cannister unplugged. I think if I can figure out why its pulling vacuum at idle I can get it to work.
I don't understand why I'm getting vacuum from that source at idle. It shouldn't be that way I didn't think. But your right it does work fine with the vacuum cannister unplugged. I think if I can figure out why its pulling vacuum at idle I can get it to work.
