surging during deceleration

[poboyjo65]

I have a aggravating surge just when I let off the throttle from cruise mode at 30-40 mph or less depending on the gear. it kind of jumps ,surges, jerky. I've moved the timing around & played with carb settings & metering rods & springs but nothing changes it.plugs look pretty good,tanish/light brownish. Is this just the lopey cam maybe? it is a 347 & 4 sp,edelbrock airgap intake, rpm heads with the smaller valves & 650 carb, although I have tried a 600 edlebrock also. here is the cam & specs;
http://www.compcams.com/Company/CC/cam- ... d=905&sb=0
this cam is made to have a choppy idle,or sound meaner than it really is but it still runs pretty good !
when you let off from a higher speed it doesnt do it until it gets down to a lower speed, or if coming down a hill it doesn't do it. & of course it didn't do this at all when I had an automatic behind it. if I had a bobble head on the dash it would get a work out .

One other thing I will try today is instead of a lean-best setting of the air screws I'm going to turn them out until it changes then back in slightly, so I guess you would call that a rich best setting. any ideas or JMO's are welcome.

[CALIFORNIA CALIENTE]

Clutch in or out?High gear or coasting?If the clutch is out and it is in high gear it could be trying to hold back the car and it has no slippage like the slush box had!! JMO , ROY.

[poboyjo65]

clutch out & coasting. any gear. when it is idling or just barely off idle. in 4th it is about 30 -40 maybe slower too. if it is much of an incline it wont do it.If your cruising at 30-40 & let off the gas it does it & if you just barely get back in it -it does it still unless you mash it down a little more. Yea it is trying to hold it back & wants to go at the same time ,jerky , lunging, quivering , on & off. today I tried it richer & with the idle higher & lower, still did it. I'm beginning to think it is the cam loping & no way to eliminate it other than a cam swap. I'll try get a video of it .

[CALIFORNIA CALIENTE]

John;do you have a vacuum canister type distributor?It could be the cam is giving the engine varying vacuum signals!! ROY.

[poboyjo65]

I do Roy but it isn't hooked up right now. I thought the same thing.

[ants875]

I can say my car does not do that and my cam is almost identical to yours, main difference is I have a quick fuel 750 on my 347. I do notice if I lug mine in 5th gear I get a bit of a stumble, seems to prefer to cruise above 1800 rpm. Have you checked the float levels again?

Ant

[poboyjo65]

Yea I set them just before I put it on. it runs good with no stumble or miss, just the little perky jerky thing goes on during decel at certain rpm & then maybe if you barely touch throttle but anymore than just a touch & it'll smooth up. or you can slow down enough to get past it too. it kind of reminds me of the jerky feeling you get if you slow down too much without pushing in the clutch .

[CALIFORNIA CALIENTE]

John;could it be motor/trans mounts?Rear end moving,U-bolts loose? ROY.

[poboyjo65]

Roy it is engine related,because I can hear it. it's like I'm tapping or pushing my foot on the gas pedal ever so slightly. I dont know if it has did it from day 1 or if I tuned it in to it. I've been monkeying with the mechanical advance , took out the big spring,put in another smaller one, bent the tabs some, built up the gap stop peg with shrink tubing so I can run more initial advance & my total adv wont be too high. it (the problem) may be a by product of more initial advance. It is running good but I'll temporarily test backing down initial timing to see if that helps, I'm also going to get a curve kit of lighter springs.

it's not a big deal just kind of annoying.

[Comechero65]

John, When I set up my dist which is an autolite dist for the year, I used a set of springs for an HEI dist. I used the two lightest springs in the set. I adjusted the springs to be approx 1/16" shorter that the tabs they hook to. With that setup I get 21 deg mechanical advance. I set my timing at 14 deg. For a total of 35 deg mechanical advance that maxes at 2800 rpm. Vac advance is about 14 to 16 deg.
With this setup it runs great and no hesitation or ping anywhere. Has worked perfect for me. That's on the 5.0 GT40 heads running an explorer cam. Maybe this will be some help.
Ron