gapimpin

i rebuilt it and it was running fine but now its surging from 1200-1800 rpms and from 3000-4000 rpms the car shakes and feels like its loosing a lot of power but right when it hits 4000 rpms it runs smooth.... i was thinking that might be a lean condition caused by the secondarys not opening but i have no way to verify that.

its a 96 4bolt 350 with 305 p&p vortec heads... beehive springs 224/230 503/510 112lsa cam. performer rpm airgap intake tr55 plugs hedman longtubes built 700r4 with a 3500 stall and 2.73 open rear.

what do you guys think?

91TTOPZ

iTrader: (4)

Well this won't help but I am having the same type of issue I have 355, with a 1406 Edelbrock, it starts fine and idles fine but when i bring it up to about 1800-2000 it vibrates and surges in and out, and up in the 3000-3500 range seems to fight itselk (lean?) I have changes the metering rods up and down with no real effect, have check over everything to insure no vacuum leaks. I have been searching ever site I know and asking a lot of people and have gotten answers from valve timing to vacuum leaks to a bad carb but have not found an answer yet but will keep you posted if I do.

Apeiron

If the secondaries weren't opening you'd be going rich, not lean.

Was it running fine after the rebuild, and started doing this sometime later?

gapimpin

seemed to be running fine after rebuild but i wasnt holding it at low rpm after the rebuild so i guess i never actually checked that... the 3-4k thing has been there since i put the engine in. why would it go rich if the secondarys didnt open??? since its vac secondarys if the throttle blades arent opening then the secondary fuel circut wouldnt be pumping anymore gas. ill be able to check that for sure this weekend though. i ordered an lc1 wideband kit thats all wired up... just need to get the sensor bung installed. hopefully that will tell me whats going on.

Apeiron

They're not really vacuum secondaries. If the secondaries don't open, you're pulling more air than normal through the primaries and it'll meter in more fuel. If the air valve doesn't open for some reason, but the secondaries do, manifold vacuum will pull fuel from the boosters.

gapimpin

maybe i can wire open the secondarys and take a spin around the block see if that does anything for the 3-4k problem... and i still have the low rpm stumble but im thinking thats just tuning that needs to be done with the idle screws... my vac gauge isnt working right... when i adjust the screws it dosent show the little drops in vac now it only moves when i loose about 5hg.

Apeiron

Wiring the secondaries open wouldn't be a good idea.

ProjectIrocZ28

1406 is a 600 cfm carb right? i had many problems w/ one on my big cammed 355. either jet that thing real rich or get a 750(1407 1408?) big cammed smallblocks seem to like a bigger (Not outrageous) carb anyway since their valve timing is so lousy for low and sometimes midrange rpm (depending on how big a cam) cyl filling. a bigger carb would simulate more intake plenum volume. this would smooth out the intake pulses to the carb, giving a better signal to the carb making fuel metering more accurate and stable at lower rpms. obviously jetting its cheaper, so try that first.

gapimpin

fixed it tonight.... the timing was so far advanced that when i originally tuned it i had to open up the idle screws a lot to keep it running. i retarded it tonight and tightend down the idle screws. the part throttle miss is almost gone barley noticable at all and the 3-4k stumble/shake is gone. sotp driving says it feels a lot better now and i can finally hear my cam loaping... sounds really nice now i just need to redo the exhaust and check the valve lash cause i here my collectors rattling and a valve tick. the project is never done...lol