Here is the deal. i just put a new 350 in my non hamb friendly car and im having some issues with the idle. I put a cam,torker 2, holley 650 mechanical secondaries. and a hei. I checked for va*** leaks and adjusted the timming to hell and back. im not good with holleys infact i **** with them. So give me some ideas and ways to tune this surge out. its got to be about a 300-500 rpm surge. Got any ideas? o and when i raise the rpm up it goes away but i cant let it idle at 2500 rpm. the cam is a 266 deal.
Maybe the floats are set too high. If so gas will drip out of the boosters at idle causing surges. Look down the carb when running, you'll see it. Watch your eyebrows.
Did you check the advance springs in the dist? perhaps one is off or they are too light?? Maybe your idle circut is too lean, try turning the screws in the metering block all the way in and then out 2.5 turns and see what it does.
non adjustable floats and i would think the thing has not been running long enough to give me a read on the plugs but ill take a look any way. I was just reading on some other sites about a peice of debris in the idle circute. i just had the front bowl off to replace the transfer tube seals. i wonder if i could have got something in there... I wish i knew more about holleys.
Brand spanking new HEI every thing looks good. I cant say how it preforms on the street yet i have not driven it cause its still up on jack stands
At surging RPM, slowly close the choke plate by hand or (slightly risky) slowly cover top og carb with your hand. If choking at some point inproves the idle, that would indicate this is a lean condition, typical cause of surging.
Have you checked the vacuum with a gauge? A big cam will not idle as well...so the first thing a guy does is turn the idle up until it smooths out. But what that does is uncover the idle transfer slots, letting even more fuel be drawn at idle and it'll run like ****.....and rich. Also there may not be enough vacuum to keep the PV closed, adding to the problem.
New carb or used carb? HEI vacuum advance plugged into manifold or ported vacuum? What is the part number or all the specs on the cam? 266* advertised or at .050, lobe center, lift, etc. (either way it doesn't sound too radical) OH - and another thing to check - make really really sure you're not hanging a valve open because you adjusted the hydraulic lifter preload too tight - try backing off the preload on each valve - heck if you want to do it the "traditional really old school" way - with engine running - back it off until the rocker starts clicking, turn in until it just stops ticking and add 1/4 turn more preload. It's messy with the oil slinging all over, but accurate.... (p.s. there are some oil diverter clips that can be put on stamped rockers to limit the squirting, but what fum would that be not to get burnt by hot oil when adjusting rockers )
I just had this same issue with mine, and closing the choke did not make it go away. This also caused a slight burble in the rpm at 1500 and up. I had a restricted air bleed in the front carb. There are 4 small air bleeds (one big and one small over each bore) that go from the venturi area into the main metering block. I took off the front bowl and metering block, blew carb spray and then compressed air through each one of them, in both directions. One of them came out with a bunch of black ****. I bolted it all back together and the surge and burble were both gone.
Running an automatic? If so, what type of converter are you running? higher than stock stall converters can often cause an idle surge. The 12" 2500 in my LT1 Caprice caused it to surge 300ish RPM at idle.
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