At what RPM does your 350 SBC idle?

[geezer#99]

Have you tried more initial?
Just a few degrees could let you decrease your idle about 150 rpm.
Is your balancer/timing tab accurate?
http://www.crankshaftcoalition.com/w...op_dead_center

[Mike_The_Grad]

Yes I have tried more initial. At around 18-20° initial it sounds like it loves it. But I was told that was to high by a few people. Some days it idles perfectly at about 675 in gear and 750-800 in park.other days it's up around 750-800 in gear and won't drop,and runs like crap,no performance,loud and not in a good way,guzzles gas without getting very far.and other times I swear I'm getting 25 miles to the gallon,and flat throttle response no matter how hard or fast I push the accelerator, on a couple of occasions I've been causing at about 45 and I'll mash the pedal and it'll downshift and I can hear it take in a huge amount of air and as the rpms fly way up I'm still doing 45 and I am not going any faster and so I let off the throttle thinking either I broke the rear-end or the trans or something. But it will keep going down the road like it never happend.and idles fine at a stoplight with no issue. But yet other times its fun as hell to drive,I've even gotten it to chirp the tires in 2nd gear. Basically no consistency from day to day,every morning has me wondering how it's gonna do. Starts up and runs every single time I turn the key whether it's 6 in the morning and 45° out or if it's 4 in the after noon and I've been driving for over an hour and it's 90 outside...

And I have verified my tab is about 2° off depending on where your standing and viewing it from...lol. it's an aftermarket bolt on one. But my balancer is new and so is timing chain.

[Gregski]

Originally Posted by Mike_The_Grad

Cold start: around 900 in park/750 in gear, after warmed up about 800 in park/and anywhere from 650-800 in gear.( seems to fluctuate for some reason.) 350 bored over.04,stock intake,comp cams XE250, H.E.I.,fresh rebuild original q-jet.

two things effect timing

one is engine RPM, your mechanical advance is controlled by engine RPM as your engine RPM increases so does your mechanical advance

the other is vacuum advance, vacuum advance is controlled by the amount of vacuum sucked by the engine, my money is on vacuum advance as caused by your cam, I would recommend performing the following tests

1. simply disconnect your vacuum advance (you can take the hose off the vacuum canister on the distributor and shove a screw inside the hose to plug it up, or remove the hose from the carburetor nipple and use a special black rubber cap to cap off the nipple on the carb.) Then start the truck, warm it up, and drive it around, you may not have ideal horse power and performance but that's ok (for now) what we are trying to see if it will fluctuate like you are saying, it shouldn't.

2. rent a vacuum gauge from an auto parts store (if you do not have one) connect it with a plastic T that should be supplied with it between the carburetor and the vacuum advance canister you will need a long rubber hose maybe 6 feet I don't know to reach in the cab, you will put the gauge on the dash of your truck and go driving around and watch it to see what happens when the vacuum needle bounces up and down, I bet the RPMs fluctuate with it, cause and effect

[Mike_The_Grad]

My vacuum advance has a ruptured diaphragm. While I had the distributor out to shim the shafts end play,I was cleaning up the weights and springs when I actuated the cans control arm with a screw driver and about an ounce of varnished gasoline shot out of the nipple connection. The leak developed soon after. I could hear a slight whistling under the hood while I was driving down the freeway. Eventually found it and capped the can and port on the carb. The engine ran cooler and smoothed out after I adjusted idle mixture screws and reset the idle speed screw.I've been meaning to replace it,but rather than replace only the can I'm gonna get one of those H.E.I. tune up kits that comes with:cap,rotor,matched coil and module,new pickup/capacitor/harness,weights,springs,adjustable can,low resistance carbon button. Pertronix and proform both have them between $80- $125. But I have a leaking brake booster that's giving me a headache and another list of symptoms.so that's on my to do list today,replace booster and all three rubber brake lines so I only have to bleed the system once. Then I think see an improvement in my vacuum gauge reading which is right about 16" Hg with a slight fluctuation of the needle at idle.