General Category > Quadrajet Carb Talk and Tips
help with 17082224
bruno:
well i’m almost certain there is no nozzle drip, i used my inspection camera to watch, and the nozzles are dry.
i also tried leaving a manifold vacuum open and lower the idle speed back to 750, i still had no control with idle screws, and it ran much worse. put it back to where it was. so i’m thinking it wants more idle fuel, and by covering the air horn, i’m acting like a choke, and causing the fuel to come from the main at that point?? as in “shifting the vacuum signal above the throttle plates”?
Cliff Ruggles:
Double check the gasket being used under the carb to make sure it seals off the "U" channel on top of the steel shim gasket. I've seen problems there with using those carbs on the early intakes.
I'm not fond of that much timing at idle and very seldom use MVA on engines like you are tuning. High compression engines don't need nearly as much timing at idle unless the cam has a LOT of overlap.
My last 455 in the Ventura was a perfect example of not wanting, needing or responding well to a lot of timing at idle speed. The idle was simply more stable with improved control using the mixture screws with 10 degrees initial timing. If I tried to hook up the VA using manifold vacuum engine RPM's increases slightly but the idle just wasn't a stable in and out of gear and I lost some sensitivity with the mixture screws. It also developed a very light "skip" in the idle note that you could hear in the exhaust. Ran OK like that but not nearly as solid as it did with less timing in it.
Your idle fuel set-up is a tad lean for what you are doing and that shows up if it likes a lot of timing at idle and any engine speed increase tipping in the choke flap or cutting off some air to it with your hand at idle speed......
bruno:
i installled threaded pipe plugs in the ends of the exhaust slot in the manilfold, so “shouldn’t” be any exhaust gases there to leak into carb. it doesn’t leak to the exterior, as i sprayed all around the base of the carb. unless i’m missing something else there?
should i open up the idle tubes, or DCR? or both?
Cliff Ruggles:
Installing plugs at each end of the exhaust channel was a good move.
However, you still need to use a later model gasket UNDER the carb to seal off the "U" channel. If you remove the carb and flip it over you will see that the factory steel shim gasket BARELY covers the channel and if positioned incorrectly there can be a small vacuum leak there. Same thing IF you use an early style (pre-1972) carb to intake gasket under the carb.
Many of those gaskets are NOT long enough in the front to seal off the channel in the baseplate. That channel often supplies "weak" ported vacuum to a tube in the front of the baseplate to route vacuum to the EGR. It's still a leak either way but may not show up at idle speed.....FWIW
I would reduce the lower IAB's to .067-.070" and do nothing else and see how it responds......
bruno:
sounds good. i don’t believe this ever had an egr, but i’ll take some pics when i take the carb off. pretty sure i made a metal plate to go between the gaskets. either way i’ll take pics, and i’ll try your recommendation, and post the results.
there is a possibility you sent me the metal spacer to go there when i ordered the original kit.
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