General Category > Quadrajet Carb Talk and Tips

Edelbrock 850 performer q jet

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Chevelless:
Something very strange is happening. Pull off brake booster hose idle goes up. Remove vac hose right near booster hose idle goes down. Idle screw is 1/2 turn past contact.ignition at idle is 16. Vac at idle is around 10 from brake booster hose.
Should this be around 17.

77cruiser:
The other hose wasn't for the vac. advance was it? 10-12 is about what to expect from that cam.

Chevelless:
Yes it was.Jim
Makes sense now.

Chevelless:
Should vac advance be manifold or port vac? Would port run leaner at idle?

Cliff Ruggles:
Removing the 3/8" line to the brake booster introduces a TON of air and HUGE vacuum leak, so it's likely to speed up some, and run rough, etc.

If you do NOT have nozzle drip, and control with the mixture screws (engine slows some when turning them in) then it's got plenty of idle fuel for what you are doing.

The 1910's were made with many different calibrations.  Edelbrock may have been experimenting or trying to figure things out with them.  Typically they are very rich at idle, with huge idle tubes and TONS of fuel to the mixture screws.  Often they are rich right off idle as well, as a lot of fuel is available to the transfer slots as well.

When tuning for idle, you just have to experiment and see if the carb is adequate or set-up correctly for what you are doing.

Typically I do NOT run a lot of timing at idle by adding a ton of it with the vacuum advance.  A well thought out engine doesn't need a lot of timing at idle.  This assumes the CID, compression and cam choice complement each other well.

If the cam is too big, or LSA too tight, then idle quality really suffers and the tuner will often find themselves dealing with crappy idle, stinky exhaust, and having to add a LOT of timing and fuel to make things happy......Cliff

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