Automobile(s): 2002 STS, 1988 Seville R.I.P., 1970 Eldorado (New Toy)
4barrel not working! (70 Eldo)
Hey guys, back again with questions about the 70 Eldorado. I have what I believe is the stock Rochester Quadrajet carb on (rebuilt). My problem, (although not preventing me from driving the vehicle) is that the 4barrels are not opening upon WOT. The engine has not been pulled or molested too bad. But I think parts of the vacuum system have been modified. Does anyone have a vacuum diagram for that year? Or any other info to what the problem could be? I donít think there is a binding issue as I can manually open the top barrels by hand. I also donít think itís the rebuilt carb as the other unit I had on the vehicle had the same problem. Thanks again for the help. -Seth
Automobile(s): 2002.5 F55 STS, 2014 Explorer XLT 4WD
MD Eastern Shore
Re: 4barrel not working! (70 Eldo)
The QJ uses an airvolume activated set of butterflies (air valve) over the secondary butterflies: You punch WOT and the secondaries slam wide open BUT the air valve (the top "butterfly") prevents a huge bog and stall because they only open in response to airflow and they should have a lockout which prevents opening until the throttle is 3/4 open+. The lockout is either vacuum operated (a diaphragm canister with a pull rod near the passenger side of the secondaries), or a mechanical tang lockout on the accelerator/secondary throttle shaft linkage. (Those top butterflies are NOT operated by engine manifold vacuum: they are operated by engine airflow demand, and you will NEVER see them open while diddling the throttle in neutral...............)
With the engine off, remove the air cleaner and any interfering baffles or pipes. Try to press open the air valve - it won't open, will it ?? Now, ease the throttle wide open - the air valve will now open. That is the setup to prevent a low speed bog and stall: A QJ will only flow the air required by the engine at any throttle/load opening - a very elegant solution to WOT/low speed power loss. When you do this, watch the secondary metering rod withdrawal - that curved hanger and cam is what pulls the rods to change secondary mixture as the air valve opens with increasing RPM/airflow.
DO NOT try to remove or bypass the secondary air valve lockout or alter the opening rate: you'll wind up with even far greater problems than you now have......
Get Doug Roe's HP Books 8 x 11 paperback on Rochester carburetors. Everything you need plus enough to get you in real trouble if you're not a QJ carb guru.
I would add, if the secondaries aren't used for a long time (like some used cars I bought), they can be stuck shut. Also there is a tang from the automatic choke, that keeps them from working until the engine is warmed up. Bruce Roe CLC # 14630