Under WOT car screams like a banshee but cruising along at 2500-4500 stumbles under light acclereration. Too rich, yes? Initial timing at 11* Scott After WOT run plugs are slightly brown, no over rich mixture. I need to pull them after a cruise across town and check also
Hmmm...a predator carb...that makes things difficult since i know nothing about them. Does the accelerator pump have a cam on it? It really sounds to me like it's going lean. You could have a friend watch your tail pipes while you're accelerating from those speeds and tell you if you get a puff of black smoke (which is what would be required to cause a stumble if rich). The best and easiest way to tune a carburetor is to have an oxygen sensor bung welded in, put a late '80's chevy O2 sensor in, and monitor the voltage-- .45 is stoich above that is rich below that is lean Other than that, i don't know a whole lot about predators, so you're on your own!
yes the oxygen sensor trick works, but it's crude and not that accurate. If you can get a carbureted motor to run at 450 mV, and run smooth, I'd like to know how. I could only get mine to around 650-750, and even then it wasn't exactly smooth. Got good mileage, though. Forget about reading it under acceleration. Tried that too, nowhere near accurate. That's why EFI vehicles operate in "open loop" (not using the O2 readings) under WOT.
We have an AIR/FUEL ratio meter on a carbed 5L. When the 650 cfm vac sec carb got dialed in, we could set the cruise anywhere on the dial by changing main jets and also see it go rich by jazzing the throttle. This is the way they work when the carb is near correct and will even hunt a little at idle with a longer cam . The EFI engine will run the meter full dial when making corrections to the injection as well as show the injection shut down during deceleration and go green at WOT. They have good value when what they are monitoring is set up correctly. It takes getting to know and relate to the meters action about what is going on and not just another light to look at. Remember that at ideal A/F of 14.6 for cruise, WOT A/F ratio only needs to be 13% richer to be correct for nearly all engines. Little known is the fact that the Ox sensors become temperature sensors when cooled off at the richer ratios.
Tuning for idle is nearly impossible with an oxygen sensor because most of them that are of the non-heated variety cool off to the point where they do not work at idle. Also, setting them to .45v only works if you've got a choke that gets you around town until the car warms up completely, and even then most non-stock cars won't idle at less than .65v. My suggestion was that you use it to tune for cruise. On a typical holley, it is difficult to tune much else (i.e. part-throttle). In tuning for cruise, you get it up to about 3500 rpms heading on a flat surface with a steady foot. This keeps you out of the power valve which will throw off any readings. In my case, i bought the autozone sensor for a '94 honda civic si (1.6 vtec) because it is a wideband o2 sensor. It is heated, and the a/f changes are realtime. Has helped me trouble-shoot many problems, but it also costs $65.
Wow! This thread got off course before I got my ? answered!! Fiqured it out, too rich.. Runs great carry on on the sensor talk!! Scott
