68 383 with 750 carb. Runs rich
can't believe they still publish junk tech like this. It's shitty to keep screwing the public with ignorant crap like that.
YR. I appreciate the second. stated a little different. Why? I think we know why. The tech writers aren't techs anymore. The website people sure as the sun come up never studied the fluid circuits in a carb.
Well, thats really good info, thanks for that. Sometimes its hard to know what to listen to when you don't have the experience. We assume manufacturers would know the product best, but obviously thats misguided sometimes. And the anectdotal info from some "helpful" people can be no better. Info like yours is clear and makes sense. My apologies to possibly steering the OP astray.
Dave
Dave - You're a class act for feeling that way and saying so, especially when its no fault of your own. Its perfectly logical to assume the manufacturer's know their product. More so when its from a company that made 100 of thousands if not millions of carbs for production vehicles. There's just a disconnect because the 99.9% of the tech people at these companies are not the same as the guys and gals who designed them and worked with the automobile makers. Its worse now because no one has had to make carbs for production cars since 80s.
Someone really interested in fine tuning PV opening without expensive test equipment* can run time trials over a consistant stretch of track with a stop watch or equivalent. The first run at steady speed, and each run after crowding [holding] the vacuum at 2" lower and lower from the first run. Each run should get faster (shorter time). If it goes flat or surges early, that tell us its too lean for that load and it needs a higher PV opening point. This is one of the last things to test for. All the steady state, including WOT and highway cruise, needs to be tuned first. Or you may just find that the engine seems to go flat at part throttle. I was having that with a carb for a long time. I tried some crowds with the datalogger showing rpm, AFR, MAP and acceleration. Its not easy crowding a vacuum. In the end it turned out to be timing related not fuel ratio.
There's been some carb guys, like Mark Whitener that Yellow Rose mentioned, who have been sharing some good testing and experience. More than that, they've shared all of the research papers and engineering books on the subject they've come across. Until the AFR curve was explained by one of those guys, I thought the carb's job was to provide increasingly richer mixtures as the throttle opened. Not only did they explain, they cited the books and even posted scans of the graphs. I reposted some of that here
Wideband O2 Sensor location advise
*If you happened to be so lucky as to know a place with NOx gas measurement and a load dyno then it can be done by observing the combustion.
"
The purpose of the power valve selection is to enrichen the mixture prior to the combustion temperatures going too high. To set a powervalve correctly requires a NOx sensor. Different engine combinations need fuel enrichment at different power levels."
Bruce "Shrinker" Robertson.
post #4 "Another Power Valve Question" archived Innovate Motorsports forum
