TheNovaMan

I tried searching (CZ28 and the whole internet), but came up with almost nothing. So far I know that you should start out with the same total emulsion bleed area as the metering block you're replacing, and that generally the lower bleeds will be larger than the upper ones (not sure if that applies to drag racing though).
Does anyone have any guidelines or rules of thumb to follow when playing with adjustable emulsion bleed metering blocks? For example, which bleed(s) would do you change if you wanted to alter the high RPM part of the fuel curve? Bigger bleed = more air = leaner, right?

TIA

WS6T3RROR

What exactly are you trying to accomplish.

Sure you dont mean high speed air bleeds?

TheNovaMan

Well, a friend of mine bought a Proform main body and a couple of their metering blocks with the changeable emulsion bleeds, so no, I don't mean the air bleeds (but we'll probably fiddle around with them a little too). We're also putting together a couple Innovate LC-1s and a DL-32 so we can get more feedback for tuning.

I called Proform "tech," and the guy said to run the blocks initially with no bleeds at all. That just doesn't seem like a good idea to me.

Edit: what we're trying to do is get the fuel curve as close to perfect as possible at WOT, and then see if we can maybe pick up a few mpg with part-throttle tuning.

mdacton

I know alot of people who run without them then go back and tune.....

WS6T3RROR

Well in that case. Larger bleeds will make a leaner main circuit mixture, and it will come in earlier in the fuel curve. Small bleeds will come in later and be richer. The lower ones usually are tuned for higher rpm situation. Less so for the ones higher up.

I just have not had to ever do anything with em really. Between air bleeds and jets etc I've always been able to get close.

For part throttle just keep leaning it out a bit with main jets until it pops and pukes at cruise then go back 2 sizes at first or more if problems still persist. To tune higher load situations you'll have to enlarge the power valve restrictors on the primary side. I dont ever run a power valve in the secondaries besides its moot except at full power situations imo.

I dont usually look for a perfect flat fuel curve, usually after I get done the thing gradually goes richer as it approaches the limiter. The important thing about the wideband is for you to listen to the engine above all, the wideband is just a tool. Give the motor what IT WANTS not what you think it should have. I have a wideband and use it, but mostly I just listen to the engine and keep an eye on the mph at the track, and I keep in mind most stumbles are lean.

TheNovaMan

Thanks, that's a big help!

My friends think that a power valve in the secondary metering block will help noticeably with mileage, but I'm with you: once you get into the secondaries, it's most likely a WOT situation. But hey, I could be wrong - it's happened before.

I'm a chemist, so I know that any instrument is only as good as its calibration, and that 12.5:1 is more of a rule of thumb than a law. Engines are complicated systems with ALOT of variables.

Thanks again.

WS6T3RROR

Your friends are wrong, most driving is done in the idle and transition circuit. At the end of the day if the cruise mixture is lean as can be with no misfiring... THAT IS IT for mileage I dont care what holes it comes out of as long as its fine droplets/vapor.

Being a chemist you know that a/f ratio is merely mass air/mass fuel. Now let us assume for a moment that you have a current ratio of 14.7 (not really stoich but we tune to that to reduce Nox). Now lets say you get it to function at 16:1. Congratulations you just gained 8% fuel mileage on what is probably at best on the highway a 20mpg car. So now instead of being at 20mi/gal you're at 21.5.... wow. Even if you drive it 10k miles a year all highway and never get on it at lets say 4.30 a gallon. You save a whopping $150 congratulations you've paid for half of the cost of a wideband.

Not ripping on you its just that energy processes and power production is my thing. A wideband is a great tuning tool and it can show you alot of wrongs in a carb and can be a big help with max power. Your big gains for mileage will be in the transition fueling and in the idle and intermediate circuits and your tuning of vac advance and mechanical advance. Also the moment you realize they call it the gas pedal is because basicly it just regulates flow, you'll stay off it as much as possible for mpg. Alot of the newer carbs i've seen the holes are all the wrong size and it makes the things run fat as can be at part throttle and they blubber and puke black smoke like a diesel. It always pisses me off when I see a high end car at a show with soot all over the bumper because the owner wont pay or doesnt know somebody who can tune a carb .