Weber, 44 IDA's Options

[Randal]

Does anyone have a altitude chart that shows which jets you should use?

[914forme]

Does anyone have a altitude chart that shows which jets you should use?

Ask Jake he will get you close to spot on.

[Randal]

What no one knows which jets to use for different altitudes? ?

[914forme]

Truth be told it changes.

Compression ratio, cam, exhaust system, and air filter stacks, the hight of your velocity stacks, are all in the mix.

Then you take the things outside of your control altitude, barometric pressures, temp, humidity, fuel quality.

Running EFI is easy, running carbs correctly takes a magician, scientist, and alchemist.

I am sure it is documented in one of he many weber books I have some where, but fuel quality has changes since most of these where written. So it would be ball park anyway.

Advantage of asking Jake, is he has the info on customer engines he has sent out there, and then any tuning that was required afterward if the customer told him. Much better than us just rolling the dice and saying the chart says this.

the only other answer I have is toss it on a dyno and work out the bugs.

[Randal]

Truth be told it changes.

Compression ratio, cam, exhaust system, and air filter stacks, the hight of your velocity stacks, are all in the mix.

Then you take the things outside of your control altitude, barometric pressures, temp, humidity, fuel quality.

Running EFI is easy, running carbs correctly takes a magician, scientist, and alchemist.

I am sure it is documented in one of he many weber books I have some where, but fuel quality has changes since most of these where written. So it would be ball park anyway.

Advantage of asking Jake, is he has the info on customer engines he has sent out there, and then any tuning that was required afterward if the customer told him. Much better than us just rolling the dice and saying the chart says this.

the only other answer I have is toss it on a dyno and work out the bugs.

We are planning on installing an air fuel gage and sending unit, but just trying to get some baseline jet informatoin before the project starts.

[J P Stein]

Going to the Parade, Randal?

[914forme]

So Sisyphus, I have said it once I will say it again, you can't tune a carb via an AFR gauge. You will chase your tail all day long, and the next and the next etc. AFR, was perfected via electronics for an electronic subsystem, it is just a sensor, and we know that the magic number isn't so magic. If you where running EFI, I would say go for a wideband AFR. Put your money into EGT, and data logging.

EFI uses a cool little device called a MAP, carbs do not, the MAP tells the efi to compensate for barometric pressure. Which we all know changes. This is why racing teams that are required by the rules to run carbs will have a weather station, and a guy who knows how to use it, and adjust carbs right before the race. Top Fuel guys will rebuild the engine and re-jet the carb for each run. Crazy I know, but in the world of winning or losing by 1000th of a second, every little bit helps.

Reality is you would be better off tuning via EGT, than AFR. AFR does not mean crap to you anyway it is just a number.

No easy way out, you need dyno time, and somebody who knows weber carbs.

To me carbs have 3 advantages, cheap ( somewhat ) maximum Power ( one given Point) and reliability you can almost always limp home. EFI kills it in every other way, drivability, broader torque band usally close to 10% increase, and that translate into more horsepower across the board, and last flexibility.

I will look tonight when I get home and see what the old weber manual says. What's the displacement and elevation your running? Oh and lets not forget what is the top end RPM wise your engine will see, as choke size (Ventures) effects jet size.

[914forme]

Better late than never, sorry for the delay.

0-5000 Ft. no chage in jets from the base line.

So I run 1.50s in mine, 5000-6500 would mean I go down ot 1.45, 6500-9800 I am down ot 1.40 and 9800-13000 you drop to 1.35s.

.05 off on any in hte chart per elevation change noted above.