Altitude adjustment for Carbs Options

[Harpo]

Good morning everyone,

Exactly what is involved to adjust the carbs for an elevation change from 4800 to 500 feet.

Thanks

David

[brant]

changing out the amount of fuel and air that reaches the combution chamber...

usually bigger (or smaller) Mains, idles, and air correction jets.
sometimes also Emulsion tubes and primary venturi's

A wide band gauge will help determine air fuel ratio for a specific motor to get it right... Borrowing one and the knowledge of an expert to help is a huge thing to be absolutely spot on.

there is also a lot of experience on this board to get a pretty good estimate for a similar motor or similar car without being exactly spot on for your motor by using a gauge.

Locally we have a guru with an engine dyno and a box of jets (thousands of dollars worth of jets). Using a pro shop with a dyno like this can actually be cheaper than buying all of those jets yourself. I don't know how precise you want to be but you may want to see if there is such a local shop in your area that specializes in porsche air cooled motors.

you can get pretty good for street use by using similar set ups that others use. Remember correct air fuel is about Altitude and Humidity. The amount of moisture in the air effects the amount of oxygen in the air and can change jetting a lot also. So your location and weather patterns need to match up with those who are giving advice.

Its really intersting to go to the local saturday night drag strip in thousands of towns across the US. A lot of the amateur drag racers are using very accurate and expensive home weather stations at the tracks to fine tune their jetting.

[larryM]

X2 above

it depends on what engine & carbs you are asking about

if you are asking for a 911 914-6 with webers, there are "tried & true" jetting specs all over the internet and in Bruce Anderson's & other's books applicable to a sea-level car (500' is close enuf)

if you are talking about a 914-4 with either webers or dellortos, get the VW performance books such Tomlinson's & ask on those VW forums - probably 3000 vw guys can tell you how to jet for a 4-cyl

if you are asking about Zeniths - say so - and post your question on the Pelican 911 Tech forum

- even better search that forum first for your specific setup, whatever it is

i can provide my weber 40-IDA jetting & venturi setup for a sixer determined via use of an 02 sensor and with reference to the above sources, - but don't reply here for the answer cuz i am not subscribed to the thread

[Harpo]

The engine is a 2270 Built by jake with the following specifications
44 mm butterfly's
Venturi: 36
Main Jet: 150
Idle jet: 55
Air correctors: 200
Emulsion: F11

Thanks

David

[DBCooper]

If I were you I'd call Raby and ask. He should know already, and in any case he gets upset when people "mess" with his tuning.

[ConeDodger]

The engine is a 2270 Built by jake with the following specifications
44 mm butterfly's
Venturi: 36
Main Jet: 150
Idle jet: 55
Air correctors: 200
Emulsion: F11

Thanks

David

If it was built by Jake, it was tuned on a Dyno and should be pretty close as he takes your altitude into consideration. Is there a problem?

Oh, I see you're moving.