how can i tell what size q-jet i have?
 

how can i tell what size carb i have on my engine. what size q-jets were/are available. my engine is a '73 model 400 but i can't be certain the carb is the original. where can i go to get this info.

Give us the numbers off the carb.

Here is pictures of both 750cfm and a 800cfm...You can see the ring in the primary of the 750 which is not on the 800 version

where are the numbers located?

is that some kind of restrictor ring?

There are two basic Q-jet castings, the "750 cfm" and the "800 cfm". The only real difference is in the size of the primary venturi. The primaries were opened up a bit on the 800s to get the extra flow. Without two carbs to compare side-by-side it can be difficult to tell whether you're looking at the smaller or larger venturis, but there is one surefire way - pull the carb, turn it upside down and open the primary butterflies. The 750 has smooth venturi walls all around the booster rings. The 800 has a "bump" in the wall of the venturi adjacent to the booster rings.

The numbers are on the driver's side of the carb on a flat between the primary and secondary side of the carb. Remove the aircleaner and get in there with a flashlight and you'll find them.

the numbers that i found were stamped on two lines, the first line reads:17056259

the second is: 0866 ASC

76 olds 350 w/AC--800cfm.

Very few, if any, of the "M", as in Modified, Q-jet models, 1975 and later is flowing the full 800cfm as the casting allows.
For full 800 cfm flow, the secondary airvalves opening needs to be adjusted to open 1.38" , measured from the rear ridge of the open valve to the back of the choke housing.
Also check that the sec. throttle plates are open 90 degrees +- 5 degrees.

If you ever want to look up a Q-jet number, just type it into Google search. Never fails for me.:D