[goatman65]

Redoing a carb for my tripower. Carb is from a 1974 Chev truck and has APT.

In Doug Roes' book he says to plug the apt system. I would like some opinions on this. Seems like the apt would allow for better fine tuning on a non stock engine.

My engine is far from stock and I want to try to custom build my own carb,then after I screw it up I'll let Cliff do it right,lol.

So, APT or not?

[steve25]

The Q jets starting off in 74 also and due to the new EGR system had those also and they ran great on the primary side for the most part so I would try to keep it working for now.

How many CID will this 2bbl be feeding?

[shaker455]

Leave the two-bbl APT alone.
If you read closely he keeps referring back to passing emissions....I'm pretty sure your all set there.
In a modified app, you may need more part throttle/ cruise fuel.

so if you do feel inclined to modify it do so after live testing via wideband O2 sensor to verify

[Tom Vaught]

Originally Posted by shaker455

Leave the two-bbl APT alone.
If you read closely he keeps referring back to passing emissions....I'm pretty sure your all set there. In a modified app, you may need more part throttle/ cruise fuel.

so if you do feel inclined to modify it do so after live testing via wideband O2 sensor to verify

Not really that up on the 2-bbl Rochester APT system but the Rochester Carb Engineers were Smart People and made changes to carbs For A Reason.

So you are wanting to take your 1974 Emissions Carb and install it on assuming a 66 model year Tri-Power engine.

Is there some reason, except for cost (you have the carb) why you would not install a non emissions Tri-Power calibration carb on the engine? Or are you just trying to learn something about carbs.

Under part throttle conditions (where carbs run the majority of the time) the carb can use a different calibration (which it has for that area of the curve) to optimize that area.
Now in 1974, the requirements were not the same as in 1966 so the Carb Engineers may have concentrated more on Lean Cruise (more lean raises NOx emissions) or lean air/fuel ratios in general that get you closer to a Stoichiometric calibration condition.

If you post exactly what you are trying to do then you can get more accurate advice.
Doug Roe put the info in his book for a reason. You need to have a reason why you want to do the mod and is it right for a 1966 engine manifold performance calibration.

Tom V.