Modified 1977 BBC, needs to pass California smog

[thumper]

Hi everybody, this is my first post and I am excited to find this wonderful resource
I own a 1977 Chevy Silverado C10 2WD Stepside with a factory 454 and 400 transmission with an 1800rpm and an 1800 rpm stall converter. Rear end ratio is 3.40.

Motor has 3000 miles on .040 rebuild. Stock compression ratio of 8.5 to 1, Edelbrock Performer Plus Cam#2162;duration@.050" lift is intake218, exhaust228. Lift at valve is Intake .500", exhast .500", Intake centerline 109, Lobe separation 114. Intake manifold is Edelbrock Performer 2.0 #3761w/EGR. Stock heads ported to match stock cast iron exhaust manifolds. Exhaust pipe is 2 1/2" all the way, passing through an X crossover into two dynomax 17748's and exiting out the rear corners, very unrestricted. No cats required, truck is 6200 GVWR.

Distributor is MSD Street Fire #8362, 20 vacum advance @ 15.2 Hg, 21 mechanical a little sooner than stock.

Original carburetor was 17057512 3396 APH, carburetor on truck now is 17057512 1867 APH. This carb was supplied as stock rebuild and has been dependable for 30,000 miles.


All original smog equipment is intact and operating. Last smog check at 25mph @1450rpm revealed CO2 12.0, O2 4.3, HC 43, CO 0.12, NO 1091(1985max).

I am needing to richen things up a bit while I wait my turn to send the Carb to Cliff's. I am not experiencing bogs, stumbles, hesitation,detonation, or overheating, Just flat response.

I will order the parts recommended and tune it up a little. Unfortunately I don't know what primary jets are in it yet.

Thanks for any help and suggestions. Thumper

[Cliff Ruggles]

Is the replacement carburetor a commercially "remanufactured" unit?

Do you still have the original carburetor?.....Cliff

[thumper]

Hi and thanks so much for the reply.

I let the original carburetor go as a core when I requested a rebuilt  . At the time I had no idea how important holding on to the original was .

On my invoice the request is rebuild carb. The part number is R4509/Rebuilt, Rochester. I paid $363.58 and received a 1 year warranty. They guaranteed passing smog, it did.

The shop is local, Neil's Automotive Repair, NCP Carburetors-Rebuilding&Repairs, Diamond Springs,Ca.95619.

If needed I can conact the shop Monday to find out the source.

Thanks again for your time and help , thumper

[thumper]

Good morning!

Called carb shop this a.m. but they could only suggest pulling the carb apart to see what primary jets are there.

Makes sense to me.

Will place an order for needed parts when I have the time. I am guessing to increase just one size to start. Also guessing I will need some gaskets...

I have another core located and am waiting to see if it is a good one, same stamped numbers,17057512. That way I have a fall back if needed for emissions testing.

Thanks for any help and suggestions, thumper.

[Cliff Ruggles]

Increasing main jet size increases fuel delivery at light part throttle, and at heavy part throttle.   It will also increase fuel delivery at full throttle.

Changing the metering rod only or adjusting the height of the metering rods changes only light part throttle fuel delivery.

Those carburetors use an APT system, if you can get it free'd up.  Some can be difficult to get loose, as the adj screw is in the baseplate between the mixture screws.....Cliff

[thumper]

Hi and thanks for the help!

I need more fuel at light part throttle, and at heavy part throttle, and at full throttle, so increasing main jet size sounds like the right change.

When I can determine existing  primary jet size in the carburetor I will call your shop for recommendations and place an order for the parts.

I will also identify the primary metering rod #'s and anything else I can.

Replacing the accelerator pump seal should be on the list too I think, unless that breaks the one change at a time rule.

Thanks again for all your help, thumper