Author Topic: Carb question (Read 3349 times)

Eagle 1 · « **on:** June 09, 2006, 04:09:38 PM »

Does anybody know what is the technical difference in a carb number 17058276 that came on the L-78 Pontiac 400 engines and a 17058266 that came on the W72 Pontiac 400 engines?
Is there a difference in perfomance and hp? If so, how much?

I am asking because my W72 engine is missing the original carb 17058266 and I purchased a 17058276 on ebay to use for now.

ta78w72 · « **Reply #1 on:** June 09, 2006, 08:45:26 PM »

You poor soul. I can't understand why anyone would take that carburetor off. They didn't realize what it was. There's one on ebay right this moment along with the intake manifold. It's from a 77.

The W72 carb was 800 CFM and the regular carb was 650 (I think). Check out John Witzke's fine paper on the W72 (which can be downloaded from this site) spells out the differences.

I can tell you when you put your foot to the floor, those secondary's roar and the car jumps forward. It's a kick!

I've seen a couple of those carbs on ebay...from 77 and from 79 but never from 78. I'm looking for hoarding material! I'd like to have one on the shelf just in case, 20 or 30 years from now....I need it.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&rd=1,1&item=8072267904&sspagename=STRK%3AMEWA%3AIT

Eagle 1 · « **Reply #2 on:** June 10, 2006, 01:22:58 AM »

I went back and read John Witzke's fine paper and it says that all 6.6 Pontiacs from 77-79 got the 800 CFM model M4MC carb.
From what I have gathered, the difference is in the primary jets, primary metering rods, and the secondary metering rods.
Here is the carb I purchased on ebay.
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=8070491853&ru=http://motors.search.ebay.com:80/8070491853_W0QQfromZR40QQfviZ1
Take a look at it and tell me if it differs much in apperance than from yours.

Why anybody would remove the original carb is beyond me.

ta78w72 · « **Reply #3 on:** June 10, 2006, 09:45:14 AM »

I can't tell if the body is identical by looking at it. It would make sense that it would fit the same as a W72 carb because it's basically the same engine. But the carb is from a 78. Do a search on Rochester carbs on the internet. I found a site which gave the code for the carb numbers....like what year, engine, division. The 8 in your number means 1978 model year. I didn't bookmark the site though.

I'm not sure if the secondaries are bigger on a W72 carb or not. I guess you could measure them to find out. You should be able to buy the same type jets. The paper also talks about the secondary hangers being shorter to give quicker response. It's hard to beat the real thing.

When those carburetors come up on ebay they get well over $200 for one that needs to be rebuilt.

Eagle 1 · « **Reply #4 on:** June 10, 2006, 05:48:57 PM »

Yea I found that website too before buying the carb.
http://www.atransam.com/Pontiac_Carb_Info.html

I would be willing to bet it could be built to perform just like the W72 carbs.
The carb I have on there now came off a 1970 GTO ram air 3, so I know how it feels when you punch it. :shock:

But, I am trying to get everything back to original as possible so that is why I am going with this carb. Changing the numbers on the carb body wont be a problem either. :wink:

gold78 · « **Reply #5 on:** October 01, 2006, 09:53:37 AM »

I have 2 such carbs on my shelf and I am looking to sell one. It works OK but has never been rebuilt. If interested email me at ajmdld@optonline.net