Author Topic: Rochester 17058266 (1978 - Pontiac W72 carb) - tuning  (Read 398 times)

Offline pega_de

  • Newbie
  • *
  • Posts: 6
    • F Body Forum Germany
Rochester 17058266 (1978 - Pontiac W72 carb) - tuning
« on: January 10, 2019, 11:15:30 AM »
Hello,

at first. In 2010 I bought a 1978 Pontiac T/A W72, but with a Holley carb, and the engine runs very sick.

Then I complete restored the car and bought an numbers correct W72 carb for it, back in the day I was very happy to get one of the very rare carbs.

Now my motor is overhauled. But the carb doesn't runs very nice with the motor.

Facts about the motor:

Pontiac 400 W72 block (XX481988) - 0,30 overbored
Pontiac #12 heads
Stock crank
Summit 2801 camshaft
TRW pistons
Edelbrock Performer intake 2156

The carb:

it was stock rebuild in 2010 from a company in the US
Primary jets are 72s

The eninge runs to lean in idle and every other situation. And no reaction with the idle mixture screws.

Is it possible to send you the carb for a rebuild and calibrate?

kind regards,

Marco


Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 3953
Re: Rochester 17058266 (1978 - Pontiac W72 carb) - tuning
« Reply #1 on: January 11, 2019, 02:36:50 AM »
Even though the 2801 is a pretty small cam it's going to act much bigger in the "low" compression later model 400 engine. 

The carb will require more idle fuel and why you are having poor results.

Is the carburetor "remanufactured" at some point by a company?

I'm not overly fond of anything that's been commercially "remanufactured" and typically do not work on them.  Of course some companies are better than others, but even with that said we've had a good many carbs sent here recently that were so "hacked" up we tossed them aside and went with a "virgin" core instead.

As I'm typing this there is a carb on my workbench we just checked out for a customer that sent it off to a very well known company to be "rebuilt".    Despite my best efforts it's HOPELESS, so I put a tag on it labeled "JUNK".  I've never seen a carb that "hacked" up in all the years I've been doing this.......Cliff 

Offline pega_de

  • Newbie
  • *
  • Posts: 6
    • F Body Forum Germany
Re: Rochester 17058266 (1978 - Pontiac W72 carb) - tuning
« Reply #2 on: January 11, 2019, 06:30:15 AM »
the problem is:
  • low vacuum at idle
  • lean mixture
  • no reaction at the idle mixture screws
I have 2 of that carbs. One ist rebuild by Carb Junkys, and the second was redone by US Carburators - IL
I can send you both carbs. Then you can look at them and give me a quote how much it does cost to redo them. Both of them have the same problems.

The vacuum in from 1200 rpm ist perfect. The biggest problem is the idle vacuum, and the lean mixture.

kind regards,
Marco
« Last Edit: January 11, 2019, 06:50:34 AM by pega_de »

Offline Cliff Ruggles

  • Global Moderator
  • Qjet Hero
  • *****
  • Posts: 3953
Re: Rochester 17058266 (1978 - Pontiac W72 carb) - tuning
« Reply #3 on: January 12, 2019, 01:43:22 AM »
I'm sure we could make a good working unit from them.....Cliff

Offline pega_de

  • Newbie
  • *
  • Posts: 6
    • F Body Forum Germany
Re: Rochester 17058266 (1978 - Pontiac W72 carb) - tuning
« Reply #4 on: January 12, 2019, 10:32:14 AM »
you got a PM

Offline BanditRich

  • Newbie
  • *
  • Posts: 2
Re: Rochester 17058266 (1978 - Pontiac W72 carb) - tuning
« Reply #5 on: January 19, 2019, 04:47:59 AM »
I've got a 78 TA with a modded out W72 similar to your setup but mine came with a 1607 Edelbrock carb when I bought it. It ran ok but not the way I knew it should with what was done to the  engine compared to my last one with the quadrajet.
So I got the correct  78 quadrajet rebuilt with Cliff's HP kit and it made a BIG difference. You will be very happy with your carb - and your car after Cliff sorts it out.  8)

Offline pega_de

  • Newbie
  • *
  • Posts: 6
    • F Body Forum Germany
Re: Rochester 17058266 (1978 - Pontiac W72 carb) - tuning
« Reply #6 on: January 19, 2019, 12:08:02 PM »
The first one from 2010/11 what I bought from Carb Junkys looks great. But the 2nd one... I don't can trust them. Same number, same build year, but one more vacuum port on the front side.

My both Rochester are on the way to Cliff.

We will see what he say.