Rochester 17058266 (1978 - Pontiac W72 carb) - tuning

[pega_de]

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

[Cliff Ruggles]

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 

[pega_de]

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

[Cliff Ruggles]

I'm sure we could make a good working unit from them.....Cliff

[pega_de]

you got a PM

[BanditRich]

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. 

[pega_de]

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.

[Cliff Ruggles]

Marco, I have your carburetors apart and have evaluated both of them.

Neither one is set up for what you are doing, too lean everyplace.  They also have multiple issues and they are not using high performance or even good quality parts.

One of them had two gaskets under the fuel inlet seat (they left one in place by mistake and it was leaking.  There were two decent size holes in the float on that one as well like someone pushed a screwdriver down thru it.

The accl pump on the second carb was stuck tight in the pump bore and it had the tiny .110" fuel inlet seat.

I can get both of them up to par for what you are doing and have them ready by the end of the week. 

Just let me know what you want me to do.

Best to reply to:

cliffshp@embarqmail.com in addition to PM here because I check that account several times a day.....tks....Cliff

[pega_de]

you got a PM