Quadrajet Problem Solving > Dialing in your rebuilt Quadrajet carburetor

17057266 1977 W72 q-jet- changes necessary?

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Mr Hand:
I have a question about about the 17057266 emissions era q-jet:


I have a 1977 Pontiac Can Am and it has this original numbers matching carb still on it. It appears to have never been opened up before and this may be true since the car only has 40K miles on it.

I have never drove the car because it needed work but it did run ok and idled very well. The engine is currently out for a rebuild due to severe oil neglect and the damage it caused so I am unable to due carb testing.

Anyway, I have the carb apart and I am getting ready to install the basic rebuild kit I bought from Cliff when I noticed it has different primary jets and rods.

17057622 auto trans carb should have 71 jets and 42K rods.....mine has 72 jets and 45L rods. Why I dunno as this was a one owner car with no history of carb work let alone a jet/rod change. Float setting was still at the OEM 17/32"

For comparison a  1978 W72 carb auto trans 17058266 uses 72 jets but has 45K rods. Not sure what the difference is between 45K and 45L rods.

As it turns out the EGR system will be non-functioning when I get the new rebuilt engine installed due to a bad EGR backpressure transducer. Instead of trying to find this rare part to make the EGR work properly I will run without it.

Will the carb need to be re-jetted to be made a little richer since the EGR is disabled? If so will it be as simple as a jet/rod/power piston spring change? Or is it ok with whats in it now? I plan on raising the float up a bit to 13/32" if that will help with anything? I'll be using a new Carter mechanical pump.

Engine will be totally stock right down to the single exhaust with the original catalytic convertor.
Just a .040 overbore and a 066 cam which is almost identical in duration to the original W72 cam with the only difference being slightly more lift at .407 vs .364

Original HEI was rebuilt to stock specs with the exception of a vacuum advance unit limiting the advance to 10 degrees instead of the stock 25 degrees...... since the EGR will be non functional this change should help avoid pinging.
 
Thanks for any help.

Cliff Ruggles:
45 L are slightly tapered at the upper section then taper all the way down to .026".  The "K" rods only taper .005" then "step" down to .026".

72 jets and fine for what you are doing, EGR or not.

It's a crap-shoot with currently available fuel pumps, some are high pressure like the OEM some are not.

If it's a high pressure OEM type pump the factory float setting will be fine.  You should be installed a new float and do NOT use a brass one.  This new fuel eats the solder out of them and they are too heavy and don't work right anyhow.

Any slight recalibration from not using the EGR can be done with the APT system.

Not sure why you would limit the VA to 10 degrees.  Those engines have really low compression and it may like, want and need a bit more timing from the vacuum advance for best efficiency.  I typically don't reduce timing from the vacuum advance for "stock" engines.  Completely different deal when you tighten up the squish, increase compression, improved cam timing, etc........Cliff

Mr Hand:
The distributor was re-curved to be all in by 3000 RPM which is the main reason the 10 degree vacuum can was used.

Would it be ok to use the original 25 degree vacuum can with this fast timing curve?

Thanks for the advice on the carb.

Cliff Ruggles:
Most of those HEI's had the timing all in about then anyhow so about all that would have been needed to "re-curve" it was to open up the "eyes" in the springs slightly or use one slightly lighter spring on one side.

I hope that whoever did the "re-curve" welded in a positive stop for the advance, they will add timing at high RPM otherwise as the weights are now able to "roll out" on the tips past the "flats" on the cam if the stock parts were retained.

If the "goofy" parts from one of those POS aftermarket kits were used it becomes a crap-shoot for timing control, they are absolutely pure junk and to be avoided.

As for adding timing with the vacuum advance those engines are really low compression and set up pretty lean for emissions.  It will like some fuel added from the carb as this new fuel lacks BTU's and needs about 5-7 percent more of it to act the same as the fuel they were originally tuned for.

They will also like a hot thermostat, and a lot of timing at cruise to be happy.  The factory set them up with pretty high initial timing specs as well.  Many were up around 18 degrees initial nearly as I can remember, around 20 degrees from the mechanical advance, and over 20 degrees from the vacuum advance.  That puts them up there pretty high at light part throttle cruising depending on the exact RPM's as the mechanical wouldn't be "all-in" till around 3000 or close to it.

So my advice would be to start out with at least 15 degrees in the VA and work from there.  I'd also use the APT system in the carb to add or take away fuel with the timing changes to find out what the engine likes the best.

My bet is that it will like a lot of timing from the advance and need 48-52 or so at light part throttle at freeway speeds in high gear..........Cliff

Mr Hand:
Reviving this old thread:

Been a while but finally got the new engine in this spring and been slowly breaking it in.

300 easy miles on it.

'77 Can Am..............040 over 400..........stock 6X heads..........066 cam......2.41 highway gear...all emissions equipment hooked up and working including EGR, CAT converter, etc. Running at a constant 190-195 degrees which is thermostat temp.

Carb is a 17057266 stock rebuild with one of your kits, rebushed throttle shaft and all internals are stock......stock rods and jets...........72 jets and 45L rods. Only change was backing out the APT almost as far as it would go to eliminate a slight off idle bog, which it did for the most part.

Engine runs great, no bog, hesitation and great idle. Smooth acceleration and very throttle responsive. Pretty good power for what it is and how it's geared.

2 problems:
Runs extremely lean. After 300 miles plugs look brand new. Almost like they just went in yesterday. I was a little surprised by this because of how well it runs. Need to fatten up the carb so it'll run richer? What is the easiest way? Thought about playing around with jets/rods but is there another way? Will bigger idle tubes help with anything else besides idle quality?

Other prob is it pings like crazy at speed once I am into the secondaries. I kept the timing specs stock just to establish a baseline and go from there......16 initial, 24 mechanical, 25 vac advance. It was re-curved to be all in by 3000 RPM.

I backed initial down to 14 but have not test driven it yet to see if it did anything, but based on how bad it's pinging I dunno if 2 degrees will make much difference. I have other vacuum cans to try if need be........a 10, a 15 and I think a 20. But is vacuum advance much of a player at heavy acceleration? There is no positive stop welded in on the advance as you mentioned in your reply earlier BUT, the guy who did the recuvre, Bob Davis, initially had only a 10 degree can installed on his re-curve job, I am the one who swapped it out with a 25 degree can. Did he put the 10 degree can on there for a reason to go with his weight/spring combo? Did I mess it up by putting on the 25 degree?

advice where to go with this?

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