General Category > Quadrajet Carb Talk and Tips

weak part throttle acceleration

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bob69:
Thanks for the info. I have the Lars write up. Downloaded some time ago, along with his other articles. Good info, I've been using for all my cars. Also remember reading an article recommending the B1 vac can which is why I used it. But after getting  everything else sorted out, it just was not as good as some I have. Really like the delco 355 -15 can, but its unobtainium.

I think I'll try changing the vac can first. Some of the high performance one are still available. I found a standard Motors VC181 that's marked B26. Very similar to to B28 (which to looks to be discontinued). Also found an echin VC1765 marked as B20 which has the same specs as B26. Just a different price.

If I have to go with jet changes, I'll make sure to keep the same jet/rod relationship. The cruze performance is right on. I'll provide an update when the changes are made.

Cliff Ruggles:
The B26 is one that I use but they add too much timing for most well thought out engine builds so need limited.

When I set those carb up here I employ the APT system by installing one of my external APT screws.  Then I can get the jets size right, and fine tune part throttle A/F w/o having to pull the carb apart. 

Since you didn't buy your rebuild parts from me plan on putting an acc pump in it for sure.  Greg bought a lot of parts from me, including my accl pump springs, but kept using the "soft" blue seals on his pumps that swell up in this new fuel.  He didn't use the high flow non-windowed N/S assemblies either, which are usually required for big block applications.  You usually don't find that out till you get a bloody nose when the car noses over at the top of 1st gear on a hard run and you bounce it off the steering wheel!.......

bob69:
Update. Finally installed a B26 adv can. That did the trick. Part throttle acceleration is strong now. However,  B26 gives too much advance as Cliff noted. The new can was giving 18° total adv when fully employed. The B1 was around 16°. I could hear a slight ping at times. Not constant and barely noticeable, but there. The exhaust is kinda loud.

Looking through the internet for ideas and decided to make a stop from brass shim stock. Shaped like a T. Bolted on with the front screw and going back to the advance slot. Advance now limited to about 13°.

Not only did this stop the ping but overall performance was noticeably improved everywhere. Obviously the over advance was hurting power.

Not sure how well the advance stop will last as it is thin shim stock. I saw a few posts talking about stops that were available in the past. Does anyone know if/where the are available.

Some measurements for the two adv cans. B1 adv started at 10 hg and fully in at 20 hg. The B26 started at 8 hg and fully in at 14 hg. B26 is the only one I found that was very close to the HP can GM used back in the day.

Fyi,  I bought two B26 cans. One checked out at 8 hg/14 hg. The other checked out a 7 hg/15 hg.

bob69:
Found a Crane 99619-1 vac adv stop in my dist spare parts box. This stop attaches to the rear vac can screw to limit the vac cans overall travel. The stop provides adj in 2° increments. More tunable than a fixed stop attached to the front vac can screw. Set the max adv to 12°. 

Forgot I had it. Did not use it at first because it will increase the amount of vacuum needed to start the advance. Using it changed the vacuums starting point to 9° from the 8° without it. Seems to be working good. Too bad they are not available any more.

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