General Category > Quadrajet Carb Talk and Tips

cam selection

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Glutenfreecarbs:
Nice dyno results Tayto! I always figured TBI heads would make excellent low-end torque with the right cam.

Sorry to hear of your idle issues. Are you using vacuum advance? Do the mixture screws have any effect?

And I would NOT run more than 24° total timing under any kind of load with those heads...at least not with American 87-octane gasoline.

tayto:
I have vac advance, currently on ported.I think I have 6-10 degrees,I have not messed with it since last summer. Have control with mixture screws,can definitely slow and speed up the engine. I dyno'd it with (canadian) Shell 91, current have 89 in there and it doesn't seem to mind it @ 26* all in... It's been very hot here lately 95-100*f  and no audiable detonation.

tayto:
Opened idle mixture screws from 0.063" to 0.089". Upon taking carb out of service found i forgot to tighten the tube nut for the brake booster vacuum supply. Got my idle screw backed out a bit, and in-gear RPMs down to 550. Still have that random surge,all though it seems to be less now. Find it hard setting my idle mixture screws as the surge moves the needle. They're currently at about 5 turns out, but as I turn them in vacuum goes up slightly but hard to distinguish,sitting at about 12" in gear currently. Tried tipping in the choke and surge is still there. My timing curve starts coming in around 800 rpm. Not sure where to go next.

Cliff Ruggles:
I'd try stronger distributor spring(s).  In almost all cases fluctuations and surging in engine speeds at idle are the timing is not ROCK solid below 1000rpm's.

I see this a LOT as nearly every troubled vehicle that comes in here for idle issues and carb work has some attempt with cheap offshore distributor spring/weight kits to get all the timing in early.

Every offshore distributor I've seen being sold these days also uses something similar and most do NOT pull all the timing out when the engine returns to idle speed.

I actually LOVE those parts, they have helped keep my wallet full for at least 40 years now by charging folks to remove all that junk and put the stock/correct parts back in place!.......

tayto:
I have 2 extra GM distributors, will check tonight for stiffer springs. I took truck on a little road trip Yesterday and got some rattle going up about a 1km Long steep incline. about halfway up i went from heavy throttle and back off then went WOT and it shifted down to 2nd and i heard rattle. Sounds like a tip in issue, but wondering if I may have to lower my total timing. I currently have no vac advanced hooked up as I am trying to only do 1 thing at a time and not confuse myself.

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