Holley carb question

[MikeB]

At least least there are few, if any, personal attacks here.

10-15 years ago I spent a lot of time on the ChevyTalk.org Performance forum. However, it's just about dead now. I think that's because several folks there jumped right into name-calling when confronted with differing opinions. I mean there were raging verbal battles which the admins tolerated. Too bad, because there were a lot of really sharp guys there, too.

[Palf70Step]

I was just talking to someone about this on my 70. The factory quadrajest are all 750 (or 850). He mentioned that a stock or mild engine the 600 650 is more than enough, but at higher RPMs they tend to make the engine run lean. So if you are gonna hot rod it a lot, go bigger, if like mine it is a cruiser the 600 is more than enough.

[MikeB]

Originally Posted by Palf70Step

I was just talking to someone about this on my 70. The factory quadrajest are all 750 (or 850).

The beauty of Q-jets was the small primaries, which made for much higher air velocity (and better fuel atomization) than even a 500 cfm square bore carb. So you could have the capability to flow 725-800 cfm without sacrificing throttle response.

[Mike_The_Grad]

Thank you guys for all of the responses. Some time has passed and I still have the 1850-3 although a little more tuned to my engine. Found out p.o. did a lot of tuning to this carb for his engine as well. Like capping off the fresh air vent for the electric choke so that it burned up the choke coil spring. So now its wired straight open all the time. Also installed a aftermarket power valve shield which consists of a hollow base plate screw with a check ball that acts like a vacuum signal passage for the power valve and the check ball will seal off that passage in the event of a backfire. The only thing is you have to block off the factory vacuum signal passage in the base plate with a lead slug and peen it over. Well he didnt do that, so I used a aluminum pop rivet ground down to a taper and driven in and peened over. Those two things alone cleared up about 80% of the problems I was having. I still get a weird whistle sound when I'm pedal to the metal and it's going through the power band. He also clipped the secondary diaphragm spring. So I bought a spring kit and ended up with the brown one but I think it's too stiff as I can only get the secondaries to kick in for a bout a second. So I'm gonna swap in a lighter one since I did all this other correcting of things and see how it reacts now. But over all I agree that holleys make more power than edelbrocks. I've had the truck up to where the speedo needle is about 1/8 inch away from 0 on the factory speedo. And it still had more it in. But that was fast enough for me. I'm ok with that.

[Ironangel]

Get that wide band AFR gauge set up, take the guess work out of the equation...

[sloGMC]

Originally Posted by Mike_The_Grad

So I bought a spring kit and ended up with the brown one but I think it's too stiff as I can only get the secondaries to kick in for a bout a second. So I'm gonna swap in a lighter one since I did all this other correcting of things and see how it reacts now.

What do you mean that the secondaries “only kick in for a second”? If you are trying to watch them open by winging the throttle with the truck stationary, they probably shouldn’t be moving at all. And if you’re going to be taking the time to tune the secondaries it’s worth adding the quick change diaphragm if it hasn’t been done already. Did you read the tuning information that comes with the spring kit? And I agree with the others that have mentioned getting the O2 sensor. It makes tuning absurdly easy.

[garyd1961]

Originally Posted by Myself

That carb is too small for your engine. I've been all through the carb rat race, tried everything and learned to tune Holley carbs. I don't care what you do......your torque and power are missing from this small carb. I LOVE the Holley Street Avenger carbs for a street rod. They're just about dialed in perfect right out of the box with only minor tuning to your specific combo required. On a 383 stroker I would go with the 770 Avenger with vac secondaries, NOT a double pumper. That engine will really come alive!

570 Street Avenger on a street 305
670 on a healthy 350
770 for 383 and 400 smallblocks


Oh,.....and after you get all your power that's missing by changing carbs, you're welcome

This^ , plus as someone else said your compression is mighty high for iron heads.