Hi all.

So just got my motor broke in last weekend (455cu). All went well. My issue is i am running the same carb as before the rebuild which is a 670 street avenger completely out of the box. Which worked ok with previous build. But have ported the heads and went with a larger cam (240 dur.) I would like a bigger carb but with the amount of money I've spent so far 500 bucks on a new carb isn't going to fly with the wife. Anyway timing is set at 14 initial and 21 mechanical all in by 2800 rpm. Issues- Slight hesitation just off idle when normal driving and at WOT would like more pull at top end. Its a 3700# car, 2500 stall, 3.73 gears. Just looking for some opinions on tuning this until able to get a larger carb.

 

Ok let me get this straight, you did all that stuff to your 455 and you expected it to run like before? With all due respect, really?
Needless to say you'll need to go up significantly on virtually everything, pump shot, jets etc.

 

Was not expecting it to run like before. Just ran out of money. Needless to say up on everything... got it.

 

Btw. If i was asking for sarcasm i wouldve asked my little brother. I was looking for advice until able to afford new carb.

 

snarkasm
just one of the many free services offered here

sorry I cannot help you other than levity

Try a used QJet?
I have a nice new one for cheap

I have found improved throttle response by using manifold vacuum for the dist'r
easy enough to undo, but won't affect WOT obviously

 

What jets, pump nozzle, and power valve are in it now?
And I'd lay off the full throttle runs until you put more jet in it. You could be doing damage to your fresh build.

 

excuse me but there isn't a real need to go changing everything Big .. at least not at this point. A carburetor meters air and adds fuel to that air, it doesn't give a rats behind what engine it is feeding there are some exceptions but for the most part the mixture ideally 14.7 to 1 is what you want. holley sets up their carbs to be very close at 2000ft I think so you may need to adjust some for that and mostly weather related variables to get the correct mixture using your spark plugs to tell if you are lean or rich .. unless you happen to have some 02 sensors installed. your flat spot is probably a loose pump cam actuator. should be no clearance at idle and at WOT you should have .015 to .020 clearance. you may also need to add a larger pump to help cover the cam otherwise should be good. having the carb too small is going to act like a rev limiter not much you can do about that you should have a silver spring in that one. adjust the idle mixture screws for the highest vacuum turning each one 1/8 turn at a time keeping both sides the same until you get your highest vacuum reading and then see if you have any flat spots you need to take care of and check your plugs to see how its running.

 

You're right, that 670 Holley is probably jetted just about perfectly right out of the box for a 455 with ported heads and a 240ish@.050 cam. Just adjust the idle screws, pump cam and you're home free!

Whatever.

 

yep that is pretty much what I am sayin lol within a few jet sizes it should be correct on whatever you stick it on if you have a cam that is too wild and won't idle right it isn't because the jets just all of a sudden became too small. It is because your idle bleed hole is going to need opened up some until you can adjust the mixture up and down both ways and make it die down then you should be able to get it running right. not the same as EFI much simpler but mystifying to most lol

 

I believe Captjim ran that carb on a mild 350 and it was lean for that! I would pull it apart and go up a couple sizes on jets to start. Your top end will be pathetic, no matter what.

 

I appreciate all the comments. Really do!!!! Even yours cutlassefi. Car runs great. But yes i know i need to go bigger. Just trying to get by for a month or so. Will look in to going bigger on jets, squirter, etc tomorrow. Thank you all

 

So today i went from a #31 squirter to a #37. Also went from 65 primary jet to a 68 and a 68 secondary to a 71 jet. It pulls a max of 10hg vacuum in gear with idle screws set and carb comes with 6.5 power valve. By looks of plugs still very lean. I know, i know... what do i expect right... car runs better. Should i swap power valve to a 4.5 and go a lot more on jets. Clearance good on accelerator pump arm. Any advice?

 

[QUOTE=mrhotrod;827288]excuse me but there isn't a real need to go changing everything Big .. at least not at this point. Really? Did you happen to read his most recent post? ideally 14.7 to 1 is what you want. QUOTE]

And sorry, but if he's able to run an air/fuel of 14.7:1 with that cam and no drivability issues then I'm a monkeys uncle. Just sayin'.

CWB - keep going in the direction you're headed with the jets and power valve. I'd go to a 4.5 then jet changes from there. Try to do one change at a time. And ideally a wideband O2 would be a big help here. Good luck.

 

Like I said to begin with the carb needs to be set up for the correct alt. and conditions from the start. from that point you should be within a few jets of perfection adjust pump shot and timing to help cover your cam and you may need to adjust the idle bleed to get a good idle. I have never had to do that myself and have not had to vary wildly from the factory settings after initial correction. and I also ran carbs sized closer to the needs 850 and later a 930 carb on my built engines. 650 spreadbore on the stock engine so this is a small carb for the engine. bottom end it should work really well but it isn't going to do well past maybe 6,000 rpm your power valve opens at the point indicated so a 6.5 opens at 6.5 inches of vacuum if your engine maintains 10 then you are fine going down to a 4.5 will make it leaner.
14.7 is merely stoichmetric the point where the air/fuel is most completely burned so ideal for emissions and you can attain that but as you said not without issues and as far as racing goes you are going to be closer to 13.0 - 1 maybe lower under hard accel all the time. so a happy medium has to be found and the best performance will be very close to being lean but not lean. all that means nada to anyone trying to tune by the seat. if plugs are reading lean you have to give it more, I am just pointing out there are a lot of other things to look at like that monkey over there lol

 

That's pretty cool , you say something, I challenge it, and you come back and contradict your initial statement. I appreciate your willingness to correct yourself.
Just a suggestion, I don't doubt your knowledge but you may want to stop and think for an extra second or two before you post. That might save having to say things twice. Just a thought .

 

hehe well don't mistake my unwillingness to participate in sniping for stupidity . I just don't enjoy or have the time for it. I do like to help ppl out when I can, I do that because that's who I am. your actions speak volumes about yourself, maybe you will make the mistake of rolling into the lanes with me someday and we will find out just how well you can put it to the track.

 

I don't drag race, never have. I'm more of a road race guy. I'm into the technology of F1 and beyond.
But here are the facts. You said he didn't have to go bigger, he did, just as I recommended. And what was the result? It ran better. Then you mentioned a stoich number of 14.7 but back peddled and said it might not be right for his application, just like I did. So what are we to think?
The irony is this is isn't Rocket science, no pun intended. There are lots of guys that would have given the same advice I did I'm sure.

I believe in shooting straight from the hip, not beating around the bush or talking out of both sides of my mouth. It's just the way I am, sorry.

Thanks.

 

f1 and beyond lmao.. ok boss you let us know when you run into Buzz Lightyear out there.

 

If you think Mark(Cutlassefi) is harsh, go to Real Olds Power and hang out with GM Rocket also known as Dale Robinson, the 400 hp 307 guy in the engine masters challenge. Mark brought the idea of a stroker small block Olds crank to Eagle. Dale told us we were all retards trying and we don't need one. Then a short time later he was looking for a, you guessed it, bigger stroke small block crank.
I was going to call him on it, just wasn't worth it. Mark helps a lot of guys on here and definitely right about this carb, lucky the guy didn't dentonate his build to death or burn a hole in a piston.

 

Ok so done with 670 AV. Going to order new carb next week. The funds are there. Question is how big do I go? 468 ci, 240 dur. Cam, air gap intake, ported heads, 2700 stall, 3.73 gears, shift rpm 5500, and 3700# 71 442. Would like vacuum secondaries for drivabilty. Cutlassefi I've heard you say due to smaller plenum size on air gaps they like bigger carbs. Any ideas?