i have decided that my new carb is a piece of junk. i currently have a holley 670 street avenger, and it is about a year and a half old. it has given me troubles all year, and i think i am just about to buy a new one. what should i go with? i have a 289 that has just been rebuilt, pretty high performance. stock heads, but bigger valves and completely redone. i have an edelbrock rpm intake. i have heard that i should stay away from edelbrock, but now im not so sure about holley. what do you think? thanks for the advice!

 

The Street Avengers are not junk. You say you have a "pretty high performance" 289, but it has stock heads just with bigger valves? That's not really high performance. What cam do you have and what's your compression and exhaust system? My bet is that your intake and carbare just too big. I'm running the 570cfm Street Avenger and prolly have more engine than you do and it runs great. And have you done anything to try and tune the carb?

 

for what you have, most likely a 570 street avenger or a 575 speed demon. the speed demon is probably the better carb out of the two, but its about 100.00 more than the holley (for good reason).

the max you would want to go on that thing would be something like a barry grant 625 road demon

 

Love my Autolite 4100 - it comes in 480 cfm or 600 cfm. Bulletproof & simple. ( I have a spreadbore converted 600 cfm on my 289 and it works flawlessly).

Get a history on this carb at: www.ponycarburetors.com

 

sorry to offend you 67mustang302. my compression is 10.5:1, and i have 2.02 intake and 1.60 exhaust valves. and a comp cam Xtreme Energy (Duration 262/270-Lift .493/.500). also bored .030 over. when i pull the throttle back manually at the carb and watch the spray in the carb, it is not spraying the entire time i am pulling on the throttle. so something is obviously wrong with the carb itself. this is my second carb, since the first carb also had a defect, but was covered under warranty. as for the carb being to much for the engine when the carb was working properly, it ran great. it was also professionaly tuned, i had the engine shop tune the carb with the engine. the jets are now at 68, which is what holley told me to run in the carb. wasnt trying to offend anyone, but just frustrated with this carb and looking for an alternative. thanks

 

You're not offending me, but the fact remains, they're stock heads. Bigger valves in stock heads aren't going to do much, unless they've had a VERY good port job done. Is your cam a roller or a flat tappet cam? I'm thinking it's the XE262H cam, hydraulic flat tappet? That's not a huge cam by any means, the cam I have is a roller cam that moves more air than that one does, but that Comp cam you have is still a good cam for a street car. Like I said, I have way more engine, bigger cam, and a LOT more head, and get along fine with a smaller carb. If you run a bigger carb like the 670, regardless of whether it was professionaly tuned or not, as the weather and what not changes, any minor tuning deficencies are going to show up more rapidly. All I did to mine recently was install a sealed hood scoop, and it threw the accelerator pump off. It doesn't take much to upset a carb.

As far as the spraying in the carb, I'm assuming you're talking about the fuel from the accelerator pump circuit. First of all, it's not necessarily supposed to discharge fuel the entire time you open the throttle, that's going to vary with the cam/squirter/spring setup on the carb, and it needs to be tailored to the engine. Generally the pump shot is completely discharged before you reach the WOT position if you open it slowly. Secondaly, depending on the squirter size, cam selection and the pump actuating arms' spring tension, the way and rate the fuel is discharged is going to change with how rapidly you open the throttle, and what position that throttle is at when you start opening it. If it's at idle, and you snap the throttle open, you're trying to deliver the entire pump shot through the squirters which are offering resistance, that gives the most fuel delivery over the longest period of time, but if you are at half throttle when you snap it open, the pump arm is already most of the way up the cam, and you only get a short low volume squirt(which is what you want, since air is already pulling fuel from the primary metering circuit, limiting the need for a alrger pump shot). The faster you open the throttle, the longer the pump shot is going to last relative to the throttle position. If you snap it open quickly, most of the shot will be delivered AFTER the carb has already reached WOT.

I can understand your frustration with carbs, they can be a real pain to tune sometimes, but don't imediately think you have a bad carb and go spend money on another one, you may just end up wasting money. You haven't even said what the problem is with the carb, what happens when you drive it, does it have a stumble, a falt spot, what? I'd be willing to bet that your carburetor is just fine, but since it's bigger than you need by a fair bit, that whatever problem you have is just a slight mis-calibration as a result of the airflow problems you're having. Bigger carbs, especially on an engine that doesn't need it, have slower velocity in the venturis, which leads to the carburetor being MUCH more sensitive to minor changes that affect the tuning. If you tell us what the problem is I'm willing to bet we can work you through it and save you the money and trouble of having to get another carburetor.

Street Avengers are good street carbs, not the best, but for the money you spend are a decent carburetor that performs well. If I can get370+hp out of a 302 with a 570cfm Street Avenger then they're obviously not crap. It's highly unlikely you have a defective carburetor. Though that may be the case, it's a very good bet that it's just a tuning issue with the carburetor

 

i cant seem to get the car to idle. it dies as soon as i get it started. it sounds aweful too when i try to keep it running at about 1000 rpms. but as soon as i get the rpms up to 1500 and above, it runs great. i just replaced te accelerator pump today, and that wasnt the problem. i am just confused because it seems like i can get the car to run perfect for a day or two, and then it is back to the same way it was before? i took it to my mechanic and he just adjusted it a little bit, and it ran great for a day. i didnt change anything, and it started acting the same way again.

 

What about your distributor, everything in it is in good shape, there's no reason to suspect that there's something wrong with it? It's not super old and crusty with ancient parts in it? Also, you used a new fuel filter when you put the carb on? And have you tried setting the floats and idle screws? Also the idle speed setting, have you messed with that? And what power valve is in it? Also, has this been occuring on the same tank of fuel, or have you fueled it up at all since this problem started? And do you know what the fuel pressure is at idle?

 

It most likely is NOT THE CARB!!! The poor carb get the blame for more trouble than it is capable of causing.
Bad idle...it's the carb....never mind I didn't check vacum.
Poor fuel milage...it's the carb....never mind the old plugs gapped wrong, the old timing chain with 3/4" too much slack, never mind the plugged with dirt air filter. Never mind the fact that the carb has never had a filter on it. Never mind that the fuel filter is clogged with dirt.
IT'S THE CARB...IT'S THE CARB...IT'S THE CARB.....BUY A NEW ONE....IT'LL RUN FINE FOR 100 MILES.

All sarcasism aside, make sure everything else is right before you go and spend another $350.00 on a carb.

 

In most instances, the main 'carb' problem is that is just to damn big for the engine. That malady is refered to as being 'overcarburated'. It's a fact.
Consider appling the hi-tech answer - 'operator problem'.
Jim