Greetings folks, hope everybody is well today.

I had always been a holley carb bigot in my younger days. Since I have had this car I have tried to stay true to the Q-Jet, mostly due to support for it here on the forum and my recent curiosity about it. I rebuilt this QJET two years ago, the car had been running pretty good for the most part, but I have had several recurring issues "off the line" stumble and WOT breakdown with it. Now it's stumbling all over the place. So while I'm not going to fully give up on it, I am going to buy a Holley so I can get the car running good and consistent while I fiddle with the QJet. So the question is; which Holley to buy? I have narrowed to three choices. My motor is a 350-250 crate with Ebrock 2101 which supports both spreadbore and straight bore with headers and 2 1/2" pipes with Flowmaster 50s.

Carb Options:

1. http://www.holley.com/0-80555C.asp

Model 4175 Spreadbore. This one seems the most straight forward choice. ince my existing fuel line would bolt right up I am also assuming my stock Cowl Air cleaner would fit right on. if anybody knows any different please let me know. The cons here are it's a Spreadbore (I believe straight bores have smoother secondary transition) and no exterior float adjustment.

2. http://www.holley.com/0-80457S.asp

Tried and true Holley 600 CFM. Only con I can think of is I have to replace the fuel supply line as well and rig it right side entry. Any others concerns here?


3. http://www.holley.com/0-80670.asp

Street Avenger 670. This is clearly the most flexible for tuning options and seems to be a pretty adaptable. I still would have to replace the fuel line and may have to consider a higher volume pump to feed to float bowls directly. My other concern is my air cleaner I really want to keep the stock cowl induction unit installed. However my gut and at least one seasoned motor guru I know says if I do this I'll never look back at the QJet.

Anybody ever try a street avenger on a 73-75 with stock cowl air?

Thanks for your time, comments and opinions as always. Driving weather is here!

 

All three are much smaller than your 750 cfm q-jet. If you can get the q-jet running right, I'd pick it over your Holley choices. The off-idle hesitation can be fixed, usually by adjusting (increasing) the tension on the secondary air-valves. WOT breakdown could be a lean out. Some richer (thinner tipped) secondary metering rods could fix that.

Perhaps 10 minutes and $10 worth of metering rods might fix your problem.

If not tell us more specifically what exactly is happening and perhaps we can offer other suggestions.

Lastly, there's nothing sweeter than a well tuned q-jet,..well, carburetor wise.

Good luck!

 

If your just going to use it as a go between carb just bolt the 4175
on it, thats what its for a direct replacement for the Q-jet.

 

Thanks for reply's. I am leaning towards the 4175 per Little Mouse' suggestion. It will certainly make swapping back and forth with the QJet much easier. Something about the street avenger keeps calling me to it tho.

I believe my stumble problems are mostly associated with the accelerator pump adjustment. However I have already broken one rod and now with a replacement on it it's all out of adjustment again. If anyone has any good tricks for adjusting the pump rod I'm all ears. Like I said I'm not giving up on the QJet.....just yet.

Any other opinions or votes on this? thanks to all for the input

 

I just put the Holley spreadbore 650 CFM on my 68 427/390. Straightforward bolt in. Runs great. Excellent throttle response. Great low and mid range torque. It is plenty of carb for your motor. I don't live much over 5,000 rpm's so this carb works great for me. I am not a big Q-jet fan. I opted for the mechanical secondaries.

 

Capevettes thanks...thats great feedback...I'll probably stick with the vacuum secondaries...I think were getting close to this being settled..

I would still love to hear that my aircleaner will fit

Anybody ?

 

Why are you so sure it's the carb? Couldn't it be ignition, or fuel pump, or clogged fuel filter, or plugged-up tank sock,....or just bad gas?
Rule the other stuff out before you get out the checkbook.

 

I have a Holley 80457S on my GM 350-330 HO crate. I really like its simplicity, and it flows MORE than you need for 250 hp with lots to spare. (The Holley web site explains how to calculate how many CFM you need.)

As I've been posting on other threads, the 80457S flows plenty of air but doesn't deliver enough fuel out of the box for 330 hp with a customer 2 1/2" true dual exhaust and high-flow mufflers. I didn't have a lean acceleration problem with the stock parts until I put on full length headers and the custom exhaust.

 

? 650 on a 427 ? That seems very small...

 

There is no "reason" to get a new carb unless you need to change size or are switching intakes. There are plenty of things that could be wrong besides the carb. Even if the carb is the culprit, you should be able to fix it fairly easily.

 

Gents I appreciate your looking out for my wallet, but it's the carb! I have been fiddle farting around with this thing for over a year now. Points are new and timing is mostly perfect. I do have a little too much VA but I really don't think thats my problem. The reason I'm so sure it's the carb is that last year while trying to adjust the accelerator pump, I went through fits, and eventually broke the rod. Using a bubba rod (welding Rod) I was able to get it adjusted where it ran "pretty good". I recently purchased a parts carb, and pulled the working unit to replace the pump rod, installed new fuel filter etc. Now when I got the new rod on, the pump rod was a good 1/4" more extended than with my bubba rod. Sure enough I cannot adjust it out without fear of braking the rod....and I got this massive and intermittent stumble. Bottom line is this thing is driving me crazy and I have the Skyline cruise and other stuff coming up where I need the car to be stout and dependable. Mixed in with honey do's and teenage softball I'm taxed on time. Oh yeah and my boss seems to think he wants work out of me as well.

So at this point it's worth the cash to me to go the quick fix route. Like I said I am challenged by the QJET and will continue to try and conquer it, but I need my car running right now. B'side's I HAVE to do a Holley vs Qjet experiment of my own at this point.

I am however now leaning back to the Avenger. It turns out the 4175 does not have an integrated filter, which means I am replacing the fuel supply line either way. So since I have the spreadbore carb (QJet) I might go ahead with the straight bore holley. One or the other will be ordered by tomorrow.

Thanks again for all the advice.

 

I would add electronic ignition into the fix.

 

Be sure to let us know how it runs when you have it in and running!!

 

That's because everyone thinks that they need 850 double pumpers on 200 hp small blocks In 1966 and 67 the factory was putting 585 cfm Holleys on 427/390 horse big blocks. They ran fine. In fact for low and mid range torque the smaller carbs actually perform better and are more fuel efficient. There are alot of charts out there that speak to engine size/horsepower and RPM's and what size carb you need. I also spoke with Holley tech. A 427/390 horse only needs 650CFM at 5,000 RPM. I rarely exceed that and usually live in the 1500-4,500 rpm range. The low and mid range torque is fabulous with this carb. If I was doing 1/4 mile blasts I would consider a 750 CFM carb.

 

You are correct!
Holley recomends something between 600 - 670.
http://www.holley.com/applications/C...bSelection.asp

 

Drop the Quadrajunk.
Go Holley!
You'll never look back.

 

Speed Demon !!!

 

Strongly being considered. I ordered the 4175 carb today, so we will see how it does and go from there. The 600 did not have enough vac ports for my needs and the SA just looked too big and complex. The 4175 650 just adapts to everything too well to do anything different. it will also make swapping the Qjet back in much easier. The SA kicked *** in the voting though. I'll save that for future reference.

Thanks to all for your input....I'll keep you posted...