jb78L-82

I have had the Holley 4175 650 CFM Qjet replacement on my 78 L-82 since 1985 and it runs and performs great! I recently rebuilt it myself 1 year ago and it forges on like it has for the past 27 years. I much prefer it to the OEM q-jet-performs very well, idles well, starts well, easy to tune and simple to rebuild. It really is a very good carb.

gerry72

You don't often hear anything good on the 4165/75 Holleys because angry forum hornets will descended on you. They are not Quadrajets, but they are very good replacements for one. Performance between them in most installations is about equal. The real upside is if your Q-jet is bad and you need an out-of-the-box replacement, you can get a brand-new Holley spreadbore that will bolt on and run right without further consideration.

I'm not a carb snob and if you want to run something other than a Q-jet, I'm good with that.

7t9l82

can't seem to find this, could you post a link?

Kid Vette

I've been running a Holley spreadbore for a few years.



I have a couple complaints. It stalls the engine during hard braking. I think it is the fuel sloshing out the vent tubes. I've added taller vent tubes but it still stalls. Next step is to install a hose to connect the 2 vent tubes.

The other complaint was there were only a couple steps on the fast idle cam which kept the idle too high for too long. I ended up swapping a fast idle cam from another Holley.

I have a couple old Q-Jets stashed away in the garage. I think I'm going to build one good one from the 2 and try that.

7t9l82

check your float level

SLVRSHRK

I've got the 4175 650CFM replacement as well. I've replaced the secondary metering plate with a metering block which has alllowed me to tune the A/F ratio in the secondaries.

Seems very solid and I have had no problems.

jb78L-82

I have not had either of these issues with my 4175 (27 years now). No stalling from hard braking nor fast idle issues-idles at 900 RPM at fast idle and 600 when warm-I just adjusted the fast idle adjustment cam that came on my carb. Maybe your fast idle cam was different.

Kid Vette

Wanna trade carbs?

Matt Gruber

7t9l82- here is my article-
.
Here is my best old school low cost replacement carb pick
If you start off with a great carb, you will be happy with little tuning. Holley put a lot of effort into their Q-jet upgrade, take advantage of their hard work and use it! It is flowing on the boosters by 1500 rpm, perfect for overdrive. (most popular Holleys don't flow anything from the boosters below about 2500 rpm cruise, too high for good manners, and the transition gives about 3 mpg less on the street, even after being properly tuned by an expert ) Square bore carbs used on the street are primative compared to a spread bore 4165-6210. Those square bore carbs may be great for racing, but too often, they suck gas on the street
The primarys on a 4165-6210 are properly jetted for Chevy V8's, but your engine needs at least 12" of vacuum at idle, and should be able to idle at 800 rpm or less to use this carb with no mods.
The 4165-6210 gives me 18-20 mpg stock with a 355 and a mild(224/224 110 LSA) cam. Improve the WOT richness, and you are done!
The 4165 has 2 inch secondary throttle plates; like on a Dominator 4500.
Note: Carbs with bigger primarys often will cruise on the idle transition circuit and get as bad as ~9 mpg. That can be improved with oxygen sensor tuning, but guys not into super tuning should just start out with a great carb in the first place: Buy the Holley 1970 street legal 650 cfm double pumper 4165 model, #6210 cat# 510-0-6210 at Jegs (8-09) for $449(or shop around) I buy mine used at swap meets for $15-50, and they ALWAYS need to be rebuilt, even the 1st one I bought in 1975. Now they can have leaky passages as they are so old. So a new one is not a bad deal.
Also get a power valve plug 510-26-36 $5.
Plug the secondary only!(not the primary)
Get jet kit 555-15020 $15(extra jets for fine tuning at the track for fastest mph)
Install #78's(.089" dia) in secondary.
Or use the maxjets .088" for $5
If you don't have the spreadbore pattern, get the Weiand manifold or the RPM QJET Then you can use this great carb and save yourself a lot of time and money,
I assume you have one or 2 of the Holley carb books, and are familiar with all the adjustments and basic set up.
The little known 4165 is fun to drive, gives excellent mpg and instant throttle response. This is because it has 1:1 linkage; the front & rear open together(after 0.24" front) With a stick it will tend to spin the tires on a quick shift even when you let up on the gas between shifts(when racing). Road racers prefer the quick response of 2 accelerator pumps and 1:1 linkage. They want to win! Automatic or stick, it doesn't matter, 2 accelerator pumps and 1:1 linkage will let you exit a corner faster.
You see, while more common, a vacuum secondary Holley carb adds a slight delay. They are progressive, first the front opens all the way, only then does the rear begin to open. You have to push the pedal more to get the car to respond. Not the case with a 4165! And the 4165 gets great mpg when you take it easy. If you don't have the stock 4 hole manifold, be sure to get the #1905 base gasket; very important! See previous page for details.
Are the primarys too small? At 0.24" throttle(it goes 1:1 by 1/4")
(rear closed) cruise is anything up to ~120 mph. If your heads have ports thought to be "too big" the 4165 may allow their use due to the increased velocity and better atomization.
Out of the box, the 4165-6210 will be very close. Holley did all the hard tuning work for you! But they don't have your combo, and don't know your driving style, so no carb will be perfect. After changing the rear jets on the 4165-6210, the remaining difference may only be about 1%, so is it really worth the time and money to pick up maybe 5 more HP? And nothing in the mpg at cruise area? Only if you are championship racing, or enjoy tuning as a hobby.
I've been using them since 1975. Had a 283 back then and it worked great with no mods. Now I use it on my 355. Friends use it on a stock 427 and a stock 454!
How did I find it? My 1st Holley, in 1972 was a universal performance, that CUT my mpg to 14 from 20! Then in 1975 I bought my C1, missing the carb. I asked my friend Al, if he thought the 600 cfm double pump 4776 would be a good pick. He said NO! IT WILL SUCK GAS LIKE YOUR OTHER ONE. THE ONLY HOLLEY THAT WILL GIVE GOOD MPG AND MAX POWER IS THE 4165-6210. It did not bolt on, so I had to go to a swap meet to find a Q-jet manifold.
So 19 years later, at the Circle Track Trade Show, I ask the Holley reps IS THERE A NEW, BETTER
CARB? They ask every detail about my C1 and surprised me by saying NO THE 4165-6210 IS BEST FOR STREET USE. And they gave me a catalog. On the cover it says SPECIAL STREET LEGAL CARB SECTION INSIDE! It is in there saying it is for 1965-1970 327, 350 and 402 Chevy. So if your 1st pick was WRONG, join the club.
As for "new school" the Summit 600 VS SUM-MO8600VS $260 gets good reviews on CF.. This is a redesign of the Holley 4010. It has removable annular boosters, and jets and pv in the bottom of the bowl. No need to drain gas to change jets! This design can't leak like a 4150/4160/4165. Can fine tune the air bleeds w/$34 kit. I tested a 4011 in my 72. The square bore model is a budget idea if a spread bore 4165-6210 can't be used. Another nice carb VS 680 cfm, check out the Quick Fuel Slayer SL600VS. Changable IFR,bleeds, jets, PVCR, all of them unscrew for fine tuning. $299. See test in Oct-2012 Car Craft.

jb78L-82

Not a chance! My Holley 4175 runs great!! After reading the problems folks have with Holley's and Qjets, I must have gold with my Holley!

68post

I bought a new #6210 about 1975 also, great carb - but no mileage with a 16 yr old behind the wheel .

The 4010 and 4011 carbs with their annular boosters are probably even better, and they should be.
(and I still love a good Qjet - but they getting harder to find in good condition)

thegazman

Matt.... What kind of choke does the 6210 have?

Matt Gruber

the summit cat says the 6210 has a divorced choke.
none of mine had the choke anymore(got them used)
it says the 80555c 4175 has an electric choke.

jackwabbit703

Stay with QJet. From my personal experience, I had professionally tuned holley 750 for about 48 hours. It was not good as QJet off the trap and not good as QJet on WOT.

I can't be more happier with my QJet and I am very picky about how my car performs in all aspect. But than again, no two cars are the same so.. it's just my personal preference and opinion.

Kid Vette

Did that a couple times.

68post

The spreadbore Holleys are that much differant than the squarebore Holleys, it is worthwhile and sometimes they are easier to understand (and tune) for some folks - compared to a Qjet.

Quadrajets are soo adjustable that they are intimadating to some !
I am a Qjet Lover also and I want my best one back !!

gerry72

Horse sheets. Every circuit that is in a Quadrajet is in a Holley -or any other carburetor. Load enrichment is different, but not in any dramatic sense. Once you understand how a spring works, you pretty much got that circuit nailed. I can go through a Quadrajet faster than I can go through a Holley. Not by much, but faster nonetheless. The only cumbersome thing about a Q-jet that slows me down is getting all the choke mechanism back in proper order. If that intimidates people, then they should probably farm out the work.

If you love your Q-jet, then we're all very happy for you and assume it's not because you don't know your way around other carbs.

68post

..did I hit a nerve ? I'm glad you are happy for me, but I sense sarcasm.

Something I said is horzshyt ? Folks that are used to changing jets or power valves in a holley - but haven't dealt with fine-tuning a qjet generaly are confused by them.

Jets with differant metering rods in them, coloums of metering rods with differant tapers to choose from, jets, hangers, cams, springs, choke pull-offs, etc..

I'd appreciate others opinions on this matter. Sorry for the hijack .

wheatpj

The turnaround time at SMI is pretty quick and they do good work.

68post

O.P. , when looking for a core there are 2 primary bore sizes that are common within the more standard types, didn't know if you were aware.