jb78L-82

I have been running a 4175 with vacuum secondaries since 1985 with no rebuilts and it still runs great. It runs rich at idle when cold but is perfect once the engine is up to temperature with no hesitation. My only issue is that the float bowels drain dry after sitting for a few days. Power is good and it idles very smooth. I do run the softest spring on the vacuum secondaries with no bog. Anyone know the cure for the draining secondaries when it has been sitting for a time?

Bob Onit

Well that problem could likely be cured very easily by adjusting the spring wind-up on the secondary rod.

Very common issue known as "QuadraBog"

Paul L

Pretty mixed reviews on that 4175 Holley carb. Is it the usual pain-in-the-butt, need a tool-kit-of repair-parts or not? A towel to mop up leaky bowls is an accessory. Bring along a Halotron fire extinguisher as well.

I had a Holley on a 1967 and it was a nightmare. Is the modern 4175 an improvement? My Q-Jet is ... just not right. I've done the usual Lars' things but it still has an off-idle stumble that gives me the heebie-jeebies. If the 4175 can solve that I will go with one.

PatG

I ran a Holley spreadbore for several years and although it worked great performance wise, I got tired of the leaks. I would find that the accel pump was leaking on the manifold many times. I did the usual parts replacement but the last time one of the threads on the main body gave way. I could have heli-coiled but I just went and got a rebuild kit for the q-jet instead. I gave it a once over, epoxy underneath to stop leaks and it works flawlessly even though the motor is warmed up well past stock for '79. It is good peace of mind to know that the carb is not leaking on the hot engine anymore.

capevettes

I put the Holley spreadbore, 650 with mechanical secondaries, on my 68 427/390. It ran perfectly right out of the box for about 4 months. I had replaced a problematic Q-Jet. Great low end torque, and great throttle response. I had been chasing a low RPM stumble and poor idle the last two months. After throwing the usual parts at it: plugs, pts, condenser, cap/rotor, wires and coil.... I took the carb apart and found metal shavings in the idle circuit metering block area. It was a factory blemish (incomplete machining) that allowed a metal flap to erode and obstruct the fuel passage. I cleaned it up and drove it yesterday and now it's running right. Not too pleased to find metal in there. I have heard of this with Demons but not Holleys. Great carb other than that.

Paul L

Does the GM air cleaner base clear the electric choke?

capevettes

My setup on the 68 is different than yours. The only problem I had was with hood clearance, even with the big block hood. I had to go with a slightly lower profile air filter. No clearance issues with the base/choke on my setup.

Paul L

I didn't realize that the Holley sits higher than this. That may pose a problem with the small block hood, especially if you had a clearance issue with a BB hood.

Reggie Dunlop

I have used the vac secondary version of the Holley spreadbore many times over the last 20+ years. The most recent version (non-emission) is a great q-jet replacement. Buy it new and it comes with just about everything you need to replace your q-jet - linkage pieces, choke lead wire, mounting studs, fittings, etc. You can do the swap in about 45 mins. I bought one for a 400 Pontiac about 6 months ago and it went on in a snap and runs perfect with no tuning other than idle settings, and this car is used for daily transportation. The old Holleys would leak sometimes, but anything made in the last 5 years or so has the new blue gaskets and works great. I have a 670 Street Avenger on my '79 vette. It's been there for 3 years - never leaked a drop, starts and idles fine hot or cold, gets me 14 mpg and perfoms super.

Paul L

No one has addressed the hood clearance issue? And the likes of Summit speak of use of the 4175 up to 1969 (trucks) and 1975-on (passenger cars). Nothing for 1974 Corvette. They further speak of "universal", "GM", "Direct Fit", and "Chevy" applications. All kinds of language but no specifics.

So if you had a 1974 Corvette with PCV, EGR, etc. what would you order?

dennis

I posted earlier, I couldn't run the 6210,(4165), on my 70 with the stock hood. The fuel bowls do not allow for the stock open element A/C. I had a L-88 hood at the time so it didn't matter.

I did have to re-locate the power brake vac hard line at the intake rear to clear those float bowls.

Paul L

Well, I guess I'll just stay with the Q-Jet and try to get the off-idle stumble fixed. I really do not wish to deal with mods. I did that on my 1967 with an Edelbrock and it was a real (and expensive) pain. Thanks for the comments.

timgman

If there is indeed a hood clearance issue, People like myself that tare using vortecs with a intake that has a slightly higher deck (an inch or more) will prob have a serious issue....
tag

Paul L

Thanks, Dennis. Very much appreciated. I put an Edelbbock #1406 on my 1967 and the mods were very $s intensive despite my own labour and tubing mods.

I will stay with what I have and just try to sort out the off-idle stumble. I have posted a note here on accelerator pump adjustment.

redwingvette

The 73-75 air cleaner will not sit down on the 4175. I had to put a 1/2" spacer on top of the carb so that it would miss the vacuum module.

rvaughn

Does anyone know how i would add a dashpot from my q-jet to the holley 4175 so the rpm increase when my ac comes on. 1980 corvette.

speedreed8

pretty old thread you dug up (2008) anyway, to add the solenoid to raise the idle when the ac compressor kicks on you will need: holley #'s, available from summit, jegs, etc.
46-74 solenoid
26-57 retaining nut
20-47 bracket.

http://www.holley.com/46-74.asp

jb78L-82

Just rebuilt my 4175 last month after 25 years-It was flawless up to this past summer. Started to be a little temperamental when cold so I figured that after 25 years it could use a rebuild. Other than a little silt in the float bowl areas it looked really good. Replaced everything that came with the kit and the Holley 4175 runs perfect once again-very smooth idle (at least for an L-82), better throttle response, perfect engagement of the vacuum secondaries, no bog at all or hesistation (I run the lightest spring for the last 20 years), and the gas mileage is good. The 4175 is a great Qjet replacement! Why?

It is relatively simple compared to the overly complicated Qjet, it is very reliable (people who quote problems right out of the box most likely have a 4175 not adjusted for their motor)-it's probably not the 4175, it is a snap to custom tune and adjust, and is easy to rebuild. The Qjet is a good carb when adjusted right and it good working condition. It's performance and reliability quickly deteriorate once it becomes "contaminated" by age, dirt, miles etc. A Qjet is a finely calibrated carburetor but the only problem is that carbs are not capable of being "finely" calibrated, that's why we have fuel injection today.My OEM Qjet became very temperamental by 1985 at 25,000 miles and I switched to the 4175-gigantic improvement all the way around-Still going strong 25 years later. I have never looked back!

Locke

Denis
Thank you so much for mentioning that the stock drop base air cleaner didn't work well with the Holley Spread Bore. I just got home from the cruise in and my car was running so poor I had pulled out the Holley Catalog to look up a 4165. I had one on my first '69 when I bought it and had to bump some clearance in the air cleaner base to get it to settle onto the gasket.
Until I can afford the LT-1 / Z-28 manifold I really want and a Holley square bore, I think I would be better off getting a rebuilt Q-jet.

Thanks for the memory jogger!

Locke

RIO68

For what it maybe worth-you can go to Amazon and look up Holley parts and compare prices you might be surprised. You can get the dash pot from them--works great on my 4175.