Re: Holley Carb problems
Holley Reference Book 36-51-7
650 CFM, 4175
1975-78 Chev/GMC, All 3/4 & 1Ton Truck, 350 4-barrel W/AC
Holley Carb Usage From .pdf file on Holley Tech Website.
Holley 4 barrel, Vacuum Secondary
Spread Bore (Preformance Quadrajet Replacment)
Type 4175 (Spread Bore)
CFM (Cubic Feet Per Minute) 650
Renew Kit 37-1537
Trick Kit 37-933
Primary & Secondary Needle & Seat (16-17)
Primary Main Jet Size 122-542
Secondary Main Jet or Plate N/S
Primary Metering Block N/S
Secondary Metering Block N/S
Primary Power Valve 125-211
Primary Discharge Nozzle Size .025
Secondary Spring Color. Black
Primary Bowl Gasket 108-92-2
Primary Metering Block Gasket 108-91-2
Seconddary Bowl Gasket 108-90-2
Secondary Metering Block Gasket 108-90-2
Secondary Metering Plate Gasket 108-27-2
Primary Fuel Bowl N/S
Secondary Fuel Bowl N/S
Throttle Body & Shaft N/S
Primary Venturi Dia.1-13/64"
Secondary Venturi Dia. 1-13/32"
Primary Throttle Bore Dia. 1-3/8"
Secondary Throttle Bore Dia. 2"
Don't sweat the fuel 'Seep' around the throttle shafts, all Holleys do it, and especially the older ones...
Spray a little 'Carb Cleaner' around the shafts, and see if the idle goes up.
If it does, you may have enough leakage we'll have to install bushings in the shafts.
If the idle doesn't go up, don't worry about the leakage, it's just ugly at this point...
As far as fuel level adjustment goes, you have the third type of common float bowl...
The one I didn't cover....
You actually have to take the float bowls off to adjust this type, and they are a pain in the butt of beginners.
(In fact, I don't even recommend beginners do the adjustment, have a pro rebuild the carb, and set the float level.)
You have to take the fuel bowl off, turn it upside down, measure the distance from the float to the bowl, and adjust the float level that way. (A rebuild kit has a gauge included, or you will have to buy gaskets and a gauge)
Be VERY careful of the fuel transfer tube to the back float bowls, that tube gets bent, or it's 'O' rings chewed up, you will NEVER stop the leak, and finding replacement parts for these carbs is getting harder all the time.
(The good news is, if you rebuild the carb, it should be good for another 20 Years!)
Auto shop teachers are a good place to start looking for someone competent that will work for cheap...
And a carb rebuild is pretty basic, so most good mechanics can do them in short order,
This is pretty delicate, so don't let just any 'Joe Blow' have the job...
If you don't have an Auto Shop (God Forbid!) teacher handy, try any of the local Auto Mechanic trade schools.
Most teachers are grossly under paid, and will 'Moonlight' for cash... Also, be generous when you pay him...
This would be a good friend to have...
Rebuild kit should be under $60. Most are around $40. A gallon of carb cleaner is around $10.
(Gunk brand Part Number CC3K works well, can be purchased at most auto parts stores, and has a small parts basket included in the can.)
Expect $20 to $40 in total labor from an individual, and $35 to $45 AN HOUR from most shops.
I can almost tell you what has happened here now...
This carb is old enough that it doesn't have the Power Valve saving anti back fire valve, and the thing is probably just filthy inside... (haven't made these sense about '79 or '80. Newer made carbs externally adjustable needle and seat float bowls)
I'd pay the extra money and have the anti-backfire valve installed (we do it for under $10 here, parts and all, during rebuild).
Here is a little tip, if you open the rebuild kit, and the carb turns out to be junk, you can not return the kit...
Have the guy tear down, and clean the carb, then go buy the rebuild kit when you are sure this carb is repairable.
On the up side...
I have used TONS of these carbs down through the years, and I like them!
(Everybody else thinks they are a pain in the butt!)
If you change the float bowls to ones that are externally adjustable, you can use the spring loaded needle and seat. (Off Road Needle & Seat...) AND you get the side pivot, round floats.
I have great luck with this spread bore arrangement.
You can really get great bottom end throttle response with those small primary venturis, and the secondaries are large enough to feed almost any small block!
There was one stupid version of this carb made that had backwards idle mixture adjustment screws...
I can't see the screws in your picture... and the book guys didn't see fit to include it in the mechanical drawings...
Get me a picture of the idle mixture adjustment screw from the drivers side... I can tell in short order from that ...
In the mean time,
1. Just inside the choke horn there will be four little air bleed holes (not the 'shooter' nozzles).
Take a can of carb cleaner, and let those suckers have it!! Get the kind with the little red tube so you can get right down in there on them! Shoot straight down in them, really give them a good cleaning, with the engine stopped, and with the engine running...
See if that smooths your idle out...
You will find 2 to 4 more in the back of the secondaries, clean them too.
2. Screw the idle mixture screws all the way in LIGHTLY! Don't crank down on these, and immediately turn them out 1-1/2 turns.
You must move these screws together at all times.
Hook up your vacuum gauge (The one I told you to get...) to the carb base plate, (or manifold vacuum if you can't get to a base plate port, but base plate is better).
Screw in the idle screws 1/4 turn TOGETHER (always one side then the other) until you get lean misfire.
You can't miss lean misfire. You will know it when you hear it...
Back the screws out TOGETHER until you get the highest vacuum reading.
Make a note of how many turns (IE: 3/4 or 1-1/3 turns out, but both EVEN) out the screws are.
Have a beer, you have just set the idle mixture the correct way.
(The only way you can do it any better is with a real time exhaust gas analyzer or dyno, and not everyone has $10 grand to blow on one...)
REMEMBER, this is not a substitute for getting the float level checked, which is almost always wrong...
So many cats, so few recipes...