Warped Holley carburetor body repair and carb rebuild questions

[Clark Coe]

Today, Ross ( my427mustang ) warned me to make sure the faces of my Holley C8OF-9510-D 600 cfm  carburetor were flat. Went home and disassembled the carb and found that the Primary was .009” warped and the Secondary was .008”. This carb/Mustang has not been used since 1997 and it is time to get it back on the road. 



It took 30 minutes with a new file to cut the Secondary surface flat. Tomorrow I will file down the Primary side. I found that the more material to be removed, the slower the progress was. This would not be complex operation for a machine shop, but I want to get this carb rebuild quickly and move on to other tasks.



Question 1: Is the .009” warped mating surface enough to make trouble with how this carb would perform? Seems like the Holley gaskets would easily make up this difference. Am I fixing something that is not bad enough to be messing with?

Question 2: What is the recommended product to soak and clean out the dried / stinky gasoline film from the inside of the carburetor? Decades ago I used caustic carb cleaner that would burn your skin, but did it cut through the crud. That stuff worked so good, I am sure it has been outlawed. Would soaking in lacquer thinner, followed with carb cleaner aerosol spray and compressed air blow out be adequate?

[My427stang]

Clark, I'll answer with more of my own advice LOL

First, with no torque on the 4 bolts, you were warped .009   Now, add heat and bolt torque, some vacuum here and there and use a non-stick gasket instead of the old shellac gaskets that used to adhere to both sides and likely use nylon washers instead of the old soft ones.  Finally, let's add a fuel that has alcohol in it and likes to creep around a bit.  Yes I think that combination could cross channel

Second, I haven't found a need to boil, soak, or otherwise go crazy on a Holley.  Good carb clean, (Gunk or others, not Autozone brand that smells oily) blown through the passages, and occasionally air if you have a fussy air bleed, usually does all you will ever need.  Especially with something that looks relatively clean

Finally, although I do use a file in a pinch, you'll find a machinist can cut less and cut far straighter.  It's cheap money in my book

[thatdarncat]

You are correct that the old Methylene Chloride based carb cleaners worked great but seem to have been pulled from the market. It's the same main chemical in most paint strippers though, but they are usually gel based and wouldn't get into the small passages. They will work to clean the black sooty stuff from Venturi's if needed. I would avoid lacquer thinner, it will clean the carb but will also remove all the gold plating leaving the carb dull grey unprotected zinc.

[Clark Coe]

Thanks for the replies and advice. The picture of the filed surface does not correctly show the filed finish. It is not as crude as the picture would suggest. To set the record straight, Ross DID strongly recommend having a machine shop perform the milling operation.

This car is a driver and not a show car. I like the idea of using an original Holley-Ford C8OF carburetor. After 18 years of setting around it is externally reasonably clean.  I will forget about the lacquer thinner and use spray carb cleaner. Hopefully the spray stuff will dissolve the honey colored/stinky residue in the bottom of the fuel bowls.  Thanks again, guys.......you are always helpful.

[jayb]

+1 on getting those surfaces flat; even a small amount of warpage can cause trouble.  And I think filing the surface is just fine.  The machine shop has to fixture the carb so that an even amount is taken off top to bottom, and front to back, and that is not always an easy task.  To do it properly would take some time and make it expensive, at $75 an hour or so.  I've filed lots of those carbs just like you did, Clark, with no problems afterwards.  Good luck on the project!

[jimeast]

Getting Flat.

If you have a small surface plate, float glass or just counter-top granite.  you can put down some fine sandpaper on it and get a very flat and well finished surface by rubbing the carb back and forth.  One thing to watch out for is if the middle is the convex side, you can get into a rocking motion where things get worse not better.  You can use wet or dry or whatever seems most appropriate.  I've never done this with a carburetor, but I have flattened a number of cast iron hand tools this way.

The upper part of the surface close to the air cleaner area might be a little tough to make consistent with the rest of the surface. 

[RJP]

.008-.009" is not bad. I've done many 4 bbls that needed a .015-.018" just to clean up. 2 bbls are much worse due to less mass. I've had several 2 bbls that needed as much as .030-.032" just to get flat. I do almost all of my Holley machine work using a Bridgeport mill, carb fixture and a flycutter. I only take .0015-.002" per pass so it can be somewhat time consuming. Do not forget to check the base of the main body, they can get wonky too. If the base is bad enough the carb will leak fuel when the engine is shut off.

[chris401]

Thanks for the tip. I ran that carb for a few years and now its for sale. Didn't leak but it may be somthing the next person may want to know.

[Clark Coe]

Dear Friends, Got more Holley carburetor questions.  Power Valves  and  Gasket Material and Power Valve Check Ball Kit.

Q1: What is the best sealing gaskets for bowl and metering blocks ?......not going to do much disassembly for tuning. Do not want puddles of fuel in the intake. I am using Holley Renew Kit #3-422 that came with black gaskets. Many years ago, the rebuild kit I used contained tan colored gaskets that are sort of waxy. The used, tan gaskets actually came off better than I remember the softer black gaskets used to.



Q2: What would be an appropriate power valve for 600 CFM? Motor is cammed with a standard 428CJ hydraulic. I cannot make out the power valve vacuum value on the new power valve that is supplied in the kit, the small, small, small stamped characters are incomplete and do not make much sense. Old power valve is stamped "6" "5". Original 1968 Ford Mustang repair manual specifies a 85 power valve.

Q3: Because I already have it, I am installing Holley Power Valve Check Ball Kit 125-500. I have never ruptured a power valve with a backfire, but it does not seem like a bad idea. Is there any down side to installing the Check Ball Kit ?

Big thanks for everyone's input, ideas and shared experience and wisdom.   Clark Coe

[Nightmist66]

For the gaskets, I like to use the blue "non-stick". If you use the other ones you mentioned, either should be ok. One thing we always did to the gaskets before the days of "non-stick" is apply a thin layer of chap stick to prevent them from sticking.

You will probably be just fine with that 6-5 power valve. If you didn't know, that stands for 6.5" of vacuum to actuate the valve. A good baseline is check the idle vacuum, and divide that number in half and that is your starting point for the power valve. So, if you had 15 inches of vacuum at idle, you should need roughly a 7.5 power valve.

I can not see any downside to installing the check ball kit. We do it on every one of our carbs. Just added assurance.

[Ford428CJ]

I see that kind of problem with a ton of carbs. Some are better then others. But after doing 25~30 carbs a year for people. Its not shocking at all. I use ultrasonic cleaners and so on. The cleaner, flatter, the better! It helps a lot....

[Clark Coe]

Got my Ford 600 CFM carb assembled but things are not going well. Poor idle quality, will not idle lower than 1300 - 1500 RPM.

Last weekend, the Mustang did cruise great at 60 mph for several miles without any fuss, but setting at traffic lights was a real challenge....needed three legs and feet.

Distributor is pointed straight forward and timing is 10 BTDC at 1300-1400 RPM....difficult to tell of sure, keeps dying.
Points - Condenser ignition system is completely stock. Coil is stock. Ignition works well enough for good crisp starting and running at 60 mph.
Manifold vacuum at the 1300-1500 rpm range is 15" but vacuum fluctuates/floats 16" to 18".....not jerky, just "hunts".
Have disconnected and plugged vacuum line to power brake booster.

Fuel level is just below bowl plugs.
Idle mixture screws are 1 and a quarter turns out.
Manual hand choke conversion and have plugged the hot air vacuum port on right side of carb body.

Unmodified Streetmaster intake with a 3/8" composite, four hole insulator. Installed carb, insulator and manifold with thin gaskets, without sealer. Victor Reinz intake manifold gaskets installed with a little smear of Motorcraft gray RTV diesel sealant.

Engine is not burning oil, no black smoke or blue smoke. After sitting for eighteen years, I was afraid there would be stuck rings or valves.
Exhaust has no harsh odors.

Hydraulic lifters with adjustable rockers. Adjusted cold to top of lifter travel, then turned down half turn-full turn, I forget exactly. Valve train is quiet.

Pulled the new Autolite 45 ( .035" gap ) plugs and they were super clean.

With all of the plugs out, tried to check compression on warmed up engine. 9.5 Badger pistons. Unknown, mild hydraulic cam, #5=152 psi, #8=148 psi, then the hose from the compression gage is spinning in the 18mm threaded fitting and will not unthread out of the head. . Everything was too hot to try to retrieve the gage hose....so it was time for a bag of micro wave popcorn.

Need some ideas to try tomorrow. I want to be driving my Mustang before the Nebraska winter sets in.

[Drew Pojedinec]

Some folks like to talk badly about the light tan gaskets, but I've been using them forever with no issues.
I buy the ten packs for dirt cheap from Summit.  They are AED brand.  I get a ten pack of bowl gaskets and a ten pack of metering gaskets.

I smear a little dielectric grease into the gasket prior to install.
I take my carbs apart every year or two just to check/clean everything out, never a problem.
I run pump gas E10 so it seems wise to check out the carbs every once in awhile.

Good luck

[My427stang]

Clark, if you can get to Papillion, I'd be happy to take a look at it.

Email me,  too bad I didn't see this yesterday, I was bored enough to take a 1984 6.2 diesel job I put off, which I have to finish up today.  Would have paid someone yesterday to be doing something else.

I will be in Plattsmouth until about 11AM and free until about 2PM. 

[Clark Coe]

Thanks Ross for the offer. We will see how the day goes. Got church and afternoon birthday party for grandson to do first. I will be in touch.

Clark Coe

[My427stang]

Sounds good Clark, I am home now, we have an engagement at 3 that requires a shower first, wife would kill me in my sleep if I miss either the party or the shower. (That sounds way more fun than what I meant LOL)

Should be around next weekend too if today doesn't work.

I will offer a couple observations if you decide to go at it this afternoon.

1 -  Point gap and coil check - Make sure your point gap is dead on.  Loosen the distributor to get it perfectly on the point cam, then adjust and make sure the points are clean.  Also, make sure your coil is wired up the right way.  "Dist" or "-" goes to point side.  I have seen a couple over the years that guys get them backwards by accident.

2 -  Set initial timing higher - 10 degrees at 1300-1400 is likely not enough timing especially at that RPM.  Get it at 12-14 at a 750 or so idle, vacuum disconnected and plugged to distributor and make sure ported vacuum is dead.  I have a hunch you have the primaries open too much, see below.

3 - If ported vacuum is not dead at whatever idle you are at, pull the carb and close the primaries and open the secondaries an equal amount.  Then reinstall and readjust. It might take a few times, you are looking for about .020 of transition slot up front and a nice 750-ish idle.  Once you get close and it idles, set timing, resent a/f mixture to highest idle then lower to 750 again.

Beyond that it'll take some thinking and listening.

[runthatjunk]

Has this happened since manifold install? Wondering about possible vacuum leak?

[Clark Coe]

This is Engine Tuning 101 and I am failing. More notes and observations.

Today, with the coil removed from car, checked Primary/Secondary resistance with calibrated Fluke meter, Primary = 1.5 Ohms. Secondary = 7800 Ohms. This is correct with Ford spec's.
Sunday, opening and closing points to fire coil, generated blue/orange arc that will jump .25" gap to ground.

Coil wiring has always been wired correctly. Seen that done wrong in the past and wouldn't forget that sick yellow spark.

Saturday, I measured point dwell = 28 degrees. That seems about right to me.

These are very old points and condenser. To get the engine to fire, had to clean points with a dollar bill to remove fine corrosion film to make contact. Have heard that most new points/condensers are foreign made and of very low quality and not reliable. So that is my excuse for keeping the old points.
I have a new Pertronix II and Blaster coil that I intended to install after the initial start-up and tune, but did not wish to introduce any changes until I had a stable patient.
Can anyone recommend a quality brand of points/condenser?

Removed carb last night to inspect intake/carb gaskets......all looked OK. Checked carb base to carb body screws.....all tight (snug?). Bowl screws are snug.

Both Primary butterfly plates have a small hole (drilled) in them. How much trouble will this cause?

Checked tightness of intake bolts....all tight.

I have never ran this Streetmaster intake before. Craigslist purchase. Seller said it did not deliver good driveability on his dad's pickup and they changed to a Performer and liked that better. Never thought too much about that statement. I guess there could be some porosity issues with this intake. before installing, I blasted it and worked with it a considerable amount and did not see anything suspicious. I did grind some required clearance between the 3/8" push rods and the intake, but not much material was removed and never thought I was close to the intake ports.

I still believe the poor ( none existent ) idle is a vacuum leak. but, I do not want to remove the intake manifold just yet.

[Clark Coe]

This is a two year old thread and I am resurrecting it because I am again working to find and correct the problem(s) to establish drivability to my ‘68 Mustang after letting it set for two more years….life has been keeping me busy.

After working on the Mustang last weekend, it now has a smelly 750 rpm idle that roams up and down 25 rpm. Vacuum at idle is 14” and it also fluctuates slightly. Initial timing is very high, not sure how high (18-20?). Engine still starts with the engine warm. Timing is difficult to read, but the distributor is rotated clockwise almost to thermostat housing. Gasoline is fresh and fuel system is clean.

The carburetor is a Ford C8OF-D 4150 style that I purchased at a swap meet 30 years ago. The primary throttle plates had small 1/16" holes that appeared to be factory, very neat clean holes, positioned very precisely. Last weekend, I replaced the primary throttle plates with plates without holes. Also opened up the position of the secondary plates to expose the secondary transitions slot a small amount.

Here is my problem/question:    My carburetor has threaded adjustment screws that are horizontally positioned in deep threaded wells in the carburetor base throttle body. These needles protrude and partially block the openings of the Primary Idle Discharge Holes. One needle is threaded so deep as to be sticking through into the air path of the throttle bores. Light weight penetrating oil will wick past the screw points, so I guess some gasoline is getting through. However these screws must effect the idle quality.

I have several 4150 and 4160 series junk carburetors and none of them have adjustment needles in the Idle Discharge Holes. PLUS, these slot head adjustment screws are very stuck, I cannot back them out. What is the purpose of these needles and how to get them unstuck? Anyone familiar with these adjustment screws? I could try to get some pictures if that would help.

[thatdarncat]

The screws in the baseplate you are describing don't sound right for a C8OF-D Holley. There should only be the idle screws on each side of the primary metering block. There is of course the curb idle screw, and the tiny screw underneath that controls the secondary plate adjustment. I just looked at a C8OF-C Holley I have and it has the tiny holes in the primary throttle blades, so that is probably correct. What throttle arm does your carb have? Is it the usual Ford style used on the 390 GT carbs? Can you post a picture?

[Clark Coe]

Kevin, here is a picture of the throttle linkage. Looks to be standard Ford issue.


The small holes in the two primary butterflies is very neatly done, it has to be a Holley factory feature.


Yesterday, a friend loaned me the Ford Holley carb from his restored '67 GT FB. This carb was recolored and restored by Holley and is a known performer. I am curious to try this different carburetor.

After I remove my carb, I will post pictures of my hidden, adjustment screws that are embedded in my carb's throttle plate.

[My427stang]

Clark, I cannot see the pictures at work, but any a/f adjustment other than the metering block is either something custom or baseplate off of some other carburetor.

Some comments though

1 - Points have to be replaced at some point, get a decent set of Accel or NAPA and associated condenser.  Set the gap and set timing and press on with the carb

2 - If those screws block the idle discharge holes and are stuck, then you have no ability to adjust the a/f, as the functional effect of that is the same as the ones in the metering block. 

3 - If you have both the baseplate screws and the metering block screws, assuming the idle passage lines up to the throttle body, I would remove and plug those screws and use the ones on the metering block. 

4 - Conversely, if you cannot remove the bottom ones, and the metering block ones are present, back them way out, then use the baseplate ones to limit/adjust

[RJP]

To the best of my knowledge Holley has never used drilled primary throttle plates as shown in your picture. In fact, earlier Holley publications have in so many words condemn the practice. It is usually done to crutch an idle problem on an engine that has a huge cam that won't allow it to idle without opening the throttle blades beyond the idle transfer slot.  To add: If you have idle mixture screws in the base plate you have the wrong base plate. Only 4180 Holleys had idle adjustment screws in the base plate and usually had "limiters" on them to prevent them from being turned beyond a very small amount, it was an emission thing. 

[thatdarncat]

To the best of my knowledge Holley has never used drilled primary throttle plates as shown in your picture. In fact, earlier Holley publications have in so many words condemn the practice. It is usually done to crutch an idle problem on an engine that has a huge cam that won't allow it to idle without opening the throttle blades beyond the idle transfer slot.

Actually Holley did use both drilled Primary and drilled Primary & Secondary plates in many carbs, both factory applications and aftermarket ones, including the HP carbs. I've just looked at a few more C8OF-C & C8OF-D carbs I have and they all have the drilled primary throttle plates ( with "211" marking ).

Edit to add - Holley even sells replacement throttle blades with various sized holes already in them.

[thatdarncat]

So I did a little closer looking, it's been quite a while since I've rebuilt one of these C8OF carbs. All the C8OF-C and C8OF-D carbs I have on hand DO have something resembling a needle tip in that hole, but NONE of them have any kind of external adjustment screw head. If they are adjustable it would have to be down inside this hole. This is a feature that must have been new for the 1968 model year, because none of my C6OF and C7OF 390 GT Holleys have that feature. Right now I can't see down into this tiny hole well enough to see what's in there, I will try to clean it up some and see if that helps. I'll be interested to see a picture of the baseplate of your carb, so far other than the screws you describe all seems normal. Sorry for not looking closer on my previous answer, but I didn't see any screws and didn't look close enough underneath.

[Clark Coe]

Yes Kevin, that is the same adjustment hole configuration as my '68 GT carburetor....thanks for the pictures and research. Looking inside there is a slot head screw. One of the screws on my carb is screwed in so tight as to almost block off the Idle Discharge Hole. I could dribble penetrating oil through it. I never made this adjustment, this carb came that way from the swap meet 25 years ago.  I sold my original 390 GT carburetor 40 years ago when it was attached to a '69 Mach 1.

How to get these screws loosen up?  Heat?  I have already buggered the edges of the slots a little when attempting to disassemble the carb in the past.

What is the correct needle position to have a clean idle?

This web site states that the C8OF-D carb was used on IMCO pollution systems.  C8OF-C carburetors were for Thermactor systems.
http://www.mustang-s.com/years/1968/1968_carburetors.htm

[thatdarncat]

I just looked in the Ford Parts book and it lists the C8OF-C Holley as 390 GT with manual transmission and Thermactor emissions, and the C8OF-D Holley as 390 GT with C6 automatic transmission with Thermactor emissions also. I'm not an expert on the two emission systems, so I'd have to do a little more research to see if that is correct. Maybe someone here knows more.

[Clark Coe]

Here is an update on tuning my C80F-D Ford-Holley 4150 carburetor. I have finally fixed the nonexistent idle condition by removing the outer portion of the obstructive adjustment needles that plugged up the IDLE DISCHARGE HOLES in the throttle body base. I purchased this carb at a swap meet and it was like this from the beginning. The left idle discharge hole is partial blocked as well. This adjustment option must have been a Ford/Holley attempt to fine tune emissions in 1968 only.


Working vertically down into the well behind the Idle Discharge Holes, I centered punched the visible portion of the needle with a start divot with a sharpened 1/8” roll pin punch. Purchased a new, sharp 1/8” diameter drill bit with a flatter 135 degree tip to prevent wander. Drilled vertically down into the idle well and drilled the needle in half. Using dental picks, I fished the remains of the needle out of the idle well. Cleaned with carb cleaner aerosol and compressed air.



The outer half of the adjustment needles with the adjustment slot remains corroded and stuck in the throttle body, is super stuck and keeps gas from running out.



Idles at 700 rpm with 18.5” vacuum. Idle adjustment screws in the jet block are one turn out. Looking back, this problem should have been obvious. I am a little embarrassed that I could not have been quicker at resolving this, but am satisfied that my car starts, idles and motors down the road. Thank you for everyone's support and input.

[My427stang]

Well done Clark, and thanks for the research and lesson on the early carbs.  I have never seen that idle a/f adjuster before.  I am sure you are correct that it was a sealed limit for emissions so you couldn't back out the top adjusters and go any richer than the bottom will allow.

So are we going to see the car at Cars and coffee  this year?  The season is dwindling away quickly!  I likely will not be there this weekend, either working on a Pontiac, or going to Speedway Motors in Lincoln for their version of Cars and Coffee and museum, or if I can pull it off, both LOL

[Clark Coe]

Thanks for the help and encouragement Ross. Yes, I will need to show up for the Omaha Cars & Coffee before September goes away. Summer is always busy for me, got a three quarter acre lot that requires mowing every fourth day, in addition to my wife’s flowers.

The Speedway Motors, Museum of American Speed in Lincoln is one of my most favorite places on the planet. I have visited the museum three times so far and will go again. Love the vintage dirt cars and the flathead ford speed equipment and the Indy Cars and the Miller/Offenhauser exhibit and the tin lunch box collection and the peddle car collection. Any car person traveling through Nebraska on Interstate 80 should make time to visit this world class automobile museum.

Also Ross, I wish to congratulate you on your promotion to a “Full Bird Colonel” as my late AF NCO Uncle Merlin used to call them. That is a hard earned title to be sure…..Clark Coe