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Holley DP rebuild

SlinktRR

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picked up my first Holley, an 850 dp. Heavily used and hasn't been run in a decade. Where do I start with this. Also what is the copper tube on top of the housing for, I haven't seen that in any stock pictures of this carb. Tips for removing the rust on the plates would be appreciated. Thanks

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I think the idea behind the tube is to equalize the venting to atmosphere. Never seen that done before. When I clean a carb, i use tooth brushes and carb cleaner. Wire wheel will help, but you need to be careful. Lots for the wire wheel to grab, and yank out of your hand. Those gallon carb cleaners work well, but to soak the main parts, you'd need to put the carb cleaner in a pan.
 
A couple other ways to remove the rust from the throttle plate are a brillo pad or soaking in oxalic acid if you can find some (removes rust, but leaves good metal alone). That copper tube is definitely not from Holley, so you may want to consider buying some new fuel bowl or just blocking those holes off with epoxy. Personally, I cannot imagine how that copper tube would help anything...."maybe" intended to help with vapor lock, but I don't think it would help.
 
x2 ^^ on that tubing. Remove it and epoxy the holes. The two big tubes pointing straight up are the bowl vents. That crossover wouldn't do anything I can see either. Too bad the choke housing is milled off too - that's the tell all for what the jetting should have been.
 
Those fittings on bowls look like they're 1/8" pipe. Couple of plugs and sealant done. oxalic acid try your local dry cleaner if all else fails.
 
Before you spend 5 cents on this rebuild check the free play on the shafts. Then the butterfly valves clearance to the throttle bores. if they are warped then think serously if it makes sense to rebuild.
 
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Another thing on your rebuild whether you use this Holley or another. Use only Holley, Quickfuel and maybe a couple of other major carb company rebuild kits. Stay far away from parts store rebuild kits. Especially ones that use a big brass nut to lock down the needle and seat. The thread pitch is not the same between them and your fuel bowl and you will strip out the bowl. I've sold lots of bowls when I worked at a speed shop so I know this one from experience.
 
How is this kit?

http://www.jegs.com/i/Holley/510/37-485/10002/-1

I am using barkeepers friend, brillo, steel wool and carb cleaner based on purple beep calling out for oxalic acid. barkeepers is an oxalic based metal polish I use frequently at work. Carb appears to be in good shape despite being modified over the years. The milled choke horn looks to be a common mod by people, with probably not much gain. I dont use the choke often anyways even in cold weather. The two tapped fuel bowl vents also do not appear to do much either.

Other than that the carb appears functional although I wont be able to run gas through it until the gaskets are changed.

Can anyone suggest a ready made fuel line kit for these with blank fittings? Right now I am using one inlet on an edelbrock carb with the other blanked but would not be opposed to dual.
 
Earls, Russel and some others make a line for the dp's. The one's that use just a chrome tube can give you issues when you try to tighten them up. They can leak, tube twist etc. Also lay a straight edge across the main body of the carb where the metering blocks and throttle plate go. If you have any warping, get it flattened out. You can get it milled [probably best], file it or sand it. I use a made up sanding block with some 80 grit wet or dry then 180 wet or dry to get them flattened out. Having the body warped can really give you some weird running issues. Depending on the production date of the carb, there may or may not be check valve block offs for the power valves. Holley finally did this after awhile. When you get a cough back through the valve, the power valve is generally ruptured then and must be replaced. I learned of an easy way to do a block off check ball on the throttle plate many years ago to put the kabosh on this and can hook a bro up with the info. I'll take a photo of the passage in question and give you the procedure. The little check ball[ or balls if its front and rear pv's]] are already in the Holley carb kits as just extra stuff you don't normally use. I would also suggest you stock up on bowl screw, bowl to block, block to body, throttle plate to body, idle mixture screw, pump squirter nozzle and base to manifold gaskets. You can't always get these when you really need them. Going by your list number, which I believe is 4782 for an 850 dp. you will be able to get a breakdown from Holley on all these components minus the base to manifold gasket.
 
Here is the procedure for the check valves . There will be two balls in the carb kit that will just fit nicely in the enlarged holes you are about to do. Ok, pointing at the backside of the plate, do you see those two holes? Those are the passages to the pv's. On the plate to main body surface, find those two holes. You will use a 13/64 bit, .203 dia, drill out the holes to a depth of .190-.200 deep. Take a small phillips screwdriver that just fits the hole and give it a couple of easy raps. Make sure the throttle plate is supported when you do all this too and drill the holes in a drill press. The purpose of the screwdriver raps is to leave four small indentations that will let vacuum by so the valve still works. Drop one ball per hole in, put the gasket on, re-assemble to the main body. What the balls do is when it coughs back through, the balls seal off the passage and prevent the pv from getting blown out. As a side note, add some pv's to your collection and maybe find a dead carb or two at your next swap meet for parts.

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Thanks ckessel. I just got back onto this project. Bowls and metering plates are pristine but the baseplate is not cleaning up well from years of sitting. There were blank nuts in place of power valves so I put 6.5 to start front and back. The jets are 85h all around. One of the plastic vent cover tabs is broken, where do I find those? Not in the trickit from Holley. Putting new accelerator pump diaphragms in as well, small up front and large in the back.
 
Thanks ckessel. I just got back onto this project. Bowls and metering plates are pristine but the baseplate is not cleaning up well from years of sitting. There were blank nuts in place of power valves so I put 6.5 to start front and back. The jets are 85h all around. One of the plastic vent cover tabs is broken, where do I find those? Not in the trickit from Holley. Putting new accelerator pump diaphragms in as well, small up front and large in the back.
vent baffle https://www.summitracing.com/parts/aed-5897
 
I had to rebuild a 750 DP this past weekend on the 55. The rubber gaskets had become brittle and started leaking.
As for cleaning I just hosed it down with carb cleaner, but I have in the past used Colgate and a toothbrush on the edlebrock carbs with some success. Never tried it on a Holley...
One thing I did find interesting when I tore the Holley down was that there were no power valves.... 1st for me but I'm no carb expert either... After doing some research it seems a lot of racers would do this for consistency...???..
Car alaways seems to run fine never had any issues on the street....
 
Power valve plugs are sometimes in the secondary location from the factory, otherwise both ends have the valves. Some people would install the plugs, for race stuff or personal preference, in one or the other block. When you do this, the jetting has to get fattened up but I don't remember how much.
 
Why would they plug both metering blocks though???
Thanks Ck!
 
Some people think its works better without. Not me though. Causes issues elsewhere on drivability. Drag stuff when you are pretty much at WOT or other racing under the same conditions maybe.
 
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