Carb. Repair vs Replace

TexasRanger101

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Jul 13, 2016
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hey all, kinda of a beginner question, I am new to the Boating world and a young handy man. I like to do jobs myself and don't mind if they take a bit of time (I can do anything from rack and pinion to stereos to cam shafts) But I have never played with a carburetor. I have a 1979 Webbcraft with a 5.8 Ford Mercruiser. (model: 990261s1 see more in attached photo). I cant find a kit for it and I don't know exactly what parts I would need to do it I kinda get the process of it but want another opinion. Is it worth it to take it into a shop or should I try it myself? Thank you in advance for reading and any advice or hints to where I can get a kit is or if there is a kit is welcome, thanks!
 

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Captaincrisp

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Id say try it for yourself for sure. Shop time will kill you on somthing like that. It will look forein to you as you take it apart but by the time you got it back together you will be ready to take on any carb. Just a few things to pay attention to along the way a carb rebuild kit is all you need. You got it in the bag
 

Captaincrisp

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You need to find number off of carb before rebuild marine carbs normally are origainal unlike older molested automotive carbs but its worth finding the id markings off carb. Then finding rebuild kit from there so your sure you have the correct kit. You got this kne just take your time
 

jimmbo

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Ford used a 4bbl Holley carb

Holley renew kit #703-47
 

Patfromny

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If it is a holley, it is one of the easiest carbs you will find to rebuild. Whenever I rebuild a carb I disassemble and bring all parts to a small engine repair shop to be sonic cleaned. You can buy the carb cleaner dip can but I like the sonic cleaning better and often is cheaper. When i had my outboard carb parts sonic cleaned i think it cost me 7 bucks. Something silly like that. Marine repair shops might have this type of cleaner tool but the one near me , for some reason, won't clean it unless they are rebuilding it.

When rebuilding the carb take special note of the metering block gasket. There will be a few different ones that look almost identical. Save each gasket and note which way they face in relation to the carb so you can match up the right ones and install the new one the correct way. Instead of turning the carb upside down to empty the fuel, just take one of the lower bowl screws out and all the fuell will empty from that hole. Coat the bowl gasket with a tiny miniscule amount of Vaseline so it doesn't stick to the carb bowl next time. You will soon see what I mean. I wouldn't take apart the base plate butterflies unless you are having problems in that area. The kit will come with new gaskets, a new power valve, and new needle and seat or two depending on the model carb. These parts are generally all you need to change as well as cleaning all pieces to get a brand new like carb. Extra parts left in the kit bag are normal with any rebuild kit so dont be worried. I would equate a holley rebuild with a snap together model. It all makes sense as to how it goes together. I am sure you can find about a million you tube vids of a holley rebuild that i would recommend you peruse. I always find it helps me to get a sneak peek at what i am getting into. Good luck
 

Scott Danforth

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rebuild it yourself. dissassemble, soak, poke, clean, adjust floats, reassemble and go boating.
 

Oshkosh1

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Rochester and Holley carbs are easy. Get yourself a can of the "Berrymans" carb cleaner from Wal Mart(about $18) and then go to the local thrift store and find an old crock pot. Drop the can of carb cleaner into the crockpot(it'll just fit), turn it on, let it get hot...Viola! Homemade "Hot tank". Anyhow...pull your carb, break it down, soak all the metal parts over night in the cleaner, find yourself a nice clean place to lay everything out and go for it. If the carb is real dirty...grab a pack of assorted brushes from HFT to scour the body and such prior to rebuild. Good luck!
 

jimmbo

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The kit will come with new gaskets, a new power valve, and new needle and seat or two depending on the model carb.

The Holley Renew kit covers a lot of different carbs, I would be checking to see if any power valve(s) included was the same as the one(s) currently in the carb. I expect it/both to be the wrong one(s).
 

gm280

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Jun 26, 2011
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Some good advice already offered. I would add to take a few pictures now as it presently sits on the engine and also the hookup linkage as well. Post a couple pictures of the carb for us to see what you're dealing with. Then buy the proper carb kit and disassembly the carb and take picture along the way if you don't have a break down pictorial to go by. Then if you have any issues when you are reassembling the carb, you can look at those pictures. If it is a Holley Carb, watch out for the power valve and the accelerator pump diaphragms. I am not sure you can use carb cleaner on the diaphragm inside of those parts. Also be sure to NOT soak any nylon or plastic parts in the carb cleaner. Some carb cleaners can dissolve such parts. Don't ask me how I know that. :facepalm:
 

Twainer

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Sounds like we have very similar set ups. Mine is a 1977 351W OMC with a Holley 4bbl. Problem I am having is I don't see too many kits that are for mechanical secondary's which mine has. Have seen where they have it listed as a 600cfm & as a 650cfm.
 

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Patfromny

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To find the right power valve you need the engine running well. The correct power valve is half the idle vacuum and then round up if you have to. As an example. If you have 10 lbs. Of vacuum, you need a 5.5 power valve. They only make them in .5's I think. At least back in the dark ages when I was playing around with them that's how they came. The wrong power valve will not effect idle. It will effect off idle response. I always kept a few of the right size around. Everytime you back fire through the the carb it blows out the valve. Something that happened often when starting the engine the first time after rebuilding or putting on new heads, etc. I was a bit of a street racer in the day and was always trying to improve. Proper jetting is important too but might not be as easy to do on a boat. If it is stock, you are probably in the right range already.
 

gm280

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Sounds like we have very similar set ups. Mine is a 1977 351W OMC with a Holley 4bbl. Problem I am having is I don't see too many kits that are for mechanical secondary's which mine has. Have seen where they have it listed as a 600cfm & as a 650cfm.

Check with Holley manufacture for a gasket set for that secondary. Other then a few gaskets, there isn't many other items for the secondary setup. If it has a secondary accelerator pump, you can buy that kit separately. In fact you can actually purchase every carb gasket or parts needed separately if need be. Just have to know what you need. JMHO!
 

TexasRanger101

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Jul 13, 2016
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Thanks all for input,

Captaincrisp - attached are pics and a link i think i have the right stuff. thanks again!
jimmbo - I think I have a Rochester on mine, maybe someone switched it from the Holley. thanks for the input
patfromny-oshkosh1 - sonic cleaning vs DIY crockpot with Berrymans. is either one much better then the other, both sound like good ideas. my only concern is how big of a crockpot will fit all the parts at once so I Don't have to cycle them over a couple days.
(I will look into Youtube videos for my carb)
GM280 - attached are pictures of how it sits right now, was hoping to get to it today but the rain wont let up. may use a go pro when tearing it apart, may just use pictures like you suggested. also thanks for the heads up about how strong carb cleaner is.Wise people learn from their mistakes, the wisest learn from others!
Twainer - Sounds very similar I have the 1979 OMC 351 but it would seem I have a Rochester 4bbl. good luck with your carb!
 

Patfromny

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Which is better? The one you use. I don't think there is much difference. I like the idea of the parts getting shaken while cleaned and I don't have to worry about getting rid of the tub o' carb cleaner either. I haven't had a whole lot of experience with Quadra jets but I believe they are simple enough. They are also a much better carb for off idle. Holleys all have a studder just off idle. Quads, are real smooth.
 
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Scott Danforth

Grumpy Vintage Moderator still playing with boats
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To find the right power valve you need the engine running well. The correct power valve is half the idle vacuum and then round up if you have to. As an example. If you have 10 lbs. Of vacuum, you need a 5.5 power valve. They only make them in .5's I think. At least back in the dark ages when I was playing around with them that's how they came. The wrong power valve will not effect idle. It will effect off idle response. I always kept a few of the right size around. Everytime you back fire through the the carb it blows out the valve. Something that happened often when starting the engine the first time after rebuilding or putting on new heads, etc. I was a bit of a street racer in the day and was always trying to improve. Proper jetting is important too but might not be as easy to do on a boat. If it is stock, you are probably in the right range already.

Boats use a 35 power valve in 95% of the applications.
 
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