SoCal Jet Boats
Tech Talk => Engine Mechanical / Electrical => Topic started by: Huklebuk on February 17, 2010, 08:41:30 PM
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So I took my carb off and the secondaries (I think) were frozen. So I free'd them up and after taking a look at it I decided that its just time to replace it which brings me to the burning question. I have very little knowledge of carbs. What should I go with? Should I go higher to an 850 maybe? I looked on ebay and there are just tons of options. The one I have now is a 750 dp I think but I'm not sure how to identify it. And I don't know all the technical jargon, vacuum vs manual secondaries and all that. I may have to go on how stuff works. Just wondering what the general consensus was from the carb experts. I have an edelbrock torker manifold I think but I'm not even 100% sure about that. Its a 455 by the way.
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So I took my carb off and the secondaries (I think) were frozen. So I free'd them up and after taking a look at it I decided that its just time to replace it which brings me to the burning question. I have very little knowledge of carbs. What should I go with? Should I go higher to an 850 maybe? I looked on ebay and there are just tons of options. The one I have now is a 750 dp I think but I'm not sure how to identify it. And I don't know all the technical jargon, vacuum vs manual secondaries and all that. I may have to go on how stuff works. Just wondering what the general consensus was from the carb experts. I have an edelbrock torker manifold I think but I'm not even 100% sure about that. Its a 455 by the way.
I use this daily...maybe it will help you...You will need a list number, this is the number stamped into the air horn on what would be the top front of the carb...
Good luck...BTW, more info would be needed to point you in the right direction (to be honest a 750Dp is a great carb).
www.mortec.com :thumbup:
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If you can post some pics of the carb and manifold we should be able to identify what you have (minus exact size of carb).
What seemed to be frozen on the carb? Before you spend too much money, have a carb shop or a friend that's into that kind of stuff look at it and give a second opinion. You might get away with a good rebuild of what you already have.
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I will post some pics up when I get home, which I shoulda done in the first place. I'm sure I am calling it the wrong thing, I will point it out in the pic when I post it. And GT, I don't know what the air horn exactly is. When I post the pics I will include pics of all numbers I can find.
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Ok here we go. The number on the front is 3310-6. Here is the pic. The circle is the flap things that were frozen. They still wont open all the way when I open the main ones. The arrow shows what I think is the choke. It moves on its own nothing really controls it. The other two pics are two different carbs I have I don't know what they are.
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Well where to start...
Carb #1 is a Holley model 4160 750cfm Vacuum Secondary. The top flap is the choke that would have been manual originally (needing a cable to operate). It could probably be rebuilt and function ok, but I think I would recommend replacing it with a 750-850 double pumper with mechanical secondaries for a jet boat.
Carb #2 is a Carter/Edelbrock AFB. It should have a 4 digit number at the forward mounting flange where the stud comes through. Most are 500-625cfm. I would not recommend this carb unless using in pairs.
Carb #3 looks like it use to be a Holley 660cfm. They were designed to be used in pairs and mounted inline. Had 1:1 mechanical linkage short single feed bowls. Great carbs but everyone thinks used ones are worth more than gold $$$
Before you buy something post some info so we can help make sure you don't get screwed. :banghead:
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Crewcheif's right, 750 Vac Sec'y carb. I disagree not good for a jetboat, but that's where he and I differ.
First, use it, remove the choke butterflies, shaft and anything to do with the choke (Crewcheif can tell you how, he and 2sav taught me on the same damn carbs).
The secondaries on a vac sec'y carb will NOT open unless the engine requires it through vacuum. Examine your linkages carefully, pretty easy to see how they work. Sounds like the vacuum diaphragm may be shot to me. Bad news is they are single pumper, so used singley, do affect throttle response somewhat. Crewcheif, GT and most others do not like this. I run two, and do not think this is a measureable issue. When I did run one of them, though, boat ran fine and idled better than any jet boat I've seen yet with a pretty wild cam. Didn't notice any throttle respose issues.
I would agree that a DP is what you should look for, but don't think you're out of line with what ya got. Can work and work well. I guess this is my novel writing coming out to make a short point. ;D
Ray
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Crewcheif's right, 750 Vac Sec'y carb. I disagree not good for a jetboat, but that's where he and I differ.
First, use it, remove the choke butterflies, shaft and anything to do with the choke (Crewcheif can tell you how, he and 2sav taught me on the same damn carbs).
The secondaries on a vac sec'y carb will NOT open unless the engine requires it through vacuum. Examine your linkages carefully, pretty easy to see how they work. Sounds like the vacuum diaphragm may be shot to me. Bad news is they are single pumper, so used singley, do affect throttle response somewhat. Crewcheif, GT and most others do not like this. I run two, and do not think this is a measureable issue. When I did run one of them, though, boat ran fine and idled better than any jet boat I've seen yet with a pretty wild cam. Didn't notice any throttle respose issues.
I would agree that a DP is what you should look for, but don't think you're out of line with what ya got. Can work and work well. I guess this is my novel writing coming out to make a short point. ;D
Ray
Ray,
I love ya like a brother man, but your trying to get someone who know less than dick about carburetion (no offense) to rebuild and use a carb that has many issues...If it were me, I would talk to a carb shop and see what you're looking at to rebuild it to factory specs and use that number for pricing it's proper replacement, I think you will be surprised at the answer..
IMHO a vacuum secondary carb, especially that square bore (all four butterflies being the same size) can run extremely well on a semi stock deal, as soon as the cams get crazy, or valve lift becomes more extreme, it will be time to change up to a mechanical secondary...You need the yellow secondary diaphragm spring (the lightest one) and I would recommend leaving the choke horn on it, but wire it open, this will keep the value up on the carb for if and when you change up to a better (or more appropriate) carb.
I don't know what your plans are for the boat, but that 750 vac sec. will run pretty good, you will probably drop $250 in it to get it to work though.....
Part two of the novel complete... ;)
GT
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Good Points GT! Didn't think about his costs and troubles with what he has. Bought mine somewhat new, knew what I had and worked with that. Works fine. When he wants rid of it, lemme know, lol.
Ok, Concludes Chapter one........... ::)
Ray
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I wont add to the novel, but I will agree a 750 vac sec should work fine on a mild motor. I ran one for years with no issues. Easy to deal with, cheap on Ebay, and they work fine.
BTW, that 3rd carb is not a 660. Its some form of a DP, not a center squirter like a 660.
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Off beat reply, but for a timer - vaccum is kinda fun too. Wait wait wait whaaaaa secondarie open up and you go :).
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BTW, that 3rd carb is not a 660. Its some form of a DP, not a center squirter like a 660.
I didn't look to closely at the body, only the linkage, and the linkage looks like a 660.
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I love ya like a brother man, but your trying to get someone who know less than dick about carburetion (no offense)
None taken. There is only one way to learn and that is by taking shit apart to see how it works. Plus alot of reading. However I don't have the time to do either because I'm working too much and mix in a drop or two of laziness. I think I'm just going to buy a new or remanufactured one, they seem to be pretty well priced on ebay. I'm thinking I'm gonna go with a 750 dp with mechanical sec, just one more question, what is the difference between square bore and not? Oh and what is the difference between a single and doulbe pump (other than the obvious) ?May sound stupid but gt pretty much hit the nail on the head.
Ray, if you want to buy the one I have you have first dibs. Let me know. For that matter if anyone wants to buy the other two I will sell them here or they are going on ebay. Thanks for all the good tips.
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The two common choices for 4bbl throttle bore design, "square bore" and "spread bore".
The Square bore are going to be about the same size primary and secondary (front & rear).
The Spread bore will have a small primary (front) and very large secondary (rear). Rochester and Carter were original equipment spread bore manufacturers and Holley made replacements for both.
You will have to match the carb to the intake manifold or use an adapter from one to the other.
The difference between single & double pump is just what it sounds like. The double pumper had two accelerator pumps instead of just one :thumbup:
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On the verge of (or well past) the point of sounding like a complete idiot, what exactly does the accelerator pump do? And whats the advantages of having a spread bore over a square bore or vice versa?
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On the verge of (or well past) the point of sounding like a complete idiot, what exactly does the accelerator pump do?
The accelerator pump literally squirts a shot of fuel into the engine to counteract the immediate lean condition when you hit the throttle.
And whats the advantages of having a spread bore over a square bore or vice versa?
Primarily fuel economy (spread bore), although tough to get it on a jet boat engine. The square bore has quicker throttle response. :thumbup:
GT
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No advantage to a spread bore vs square bore on a jet boat. The idea is to match the carb to the intake manifold. If you were removing a Rochester Quadrajet carb and wanted to replace it with a Holley, you could either buy a spread bore Holley as a direct replacement or you would have to install an adapter to install a square bore type carb.
The accelerator pump is what gets the initial shot of fuel going into the engine until the engine starts drawing enough air in to pull the fuel out of the carb. Most performance engines require more fuel to accelerate from a stop than a stock engine, so a larger or additional accelerator pump is needed to keep up with the fuel requirements.
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Fantastic information. Just what I was looking for. I think the 750 dp with mech sec is the route I'm going to go. Since it seemed to run fine with the single pump is it safe to assume I will see a better throttle response with a dp?
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go with a 750 dp it will work now on a stock motor and if you want to bump up hp some later it will probably still be ok.
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Its been said before, it's hard to over carb a jet boat. You will be good with a 750dp and would probably be good with an 800.
I have two 600 vacuum secondary carbs on a mild bbc with no problems. I think I could get better performance with a single 800dp, but I haven't had the chance to try it.