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List # 80785, Keith Dorton edition HP830.

I got this carb for a new 509" N/A, 9:1 motor (28' lake boat). We tried to run it on the Dyno, but it was too lean, up around 14.8. We jetted it up, but still too lean, so I gave up and ran the motor on the dyno with the 800cfm carb I had on the Boat before.

Now that I have had time to mess with it, I'm trying to find the correct combination of AB's and jet's to get a good starting point to try the carb on the Boat. The carb guy I bought it from say's to do 1 thing, and Holley say's to do another.. Not sure which way I should go, since I don't know crap about carburetors :mad:

Here's what I know about the carb;

Stock configuration per Holley (set up we ran on the dyno);

86, sq jetted
72, main AB's
32, Idle AB's
6.5 PV, primary. no secondary PV

Holley tech help;

90, sq jetted
72, Main AB's
32, Idle AB's
28, prim squirter
29, Sec squirter
6.5 PV, prim and sec

Carb guy's solution;

86, prim jets
90, Sec jets
78, Main AB's
32, Idle AB's
6.5 PV, prim only, no sec
 

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IMHO, that 830cfm carb is "too" small for the cubes you have! :)...i personally would try a box stock 850cfm dbl pumper mech sec & see how it runs...you could also go to a Dominator 1050cfm carb!...thats alot of cubes & you need to feed them :)...just sayin' my .02 cents :)
 

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I am not a carb expert, there are those much more experienced than I but Holley ususally sets carburetors up on the rich side. Point being is, better to start rich and tune to lean. If you remove and block the power valve you would usually want to increase the jet size 6 to 8 bigger than was used with the power valve. To richen the transition with air bleeds, you want to go to smaller size. The bigger the air bleed, the more air that is mixed with the fuel and leaner the mixture. Do you know what your vacuum reading is at idle. A 6.5 Power Valve is typically used when idle vacuum is 13-15 inches. You are going to have to decide how you want to use the boat. Do you want to cruise around or are you going to be wide open all of the time? Using power valves will generally give better fuel economy but are something else to tune and keep track of. Each engine is going to be different. There will be no one answer. The best you can do is start at baseline similar to the Holley suggestion and tune from there.
 

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Discussion Starter #6
Excuse this question as I am not at my work computer where I keep all my notes, but isn't that a circle track carb for 350-358's cid's ?
MMMMM.. well that could explain why it was for sale for 2 years :)hammers

Perhaps I've been duped.. :((((((
 

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Yes it is a Nascar approved track car carb. But doesn't mean its will not work on a BBC. Little small, for a 509, but the actual flow difference between it and a stock 4781 850 is nil. In fact, the Dortan 830 may out flow the 4781. If the engine doesn't rev that high, its may be fine.
You gave up awful easy. The stock jetting for the thing is 84 square and a 6.5 PV in the SECONDARY! You went up 2 jet sizes?


The set up Holley is considerabley richer than the what the carb gave you. In fact carb guy would be leaner than stock almost across the board.

Go with what Holley gave you. Its considerably richer than the stock setup. I bet you don't have to do much but adjust the main jets a size or 2 one way or the other. Once you get it working, you may be able to dump the secondary PV and jet up 4-6 size.

No one told the carb it is going in a boat, and it didn't know that on the dyno. And it doesn't much care what size the engine is, it only cares about the amount of air moving thru it. Surprised it is lean at all. Usually when a carb is set up for a smaller engine they have a tendency to run a little rich because of the stronger booster signal.

Is this a 80509 down leg carb, or a 80511 annular booster



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Discussion Starter #9
Yes it is a Nascar approved track car carb. But doesn't mean its will not work on a BBC. Little small, for a 509, but the actual flow difference between it and a stock 4781 850 is nil. In fact, the Dortan 830 may out flow the 4781. If the engine doesn't rev that high, its may be fine.
You gave up awful easy. The stock jetting for the thing is 84 square and a 6.5 PV in the SECONDARY! You went up 2 jet sizes?

I actually went up 6 jet sizes, first to 84's, then to 86's. The carb had 80's in the primary's when I got it from the carb guy. I did give up quick, but I was running out of time on the Dyno.


The set up Holley is considerabley richer than the what the carb gave you. In fact carb guy would be leaner than stock almost across the board.

I'm questioning his credibility, as his resolution was to put larger Main AB's in to richen it up. Everything I gathered so far say's that a larger bleed, results in a leaner AF mixture, not richer as fastmarlene mentioned.

Go with what Holley gave you. Its considerably richer than the stock setup. I bet you don't have to do much but adjust the main jets a size or 2 one way or the other. Once you get it working, you may be able to dump the secondary PV and jet up 4-6 size.

No one told the carb it is going in a boat, and it didn't know that on the dyno. And it doesn't much care what size the engine is, it only cares about the amount of air moving thru it. Surprised it is lean at all. Usually when a carb is set up for a smaller engine they have a tendency to run a little rich because of the stronger booster signal.

Is this a 80509 down leg carb, or a 80511 annular booster
It's actually a 80785. The guy I spoke to at Holley said this carb was discontinued some time ago and is not even listed on their site. It looks exacly like the 80509 with the down leg boosters. main body say's 4150 HP series, list 80785.. several other numbers, but I don't know what the hell they mean..
 

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Surprised it is lean at all. Usually when a carb is set up for a smaller engine they have a tendency to run a little rich because of the stronger booster signal.
Yes, more air thru the boosters does pull more fuel, but be careful with that. Look at same manufacturer and cfm carb installed on mild small block vs mild big block.

If you have swapped even a small handful of carbs between 'like' small and big blocks then you'd see this is not really true.

Anyways, I brought that up about the 830 because I have run into a few way back in time that I had tried on different motors and had a hard time grabbing a tune on them. Going way back I believe one was a rowdy 355 street car motor and another a basic performance 454. I don't remember the 830's I played with briefly to be the Dorton version.

Anyhow, if you run into an application specific carburetor, many times they are very difficult to tune for another motor. Generic performance carbs (3310 vac sec, 750 DP, 850 DP) etc can be made to run reasonably well on many different type motors quite easily.
 

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Discussion Starter #13
Bringing this back up.. I decided to screw with this carb this weekeknd on the Boat. Put in the 90's, square, 6.5 PV's in both ends. Bigger squirters (37's) and changed to the 50cc pumps (Cams and arms as well). Fired right up and seems to run good... no stumple, sounds crisp. But, when I took a plug out to look at it, it was way rich...Black. I ran it on the trailer, warmed it up and set idle, reved it up to about 3500rpm's for about 20 seconds and shut it down.

My question is, am I worrying over nothing running it on the trailer, and it looking so rich? Will the plug reading change that much when I put it in the water and run it.

Thanks for any help
 

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First, you can't tell anything sitting on the trailer. Second, your way rich. If your going to square jet it AND run PV front and rear, you need to be down around 84s, to start.
If you pulled the PVs out and hammered the thing it MIGHT be pretty close. But it will be rich every where else.
I agree with GN-7 on part of this. trailer tune will always show fat! Get the boat on the water and run it, then shut it down and read the plugs. It's hard to find a perfect world for a 28' boat with a 509 bbc. The average person wants a boat that idles clean and runs off the hook on the top. Trying to build a dual purpose boat is a bitch and the tuning will be a ton of fun. Best of luck. M
 

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Discussion Starter #16
First, you can't tell anything sitting on the trailer. Second, your way rich. If your going to square jet it AND run PV front and rear, you need to be down around 84s, to start.
If you pulled the PVs out and hammered the thing it MIGHT be pretty close. But it will be rich every where else.
Thanks GN

OK I got a wide assortment of Jets yesterday, put the 84's in it square and ran it on the trailer. Sounds good, but no more puffing black smoke :happy:. Taking all the parts and pieces to Havasu this weekend, so that the Wife and I can have some quality time together with a vacuum guage :thumb:


Dave
 

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Discussion Starter #17
Here's what I ended up with.. after several runs, plug checks and 3 jet changes.

86's in the primaries
90's in the Secondaries
6.5 pv in both ends

Vacuum was 11" @ Idle, 8" @ cruise and 0 @ full throttle

Noticeable acceleration improvement at the top end, gained 200 rpm's and about 5 mph. I realize some of this can be attributed to the cool weather last weekend, but I'm pretty happy with it.

Here's some plug pics

Plugs 002.jpg Plugs 003.jpg Plugs 005.jpg
 

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surprised you aren't pulling more vac than that WOT at full speed.
I am not sure why you are still running the secondaries that much larger than the primaries. I would try 86 in the rear. it impossiblw to read plugs on the internet, but it looks like you could affort to take 4 sizes out of the secondaies.
I'm gonna put a new set of plugs in it and try it with 86 Prim, 88 sec's. When I had the 84's square in it, the plugs looked pretty white. I think what's making this tough is the fact that the secondaries start opening when the primaries are only open maybe 1/4 of the way.. they start a lot sooner than the 800 did.

Isn't it a good thing to have 0 vacuum at WOT??
 

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