Holley 715 CFM #3259 float level adjustment

[mygt350]

My 3259 was pushing out so much fuel enriched exhaust, my neighbors prius was crying. Car was bucking like a pissed bull. Sent it off to Drew with engine specifics and my driving style and when he sent it back, only adjustment was curb idle. Now its running like a 60's muscle car.
+1 for Drew

[maxjets]

  Let me add to this a bit.
     "ALL" engines will ONLY flow a specific amount of air through a carburetor REGARDLESS of CFM capability of the carburetor. Now it would be stupid to take my statement and put a ONE barrel , 6 cylinder carb on a 427 or vice versa. Those who subscribe to the 289=600cfm rule as an absolute are WRONG. Last time I checked there are about 60 DIFFERENT 600cfm Holleys and only about 5 or 6 that really work well on a 289. WHY? Because they are "generic" in design. In late '64 , Holley engineers spent allot of time calibrating an existing Holley four barrel to work on a 289 High performance engine with a "high rise" intake and tubular steel headers. The result is the 3259 , "GT350" carburetor. It was revised ( better front metering block) and given the 3259-1 list number and the S2MS9510-A ID number added . The adjustments made allowed this former 427 FE carburetor to work on the smaller 289. While the maximum air flow potential is 715CFM , (again) the 289 will only flow a lesser number as produced. The extra air capacity does NOT  "flood" the engine!!!!!!! THAT is a physical impossibility! Pure and simple. Carburetors are not designed to POUR fuel into an engine , they are designed to add fuel to air SUCKED in by the engine underneath it. The vacuum "signal" that the "boosters" "see" , pulls fuel out of the float bowls. YES a smaller CFM carburetor "can" be easier to calibrate because the smaller venturi helps the "pull" on the fuel. The amount of air flowing through the carburetor is UNCHANGED from the 715. Now change the camshaft , port the heads etc . and the AIRFLOW the engine creates will change and a larger carburetor "might" be needed. Random picking of a carburetor by size alone "may" not provide perfect calibration and require adjustments ( much like Holley engineers did on the 3259). There are at least 30 different 750 cfm carbs and "most" of them would require adjustments to fine tune them to a specific engine.
     This is what keeps carburetor specialists like Drew busy. Drew has the experience needed to match a carburetor to an application OR tell us it won't work. Most of us can change jets , power valves , gaskets .FEW of us can "optimally" tune a carburetor with air bleeds, power valve restrictions etc. like an expert does.
    Randy

That is GOLD! Great explanation.

[Helmantel]

I lowered the primary floats a little to prevent them from bottoming out, but the engine runs just as rich as before: 12,5 at idle (tuned for best idle setting, ~3/4 turns out, 18" vacuum), ~10 at light cruise, ~11-12 at highway cruise and ~12,5 under acceleration. It idles smoothly and doesn't run bad otherwise but smells fuel and fuel consumption is high.

It seems that something is leaking fuel but I can't figure out what. A leaking power valve could be a possibility but it worked fine when I tested it with a vacuum tester (pulling vacuum on the membrane side) and all gaskets seem fine (the blue non-sticking type on the metering blocks). I didn't have any new ones handy but I guess I'll buy some and see if that helps.

Unless the specific calibration of this carb works ONLY on a GT350 engine and not at all on my 289 (short duration but .533 lift roller cam, Shelby Hirise manifolds, 351W heads with mild porting, headers, 10:1 compression), but that seems unlikely.

[67350#1242]

It is possible that the float bracket is tweaked such that the float will contact the front of the bowl before fully seating on the needle.  This can be fixed by bending the bracket such that the float is moved away or outward from the bowl.  This adjustment is not done with the tang that contacts the seat, but where the bracket makes a 90 degree bend.  Readjust the tang afterwards to set the float level to spec.
Kurt.

[Helmantel]

Thanks for the suggestion but that doesn't seem to be the case. Although Now that I look it it, it does seem possible to bend the tab and the float bracket in such a way that a 3/8" setting can be achieved without the float hitting the bowl.

[shelbydoug]

It has the symptoms of the fuel level being set too high.

You need to verify that you have the correct needle and seat part in the carb.

I would use only a Holley replacement needle and seat. Some of the aftermarket ones are too short.

It's better to have the levels a little too low then too high.


You need to use a "power valve" tester to verify the power valve is good. I've had a number of them bad out of the box most likely due to age. Make sure the power valve gasket is the right one. There are other gaskets in the kit that are similar but not quite right.

If you have a fuel level that is "dripping" into the intake it will make the idle too rich as well.


With all due respect to Drew, setting the float levels just right is no longer a simple task like it should be. Ethanol in the fuel has something to do with it and they will also stick closed after being run and sitting for a week or so.

I have also found the Holley dry float settings too high. Not everyone can just eyeball them and get them right the first time.

The Lemans bowls are more difficult because you have no sight plugs to check the level with.

[Helmantel]

I had set the float levels set to the (somewhat confusing, see first post) recommendation of 3/8" front and 1/2" rear. Now the fronts are a little lower due to the float interference with the bowl. Since the engine ran much better I thought I was on to something, but it's still running rich. I guess I can give it a try and set the floats lower. All this fiddling with the floats sure makes me long for externally adjustable floats and side plugs I'm still considering drilling and tapping my bowls for side plugs: there's a patch on the bowls already.

I wonder if the ethanol fuels require a lower fluid level in the bowl or if  the fluid level should be the same but that the density of the fuel requires a lower float dry setting? Or maybe a combination of both.

The needles in seats are in like new condition and the power valve tested as OK, but will replace it anyway and see what that brings. I will also check for any signs of fuel dripping at idle.

[shelbydoug]

The only other thing that you haven't mentioned that you looked at is the metering block.

The block has emulsion tubes in it for both the idle circuit and the main circuit. I don't think they were ever intended to be serviced after manufacture.

Drew has a video on his Facebook page that shows you how to service them.
since you are having issues with the idle circuit, you need to consider servicing them.

There are also air bleeds in the main body and need to be cleared out with a numbered drill bit. They are small and clog easily.


It wouldn't be a bad idea to ask Drew to go through that carb for you, set it up and test run it for you? The issue is he's a very busy guy and it might take a while for him to get to it?

[67350#1242]

I wonder if the ethanol fuels require a lower fluid level in the bowl or if  the fluid level should be the same but that the density of the fuel requires a lower float dry setting? Or maybe a combination of both.

I think you are correct about that.  Less dense fuel will make the float ride lower in the fuel - causing a higher actual fuel level before being cut off at the needle.

[Drew Pojedinec]

You'll find the difference is negligible....
Specific gravity of .748 vs .756 etc. the range from E0 to E10 is well within the range of gasoline variability.

Fuel pressure variation and needle/seat diameters have a much greater impact.

[Helmantel]

The only other thing that you haven't mentioned that you looked at is the metering block.

The block has emulsion tubes in it for both the idle circuit and the main circuit. I don't think they were ever intended to be serviced after manufacture.

Drew has a video on his Facebook page that shows you how to service them.
since you are having issues with the idle circuit, you need to consider servicing them.

There are also air bleeds in the main body and need to be cleared out with a numbered drill bit. They are small and clog easily.

It wouldn't be a bad idea to ask Drew to go through that carb for you, set it up and test run it for you? The issue is he's a very busy guy and it might take a while for him to get to it?

For what it's worth, this carburetor is hardly used and everything inside looks brand new and clean, including the air bleeds. I don't know about the emulsion tubes though.

I'm sure Drew could get it right. I do live in Sweden though, so shipping it back and forth would be a bit of a hassle. Also, I had this carb intended for a new engine build I have planned (if I ever get to it....) so if I can't get it right, I might have Drew look at it for that application instead.

You'll find the difference is negligible....
Specific gravity of .748 vs .756 etc. the range from E0 to E10 is well within the range of gasoline variability.

Fuel pressure variation and needle/seat diameters have a much greater impact.

Yeah, you're right. Density is probably not much affected by the ethanol.

I wondered about the (strong) influence of fuel level on the mixture. Initially I thought that the pressure of an inch (or thereabout) of fuel would be negligible, but when looking into the vacuum created in a booster venturi, I found that the vacuum at cruising speed for a 289 is probably only 1-2" of water or so (~40CFM per venturi at 2000 RPM/half load). Compare that to an inch of fuel (~3/4" of water) and it becomes obvious that the influence of the fuel level will be significant at low airflow levels.

When running on the idle and transfer circuit, the holes are directly exposed to the manfold vacuum (or whatever the vacuum will be right at the tip of the throttle blade) so it is much higher than in the venturi booster. Could there be an effect of the exposure of the different emulsion tube holes, with the holes being under or over the fuel level under different operating conditions? Thereby affecting the amount of air that enters the emulsion?

[shelbydoug]

Drew is the only one that I know of who as "played with" the Holley emulsion tubes.

I can tell you that with drastic changes of the emulsion tubes in a Weber 48ida you do get significant changes BUT there are three commonly used in 289's that are similar, F5, F7 and F11 that have only subtle changes at certain rpms.

In Webers, the location of the holes in the tubes effects the leaning or enrichening of the fuel mixture at one particular rpm.


Does that vary according to the engines vacuum draw related to engine size? Yes. The draw of a 427 is different then a 289.


Drew pointed out to me that the idle emulsion tube in a Holley metering block is used to keep the main circuit from coming in too early. So from his empirical method of learning Holleys, he has a different definition of an emulsion tube rather then a textbook one. Who am I to argue? I ask him for help and not the other way around?

That design happens to be Holley's application to their specific issue solution but not the traditional use of an emulsion tube.


What he told me to do is probably what you should do also. You need to remove the brass caps on the idle tubes. Those you drill out with a #1 drill bit.

New caps are available and reinstall easily. Now in theory you thread in a 8-32 screw into the top of the tube and pull it out. In theory.

Mine wouldn't come out and you need to go to the next step and use heat on the metering block. How much heat? 'don't know but keep in mind Holley metering blocks do warp just from engine heat and if they do, will leak past the gasket at the pump transfer hole.


Again, on Drew's Facebook page, he shows you what the removed emulsion tubes look like and take it from me, those are what emulsion tubes do look like.

You can see the holes in them, just like the Weber tubes at various heights.

Now don't ask me if they have different part numbers like the Webers do BUT one of the things that Holley did to that carb to make it acceptable to use on a 289 was "re-calibrate" it, which absolutely would include the emulsion tubes so count on the 3259 being just a little bit uniquely calibrated for a 289.


Drews point was that those tube transfer holes OFTEN are clogged and create crazy rich idle characteristics very similar to what you are going through with the carb right now.
Sometimes that shows in the response of the engine to the idle set screws.


I just went through this and still am. I have a little bit of a unique situation in running 2x4's on a C60A T/A intake on a 347. I'm set on 1-1/8 turns out and that's where that sucker wants to run.

What I think is happening with mine, I think, is that at 1-1/8 turns, it is idling partially on the mains. A purist will say, no it shouldn't, that's wrong but this intake has just a little different idling characteristics then a COBRA high rise does. It was never put on a production car and what I am experiencing MIGHT just be the reason? I don't think you could sanely use it with an automatic transmission at all.

It's difficult for the Doctor to tell if you are absolutely nuts or just a genius because he has no one else to compare you too? I suppose it is at least entertaining?



Now the point of taking out those tubes is to clean out the transfer holes and the idle passage at the top of the tube if it is located there. That orafice can be located in one of three spots in the carb. The one at the top of the tube is an .028 (look at your numbered drill set to see how small that is) and can clog if a cow in China farts 10,000 miles away from you? 


My suggestion is to get Facebook just to see his page. He is a very helpful guy and readily shares what he knows but I think being offshore for 4 weeks at a time on a tug the crew and diesel fumes get to him and he starts throwing around wrenches if you piss him off? That would make me temperamental too for sure? Especially with a crew of 9 and cookie making fried Spam three times a day and only having condensed milk for your coffee the whole time? Yikes, I'm getting anxiety already?

[Drew Pojedinec]

I think perhaps you misunderstood some of what I said... or perhaps I described it badly.

3259's  do not have an idle emulsion tube. Never did, nor do any other 4150 performance carbs.
The mainwell has a tube, but best to leave it alone for the layman.

I was showing you the idle feed restriction which is under the cup plug inside the idle well. Important to clean those.

[shelbydoug]

Yes, idle feed restriction mentioned above. One metering block had it located there under the cap, the other was in an accessible part of the block.

.028 sounds big until you see how small it is.

Thanks for that information. It helped.

[Drew Pojedinec]

Lol, and .028 to .035 seems like a small change until you do the math and figure the area 😀