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Old 09-24-2004, 01:35 PM   #1 (permalink)
crazypete
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Default Any gains from removing holley choke horn?

Good day folks,

I'm doing a sizeable rebuild/porting right now installing my gt-40p's and I stumbled across a few articles on carb porting. I was wondering:

I have not used the choke on my carb since I got the carb 2 years ago. The engine simply wont run if the choke is engaged at all. I know how to set idle/choke and I go back every year and try to put it back on and always recieve the same impression: the engine only runs if the electric choke is set to basically flip all the way open almost immediatley when the motor is started.

So what kind of gains would be had if one was to saw the choke horn right off the carb (carefully) so the top was flat. It seems like quite a restriction in terms of air flow and direction. I mean the air needs to smack into the side of the horn and then move up and then reverse direction to go down the carb throat....

If I should do this, should I leave the snorkels original at their original chorn horn length or hack them flat too?

Thanks!

Pete
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Old 09-25-2004, 08:02 AM   #2 (permalink)
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LOTS of guys whack off the choke horn, it's a good idea. Leave the snorkels though, those are bowl vents. Cut them too short, and you'll have fuel running out of them, which is a bad thing. I set my car on fire this spring because my floats stuck, and pumped fuel out the vents.

Ever thought of a Proform main body? It's another $100, but well worth it! I got a Mr. Microphone, and I love it! hehehehe
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Old 09-25-2004, 10:44 AM   #3 (permalink)
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I've seen studies that say it's better and I've seen studies that say it's worse. I mill the choke tower off of my carbs, but I never need a choke in So Cal. It's really up to you. I don't think you'll notice any difference, but it does look cool.
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Old 09-25-2004, 11:20 AM   #4 (permalink)
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Default Stub stack?

A really easy thing to do is put on a "stub stack" from K&N or Mr. Gasket. They supposedly help ease the directional change in the incomeing air and add a few CFM to the carb. I've heard they are good for a few top end HP sometimes and cost $30-40. I doubt you would even see it for sure on the dyno, but you wouldn't be risking much $$$ either and its totally reversible.

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Old 09-27-2004, 08:32 AM   #5 (permalink)
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So the general consensus is that it wont hurt but it wont do a ton of good either. I think I'm gonna do it anyway with tons of tape to keep the passages clear. I survived 2 new england winters chokeless. Yup, it's a snow loving mustang: I zoom around in the snow with tirechains on while I see SUV's stuck in the snow by the side of the road. Hell, I climb my ~25 degree slope driveway and descend it through a gate with 6 inches clearance on either side through thick snowbanks. Just takes some rubber undercoat and silicone to keep the rust away.

Anyhow. Thanks all!
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Old 09-27-2004, 07:05 PM   #6 (permalink)
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Quote:
Hell, I climb my ~25 degree slope driveway and descend it through a gate with 6 inches clearance on either side through thick snowbanks.
That's gonna be a bitch with those 4.56's. But it'll be fun too.
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Old 09-28-2004, 07:53 AM   #7 (permalink)
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You would be SHOCKED at how much of a difference tire chains make. Turn any car into a snowmobile. One could easily outmanuver 4x4's once the snow hits. Just gotta make sure that they are quality pieces so they dont come loose and tear up the rear 1/4's. I was once driving down rte 2 in western mass at 2 in the morning in a _blizzard_, no plows anywhere in sight. Well, an 18 wheeler decided that I was plowing the snow well enough for the both of us with my ground effects so he stayed behind me for almost an hour back to boston.

Ok, I ground off the choke horn but now it looks.....kinda messy. The alternative main bodies just have no choke horns, right? If thats the only difference, I'll dremel some more and get to the same end result. I tried to keep it clean but at this point, I might as well go buckwild and then clean it out as best I can.

Does anyone make a vacuum -> double pumper "kit"? I figure that this is an excellent time to do that if it exists.
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Old 09-28-2004, 01:42 PM   #8 (permalink)
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Pro-form doesnt make a vacuum secondary 670 cfm body, only a 750 cfm body. Does dropping a 750 mainbody on a 670 avenger base turn the 670 into a 750? I dont think I'm running enough cubes to run well with a 750. I assume the 650 mechanical body they have lacks the vacuum port to operate the vacuum diaphram secondary. Anybody else make aftermarket holley bodies?


I think their 25-50 hp boast is a bit steep! But if it makes 10, thats $100 well spent
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Old 10-14-2004, 04:38 AM   #9 (permalink)
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Are you trying to turn a double pumper into a vacuum secondary, or vise-versa?

If you keep the body you milled the choke off of, don't forget to fill the hole where the choke linkage went through the body next to the horn. JB weld works well. If you don't plug that hole, you will be allowing unfiltered air (and dirt) directly into the engine.
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Old 10-14-2004, 07:25 AM   #10 (permalink)
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I was trying to turn the vacuum secondary into a double pumper. Good call on the choke linkage port! I was wondering why the carb wasnt squeeky clean on top. I guess it was getting some dirt in there. Even worse, the pcv tube would occasionally belch some oil into the carb before I removed it.

Even though I've done the paper clip trick, I'm never quite convinced that the secondaries are actually opening so I picked up a holley 0-80540-1 off ebay and it's in excellent condition. It's a "true" double pumper and the progressive secondaries look like they wont open before maybe 60%. Plus I think the 670 was too big so this DP is a 600. Only problem is that someone drilled holes in the butterflies...I assume for some overcammed engine. I'll see if this runs at all....dont I just need to back out the idle screws to compensate for the extra air?

Now, the original holley is reserved for the eventual emissions test or if the 600 DP turns out to be too much of a guzzler. I'm having quite a time trying to clean the carb. I've soaked it in gas, laquer thinner, boiled in silver polish, boiled it in soap+fast-orange+water and, alas, when it dries, it looks like it's covered in white stuff that looks like mold if I didnt know any better. What is the definitive way to clean a carb? This is the 2 metering blocks, base and body minus all small parts.

Thanks!
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Old 10-15-2004, 11:51 PM   #11 (permalink)
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It's very difficult to turn a vac. secondary body into a double pumper because the passage between where the accelerator pump goes, and the squirter, doesn't exist. You'd need a new bowl and a new secondary metering block as well. The easiest way to take care of the secondaries in a vac. secondary Holley is to change the spring in the vacuum housing on the side of the carb that controls the secondaries. Get a spring kit for $20, and put in the lightest one (white or yellow, I believe). Then your secondaries will open for sure.

As far as the holes in the butterfly valves, just get two correctly sized set screws, and tap the holes for them. Use some thread-locker when you install them.

I clean my carbs in my solvent tank, which has a 50/50 mix of mineral spirits and water. What that doesn't clean, I use a fine wire wheel on, and lots of compressed air.
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Old 10-16-2004, 07:38 AM   #12 (permalink)
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Thanks dude!

I got 4 of those domed-round topped screws that can be found under the car holding in the back flap of the wheel wells. They looked aerodynamic enough and had the right threads. I popped the base off, put the screws in, dremeled the stems off, polished them almost flush and thread lockered the top of the screws. Looks really good actually!

Mineral spirits have already failed so I'm trying boiling in vinegar, a trick suggested by some old guys at work.
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