Could it be THIS simple?

[PKRWUD]

Originally Posted by ~The Jester~

Don't forget that most people think of the power valve "rating" BACKWARDS!!! If you have a 6.5 PV, it's open BELOW 6.5 hg.

Above that, it's as tight as an ugly 4th grader!

Correct, which also means as you're getting into your top end, and the vacuum is rising again, a 6.5 PV will close up sooner. That's why I feel pretty confident about suggesting an 8.5 PV.

[82 GT]

Originally Posted by PKRWUD

You've got the right idea.

I'd like to know your vacuum at idle, in Park. It would be really nice to know what your vacuum is when you feel you're losing your top end power, too. I'm guessing it's between 7" & 8".

Either way, an 8.5 PV will suit your set up better than a 6.5 PV will. May not solve all your problems, but it's a step in the right direction.

Throttle response has nothing to do with vacuum or mechanical secondaries, it's in how the accelerator pump is set up, the idle mixture, and the throttle plates. The reason your car should do better with a 3310 is vehicle weight and an auto tranny. That combo is difficult to tune mechanical secondaries for, whereas vacuum secondaries are tuned by engine demand. You just fine tune them with jets and the secondary spring.

Are you experiencing a bog, or it just feels like the carb runs out of juice way too soon? If it's the later, a 3310, properly set up, should solve it. In the mean time, an 8.5 PV will help.

There's no bog at all. It takes off like a freakin rocket! I don't really feel anything.My 15yr. old son once said it looks like my car slows down after the 1/8 mile....I don't know...it's possible I guess. The 12.85 at only 102MPH is what has me baffled. It should be around 105-107mph....despite the excellent 60' times I'm pulling. I'll try the 8.5 valve and see what happens.

[82 GT]

I ordered the new 8.5pv today along with a set of 74 jets for the front. If the 74's are too rich, then it's still ok 'cause I can use them next year when I finally hook up my nitrous. I'll need to jet up for that anyway.
PKRWUD, the 15hg I have at idle IS when it's in park.

[82 GT]

I just check my vacuum reading again. It's close enough to call 17hg in park and between 14-15hg in gear. A 7.5 valve is what's called for, according to Holley but an 8.5 will give me a slightly earlier opening and later closing.
It won't be until October when I get back to the track but you can bet I'll be back here with the results when I find out! Hopefully, it IS THIS simple...after all this time!

[Dark Knight]

Why would you need to jet it richer for N20?

[82 GT]

It's recommended that you jet up when you use nitrous as a precaution against a lean fuel/nitrous mixture. It's better to be slightly richer, rather than lean when running nitrous. A lean fuel/nitrous ratio is what melts pistons and all that other good stuff you don't want to happen.

[~The Jester~]

Originally Posted by 82 GT

It's recommended that you jet up when you use nitrous as a precaution against a lean fuel/nitrous mixture. It's better to be slightly richer, rather than lean when running nitrous. A lean fuel/nitrous ratio is what melts pistons and all that other good stuff you don't want to happen.

I've learned 2 things about Nitrous.

#1. Don't GIVE any advice.
#2. Don't TAKE any.

Think about that for a few, you'll "get it"...........

OK, now I'm gonna break Rule #1. Leave the carb alone if you're running a plate system.

[82 GT]

Originally Posted by ~The Jester~

I've learned 2 things about Nitrous.

#1. Don't GIVE any advice.
#2. Don't TAKE any.

Think about that for a few, you'll "get it"...........

OK, now I'm gonna break Rule #1. Leave the carb alone if you're running a plate system.

How are you supposed to regulate fuel/nitrous ratio? I don't want melted pistons or spark plug electrodes.

[lx mike]

Originally Posted by 82 GT

How are you supposed to regulate fuel/nitrous ratio? I don't want melted pistons or spark plug electrodes.

Most companies have it set that the recomended jetting is a bit rich.

[~The Jester~]

Ya have to start thinking of carb and N2O as two different systems, cuz THEY ARE!

If the car is runnining "OK" leave the damn carb alone. Change spark plugs, adjust base timing, and let her rip. N2O plate will take care of itself.

Please refer to the first 2 nitrous rules of this thread.

[~The Jester~]

OK, now that I don't have so much beer in me , I can clarify that last statement! LOL


All I meant was the carb should be tuned seperate from the nitrous system. Get the carb setup right first, then hit the spray. If you want to run the carb a little fat, that's fine. A little insurance never hurts. But remember one of my rules: "Fat is safe, but Lean is Fast!" (Maybe I should start righting these down? LOL)

Then all you have to do is fire up the nitrous plate, and if the thing gets PIG fat, lean up the plate a little, but leave the carb alone. Same story for the lean direction. If you have problems on the spray, tune the plate, not the carb.

Dammit! I broke rule #1 again, didn't I? LMAO

[rwhite65]

Originally Posted by ~The Jester~

"Fat is safe, but Lean is Fast!" (Maybe I should start righting these down? LOL)

This was kind of one of our rules from last night, but I won’t elaborate right now.
Ryan

[HeadDoctor]

Brian

Is this why you're going for the 4-corner idle circuit?
You know that you can take the power valve out completely and just square jet the thing and it'll run fine. So long as you run the power valve you have to use a 10-Point spread in the jets. Seems simpler to me to remove the PV.

Denny@JDS Induction Products

[82 GT]

No, that's not why I want 4 corner idle. I think I'm running rich at idle(burning eyes syndrome) and my jetting isn't overly rich either(72/80).
As far as removing the PV, I don't want to do that because I still drive this on the street and was told that wouldn't be a good idea because I would be rich ALL the time.

[HeadDoctor]

Brian
It was just a thought I didn't know you still drove it on the street - yes then it is best to change over to the 4-corner and 2 power valves the engine will run a bunch cleaner. When I convert Holleys to 4-corner I always use 3310 metering plates. I don't have the part # handy but its in their parts book.

That overly rich condition is common for Holleys

The main jet has nothing to do with the idle circuit and only partially controls the intermediate transfer slot just above the the idle hole in the base-plate.

I'm assuming that you have a 4779-2 750
It doesn't have holes drilled in the butterflyes and to get it to idle you have to turn the RPM screw about 3 to 5 turns to get idle speed. If that is correct then with the blades open that far the boosters are trying to dribble causeing the rich idle.

To find out - hold the throttle lever tight against its stop (you might want to have someone help you with this) and unscrew the adjustment until it is completely closed - then turn the screw in 2 turns - Start the car and see if it will idle there out of gear - if not then you are going to have to drill holes in the butterflyes to conpensate for the added air/fuel - Of course this may not be the problem at all! It could be something internal ????

At this point all we can do is make suggestions

Denny@JDS Induction Products

[Gearhead999]

Burning eye syndrome is usually "Lean" not rich.

[82 GT]

Head Doctor, I can't do that test for you because I already have the carb. off ready to be shipped out for the 4 corner idle to be done. Should I also tell the guy to drill 3/32 holes in the butterflies while he has it or will the 4 corner idle negate the need to do that?
I don't remember, offhand, without looking but I "think" it is a 4779-2 model. I sort of recall it taking quit a few turns to get it to idle speed when I first hooked it up.

Will it hurt to have the butterflies drilled if it doesn't really need it, although, I don't think it would pass that test you just mentioned
I don't think 2 turns would be anywhere near enough to get it to idle clean, which, right now is about 1000rpms. I don't know if that's normal or not though(1000rpms to idle clean)

[rwhite65]

Originally Posted by 82 GT

I don't think 2 turns would be anywhere near enough to get it to idle clean

Brian I too still have this problem. I am quite sure that I am past the two turns to keep mine idleing, although I dont have mine that high (900-950). So much has changed on mine in the last week or two, it will be some time and some small tuning before I get it.

Ryan