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Discussion Starter #1
Well it seems as if something is wrong with the two 9776 450's we have on our tunnel ram. I was just messing with the idle mixture screws to try and lean out the idle mixture a bit and turning the screws makes absolutely no difference what so ever. Idle does not go up when leaned out and does not go down when made richer. Car is idling at 1000.


Also one side of the engine is richer than the other. You can rev it up and it clears out then starts loading up after a couple seconds on the drivers side. I currently have all 4 idle screws at 1 1/2 turns out. I turned them all the way in and it made no difference. I did not think it would run with the screws all the way in?

Does it sound like junk in the idle circuit or something else? The carbs sat for almost 4 years on the engine they were on. I am thinking about getting 2 kits and rebuilding them.


Anybody have any ideas?
 

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A carb that is jetted high will have this condition.

Power valve failure?

Vacuum leak?

just a few things to check.

Kit is a smart idea.

Al
 

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I doubt there is anything mechanically-wrong with your carbs. When you mentioned how high your engine was idling in a previous post, I figured you might be noticing problems like this in the not too distant future.

I believe in the other thread you stated that you had to set the idle to like 1600 RPM out of gear and then it would drop to 1200 in gear or something to that effect. This is the part where the tuning of a Holley carb comes into play.

Your cam is not that radical that it should need to idle that high. It's a fairly moderate cam with a radical induction system. That doesn't mean you can't get it to work good though. It's just probably going to take more than bolting on the carbs and turning a couple idle mixture screws to get it all working good.

At 1,000 RPM your transfer slots are probably over-exposed and you are already into the transition circuit. Your vacuum is probably too low for the power valves in your carbs. I think the 450 carbs have like 8.5 power valves in them. They are probably actuated at idle which is why you have no response from the idle mixture screws. Your tail pipes are probably black with soot and your plugs are fouling and the fumes are enough to gag you as they burn the nostril hairs out of your nose.

Am I on the right track?
 

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Discussion Starter #4
I doubt there is anything mechanically-wrong with your carbs. When you mentioned how high your engine was idling in a previous post, I figured you might be noticing problems like this in the not too distant future.

I believe in the other thread you stated that you had to set the idle to like 1600 RPM out of gear and then it would drop to 1200 in gear or something to that effect. This is the part where the tuning of a Holley carb comes into play.

Your cam is not that radical that it should need to idle that high. It's a fairly moderate cam with a radical induction system. That doesn't mean you can't get it to work good though. It's just probably going to take more than bolting on the carbs and turning a couple idle mixture screws to get it all working good.

At 1,000 RPM your transfer slots are probably over-exposed and you are already into the transition circuit. Your vacuum is probably too low for the power valves in your carbs. I think the 450 carbs have like 8.5 power valves in them. They are probably actuated at idle which is why you have no response from the idle mixture screws. Your tail pipes are probably black with soot and your plugs are fouling and the fumes are enough to gag you as they burn the nostril hairs out of your nose.

Am I on the right track?

We fixed the high idle issue. The car had a stock converter in it and we put a new 3000 stall so it no longer slams in gear. Before I installed the tunnel ram I had the vacuum secondary 750 idle at 900.

You very well may be right about the transfer slots. We just picked the car up yesterday from a relatives fabrication shop. He messed with the carbs. He said the floats were set to high so he set them and he messed with the idle mixture screws. Well honestly it ran much better before he touched the carbs.

Your right it will just about gag you and burns the nose pretty bad. Now that he messed with them it seems as if a cylinder is loading up on the driers side. It is blowing a little black smoke out of the drivers side only.


Here is an idle video BEFORE he messed with the carbs. Sounds and runs good in this video. Was rich in this video but not loading up. It would foul a plug once in a while though. The plugs I changed yesterday were all jet black and sooty.


http://vimeo.com/4681741


I am going to order two renew kits and go through the carbs. What power valves would you suggest?
 

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I wouldn't waste the money on the 'renew' kits yet. They're probably not going to do anything for you. Carbs don't wear-out from sitting a couple years if they are new and never had any gas in them. Save the kit for the last resort. You have all the classic symptoms of running too high a power valve value for your application. You want a power valve that will be fully-closed at idle but will open up just above idle.

You need to connect a vacuum gauge to a manifold vacuum source either on the carbs or the intake. Take a reading at idle and divide that number by 1/2. That's the power valve value you want to try first.

When you first fired-up your engine, everything was fresh. The more you run it, the more fouled the plugs will become. You probably notice it more now because it's idling more where it should be and not at 1600 RPM.

Everything works together. You also want to make sure your ignition is advanced properly so that you can close the throttle blades as far as possible at idle. Maximize your vacuum signal because it's going to be low enough with a tunnel ram. Then take your vacuum reading and go buy new power valves and install them. Take the car out for a spin and see if it has a lean hesitation or surging. If it does, you may need to go up to the next value. Chances are that it will be OK though.

Once you get the correct power valves installed, you'll have full response from your idle mixture screws and your idle will be clean as a whistle. Your plugs won't foul either.

If you don't have a vacuum gauge, go buy one. They are inexpensive and you can't properly tune an engine without one.
 

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IMHO pull the carbs and set the primary throttles to expose .02 of the transfer slot. They should look like a square. Then make all other speed adjustments with the secondary throttles. The power valves do not affect the idle or part throttle at all unless they are ruptured. Check them while you have the carbs apart but don't change them. They only affect heavy (not full) throttle after the mains come in. You pick the right power valve by driving the car with a vacuum gage and checking for lean surges at certain vacuum levels. There is no formula that works for this. While the carbs are apart try putting a .018 wire in the primary IFRs. The idle and transfer slot mixture is too rich on these carbs. A lot of fuel comes thru the secondary idle as well. I don't know what application Holley designed them for but they sure are strange. (If you go to the Holley web site and search for 9776 it comes up empty. Discontinued?) For a street tunnel ram everyone seems to recommend the 390 vac or 600 vac. I converted mine to vac sec and now I like them.
 

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Discussion Starter #7
Alright guys you are confusing me! One says the powervalves will be open and richen the idle if they are incorrect and the other says the powervalves will do nothing to the idle?
 

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Discussion Starter #8
I wouldn't waste the money on the 'renew' kits yet. They're probably not going to do anything for you. Carbs don't wear-out from sitting a couple years if they are new and never had any gas in them. Save the kit for the last resort. You have all the classic symptoms of running too high a power valve value for your application. You want a power valve that will be fully-closed at idle but will open up just above idle.

You need to connect a vacuum gauge to a manifold vacuum source either on the carbs or the intake. Take a reading at idle and divide that number by 1/2. That's the power valve value you want to try first.

When you first fired-up your engine, everything was fresh. The more you run it, the more fouled the plugs will become. You probably notice it more now because it's idling more where it should be and not at 1600 RPM.

Everything works together. You also want to make sure your ignition is advanced properly so that you can close the throttle blades as far as possible at idle. Maximize your vacuum signal because it's going to be low enough with a tunnel ram. Then take your vacuum reading and go buy new power valves and install them. Take the car out for a spin and see if it has a lean hesitation or surging. If it does, you may need to go up to the next value. Chances are that it will be OK though.

Once you get the correct power valves installed, you'll have full response from your idle mixture screws and your idle will be clean as a whistle. Your plugs won't foul either.

If you don't have a vacuum gauge, go buy one. They are inexpensive and you can't properly tune an engine without one.

The carbs werent new. They were run on this same tunnel ram on our friends 327 for 2 years. Then they sat for a couple years. Then he fired the engine up just before he pulled the engine to sell us the car. He put that 327 in a S-10 Blazer and dropped a valve and destroyed the engine.


I was just outside doing some tinkering and got it back to the way it ran before my relative messed with it. Then I did something and it went right back to running like crap. Tried for another 20 minutes to get it back again and never could. Something seems screwy inside the carbs.
 

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Scroll down a bit and read the power valve section. http://www.carcraft.com/howto/116_0501_carbs_tips_tricks_cheap/index.html My motor makes 9" at idle but it rises to 14-18" at cruise. I run an 8.5 pv. Stepping into the throttle harder and harder while watching the vacuum gage gave me lean surges with a 6.5 valve. The 8.5 valve fixed it. If I kept the 6.5 valve or used a 4.5 like some formulas say I would have to increase the main jet size to clear up the surge. There goes even more mpg out the tailpipe. If you're only interested in idle and full throttle you tune one way. Trying to get power and mileage makes you tune another way. 90% of street driving is part throttle. Thats where the transfer slots and power valve work.
 

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Alright guys you are confusing me! One says the powervalves will be open and richen the idle if they are incorrect and the other says the powervalves will do nothing to the idle?
Power valves are a direct operation of manifold vac.

If you have a 8.5 power valve and manifold vac is below 10inch this the valve will open the rich circut.

Also a bad power valve will have the fuel circut open.

I have always used a 4.5 power valve on street use dual carbs. No matter what the intake vacuum is. The throttle valves with dual carbs has a dramatic vac drop and slowig down the transfer with low vac responce powervalves helps.


I believe installing new kits and 4.5 power valves is a smart direction.:yes::D

Also if the throttle plates do not have the powervalve protection I would install these also.

Later I will take a pic of what to look at in referance to power valve protection. Later tonight. Don't have time right now.

Take the time to read this article.
http://www.chevyhiperformance.com/techarticles/74058_carburetor_valve_problems/index.html
 

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I'm going the other way here. Check your timing.
Set the idle mixture screws at 1-1/4 to 1 1/2 out and loosen the idle screw all the way out. The turn it back in till it just move the throttle plates. Then start the engine and see where the timing is. I bet the timming is slow and the idle speed has to be turned up so much it's running on the transfer slots.
 

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Discussion Starter #12
The timing is locked out and set at 36.


Here is what I got directly from holley

"POWER VALVES:
The number stamped on a power valve, such as 65, indicates the manifold vacuum below which the power valve is operational. In this case, all manifold vacuums below 6.5” Hg, the power valve is operating. Generally a 65 power valve is sufficient for most high performance applications that have a manifold vacuum of 12” Hg or higher. However, some problems can result with radically cammed engines equipped with automatic transmissions. These vehicles often “idle” at 2000 rpm, approx. 6.0” Hg. At this point the main nozzles are starting to feed and richen the mixture (supplied by the power valve) and the engine will probably “load up”. To correct this problem, install a 45 or 35 power valve. If the engine has a manifold vacuum of 12” Hg or less, a good way to determine power valve size is take the manifold vacuum at idle and divide that number by two. The answer is the power valve size. This will provide idling and proper fuel flow under wide open throttle conditions when manifold vacuums seldom rise above 1” Hg."


I am wondering how much vacuum this 355 should make with this cam? Anybody have a rough idea?

# Advertised Duration (Int/Exh): 276/284
# Duration @ .050 (Int/Exh): 233/241
# Gross Valve Lift (Int/Exh): .504/.525
# LSA/ICL: 110/106
# Valve Lash (Int/Exh): Hyd/Hyd
# RPM Range: 2200-6400
 

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Look down the carbs (with a mirror?) while you slowly raise the idle speed. Have someone watch the tach and note when fuel starts coming from the boosters. That's when the mains start feeding fuel. If that's where your engine normally idles and you have under 8.5" of vacuum at that rpm then the power valve can make a difference. FYI my 406 with dual 450s starts feeding from the mains at around 2900 rpm. It has over 20" of vacuum at that speed in neutral.
 

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Like I mentioned earlier, it's virtually-impossible to properly tune a Holley without a vacuum gauge. It's hit or miss. As for the section from the Holley website that discusses proper power valve selection, they didn't always say that. Up until about two years ago they were still recommending the old "1-2 values above your vacuum signal at idle" rule.

Well I've been playing with Holleys since the 1970s and that old rule never worked for me in the real world. Glad to see that Holley finally saw the light.

As for the statement, "The power valves do not affect the idle or part throttle at all unless they are ruptured."

A power valve that is open at idle due to it being too high of a rating for the vacuum signal acts exactly the same as one that is ruptured. Open is open whether it is ruptured or open from the vacuum signal. The "windows" that the gas flows through are what regulates the gas flow when they are ruptured or open. It doesn't know or care if the gas flowing through it is from a ruptured valve or an open one. It just knows there is gas flowing. The flow will be the same.

I like the actual vacuum of my engine to dictate when the power valve opens just above idle, not simply by the position of the throttle blades like some guys profess which means they might as well be running a ruptured power valve if it's going to be open all the time and the only thing stopping the power enrichment circuit is the physical positioning of the throttle blades.

They have been using those 450 Holleys on tunnel rams for decades now. They are probably the most-common carbs you will see on one for a street application.

I think Al is probably pretty-close when he says he thinks you'll need 4.5 power valves. I didn't want to come right out and say that though because I thought you might just go buy some power valves without getting a vacuum gauge. I think your vacuum signal will be around 8-10 at idle with your combo. It might be a little more though. It shouldn't be too much lower unless your initial timing is too retarded and you have the primaries open too far at idle to keep it running.

I'm glad you got the gauge. It's one of the most-valuable tools in any mechanic's toolbox and you will need it again in the future after this.
 

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Next time you have a Holley apart trace out where the circuits go. A blown power valve (ruptured) will suck fuel from the float bowl straight into the engine thru the power valve vacuum hole, which for my 450s is .125 dia. An open power valve will open the PVCRs to the main well which is already open to the main jets and is just waiting for enough airflow to start flowing out the boosters. If you change main jets it doesn't affect the idle. 2 different circuits. You can take the main jets out completely and the motor will still idle just fine.
 

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Discussion Starter #19 (Edited)
Do you guys recommend standard flow or high flow power valves? I am going to test the vacuum tomorrow then order up 2 kits and power valves.

Do these carbs require 2 power valves or just one?
 

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if it wuz me

something i wish i would have tried with my 2 450's , was to block the constant idle port in the secondarys and drill the hole for the passage to feed idle mixture fuel to the back barrels. This should give you better adjustment to your idle mixture screws. Why Holley doesn't drill this for you amazes me but oh well.

I wouldn't buy 2 kits yet , i bet ya the power valves are busted or stuck open.

you might try a KN type air filter too ,,, and as big as feasable

Spray some carb cleaner down the air bleeds too to make sure there isn't a problem there

If you want to try blocking the constant idle port , it could be done very easy and reversible with silicone ( blue RTV ). Its steady fuel flow that when using 2 carbs may not be required. If you look for the transfer slot in the secondarys , there is a small hole directly under them ,, you could put a small amount of RTV in the hole from the top of the base plate so that it will block fuel flow from the constant idle port , and make sure the transfer slot is still uncovered so fuel will still flow there, this might help you get some more adjustment, If it doesn't help , pull the RTV out

area where the constant idle feed port is , but in secondary

http://image.mustangandfords.com/f/9348134/mufp_0603_19z+carburetor+idle_transfer_slot.jpg

pic of top of base plate , see the hole with the slot toward the barrel ? put some RTV in the bottom of that hole but leave the slot uncovered
http://www.hangar18fabrication.com/images/blowthru/remove_pvprotector.JPG


if you want to try drilling the hole that will give idle mixture fuel to the back barrels , send me an IM , i'll tell ya how to do it and its also reversible

any action with the carb should give a re-action with the motor than might need another action from yourself so you might have to chase it a lil bit.

the 2 450's i had drank so much fuel i pulled them , now i wish i would have tried a few things before i did now that i've had time to think about it ,, just my .02
 
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