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Swapping holley carbs and questions

T

the_last_hour

Member
"If I'm swapping my holley

"If I'm swapping my holley carbs on my 5.7's, is it necessary to replace gasgets ( they are 1 year old), Is there anything special I need to know about removing the metal fuel line to the carb? (special tool,sealant?) The reason for the swap, is one engine burns 15-20% more fuel according to floscans, it is evident at all rpm ranges, including idle. I want to see if the efficiency problem follows the carb. The carbs only have two mixture screws to adjust, one left and one right. How should they be set? The carb that is not efficient does not react much when the right mixture screw is all the way in, but needs some idle screw adjustment to get up to 750. The efficient carb is very sensitive to the right mixture screw and the only way for me to get it below 750 rpms is to close it a little. The timing is the same on both engines."
 
"You may have a leaky fuel inl

"You may have a leaky fuel inlet valve, keeping the fuel bowl overfilled. The best way to adjust idle mixture is to use a vacuum gauge, adjust for max vacuum, using the butterfly stop screw adjusted for 750 rpm."
 
"Unless things have changed, t

"Unless things have changed, the floscan calibration process effects both sensors the same - the difference is there, the absolute value may be in question..

Most of the holleys have inspection ports - have you visually inspected it for fuel level or excess fuel in the venturi areas?

It is also good practice to replace any gasket after it has been compressed, the carb base plate is no exception. regarding the fuel line - three tips: Don't over-torque, use the correct wrench, take your time. Mistakes in this area usually don't allow for 'second chances'."
 
"..." floscan calibration

"..." floscan calibration process effects both sensors the same.."

Correct, but the flowmeter on the "bad" engine could be seeing air being sucked in before it, which screws up the readings big time.

Jeff"
 
"I went to the boat yesterday,

"I went to the boat yesterday, and experimented with the idle mixture screws. The engine in question will still run decent with the idle screws all the way in with only minimal rpm loss at idle. What's next?"
 
"When a Holly doesn't adju

"When a Holly doesn't adjust it's usually rebuild time. MakoMark is probably right. You might want to check the needle and seat on the secondaries and see if the carb is spilling fuel into the venturis at idle. If you are lucky it's just a piece of crap that's stuck to the needle and seat that was shaken loose by the ethanol. If it is spilling fuel remove the screw from the side of the fuel bowl and remove the screw from the top of the needle and seat. Use a syringe with the red plastic tube from a can of gumout inserted into the end-perfect fit-and remove some fuel from the fuel bowl. Then, spray some gumout into the hole on the top of the needle and seat. Put it back together and see what happens. Sounds complex, but it should only take a few minutes. I have to do this periodically on my 502. Even with the 10 micron filter junk sneaks through. Sorry about the lengthy post. Stu"
 
"Steve:

go here:
[url=""]h

"Steve:

go here:
http://holley.com/TechService/

They have several sections that may help you.

Stu's thought can't be off. If the mixture screws are in and the engine is still running, fuel is flowing somewhere and it shouldn't be. He also correct about the ability of fuel to 'grow stuff' irregardless of the efforts to filter it.

Have you "looked inside" the carb, while running, to see if it is flooding?"
 
"when a holley carb continues

"when a holley carb continues to run after running the screws in with little or no difference in rpm, its usually the power valves popped. they are in the front metering blocks, behind the float bowl.it takes a one inch boxed in wrench to remove them,and when reinstalling them, use a 12 point socket with light hand pressure only.[no ratchet on socket]This should get you going after adjusting[start with 3/4 round out on mixture screws ,and go from there. keep us posted. .Turboman ROLL TIDE"
 
"also on the holleys ,under th

"also on the holleys ,under the secondary arm where the vacuum diaphragm is located on the bottom of the base plate, looking up should be an idle screw to adjust the secondary blades [just like the primary,but hard to get to because they are not used unless primary idle screw is backed off all the way ]This screw should not be turned more than 1/2 to 1 turn either way as it has a big effect on the rpm"
 
"Whoa, Everett is probably rig

"Whoa, Everett is probably right. I forgot about the power valves! If you have 4011 Holleys the power valves are under the fuel bowls I believe? Stu"
 
"..."when a holley carb co

"..."when a holley carb continues to run after running the screws in with little or no difference in rpm, its usually the power valves popped. "

Not so--it's flooding. The power valve is like an adjustable main jet--it richens the mixture with added throttle.

You need to rebuild the carb.


Jeff"
 
"on the holley carb, it uses a

"on the holley carb, it uses a diaphragm style power valve ,and the center of the diaphragm is rubber. whether from age back fire or any number of reasons,they pop and allow extra fuel in. this valve works off of vacuum and the valve will be stamped on the front with a number that indicates at what vacuum it opens up to allow extra fuel in. I might have missed in the first post where he said that it was flooding,but usually holleys that don't adjust with the screws have a blown power valve. the power valve is not adjustable, its either open or its closed, no in between.it used to be called an economy valve[lol].anyway keep us posted as to what you find TURBO MAN ROLL TIDE"
 
"Everett's got a good poin

"Everett's got a good point. Turn BOTH idles mixture screws in; if engine dies, power valve ok. If engine keeps running; power valve ruptured.

If they are ruptured, they will supply the fuel.

If the engine has had this extra fuel consumption a while, and runs ok otherwise, I'd go straight for the power valve"
 
"No, no, no! The power valve

"No, no, no! The power valve has nothing to do with the idle. If the motor continues to run with the idles screws in, then the carb is flooding.

Jeff"
 
"Jeff ,I'm not trying to a

"Jeff ,I'm not trying to argue ,just offer suggestions. on holleys, when the power valve ruptures, the extra fuel leaks past the diaphragm[ rubber part in the center of the valve]due to split from age, back fire, any number of reasons, but this extra fuel can amount to a lot of non-metered fuel that gets dumped into the motor.the power valve has a lot to do with idle, when its blown, simply because it is supplying fuel when it shouldn't[ and as I said before,non-metered]. screwing the the idle screws in to shut off the metered fuel allows the extra fuel supplied by the blown valve to keep the process going. Maybe STEVE can tell us if fuel is pouring out of the boosters which would indicate a flooding condition, but I would think that this would also cause starting problems among other things. Sorry about the long post, but just trying to help the man. STEVE, give us a shout about your progress and let us know. TURBO MAN ROLL TIDE"
 
"The power valve is not in use

"The power valve is not in use at idle, only when transitioning to the main jets, and while operating on the main jets. It has nothing to do with idle whatsoever.

The carb is flooding.

Jeff"
 
"JEFF, I think your missing th

"JEFF, I think your missing the point. It's an issue of adding fuel at all times WHEN its not supposed to. you are correct in that it's not in use at idle WHEN its not popped. BUT, when the power valve blows, it adds fuel AT ALL TIMES, at idle ,mid point ,wide open throttle, PERIOD....NOW as to when it comes in to play when operating correctly, that depends on what power valve you have. As I stated before, the holley brand power valves are stamped on the edge or front [depending on if its a two stage or single stage]at what vacuum point it opens up to allow the extra fuel to enter.This is if its not blown.One of the most common is 6.5, which indicates it opens at 6.5 inches of vacuum, and there are many more to tailor the carb to the conditions that you have with your boat ,car, or what ever you have the carb on.IN a nut shell if its operating correctly ,the power valve will not open until reaching its stamped opening vacuum point, if its blown its dumping extra fuel ALL the time. Once again ,sorry about the long post , just trying to help JEFF understand how a holley carb works.STEVE, what about the carb, is it flooding out of the boosters? Let us know what you find. TURBO MAN.ROLL TIDE 10-0"
 
"Boy am I glad I don't hav

"Boy am I glad I don't have carbs.
biggrin.gif


Rick"
 
"wow, what a can of worms I op

"wow, what a can of worms I opened!!! Sorry about the debate guys. I will not be at the boat until next week, so I can not answer yet. Please explain to me exactly what I am looking for to see it flooding out of the boosters, Laymens terms please. (Remember, I'm not a mechanic, I just don't have a choice not to do my own work, since no one works on inboards in my area)."
 
"Hey Steve, no matter how they

"Hey Steve, no matter how they work the bottom line is a bad power valve will cause excessive fuel consumption-as will a bad needle and seat-or a damaged float. Stu"
 
"NO, repeat, NO fuel comes out

"NO, repeat, NO fuel comes out of the power valve or the main jets at idle. Not a drop.

The carb is flooding!

Jeff"
 
"how bout we just say...either

"how bout we just say...either way...there is too much gas getting into the floats. In either case, its a rebuild. Yank it off, take a look, fix it."
 
"AMEN, it's not worth givi

"AMEN, it's not worth giving a lesson about how carbs work . If STEVE wants to send me an em, he can reach me at my address listed under my profile. Long story short,if the valves are leaking ,pull the front bowl and metering plate ,unscrew the valve, put it all back together, about 30,45 min.Holley power valves about12,15 bucks if you don't tear your gaskets,and as MAKOMARK said, replace the base plate gaskets"
 
"thank you sir. your in put on

"thank you sir. your in put on this post hopefully will straighten this issue out once and for all. Having built holleys,demons, edelbrocks[carter remake],webers,q-jets ,carters,[and some carbs that are no longer made] for the past 36 years,I feel that it was useless to continue this discussion with some one that didn't understand what we were trying to get across.I never said that the carb wasn't flooding,just how to check for a blown power valve. your,along with all the other masters of technical information ,opinion are greatly appreciated.THANK you for clarifying this, so that we can move on to help others. TURBOMAN ROLLTIDE 10-0"
 
"re:power valve. summit racing

"re:power valve. summit racing has holley power valves ,hly 125-65 standard flow $9.39 w/power valve gasket,high flow $13.95,w/gasket.Also, when you get the bowl and metering gaskets off, spray them down with some non stick cooking spray[PAM], it will make future removal a lot easier. TURBOMAN ROLL TIDE 10-0"
 
Will do. I'll let you kno

Will do. I'll let you know what happens after the power valve gets replaced. I have a friend in Lake city that is going to give me a Holley carb lesson if I can get it off the boat and bring it to him. Soon I'll be able to understand how these things work.
Steve
 
"Hopefully, there won't be

"Hopefully, there won't be any need for future work,but its nice to know what to do on simple things such as this.Good luck,and keep us posted.Hope this solves your fuel problem. TURBOMAN ROLL TIDE 10 -0"
 
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