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Someone put a 1471 little field blower on a 496 chev. It is 23% under driven. Can the carbs get a false reading at idle due to so much under driven?(BOUGHT IT THIS WAY) Just hving problems with idle it seems like it wants to die until i hit the throttle attle. The carbs are 750s boost ref jets 78 prim 84 second i belive 10.5 power valves.
 

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Someone put a 1471 little field blower on a 496 chev. It is 23% under driven. Can the carbs get a false reading at idle due to so much under driven?(BOUGHT IT THIS WAY) Just hving problems with idle it seems like it wants to die until i hit the throttle attle. The carbs are 750s boost ref jets 78 prim 84 second i belive 10.5 power valves.
If its idleing slow , with that much underdrive you will probably need to check vacuum at the carb to see if there's enough to hold those power valves closed. Probably just needs some different power valves.
 

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1471

vacuum is at 5 inches power valves should be closed until boost? YES NO MAYBE? I thought with boost reference you want them closed cause when you boost the force of the air opens them? vacuum coming of the intake manifold for the carbs.
 
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Someone put a 1471 little field blower on a 496 chev. It is 23% under driven. Can the carbs get a false reading at idle due to so much under driven?(BOUGHT IT THIS WAY) Just hving problems with idle it seems like it wants to die until i hit the throttle attle. The carbs are 750s boost ref jets 78 prim 84 second i belive 10.5 power valves.

have you tried to lean or richen the idle screws to get the engine to respond? can you pull a vacuum reading off the throttle base to see what it is?, and I never ran ANY Holley carb with a Power valve one small sneeze and they usually give up, ....and removing them only requires a plug, and up a jet size or two.....but then I am Old School and dont like chasing shit like a dead power valve that have only a small effect on drivability.....unless you backfire and kill it, then the engines run like crap so why bother with them if you can bypass their function. positive floats are correct ?. easy way to tell if the engines to lean at idle is to put your hand over the primary side(s) and gradually choke the engine down, if the engine speeds up.....Bingo....she's lean.....if it has a blown power valve usually makes the engine run rich....
 

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Power valves into the garbage can...problem solved.. also at 23 under whats kind of boost r you making? If ur going for a low boost deal all the time id ebay the 14 and get a good 10-71 that you can turn faster. IMHO
 

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vacuum is at 5 inches power valves should be closed until boost? YES NO MAYBE? I thought with boost reference you want them closed cause when you boost the force of the air opens them? vacuum coming of the intake manifold for the carbs.
NO! they're not closing if thats the case.
Lets understand I'm no carb guru but the 10.5 means it takes 10.5 of vaccum to close them, and you only have 5, so there's your problem. Try a set of 3.5's would be my suggestion, but I'd double check that with a good carb guy.
As soon as you begin to accelerate the vacuum goes away and then boost comes on, all that time the powervalves will be open and supplying extra enrichment then when you idle and have the vacuum back the valves will close and idle will lean back out.
For a little lake deal , I wouldnt do away with the power valves as your economy will go out the window.
My .02

p.s. You'll probably need to put the vacuum guage back on it & reset the idle mixer screws after you get the power valves closing because if you been messing with them , closing them down to try to get it to idle then fix the power valves, it'll be to lean on idle and you'll have to open 'em back up a little. Best to do it with the vacuum guage though. Good luck, Hass
 

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I am assuming that your checking the vacuum from the manifold and not the carb plate.My experience with blowers is that you will always have vacuum under the carbs regardless of engine speed, thats reason for boost ref. I agree with QuickCP powervalves in the trash .Get your self two summit jet kits and start from there. But if you decide to run them than go 3 inches less than your idle vacuum . If this was a purpose built blower motor with a blower grind cam you should have more than 5 inches vac. at idle . Check your timing first after all thats free.
 
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Power valves into the garbage can...problem solved.. also at 23 under whats kind of boost r you making? If ur going for a low boost deal all the time id ebay the 14 and get a good 10-71 that you can turn faster. IMHO


A roots blower, is a Positive displacement device, the drive (under or over) ONLY detemines "WHEN" the blower makes max boost....not how much Max....the faster you spin a Roots, the quicker it makes full manifold pressures, the slower, the longer it takes......., both setups, will make the SAME Max boost....one sooner, the other later.....if it's real far under driven, and 23% is a LOT, it may never catch up to the engine and make all it can, depending on sizing, I ran the Blower on our engines in the 61-73% over range, ...73% for a 14mm drive was as fast as you could spin one, how well the Blower is clearanced, or sealed is a big factor as well, if it's loose, it wont make a lot of pressure because it bleeds off internally.

hope that Helps


 

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10.5 power valves open at that vacuum. If you are making 5# vacuum they are already open. Change the power valves to something smaller than 5#. Richin your idle up by turn your idle mixture screws out a little. Try 1/4 at a time till it stays running.
 
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The power enrichment system supplies additional fuel to the
main system during heavy load or full power situations. Holley
carburetors utilize a vacuum operated power enrichment system
and a selection of power valves is available to “time” this system’s
operation to your specific needs. Each Holley power
valve is stamped with a number to indicate the vacuum opening
point. For example, the number “65” indicates that the power
valve will open when the engine vacuum drops to 6.5" or
below. An accurate vacuum gauge, such as Holley P/N
26-501, should be used when determining the correct power
valve to use. A competition or race engine which has a long
duration high overlap camshaft will have low manifold vacuum
at idle speeds. If the vehicle has a manual transmission, take
the vacuum reading with the engine thoroughly warmed up and
at idle. If the vehicle is equipped with an automatic transmission,
take the vacuum reading with the engine thoroughly
warmed up and idling in gear. In either case, the power valve
selected should be 1/2 the intake manifold vacuum reading
taken. EXAMPLE: 13” Hg vacuum reading divided by 2 = 6.5
power valve. If your reading divided by 2 lands on an even
number you should select the next lowest power valve. EXAMPLE:
8” Hg vacuum reading divided by 2 = 4 power valve.​
Since there is no #4 power valve you should use a 3.5.
 

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NO! they're not closing if thats the case.
Lets understand I'm no carb guru but the 10.5 means it takes 10.5 of vaccum to close them, and you only have 5, so there's your problem. Try a set of 3.5's would be my suggestion, but I'd double check that with a good carb guy.
As soon as you begin to accelerate the vacuum goes away and then boost comes on, all that time the powervalves will be open and supplying extra enrichment then when you idle and have the vacuum back the valves will close and idle will lean back out.
For a little lake deal , I wouldnt do away with the power valves as your economy will go out the window.
My .02

p.s. You'll probably need to put the vacuum guage back on it & reset the idle mixer screws after you get the power valves closing because if you been messing with them , closing them down to try to get it to idle then fix the power valves, it'll be to lean on idle and you'll have to open 'em back up a little. Best to do it with the vacuum guage though. Good luck, Hass
like I said ;)
 

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If that boat is not a full on race boat running on Alcohol you have TOO much blower. Get rid of it and get a 8-71. Even if you were racing I dont think I would go any bigger than 10-71. You are going to use too much HP to turn that beast and you won't get any kind of good performance out of it. :(:( :)devil
 

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B.A.M aka "Black Azz Mike
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have you tried to lean or richen the idle screws to get the engine to respond? can you pull a vacuum reading off the throttle base to see what it is?, and I never ran ANY Holley carb with a Power valve one small sneeze and they usually give up, ....and removing them only requires a plug, and up a jet size or two.....but then I am Old School and dont like chasing shit like a dead power valve that have only a small effect on drivability.....unless you backfire and kill it, then the engines run like crap so why bother with them if you can bypass their function. positive floats are correct ?. easy way to tell if the engines to lean at idle is to put your hand over the primary side(s) and gradually choke the engine down, if the engine speeds up.....Bingo....she's lean.....if it has a blown power valve usually makes the engine run rich....

I agree 100%!!!!!!!


Good info here
 

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B.A.M aka "Black Azz Mike
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Power valves into the garbage can...problem solved.. also at 23 under whats kind of boost r you making? If ur going for a low boost deal all the time id ebay the 14 and get a good 10-71 that you can turn faster. IMHO

Yup, can the Pv's!

BUT, keep the 14-71 and speed it up!!!!!! Make some power and enjoy it!!!!! there isnt too much difference between the 14 and 10. I would speed her up and let it rip. or, get ballsy and overdrive it and get NASTY and WILD!!!!!!!
 

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B.A.M aka "Black Azz Mike
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If that boat is not a full on race boat running on Alcohol you have TOO much blower. Get rid of it and get a 8-71. Even if you were racing I dont think I would go any bigger than 10-71. You are going to use too much HP to turn that beast and you won't get any kind of good performance out of it. :(:( :)devil

WRONG INFO here buddy!!!!!!!!!!!


Ive been through this deal with several guys! Call the guy @ Littlefield and he will explain blowers in DEPTH to you! Like I said, Speed up the monster and enjoy it :) You will be happy with the wind ripping your cheeks back across your face:D


You are going to use too much HP to turn that beast and you won't get any kind of good performance out of it.
Have you spun a 14 before? My 14 spins as easy and smooth as my lil Weiand177. I would rather have the largest blower than a small blower. You might as well tell him to buy a 6-71 or a 420!

If I were to purchase a NEW blower, I would buy the 8 or 10 yes. BUt, if I got a smoking deal on a 14 like I did, then I wouldnt sell it to go smaller...

Just my lil ole 2 pennies
 

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i have a 1471 on my 496 under driven by 21 percent 5 pounds of boost prim jets 90 sec jets 99 boost referenced does not miss a lick idles like a kitten purring,aed did the carbs,i am now trying 10 pounds of boost with ave gas still under driven,its allways nice to make boost and still be under driven
 

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x2 on the bigger blower! when I still had my jet, I was running a 12-71
at 2% over, and it would make 16lbs @6400rpm w/ an Agressor A. before
the swap, the 6-71 that was on it would make around 12lbs, but it was
driven at about 11% over! ALWAYS BETTER TO RUN THE BIGGER BLOWER,
AND TURN IT SLOWER! it's more efficient, and makes less heat.:)bulb
 

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Discussion Starter #18
1471

What do you guys think of paul paff hes said he could adjust my carbs no problem maybe a hour or two for about $150 that sounds like a good deal what do you guys think, Has any body delt with them i think his name is Goordy or something like that. They seem real nice.
 

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Gordon "Gordy" Jennings is one of the best around, and he is a real nice guy. He is on these boards as "the real k-boat king". Go have him tune your motor, you won't be dissapointed........
 

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A roots blower, is a Positive displacement device, the drive (under or over) ONLY detemines "WHEN" the blower makes max boost....not how much Max....the faster you spin a Roots, the quicker it makes full manifold pressures, the slower, the longer it takes......., both setups, will make the SAME Max boost....one sooner, the other later.....if it's real far under driven, and 23% is a LOT, it may never catch up to the engine and make all it can, depending on sizing, I ran the Blower on our engines in the 61-73% over range, ...73% for a 14mm drive was as fast as you could spin one, how well the Blower is clearanced, or sealed is a big factor as well, if it's loose, it wont make a lot of pressure because it bleeds off internally.

hope that Helps


I don't get what you are saying here.
If his 1471 is 23% underdriven he is making about 5lbs boost. Take a 871 and spin it 10% under and you are getting about 5lbs boost.
Are you saying that the 871 is going to be more efficent and come on boost faster than the 1471? I would think it would be exactly the same, but the 1471 would be a cooler charge and maybe alittle more hp to turn. Am I wrong?
 
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