Power valve question

[bikerboyriley1]

Someone was telling me i may possibly be running rich because my power valve in my holley street avenger is the stock one and with a lumpy cam you should get a higher number one?



I dont know much about this just wondering if its true?

[Melonhead]

Power valves are set on vacuum. When you have none with that cam the power valve is open. You need a lower number. The valve opens at a preset vacuum reading. If your engine runs idle at 10-12 inchs and the stock power valve set at 6.5, yea you gonna run rich. I would think a lower number of a 4.5hg would work better. http://www.s10v8.com/images/smilies/icon_biggrin.gif

[bikerboyriley1]

yah i just read up on it some, i take my vacuum reading then get a power valve 1-2 '' below the reading, And my vacuum is 4'' so im thinking a 2.5 power valve would work well

[onthecheap]

i saw a clip of the holley tuning dvd and it said to see what your vacuum is and use a valve that opens at half of the reading, example 10-12 inches use a 5.5 power valve

[Scotty_S-15]

So you've got 4" of vacuum at idle? How many RPMs at idle? I know you've got an overly-serious cam..... But with just 4" of vacuum, I'm thinking that the power valve issue may be the least of your carb & idle problems.

[eigthmile]

Try and tune that thing with the vacuum gauge. Sounds low like scotty mentioned. Idle air mixture screw adjustments make a big difference.

[bikerboyriley1]

the carbs been tuned with vacuum guage. thats at 800 rpm while in drive

[Scotty_S-15]

Does turning your idle mixture screws make a difference? And what are they set at, 3/4 turn out, etc.? If they do make a difference, then it indicates that your carb is in the ballpark.

[bikerboyriley1]

i will have to check that today, it could be my vacuum guage is off... heh you never know

[91xcabpro]

if your idle is set where you want it and your power valve is proper for your vacuum and your idle adjustment screws dont lean it out try this--pull your carb off the intake, turn it upside down and look to see how much of your idle transfer slot is showing--at idle you should only see about .020 of the slot--adjust the curb idle screw to set the butterfly to only expose the .020 of the slot then reinstall the carb--now your truck may not want to idle at this setting because big cams need more air than may be getting past the butterflies--if you adjust the idle up with the curb idle screw you also expose more of the idle transfer slot which richens the mixture--I had the same problem and had to drill holes in my butterflies to get it enough air with the butterflies in the proper position to the transfer slot--started small and went larger until it would idle properly--i also dropped to a 2.5 power valve--I believe some Demon carbs have a fix for this problem on some of their carbs called idle ease--buy a book and/or do some searches to verify this fix--hope this helps

[coppergmc]

Just get rid of the power valve using the block off. Go up about 6 to 8 steps on the jets to compensate.



Just how big is that cam and what kind of compression are you running? The vacuum does seem a little low if you aren't running a big cam and low compression.

[bikerboyriley1]

300 duration @ 50 600 lift + 1.6 rockers



10.8:1 compression running 94 octane

[Melonhead]

OUCH http://www.s10v8.com/images/smilies/icon_eek.gif http://www.s10v8.com/images/smilies/icon_eek.gif

[Scotty_S-15]

On 2007-08-14 12:15, bikerboyriley1 wrote:

300 duration @ 50 600 lift + 1.6 rockers



10.8:1 compression running 94 octane



http://www.s10v8.com/images/smilies/icon_confused.gif Who's cam is it, and which model or grind # is it? Something doesn't seem right.

[stroker1]

I agree with Scotty. Something doesn't seem right. And that 300 Deg. of duration at .050" lift??!! WTF I dont even know anyone using a cam that big in a small block. And if they where they wouldn't be having a 10.5:1 compression. Are you sure it isn't 300 deg. advertised duration? I'm running 258/270 duration at .050 and .604/.604 lift with 106 LSA. I'm running a 4.5 power valve and it works great. Someone mentioned earlier the transfer slots and throttle plates. Might want to check this out. Do you have fuel dripping from the venturis at idle??



What exactly is the main-most problem BUD?? http://www.s10v8.com/images/smilies/icon_biggrin.gif



Stroker1

[bikerboyriley1]

Hmm yah im going to go find my cam box haha that was ballpark from what i remember but i could be wrong, its the biggest roller cam that comp makes, Hmm i checked my vacuum again today with a different guage and it jumps from 3-5'', I put in the 2.5 power valve and its not running well at all, i have crappy throttle response and im pretty sure i had a lean pop the other night when it hit 5800rpm, by changing the power valve do I need to change other things such as timing ? ANd it still smells rich!!!! http://www.s10v8.com/images/smilies/icon_mad.gif

[bikerboyriley1]

hmm i just remembered i switched the primary jets to 64's because i thought it would help the running rich problem, but now with this new power valve it should be running correctly, so i bought some 67's and i will put them in tonight and hopefully it all works out!