Hi all,

How would you tell if a power valve openes too late? I have a Holley 770 Street Avenger & lately it's been surging under load.

It seemed to get worse when I adjusted my timing. I have about 12-14 initial & 23 centrifigual. I just switched to lighter springs to bring in the advance by 3K.

I have done the following: Checked fuel pressure, found it dropping to about 2.5-3 psi hot. Installed another pump, now it won't go less then 5.

Pulled off fuel bowl & metering block to get at the power valve. Checked it with a vacuum pump, holds pressure.

What else can I do?

what's your vacum @ idle ?? ,check it then select your proper power valve.a surge at part throttle or tip in does indicate a to low HG. power valve

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1972 chevy camaro ss 350 sbc 425 hp/356 @ the wheels,350 trans,373 gears,daily driver with restification in progress for the old school / day 2 look
future plans- turning it into a baldwin motion Z30 clone

"IF IT'S TO LOUD YOUR TO OLD"
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Thanks for the quick reply. I'm runnig a Comp Cams Xtreme Energy 268 cam that gives about 15in HG @ idle.

The power valve that came with the carb is a 6.5.

I have the 770 Street avenger carburetor as well and switched to an 8.5 valve. I am pulling right at 15" of vacuum at idle and noticed a little better throttle response with the change. My guess would be that the surging is coming from changing to lighter springs in the distributor, especially if you used the lightest springs that come in the advance kits. I have found using factory weights allows me to use heavier springs with the same results. The real light springs allow the weights to bounce around and can cause surging.

The springs I used weren't the lightest ones. They're the middle ground ones (silver) in the Accel kit. I'll try the 8.5 Power Valve & see.

<font face="Arial,Verdana" size="2">Originally posted by Wicked 79 Z28:
I have the 770 Street avenger carburetor as well and switched to an 8.5 valve. I am pulling right at 15" of vacuum at idle and noticed a little better throttle response with the change. My guess would be that the surging is coming from changing to lighter springs in the distributor, especially if you used the lightest springs that come in the advance kits. I have found using factory weights allows me to use heavier springs with the same results. The real light springs allow the weights to bounce around and can cause surging.</font>

nope surging or a bog off idle "lean tip-in" at part throttle is a indication the power valve is wrong.try a 8.5 and see what happens maybe even go up to a 10.5

I have definitely experienced surging under load from using too light of springs in the distributor. I know this because when I went to a firmer spring the surging stopped. I have experimented with this on several cars and seen these results more than once. I am not saying for sure that this was the problem, only talking from my experience.

Thanks for the replies. I've changed the springs to one light & one heavy, one medium & one heavy while checking the timing.

Also checked the mixture with a vacuum gauge.

Needless to say, the problem is still there! I'm going to try replacing the power valve next & see. Will let you all know the results.

If its surging at cruise probrably need more primary jet, if it hesitates on light acceleration or tip in probrably a P-valve that opens sooner or a diferent pump cam or pump cam setting.
You say lately its been surging, so it was running great? What happened to make it surge? did you adjust anything ? If it ran good it should run good unless theres trash somewhere maybe air bleeds or accel pump discharge or in the main fuel metering circuit?

[This message has been edited by Mwilson (edited March 24, 2005).]

Well, it has always run so-so. I mean I haven't been driving it alot. It took me awhile to get the trans swap done. Now that the swap is done, I've been driving it more.

It has always seemed sluggish, so I looked into the advance curve, which had been stock. When I changed it to come in sooner is when I noticed the surging problem.

The carb's very clean, has seen very little use. On initial take off, it does okay, so I don't think there's a problem with the accelerator pump. It just doesn't seem to be getting enough gas in transition.

I do not have the lightest spring in the secondarys. It does this even with the stock spring.

go up to 10.5 power valve for the transition problem and go up a couple jet sizes on the primary side for the surging.

UPTADE:

Went out & bought a 8.5" power valve yesterday, the largest I could find locally. Installed it last night & took her out for a drive this morning.

http://www.nastyz28.com/ubb/frown.gif The problem is still there! I don't think the jetting is too lean. I've verified that I have #72 jets in the primary when I replaced the power valve.

In looking over the carb specs, I noticed that it has the smallest acclerator pump of all the Street Avengers. Would this cause the problem? The nozzle size is 0.025.

Thanks for your time.