My camshaft is robbing me!

[slimbo]

Holleys have power valves that open under a certain vacuum. If you had a 13 power valve in there n ur engine only pulls 11.5 inches at idle your power valve will be open at idle thus flooding the pi$$ out of your engine. when you put it in drive ur vacuum might drop, thus opening the power valve prematurely and making it idle like crap.

uhhhhhhh...wrong. a holley power valve feeds the booster circuit. the only time an open power valve will put fuel into the engine is when the mains are flowing. generally this is between 2500-3000. at idle the carb is being fed by the idle circuit and if the blades are too far open they will also feed into the transfer slots. its a big misconception that a too high vacuum rated power valve will flood a engine at idle. my last cam 248/254 @.050 would idle at 850 without issue. my new one 262/[email protected] likes about 1000.

 

[slimbo]

YOU CAN'T JUST "SLAP" CARBS ONTO AN ENGINE AND EXPECT IT TO RUN RIGHT. CARBS HAVE TO BE TUNED TO EACH INDIVIDUAL ENGINE. 10.5 TO 12 INCHES OF VACUUM, (I WISH I DID) I HAVE ABOUT 6 INCHES OF VACUUM AT IDLE. N MY CAR IDLES FINE IN PARK AND DRIVE.

I THINK YOUR "CULPRIT" IS YOU NOT KNOWING HOW TO ADJUST A CARBURETOR.

if you only have 6 inches of vac something is wrong.......with 248/254 110lsa i had 10 inches. and with 262/269 112 lsa i have between 8 and 9. maybe you need to learn how to tune a carb as well.

 

[Betcha618]

Nice try, I had my carb built. And tuned by a pro. My car runs mint and has fuel injecvtion like responce.

 

[lurchsmalibu]

Nothing new here, but off the Holley power valve selection...."To properly size a power valve, take a vaccum reading at idle and if it is above 12" for a standard transmission a 6.5" will be safe to use. For automatic transmissions take a vaccume reading in gear at idle and if the vaccum is below 12" divide that in half for proper size. Example 9" of vaccume in gear at idle will require a 4.5" power valve."

If a power valve is damaged by backfire and the diaphragm isn't leaky, just warped then why does it drip fuel? (not seating properly?) when I put a new PV in the carb it quits. I too have been around the block on the too high vac setting on PV's compared to what my engine was pulling in gear and if you vacuum is below what the PV opens at then the little spring on the PV WILL open the PV circuit and in my experience also it WILL drip fuel.

I'm NOT disagreeing with ANYONE here, just had same experience with carb dripping and a lower vacuum rated PV did the trick. I experimented with lower fuel levels, timing, ect. and only the PV did the trick. 8)

A higher stall rated torque converter helped even more with the idle and in gear RPM issue too. 8)

 

[Betcha618]

Thank you. That was my experience also!!

 

[t5montecarlo]

I am not an automatic fan, but if the torque converter is still stock, it may be part of the problem.

 

[slimbo]

the reason an engine floods when a power valve tears is the other side of the power valve is open to manifold vacuum. when the power valve opens it feeds into the same area the jets feed which leads to the boosters. so if your saying when the power valve opens it will start flowing this is incorrect since the jets are always open and they dont feed all the time....the only time a power valve feeds is when the booster is flowing.

 

[lurchsmalibu]

Maybe this is a possible culprit.... :-k

"Tip: Use a power valve that is about 2 inches of mercury below the LOWEST manifold vacuum reading you get on cruise and idle (in gear for automatics). If the power valve flutters open at idle, it can act as a pump, and push extra fuel into the main well, causing a drip from the booster venturis.

That is from....http://www.bob2000.com/carb.htm 3/4's down the page. Maybe a possible answer for some of us.


I didn't post a tear in a PV, just a damaged/warped diaphragm caused by a backfire. A tear should be a no brainer even for the guys new to a Holley with a PV. 8)

 

[fastheavychevy]

I had the same damm problem on mine Im running a comp cam also. I finally did a total timming setup on it. It ran like a champ no more issues. It runs stronger than ever and idles smooth and the idle stays the same in park or in gear. Just disconnect the vacum advance on the distributor and plug it. Adjust the timming at about 34-36 at about 2500 rpm's and leave it there. I never liked that way but I did it and its good to go. just leave the vacum off on the distributor. You might have to run medium or super fuel I run medium because I dont think there selling to much super now a days and the super sits in the station tank forever and gets stale. But try that and see how it acts. It cant hurt. But that called total timming. With a performance cam thats the way you need to do it.

Im having problems with my power accesories from my cam. I have a Comp Cams 279THF7 cam. It has a .479/.465 lift and adv duration is 279/297 and @.050 duration is 227/241..

It runs nice and strong at idle in park. As soon as I put it in gear its real choppy and the rpms drop a couple hundred. My vac is reading anywhere from 10.5-12 pounds of vac at idle. It doesnt really change in gear.
-I have checked everywhere for vac leaks with carb spray and found none.
-Tried timing from 6 to 16 initial and 36 all in. Im now at about 16 initial and its the best so far.
-Checked all lines & hoses and no problems.
-Carb is adjusted all around.
I also noticed with my power steering, when I turn the wheel some the idle drops a little.

I read around some and I think my cam is the culprit and is robbing me. Would a vacuum reservoir canister help me out or am I basically screwed?

T.I.A.

 

[gbodyera]

Thanks fastheavy chevy. Ill also give that a shot and let you know.