ZZ502 w 741 cam issues
01-14-2008, 05:11 AM
#61
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01-14-2008, 07:54 AM
#62
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FYI, powervalves have no effect on idle quality, as they are part of the main metering system which is not active at idle. Powervalve could be an issue if its "blown", then it would leak. Are the mixture screws responsive? If not, that could indicate a blown powervalve.
Checking the valve adjust is a good suggestion, if they are too tight the valve will be held open and vacuum stuffers, probably not good for plugs either.
I suggest doing the leakdown. Myself and a buddy both run ZZ502 heads and we both had issues with poor valves sealing on NEW heads. We had very very high leakdown rates. You can just take the rockers off to make sure no valves are open when doing the test. With that low a vacuum, something is way off.
Checking the valve adjust is a good suggestion, if they are too tight the valve will be held open and vacuum stuffers, probably not good for plugs either.
I suggest doing the leakdown. Myself and a buddy both run ZZ502 heads and we both had issues with poor valves sealing on NEW heads. We had very very high leakdown rates. You can just take the rockers off to make sure no valves are open when doing the test. With that low a vacuum, something is way off.
01-14-2008, 09:34 AM
#63
Geronimo36
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If the cam is big enough it can/will activate the powervalve depending what size PV you're running... Also if you're not running powervalves it can also draw fuel thru the main fuel metering circuit and you have to adjust the secondary butterfly so the primary isn't open as much.
01-14-2008, 01:42 PM
#64
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If the cam is big enough it can/will activate the powervalve depending what size PV you're running... Also if you're not running powervalves it can also draw fuel thru the main fuel metering circuit and you have to adjust the secondary butterfly so the primary isn't open as much.
If your pulling from the mains at idle something is very wrong. That's why there's a idle and transfer circuit.
01-14-2008, 02:08 PM
#65
Geronimo36
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Yes.... check around...
Big cams with little or no vacuum activate the PV's and begin dumping fuel thru the venturi's...
big cam requires the throttle plates to be open more so the engine can idle...
It's holley 101.
01-14-2008, 02:21 PM
#66
Geronimo36
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Here's a Q&A taken directly from the Holley website, this is all public knowledge...
"QUESTION Why is my engine running rich and my mixture screws do not have effect?
ANSWER The first thing you need to ckeck is your float level. No fuel should run from the sight hole unless you shake the vehicle. Next check the engine vacuum at idle. (in gear if A/T) if it is 12" or more a 6.5" powervalve will usually be fine. Anything below 12" divide in half. For example 9" vacuum will use a 4.5" power valve. Another possible cause associated with performance cam shafts are exposed transfer slots. You should not see more than .025"-.030" of the transfer slot exposed past the throttle plate at idle. "
"QUESTION Why is my engine running rich and my mixture screws do not have effect?
ANSWER The first thing you need to ckeck is your float level. No fuel should run from the sight hole unless you shake the vehicle. Next check the engine vacuum at idle. (in gear if A/T) if it is 12" or more a 6.5" powervalve will usually be fine. Anything below 12" divide in half. For example 9" vacuum will use a 4.5" power valve. Another possible cause associated with performance cam shafts are exposed transfer slots. You should not see more than .025"-.030" of the transfer slot exposed past the throttle plate at idle. "
Last edited by Panther; 01-14-2008 at 02:23 PM.
01-14-2008, 02:55 PM
#67
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PV is not his problem. If it was, all plugs would be fouling. The low vaccum is probably b/c of the deal cylinders (fouled or something is wrong mechanically).
Should put a timing light on that wire to make sure there isnt a ignition problem after a new plug is installed.
Should put a timing light on that wire to make sure there isnt a ignition problem after a new plug is installed.
01-14-2008, 07:39 PM
#69
Geronimo36
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PV is not his problem. If it was, all plugs would be fouling. The low vaccum is probably b/c of the deal cylinders (fouled or something is wrong mechanically).
Should put a timing light on that wire to make sure there isnt a ignition problem after a new plug is installed.
Should put a timing light on that wire to make sure there isnt a ignition problem after a new plug is installed.
01-14-2008, 07:58 PM
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Agreed that may not be the cause of his problem but your statement implied that powervalves don't effect idle in general and it is false... also, the front two plugs usually fowl first. If you run a big enough stick you'll run into PV problems at idle if you don't set up the carb properly...
We'll, I still think that PV is inactive at idle - if your pulling from the mains at idle something else is up. My motor doesnt pull from the main circuit till over 2000 rpms.
