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I know this is novice level but I've searched the archives and get a little confused. 66 327 newly rebuilt engine and holley carb was running great. last week end after a cold start(rough start) car has not been the same, had to turn up idle speed to keep from stalling, smells of gas, spits alot of carbon out the exhaust, and runs colder and louder than it had been running. when it gets up to higher temp it runs almost back to normal(it doesn't reach the temp it used to, can't get it over 160 degrees, it used to run great just under 200, probably around 170. the carb was rebuilt less than 1000miles ago, the heat riser works fine. i was told that the power valve was the likely culprit . does this sound right? am i doing damage by running rich if that is in fact what i'm doing? is there a reliable easy test to trouble shoot this issue? can a carb be fine and then all of a sudden be totally out of adjustment? thanks joe t
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Re: running rich
Joe,
I don't think your engine temps have anything to do with the rich problem, sounds like a power valve. Check archives on this subject, I think if you hold your finger over the vent tube and the engine stalls this is a sign of blown power valve. If the engine oil smells strong with gas or the level on the dipstick is higher than normal I would change the oil and not take a chance. -
Re: running rich
Could be a stuck float, dirt on the float needle, or a bad load of gas. When it is running rough check to see if gas is dripping into the air horn.
Check the float levels. With a newly installed carb, tighten down the carb to manifold nuts.
Jerry Fuccillo
#42179Jerry Fuccillo
1967 327/300 Convertible since 1968Comment
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Re: running rich
Did it backfire furing the 'first' rough start? if so that makes a case for a bad power valve even stronger. beside the carb to manifold bolts, check the bolts that hold the bowls on as well as the intake manifold bolts if the intake was recently put on and not re-torqued..'recently rebuilt engine'
Sudden problem would support sudden change in the carb: dirt, bad float, power valve, air leak via boltsComment
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Re: running rich
Joe your rough start is likely the creation of your 66 not running right. All it takes is backfire or reverse flow of pressure on startup to rupture the power valve and cause the problems your are experiencing. The good news is that it is really an easy fix, new power valve, new metering block gasket, and new fuel bowl gasket from Auto Zone or any other parts place that sells these Holley parts as individual pieces. Does not hurt to buy an extra supply to keep handy in the glove box, never know where you will be and need to do this again. The test mentioned usually works well to isolate the problem to the power valve.Comment
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save your power valve
holley sells a kit to install a power valve check ball kit,part #125-500. installing this will prevent back fires thru the carb from blowing out the power valve.holley performance carbs built since 1992 have this featureComment
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