Blown power valve symptoms

Discussion in 'Holley' started by sootie007, Nov 15, 2010.

  1. sootie007

    sootie007 65 Skylark -455 - T350

    I have had this Speed Demon Mech secondary carb approximately 1 year. It started ,idled and ran great when I first got it. My car was down for quite a few months as I had to replace my trans.....the first time I tried to restart it - it took quite a long time to get it started but then it ran fine ...during that process I had a few minor intake backfires but no booming backfires etc. Now the car will not start worth a damx. Up until this point this carb was my favorite of all time as far as adjustability , idling, awesome power throughout etc.

    What are the symptoms of a blown power valve ? Is hard starting one of them ? Because my gut tells me its flooding out now when trying to start it cold.
     
  2. doc

    doc Well-Known Member

    The most evident thing about a busted power valve is extreme surging at idle..... that you cannot tune out..... and every time it surges a puff of black smoke comes out of the exhaust pipes... and the smell of the exhaust is extremely rich .... the spark plugs are naturally black and sooty.... and the car is hard to start because of the fouled spark plugs and the rich mixture.....:Brow:
     
  3. CJay

    CJay Supercar owner Staff Member

    Unless its a really old carb, most newer Holleys have power valve blowout protection.
     
  4. sootie007

    sootie007 65 Skylark -455 - T350

    Thanks guys.....sounds like its not blown....yes you are right supposedly all Holleys built after 1992 have built in pv protection to prevent blowout....mine isnt idling funny once it gets running so I guess that also rules that out.

    I will get to spend some time this weekend on it ....I am going to read , change plugs out anyway and maybe make another jet change.

    I will also check everything else....

    idle transfer slot squared

    mixture screws

    idle screw hasnt drifted etc.....

    If I find the solution I will post here ...... thanks for the tips.
     
  5. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

  6. sootie007

    sootie007 65 Skylark -455 - T350

    So I go out in the garage tonight for round two of why wont the car start all of a sudden. I pump it twice and try to start it several times and it never starts ..few more pumps ..after probably 15 tries still no start.

    I go look at the Demons fuel bowl sight plugs and the gas is in the lower third of the bowl window up front and even lower at the 25% mark out in the back bowl. Should be enough fuel though right ?

    So old schooling it and pretending I didnt see fuel in the bowls I take a small container and fill both front and rear bowls via the bowl vents to their 1/2 marks....

    Get in the car and turn the key and it starts right away ?

    Are those float levels that sensitive in the Demon-Holleys where if its not at the 50% mark it wont start ?

    Or am I just not pumping enough shot in before I try turning the key ? As you guys know the double pumpers drop a ton of fuel in each time with each peddle pump. How many times do you guys usually pump the pedal before trying to start ? Maybe its just me.
     
  7. Golden Oldie 65

    Golden Oldie 65 Well-Known Member

    1/2 pump on mine when it's cold and it fires right up, no pump when it's hot.
     
  8. doc

    doc Well-Known Member

    When it is cold weather 2 pumps,,,, when the engine is warm, like Bill, i can start up with out touching it at all.......
     
  9. sootie007

    sootie007 65 Skylark -455 - T350

    Findings today troubeshooting my hard start problem ........float levels both down ....so I got a small squirt bottle and tried to fill the fuel bowls from the front vent tube...the bowls would NEVER fill no matter how much fuel we put in then I realized it was all overflowing down the butterflies somehow . So I suspected the needle and seat was hung open. Upon pulling the front bowl off their were 3 pieces of machining flash-debris near the main well cavity floating around. The 3 pieces were all the size of bb's. I had heard of this casting - machining flash happening on the Demon carbs from reading on the internet and causing people problems ...after removing the 3 pieces of metal I blew out the metering body, fishing lined all the orifices and removed the needle and seat which felt rough and wasnt moving up and down freely. Remember this is only a 1 year old carb ? The front stock bowl gasket had already begun to stick to the carb body and came off in 3 big chunks. I had to scotch pad the leftover gasket material off the mating surfaces. I have never seen this before on such a young carb ? MUST be the ethanol blends these days ? They must be hard on gaskets ? So after reassembly of the front bowl I reconnected the fuel line.....pumped it twice.....cranked it 3-5 times, the fuel bowl levels rose to the midway point in the sight plugs as they should and it fired right up. So I dont know 100% if its fixed until I try to start it again tomorrow after sitting all night but I am pretty sure I fixed it today. Now I am debating whether or not to pull the back bowl off to check it as well for machining debris. So chalk up another Demon filled with machining shavings which hung the needle and seat open. If you pay good money for a carb you would think they would have better quality control at their factory. Numerous people have documented this problem on the internet as well. Anybody else seen this ?
     
  10. sootie007

    sootie007 65 Skylark -455 - T350

    Its fixed for sure....so if your Demon all of a sudden starts running or starting like crap pull off the bowls and look for metal machining debris floating around inside.
     

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