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Thread: New 496 wont run??
          
   
   

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  1. #31
    Camaro350 is offline CHR Member Visit my Photo Gallery
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    Okay sorry for the late reply, thanks for all the good info. I have it running but like I stated I have to have the idle really high, over 1200rpms to keep it running. Fuel pressure is about 7psi at the carb. I have shut the idle screws and the vehicle does die after a min, it will run with the screws about 1/2 turn out but beyond that it struggles and smells really rich. I reset the choke and fast idle and still no change. When I read vacuum from the carb full manifold vacuum port it’s around 13-15 psi at 1400rpms. But when I close the throttle to bring the idle back down the vacuum drops and the vehicle will eventually die. I sprayed down the whole intake and carb with carb spray and no leaks were detected. Not sure how it’s running so rich with only 1/2 turn out on the mixture screws u less I have a power valve issue. I even checked the breathers on the valve covers to see if they were pulling vacuum under load and they were not so I don’t think the intake manifold is leaking either.

  2. #32
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    have you tried another carb ? first step i take .

  3. #33
    Camaro350 is offline CHR Member Visit my Photo Gallery
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    I have not tried a new carb, I donít have another one to swap out and try. If I could for sure know that it is a carb issue I could then possibly get another one or take this one apart

  4. #34
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    sounds like a power valve problem. loads up at idle . but all i can do is guess . denny is the big block guy i check to . our old bracket car was a bitch to to tune . had to drill the butterfly's to get it to idle right ..

  5. #35
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    You are running way too rich at normal idle speed, your vacuum is way low at normal idle speed. Logic tells me your power valve is opening at normal idle speed because the vacuum is less than the power valves opening threshold. You probably have a 6.5 power valve, try an 8 or 10 see if it gets you an idle.

    I’ll reiterate my previous post and highly recommending you take it to a experienced tuner before damage occurs...
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  6. #36
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    why are you running 7 psi on fuel pressure ? is it street driven or an 1/8 mile car ?

    divide your vacuum at idle x2 . this will give you the size power valve you need. if you have 13-14 then the 6.5 will work . most likely the valve is blown .
    Last edited by shine; 02-03-2020 at 12:53 PM.
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  7. #37
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    Quote Originally Posted by shine View Post
    why are you running 7 psi on fuel pressure ? is it street driven or an 1/8 mile car ?

    divide your vacuum at idle x2 . this will give you the size power valve you need. if you have 13-14 then the 6.5 will work . most likely the valve is blown .
    Agreed, 7 psi is a little high, while the manufacturer may claim higher psi is OK, I, like you would not.

    Also agree under normal circumstances this is the formula for power valve tuning, normally with a tuned carb this will allow the power valve to open under acceleration, and good a starting point to tuning the circuit.

    However, and JMHO,
    Not getting enough fuel at WOT is not the OP's case, and a lower value power valve may make matters worse until the cause of the way overly rich condition is sorted out. The power valve may be bad (blown), and why I recommended a higher value power valve to help source the cause for the problem.

    Again, JMHO, I believe there is more going on here than the OP has the skills and knowledge for, and his continued hit and miss approach may cause damage to his motor before he sorts it out.

    I reiterate my recommendation for the OP to seek the skills and experience of a motor tuner knowledgable in carbs to help sort this out. A few dollars spent on a skilled tuner now may save thousands of dollars later.
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  8. #38
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    i would stick another power valve in it . even though they clam the problem is fixed you can still blow one with a back fire . 99% of the holley problems turn out to be a power valve .

  9. #39
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    Hey guys so I took my carb out and checked the power valve itís a 6.5 and itís not blown i tested it with my vacuum gauge. I also removed my intake manifold and changed the gaskets and resealed it. Put new plugs in and changed the oil and filter and started it up and same results.

    I think Iím still possibly off timing, I removed my valve cover and set number one cylinder on compression stroke and tdc with my balancer set at around 13 and the distributor rotor was pointing past number one closer toward the center of the engine, but I set the cap on and put number one plug wire on where the rotor was. Like I said before it starts but I canít get it to idle to set my initial timing. According to the engine builder initial timing is 13 total 36.

  10. #40
    DennyW is offline CHR Member Visit my Photo Gallery
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    Quote Originally Posted by Camaro350 View Post
    Hey guys so I took my carb out and checked the power valve it’s a 6.5 and it’s not blown i tested it with my vacuum gauge. I also removed my intake manifold and changed the gaskets and resealed it. Put new plugs in and changed the oil and filter and started it up and same results.

    I think I’m still possibly off timing, I removed my valve cover and set number one cylinder on compression stroke and tdc with my balancer set at around 13 and the distributor rotor was pointing past number one closer toward the center of the engine, but I set the cap on and put number one plug wire on where the rotor was. Like I said before it starts but I can’t get it to idle to set my initial timing. According to the engine builder initial timing is 13 total 36.
    Wow, I posted some info, and got no answer. The crowd has left the building...
    Last edited by DennyW; 02-26-2020 at 07:32 AM.
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  11. #41
    Dave Severson is offline CHR Member/Contributor Visit my Photo Gallery
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    Try setting your total timing first, usually all the advance should be in by about 2200 RPM. Try holding the RPM steady at about 2500 RPM, set the total timing, then see if it will idle down to check the initial timing. Oh yeah, without going back and reading all the posts, are you using vacuum advance or just mechanical advance in the distributor?
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  12. #42
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    Quote Originally Posted by Dave Severson View Post
    Try setting your total timing first, usually all the advance should be in by about 2200 RPM. Try holding the RPM steady at about 2500 RPM, set the total timing, then see if it will idle down to check the initial timing. Oh yeah, without going back and reading all the posts, are you using vacuum advance or just mechanical advance in the distributor?
    Iím trying to reset my carb after messing with all the adjustments. I am running only mechanical advance. The engine builder told me not to run vacuum advance on the motor so I have that blocked off on both the carb and the distributor. I pulled the distributor and rechecked all the timing, set rotor exactly on number one and 0 tdc and now it wonít start. So I have to figure out what happened now. It cranks strong but now no start.

  13. #43
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    There is a possibility that you are 180ļ out in timing
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  14. #44
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    I like to verify dizzy by putting the engine on the timing mark, and rock the dizzy back and forth with ignition on, looking for spark: with a plug laying on the block.
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  15. #45
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    I've stayed out of this discussion, but noted that in your original post you mentioned not being able to move your distributor to point to your #1 cylinder on the cap with the balancer at zero. In post #39 you again mention being out of position with the rotor. It sounds to me like you're one tooth off on the distributor to cam gear, which is making your distributor position cockeyed to the engine and limiting your travel for adjustment.

    You've said that you lack experience with "old school carbs & distributors", yet you're continuing to risk damage to an engine that I expect set you back close to $10K. I agree 100% with 36 sedan. You need to trailer your car to a good mechanics shop that has a good tuner, and let them sort out your problem before you end up damaging your engine and costing yourself a bunch of money. Good luck getting this beast running right, so you can enjoy some cruising!
    Last edited by rspears; 03-02-2020 at 09:52 AM.
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