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Thread: running out of gas on top end

  1. #1
    chaparral2350sx
    I currently have a chaparral 2350sx and a new 454 with +.040 overs with a 9.5 to 1 compression, cam is a .500 lift on intake .510 on exhaust running a 750 quadrajet orginal carb.I know that it is running out of fuel on top end (4900/5300). As of now I can only get 4900rpm out of it. should I change needles in the carb or switch to a marine Holley.Oh yea the motor was a 454mag before I got a hold of it.Please help with this problem.forgot to say fuel presure is fine 5 and a half to 6 psi.

  2. #2
    Fiat48
    Check your fuel pressure at wide open throttle. Move the gauge if necessary so that you can read it at maximum RPM. If you have fuel pressure of at least 3 lbs, then you are not running out of fuel and larger needles and seats or fuel pump is not the problem.

  3. #3
    Hotcrusader76
    Originally posted by chaparral2350sx:
    I currently have a chaparral 2350sx and a new 454 with +.040 overs with a 9.5 to 1 compression, cam is a .500 lift on intake .510 on exhaust running a 750 quadrajet orginal carb.I know that it is running out of fuel on top end (4900/5300). As of now I can only get 4900rpm out of it. should I change needles in the carb or switch to a marine Holley.Oh yea the motor was a 454mag before I got a hold of it.Please help with this problem.forgot to say fuel presure is fine 5 and a half to 6 psi.
    Switch to a Holley bro! They're easier to tune and modify! I can get you set-up with a custom model when your ready.
    Hahaaa....not a biased a opinion at all!
    Thanks
    Ty Lofstrom
    TPC Racing
    sales@tpcracing.com

  4. #4
    Infomaniac
    Try taking the fuel filter out of the inlet. If the pressure is good this is probably dirty or too restrictive. Raise the float level also.
    Buy a Holley when you get a chance.
    I have seen many times the fuel supply line or the tank fitting is not large enough. Make sure the anti siphon valve in the tank is not holding you up.

  5. #5
    chaparral2350sx
    Yea Guys:
    you have the same idea I do about the Quadrajunk.The idea about the anti siphon valve would be vaildated if the fuel presure drops off at 4900 rpm if the fuel presure is good and I am still running out of gas we all know what to do. Sell the Quadrajunk on Ebay and buy a Holley. which is what I want to do in the first place.Thanks for the ideas and I will find out this weekend if the fuel presure drops off on top end as soon as my budy gets in the boat and watches the fuel presure gauge while I drive.
    2350sx

  6. #6
    Infomaniac
    Don't forget about the fuel filter. It is after the fuel press gage !!!!!!!!

  7. #7
    Hotcrusader76
    Originally posted by chaparral2350sx:
    . Sell the Quadrajunk on Ebay and buy a Holley. which is what I want to do in the first place.
    Hey! When your ready drop me a line or email me, and I can get you set-up with a carburetor.
    I will send you a form that you can fill out for the engine specification questions.
    Thanks
    Ty Lofstrom
    TPC Racing
    sales@tpcracing.com

  8. #8
    chaparral2350sx
    HI Hotcrusader
    I did find out that fuel delivery is not the issue it most likely is in the jetting. You said you could help with jetting a carb to my boat. I will give you my email address and you can give me a ballpark figure on how much it is going to set me back.Thanks guys for all the help and I will keep a eye the forum for good info.
    Thanks
    burn4602@bellsouth.net

  9. #9
    CV-23
    If you go with a Holley, make sure its a 800cfm. The 750cfm Q-Jet is good to 600hp according to Dennis Moore so don't count it short. I'm a Holley Fan but the Q-Jets work fine and are easy to tune with less fuel mess. They are sensitive to vacuum changes, something the Holley Double Pumper is not....Mike.

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