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Falls on face above 5000 rpms.

This is a discussion on Falls on face above 5000 rpms. within the General Help forums, part of the LSx Technical Help Section category; I need to say that this is not a LS1 Question, but I hope that I can get some replies ...

  1. #1
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    Question Falls on face above 5000 rpms.

    I need to say that this is not a LS1 Question, but I hope that I can get some replies back. I have a 77 camaro that have a 350 bored 60 over. Vortec heads,194/150 valves,a 480/480 lift cam,headers,2500 stall, RPM intake,and a Accel Dist.The heads have been setup to accept up to 525 lift. I also have a little better than stock fuel pump. The problem I have is that the car runs great, but if I run it up to 5000 rpms in 1st gear it falls on it's face. anything below that and it's super,gets side ways coming off the line. The trans is a turbo 350 with a shift kit.The rear is 342's. What do you guys think? Also I need to add that the carb. is a 750 vac. with stock jets.Is there anything to the MSD ignition will it help my setup?
    Last edited by Street Fighter; 03-19-2008 at 04:12 AM.

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    Senior Member Orcus79's Avatar
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    It could be a fuel starvation issue, did you plumb in larger lines from the tank to the carb? that is generally the frst place that gets over looked when building a high output motor.

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    Moderator Firebirdjones's Avatar
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    I agree, sounds like classic fuel starvation. I would start diagnosing things and eliminate possibilities.

    I have a fuel pressure gauge with a long line specifically for this, if the car in question doesn't have a gauge already.
    I plumb it in the fuel line as close to the carb as possible and duct tape the gauge to the windshield and go for a drive,,,watch to see what is going on.

    Should have a steady 5-7 lbs. If you get 4 lbs. or less you have a fuel pump that can't keep up,,,possibly fuel line too small, a pickup problem, clogged fuel filter etc......

    You mentioned 750 vacuum sec carb......I assume you are talking a holley, which has dual float bowls,,,,,thats one problem eliminated, since they have extra capacity it's harder to run them dry. If you had any other carb like a Q-jet, Edelbrock etc....they are nortorious for running dry if the fuel system is even marginal.

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    down with the lot lizards blackhawk01's Avatar
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    change the fuel filter..best 7 bucks ull ever spend

    nevermind im sorry I didnt read the whole post..did not relalize it was a carbed car..my bad

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    The fuel line is the stock 3/8 line, do you think it's too small for a mild setup like the one I have? I will be doing a new line and see what happens, if it works, i'll be doing the same to my charger,it have the same problem.

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    Senior Member Orcus79's Avatar
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    It will either be the line or the pump. If you running the origina tank and have never droped it. Drop it and pull out the sender and pick up. Check the strainer sock to see if it is clogged with rust and crap.

    Also get a read on fuel pressure and try swaping in a a high GPM electric there might just not be the capacity to fill both fuel bowls under WOT conditions.

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    Moderator Firebirdjones's Avatar
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    For the mild setup you have I think the 3/8 line you have would be fine. Question is,,,,is the fuel pump strong enough to keep up?

    Only way to tell is to do as I suggested,,,,get a gauge on there and go for a drive. See what is going on, and go from there.

    Another possible issue could be heat soak. More of an issue on a carb car due to lower fuel pressure requirements. If you have a fuel line close to heat it can cause fuel pressure problems as well. Especially with winter grade gas with it's lower flash point.

    This can be attacked in a couple of different ways, but before I get into all that I would rather get a fuel pressure reading first so we aren't chasing our tails here.

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    I have a fuel gauge mounted in the carb. line. I also have a fuel pressure tester,Which one should I test with and how would I make the connection from the carb. to the test gauge?
    Thanks for the help.

  9. #9
    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by Street Fighter View Post
    I have a fuel gauge mounted in the carb. line. I also have a fuel pressure tester,Which one should I test with and how would I make the connection from the carb. to the test gauge?
    Thanks for the help.
    There are different ways to go about it. Generally when I get a car in the shop that doesn't have a gauge, I find a spot that is easy to access somewhere in the fuel line between the pump and carb,,,preferably as close to the carb as possible.

    I have various fittings and use an old R12 refrigerent gauge that has a hose about 6 feet long, for testing, with shrader valve type connections, flare fittings etc....depending on the car I am working on dictates how I connect it. Then simply run the line over the cowl, gently close the hood and tape the gauge to the windshield, go for a short drive. The R12 high pressure line works good here because it doesn't compress or collapse easily,,,and the weather stripping at the rear of the hood gives it some cushion too.

    If there is rubber fuel line between the pump and carb, I would cut the hose and install a temporary T-fitting (hose barb) and run a gauge off of that.
    If you have hard line, the methods can vary alot.

    Generally when I bend up hard fuel lines for cars, I like to use brass T-fittings for flare nuts on a dual inlet carb and cut and flare my own lines. I sometimes drill and tap this fitting with 1/8 inch pipe thread for a fuel pressure fitting, which can be plugged when finished or used to plumb a perminant gauge if desired.

    If you could get a picture up here of the engine compartment so I can see what you have to work with I could give you some better ideas.
    Too bad you're not close, I could iron this out for you, this old stuff is what I work on for a living. Hope this helps.
    Last edited by Firebirdjones; 03-21-2008 at 06:15 AM.

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    I thuoght about a T in the line also,but I felt that it would take some of the true pressure going to the carb. and give a false reading.After thinking about it, it should work, once the pressure is up on the gauge it should stay because it's not going anywhere, unless it starts to fall.will do it today and see what happens. I also work on old cars I own a yard full of them,but some times the best can't see what's right in front of them.

  11. #11
    Moderator Firebirdjones's Avatar
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    Quote Originally Posted by Street Fighter View Post
    I thuoght about a T in the line also,but I felt that it would take some of the true pressure going to the carb. and give a false reading.After thinking about it, it should work, once the pressure is up on the gauge it should stay because it's not going anywhere, unless it starts to fall.will do it today and see what happens. I also work on old cars I own a yard full of them,but some times the best can't see what's right in front of them.
    LOL,,,,you have the right idea. Once the pressure reaches the gauge it will dead head,,,and have no affect on fuel to the carb,,,

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