Carb Problems (need some help)
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Carb Problems (need some help)

  1. #1
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    Default Carb Problems (need some help)

    I have a jet boat with a chevy 454 big block and a holley double pumper 750cfm carb. The boat used to start but would load up with fuel and just bog. I rebuilt the carbs (first time rebuilding a holley) and some how managed to make things worse. I crank over the engine it pops right away then just continues cranking. I pull the plugs and they are soaked. I take plugs out and let them dry and install them again after a couple of seconds of cranking there soaked again. Is there a way to check fuel pressure on an engine that wont fire?

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    Senior Member 67weiman's Avatar
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    Check your float levels. Sounds like your floats are to high or your needle and seat are stuck open.

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    i adjusted the floats either direction and nothing changed!

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    Take the needle and seats out or tap the top of the float bowls with a screw driver. That should pop the needle and seat loose. Also when you start the boat take the air cleaner and scoop off if you have one. It sounds like fuel is dumping in through the vents

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    The needle and seats were replaced. where are the vents located? the problem is i can not get the boat to start.

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    Senior Member jet pilot's Avatar
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    Quote Originally Posted by dremmick View Post
    The needle and seats were replaced. where are the vents located? the problem is i can not get the boat to start.
    I have a edelbrock performer manifold and a 850 cfm edelbrock marine carb, a year old,I'm running a 454 also. I'm getting rid of the set up because I just got a Tunnel ram for mine. PM me if interested

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    Senior Member 67weiman's Avatar
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    Vents are the tubes on each side. They vent the fuel bowl, so if your float is too high, it will push fuel out the vent into the carb. I would bet your float level is wrong. Does it have sight windows or plugs on the fuel bowls? If its plugs, pull them and crank it over. Fuel should barely seep out of the plug. If it has the windows, you can see the level. You want the fuel about the middle of the windows.

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    The carb has plugs on the fuel bowl. if i crank the engine will the bowls fill up if i have a manual fuel pump? Vents are the tubes on each side. One thing i remember is there is only idle mixutre screw on one of the metering blocks and not the other. Is this normal?

  11. #9
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    It's pretty easy to check float levels. Pull plug out of front bowl, crank motor over. If gas comes flowing out hole, level is too high. If fuel does not just trickle out or is so low you can't see it, level is too low. Then do the same with the rear bowl. Make adjustments if you have to. If that doesn't help, I would take scoop or air cleaner off. Then have somebody crank motor over, while you are looking down the throat of the carb. See where the excess fuel is coming from.
    Here is a link to a webpage that is kind of like an overview of Holley carbs. It has some various links and info on stuff like setting float levels and a few other adjustments that can be made.
    Carburetor Tuning the Scientific Way
    Last edited by S&S; 04-10-2012 at 04:11 PM.

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    I wouldn't look down the carb in case it backfires. Maybe you forgot the gasket between the base plate and the main body? To me it sounds like the floats are stuck, regardless how much you adjust them. I would take the air cleaners and scoop off and crank it. If fuel comes out of the two brass tubes sticking out of the carb( the top of the body) then the floats are stuck.

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    While doing the rebuild did you check the floats themselves? Are they brass or the newer black floats? No offense but how extensive was your'e rebuild in the way of clean-up? Also are you running rubber fuel lines? I think alot here have ran into rubber fuel lines coming apart from the inside out and clogging the needle and seat right of the bat! Qwik check on that with a mechanical pump is to pull the fuel line and pump into a clear container, but carefull the engine may want to fire without the added fuel. also if you pull the coil wire be carefull were you park the live end! M

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    Senior Member 67weiman's Avatar
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    You should have idle mixture screws on each side of the primary metering block. It is common to not have the idle mixture screws on the secondary metering block. Yes, your mechanical pump will feed fuel to the carb when cranking.

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    WHERE are you???? There may be a PB Holley expert around the corner from you if you show WHERE you're located!!!!! I see these threads and cringe, Holleys are really so simple I get frustrated when people have problems like this and there is a chance they're down the street from me....
    Ray
    LOUD BOATS SAVE LIVES

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    I'm located in Fargo north Dakota. The floats are brass the carb was rebuilt using a genuine Holley rebuild kit. I thoroughly cleaned Everthing with carb cleaner. The fuel is rubber so I will have to try the test you mentioned.

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