Olds 455 Mechanical Fuel Pump
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Olds 455 Mechanical Fuel Pump

  1. #1
    Junior Member oldsbutgold's Avatar
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    Default Olds 455 Mechanical Fuel Pump

    Hello All,
    I have discovered that my fuel pump on my rig simply won't keep up with the demand of the engine at full throttle. As soon as the vac secondaries open the engine falls on its face. I can't pull any more than 4000rpm as I stated in my other thread. I would prefer to keep a mechanical fuel pump on it, but i understand if this would be a foolish option, and would like someone to tell me flat out if I am wasting my time.

    That being said, would one of these be a viable mechanical option?

    http://www.summitracing.com/parts/crt-m6109/overview/

    http://www.summitracing.com/parts/crt-m4871/overview/

    Thanks guys

    Took probably my last trip to the lake yesterday, found my last few things to add to my list of stuff to fix this winter. can't wait til next year.

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    Senior Member jetboatperformance's Avatar
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    Quote Originally Posted by oldsbutgold View Post
    Hello All,
    I have discovered that my fuel pump on my rig simply won't keep up with the demand of the engine at full throttle. As soon as the vac secondaries open the engine falls on its face. I can't pull any more than 4000rpm as I stated in my other thread. I would prefer to keep a mechanical fuel pump on it, but i understand if this would be a foolish option, and would like someone to tell me flat out if I am wasting my time.

    That being said, would one of these be a viable mechanical option?

    http://www.summitracing.com/parts/crt-m6109/overview/

    http://www.summitracing.com/parts/crt-m4871/overview/

    Thanks guys

    Took probably my last trip to the lake yesterday, found my last few things to add to my list of stuff to fix this winter. can't wait til next year.
    FWIW any Olds mechanical will work assuming they provide adequate pressure and volume , most we have researched and sourced that are available for Olds however are not "marine approved" , you didn't mention what carb would assume its a Holley ? Holleys like 6 to 7 psi if the marine thing concerns you, have seen folks drill and tap the top of the pump main body to add a "diaphragm rupture vent" be advised not sure if this mod is acceptable or satisfies as far as CG safety requirements. We swap to Holley electric marines

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    Junior Member oldsbutgold's Avatar
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    Thank You. I'm not positive that the pump that is on there now is a marine pump. It is a 750 Vac Secondary Holley. I'm not sure if it is a fuel pressure or volume issue, as I didn't have anyone to ride along this time and check a fuel pressure gauge, so over the winter i was planning to upgrade to something with more volume and pressure. Everyone and everything keeps telling me to go to an electric pump, so it may be the way I'm headed.

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    Junior Member oldsbutgold's Avatar
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    Quote Originally Posted by jetboatperformance View Post
    FWIW any Olds mechanical will work assuming they provide adequate pressure and volume , most we have researched and sourced that are available for Olds however are not "marine approved" , you didn't mention what carb would assume its a Holley ? Holleys like 6 to 7 psi if the marine thing concerns you, have seen folks drill and tap the top of the pump main body to add a "diaphragm rupture vent" be advised not sure if this mod is acceptable or satisfies as far as CG safety requirements. We swap to Holley electric marines
    Are all the Holley electrics marine approved? or can someone point me to a certain part number?

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    Senior Member jetboatperformance's Avatar
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    Quote Originally Posted by oldsbutgold View Post
    Are all the Holley electrics marine approved? or can someone point me to a certain part number?
    Check Summit of Jegs , search for Marine Electric fuel pumps ...

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    Default "Driver's eye"

    Quote Originally Posted by oldsbutgold View Post
    Thank You. I'm not positive that the pump that is on there now is a marine pump. It is a 750 Vac Secondary Holley. I'm not sure if it is a fuel pressure or volume issue, as I didn't have anyone to ride along this time and check a fuel pressure gauge, so over the winter i was planning to upgrade to something with more volume and pressure. Everyone and everything keeps telling me to go to an electric pump, so it may be the way I'm headed.
    Re mount the f/pressure gauge where YOU can see it from the driver's seat. If its one of the small ones "tee'd" off the fuel line up by the carb put an elbow in the hole and screw the gauge in pointing forward.. AND, its not unusual for boat carbs to get all "gummed up" inside... When the boat is parked for an extended time the gas evaporates out of the bowls and leaves a varnish (brown residue) in the small passages. Vacuum open the butterflies to air, but the fuel supply is either restricted, or shut off completely. Before you do anything else verify your fuel pressure, especially when it "acts up" and seems to be starving for gas.. I've ran a 2X4 Olds set up with a bone stock mechanical pump and it didn't have any problems maintaining 6-7 lbs pressure.
    What you DON'T want to do is go to changing a bunch of stuff, (F/P, carb rebuild, ignition timing etc etc).. Change ONE thing at a time and "test" your results. When you get all ambious changing stuff you will usually wind up chasing your tail and never KNOW what change 'fixed it"...
    Ray
    PS Jeg's/Summit/Hebert should carry the "HP" version of the stock mechanical pump. They're not cheap, but they are waaay more "user friendly" than any electic pumps... (Ask me how I know that)...
    LOUD BOATS SAVE LIVES

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    Default Last trip??

    If you're parking the boat for the winter, drain the gas out of the carb using a lower bowl screw. THEN refill the bowls through the "vent tubes" with a 50-50 mixture of gas and Mystery oil. It's OK to fill until it starts dripping from the Venturi.... What happens is the gas dries out, evaporates, and leaves a film of Mystery oil inside the carb... Next spring, refill the bowls to the "sight" holes with the same 50-50 mixture and let it sit for a day or so. Exercise the acc pump, making sure it's squirting, and most of the time the carb will be fine to use without further work.... Yeah, the engine will throw some Mystery oil smoke for a few seconds when you fire it, but that will go away real quick...
    Ray
    LOUD BOATS SAVE LIVES

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    Junior Member oldsbutgold's Avatar
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    Thanks Moneypit and JBP, I will be sure to check everything over before I change anything. Late last night i found a few thing that may have contributed: I found a cheapo hidden inline fuel filter that may be restrictive Name:  images.jpg
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Size:  7.0 KB(Boat is still fairly new to me, I find previous owner's bad decisions every time I look at it), and my rear fuel bowl was leaking which is not safe (especially with the dog house on) and could have drained the bowl and gummed the carb up as MoneyPit stated.

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    Senior Member Texgo's Avatar
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    That's what I have on my lawnmower.

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    Junior Member oldsbutgold's Avatar
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    Yeah I know. It's a joke. And I'm kicking my own ass for not going through this top to bottom before I started asking questions.

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    Quote Originally Posted by jetboatperformance View Post
    have seen folks drill and tap the top of the pump main body to add a "diaphragm rupture vent" be advised not sure if this mod is acceptable or satisfies as far as CG safety requirements.
    I doubt this mod would be compliant because it's still a single-diaphram pump. But in the event of a diaphragm rupture, the fuel will flow out the vent into the carb, maybe. It will also flow into the oil pan, and you may not see fuel in the vent. So this mod may not reveal a pump diaphragm failure, which is the whole purpose: to alert one to a diaphragm rupture.

    The approved pumps are dual-diaphragm. The plate sandwiched in the middle has the vent tube attached to it, that then goes to the spark arrester, or in earlier installations had a glass bowl with a tag "if fuel appears in this bowl, replace pump". The idea being if the lower diaphragm ruptures, fuel is forced into the bowl or tube where it will be notices, and the pump replaced, without being introduced to the oil pan where it becomes explosive as crankcase fumes may be introduced to the bilge atmosphere.

    There are "approved" electric pumps. I don't know if the Holley is one or not.


    To the OP: Don't overlook the possibility of restrictions on the inlet side of the pump causing pressure / delivery issues. The only thing pushing fuel into the pump inlet is 14.7" of atmospheric pressure. Also, keep in mind that ethanol laced modern gasoline will cause old fuel hose to swell up internally, and cause a very difficult to diagnose restriction. Most hose is dated. If the hose is over 10-ish years old, it's probably not ethanol compatible.
    Last edited by 70 Weiman; 09-24-2014 at 01:02 PM.

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    Junior Member oldsbutgold's Avatar
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    Quote Originally Posted by 70 Weiman View Post
    I doubt this mod would be compliant because it's still a single-diaphram pump. But in the event of a diaphragm rupture, the fuel will flow out the vent into the carb, maybe. It will also flow into the oil pan, and you may not see fuel in the vent. So this mod may not reveal a pump diaphragm failure, which is the whole purpose: to alert one to a diaphragm rupture.

    The approved pumps are dual-diaphragm. The plate sandwiched in the middle has the vent tube attached to it, that then goes to the spark arrester, or in earlier installations had a glass bowl with a tag "if fuel appears in this bowl, replace pump". The idea being if the lower diaphragm ruptures, fuel is forced into the bowl or tube where it will be notices, and the pump replaced, without being introduced to the oil pan where it becomes explosive as crankcase fumes may be introduced to the bilge atmosphere.

    There are "approved" electric pumps. I don't know if the Holley is one or not.


    To the OP: Don't overlook the possibility of restrictions on the inlet side of the pump causing pressure / delivery issues. The only thing pushing fuel into the pump inlet is 14.7" of atmospheric pressure. Also, keep in mind that ethanol laced modern gasoline will cause old fuel hose to swell up internally, and cause a very difficult to diagnose restriction. Most hose is dated. If the hose is over 10-ish years old, it's probably not ethanol compatible.
    Thanks Weiman, I will be going over the entire fuel system from inside the tanks to the carb this winter now. I had to replace one line from my left tank to my T-valve before the last trip. Should have been an indicator to go through everything. I'll check and make sure that the tanks are venting correctly as well. May be a fine time to go braided -8 on it all.

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