RPM's Lacking.. Wondering if its Timing??
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RPM's Lacking.. Wondering if its Timing??

  1. #1
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    Default RPM's Lacking.. Wondering if its Timing??

    Im scratching my head here trying to figure out why this thing wont pull the RPM's. Ive read through most of the posts on Timing and Advance trying to get some clarification and understanding what I am looking at, but still find myself wanting to ask questions to get a better understanding of what to check and adjust.

    What I do know:
    90' 20.5 Carrera Elite
    454BBC 4-Bolt
    Edelbrock Hi-Rise Manifold
    750cfm Holley Marine - Rebuilt, had a TON of corrosion
    Mallory ProComp 9000 Megnetic Breakerless Ignition (Mechanical Adv)- New
    Mallory Coil - New
    Pump Super Gas
    New AC Delco MR43T's
    No Leaks, just got done cleaning up corrosion on exhaust manifold and resealing
    12JG Pump completely rebuilt with new split bowl, new shaft, new Impeller by Dan at Jett Marine Performance. He said he cut the imeller back and put an A/B cut on it.

    Everything is fresh, but its only turning 4500 RPM.

    We went to checking the timing this weekend, but forgot to grab some timing tape, but we decided to at least check it anyway.


    It fires up with a little pump/help from the throttle, and idles at 900rpm on the water. When we hit it with the timing light, it was a solid 8 degrees BTDC. Because the timing marks only go to 16 on the plate, we really couldnt get an accurate reading, but at 2000rpm, it was about 3/4" past the 16 degree mark. When I spoke with Dan, he said it should be pulling a solid 4600-4800 rpm's with bone stock motor with the cut he put on the impeller. So now its down to trying to figure out why this thing wont pull the RPM's. We pulled the plugs. They look good, they arent brown or black.

    So now its down to timing and advance, or there is still some crap in the carb. This carb appears to have had a bunch of custom work done to it by JP Marine. I bought this boat in Huntington Beach, CA, if that makes a difference. Im not trying to factor in the MPH here, but its only pulling 51mph on GPS with a place diverter, when it should be 55-58mph.

    My cousin has 20.5' Eliminator Daycruiser with a 454bbc 2-bolt, 600cfm holley, no hi-rise intake, and completely stock pump from 1988 w/o a diverter and he's pulling 4700rpm and 52mph.

    Nevertheless, something still isnt right, and I already have enough gray hair...

    So should I be looking at the timing and advance, or looking back into the carb, or both?

    Thanks in Advance

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  3. #2
    Senior Member slow67's Avatar
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    Use a dial-back timing light and check it again

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    Cas
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    4500 with a fresh pump isn't unusual at all on a, I'm assuming, stock engine. More than likely, the engine is going to need more power to get it up into higher rpms. Once it's tuned properly will definitely give you a better idea if that's true.
    It would be best to get a GPS reading to see what kind of speeds it's running. As far as your cousins boat, it's probably turning higher rpm due to having a pump that has some wear and larger clearances. Rpms really are not an indicator of speed.
    Last edited by Cas; 04-19-2010 at 10:45 AM.

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    Senior Member Luckie Stiff's Avatar
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    Quote Originally Posted by slow67 View Post
    Use a dial-back timing light and check it again
    There's your answer. 36 degrees at 3000 RPM
    "Don't you realize that there are already enough people in the world to hate without you putting in so much effort to give me another?"

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    Quote Originally Posted by Luckie Stiff View Post
    There's your answer. 36 degrees at 3000 RPM
    Well, $100 bucks for a dial back or 5 bucks for timing tape...LOL Thats my dilema... Ive asked around to see if anyone I know has a dial back, but everyone Ive talked to has a normal one.

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    Senior Member slow67's Avatar
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    Quote Originally Posted by headshothills View Post
    Well, $100 bucks for a dial back or 5 bucks for timing tape...LOL Thats my dilema... Ive asked around to see if anyone I know has a dial back, but everyone Ive talked to has a normal one.
    I think I paid $35 for mine at oreilly's

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    Quote Originally Posted by slow67 View Post
    I think I paid $35 for mine at oreilly's
    No Sh(:Censored

    Well, I got to thinking mathematically, And figured I might put my brain to work. If I wanted to make my own Timing Tape, this is what I came up with. Any math majors, point me in the right direction if Im off track...

    I think the Balancer is 7"

    Converting to metric

    7 x 25.4mm = 177.8mm
    177.8mm x 3.14159(pi) = 588.574702mm
    588.574702mm / 360 degrees = 1.551596394mm (Per Degree)
    1.551596394mm x 36 Degrees = 55.8574702mm

    So if I take a piece of duck tape, or paper for that matter, measure it out from 0 to 55.8mm, then lay that on the balancer, mark it off, that mark will now be my 36 degree mark...

  10. #8
    Senior Member slow67's Avatar
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    Quote Originally Posted by headshothills View Post
    No Sh(:Censored

    Well, I got to thinking mathematically, And figured I might put my brain to work. If I wanted to make my own Timing Tape, this is what I came up with. Any math majors, point me in the right direction if Im off track...

    I think the Balancer is 7"

    Converting to metric

    7 x 25.4mm = 177.8mm
    177.8mm x 3.14159(pi) = 588.574702mm
    588.574702mm / 360 degrees = 1.551596394mm (Per Degree)
    1.551596394mm x 36 Degrees = 55.8574702mm

    So if I take a piece of duck tape, or paper for that matter, measure it out from 0 to 55.8mm, then lay that on the balancer, mark it off, that mark will now be my 36 degree mark...
    You are correct, assuming your balancer is exactly 7" diameter.

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    Senior Member cruzer's Avatar
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    Don't know whay you converted to metric, but your calculations are probably "Close enough". Assuming you didn't fat finger the calculator or something.

    Dang, I said close enough and assuming in the same post. Might be a bit of risk here.....
    Cruzer
    21 Eliminator Daytona. Blown 540

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    About 500' AGL MudPumper's Avatar
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    Have you verified you are getting full throttle?

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    Is the tachometer accurate? Can you check it against another one?

    Doug

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    Quote Originally Posted by MudPumper View Post
    Have you verified you are getting full throttle?
    I will definitely check that.. Didnt really think of it, but definitely worth a check...

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    Quote Originally Posted by Real McCoy View Post
    Is the tachometer accurate? Can you check it against another one?

    Doug
    Yah, I can throw another tach in it...

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    Quote Originally Posted by Luckie Stiff View Post
    There's your answer. 36 degrees at 3000 RPM
    I agree that all the timing should be in at 3000 rpm's But when I had my 496 on the dyno I originally set the timing at 36 degrees. It made 632 hp. I then set it up to 38 degrees and it made 626hp. So I started retarding the timing until I got the best hp number. It made the most hp at 29 degrees?? 648hp. Of course these weren't the only changes but 29 degrees was where I got the most.
    Once you get a good light. or tape. Go out on the water and have someone check the timing to make sure it is all in at 3000rpm's Then make a blast. Then go up and or down in timing no more that 2 degrees at a time until you get the most rpm's. Make a blast every time you change the timing. Check your plugs after each run for detonation. If you need more timing you may find you have to richen the carb by one or two jets and adjust the idle setting down on your carb. If your motor needs more fuel it will cause a negative effect on the amount of rpm's Once you have found where it starts to make the most power narrow it down by 1 degree and then to 1/2 at a time..Hope this helps.
    Kojac

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