RPM falls off?
+ Reply to Thread
Results 1 to 6 of 6

Thread:
RPM falls off?

  1. #1
    Senior Member Luckie Stiff's Avatar
    Join Date
    Dec 2007
    Location
    Bakersfield
    Posts
    1,189

    Default RPM falls off?

    Was at the river this weekend and occasionally my rpm would fall off by a few hundred, back out of the throttle, hammer down, rpms are back for a while. What do y'all think it is?
    "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?"

  2. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  3. #2
    Senior Member lbhsbz's Avatar
    Join Date
    Oct 2008
    Location
    Long Beach
    Posts
    1,617

    Default

    Quote Originally Posted by Luckie Stiff View Post
    Was at the river this weekend and occasionally my rpm would fall off by a few hundred, back out of the throttle, hammer down, rpms are back for a while. What do y'all think it is?
    Fuel pump can't keep up.
    GN7: "If you were to have ever had two brain cells you could rub together and make heat, you be dangerous"

  4. #3
    Senior Member
    Join Date
    Dec 2007
    Location
    Newbury Park, Ca/Mohave Valley, Az
    Posts
    8,168

    Default Need more details??

    Quote Originally Posted by Luckie Stiff View Post
    Was at the river this weekend and occasionally my rpm would fall off by a few hundred, back out of the throttle, hammer down, rpms are back for a while. What do y'all think it is?
    My first guess, and only a guess based on the available info, would be fuel supply. Do you have a fuel pressure gauge? If you do, what was the pressure when it dropped off? Has it ever done this before? Any changes, any thing at all, since the last trip when it didn't drop the Rs? What is the history of this current set up? The idea that it regained the Rs by simply backing out and stepping on the gas again would seem to me to be fuel related. Either pump, filter, supply from tank(s) dropping due to vapor lock, or possibly a vacuum issue from the tank vent.... When you backed off and dropped the nose, the fuel would shift in the tank and maybe re-cover the pick up....Many, many possibilities, but I think an ignition issue would not "fix it's self" that quickly. However, I've seen marginal coils do some funny things in an intermittent hit and miss condition...More info Lucky??....
    Ray
    LOUD BOATS SAVE LIVES

  5. Remove Advertisements
    PerformanceBoats.com
    Advertisements
     

  6. #4
    Senior Member Luckie Stiff's Avatar
    Join Date
    Dec 2007
    Location
    Bakersfield
    Posts
    1,189

    Default

    Quote Originally Posted by Moneypit View Post
    My first guess, and only a guess based on the available info, would be fuel supply.
    Do you have a fuel pressure gauge? YES , 6.5 PSI is where the regulator is set, it didn't drop when this happened
    Has it ever done this before? Nope
    Any changes, any thing at all, since the last trip when it didn't drop the Rs? Added a Place Droop with rideplate
    What is the history of this current set up? Same setup for the past 3 years
    More info Lucky??....
    Ray
    When I say I got out of the throttle and back into it, I'm talking foot off, foot right back on the throttle, no time for the nose to drop.
    "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?"

  7. #5
    Senior Member
    Join Date
    Dec 2007
    Location
    Newbury Park, Ca/Mohave Valley, Az
    Posts
    8,168

    Default Pedal job

    Quote Originally Posted by Luckie Stiff View Post
    When I say I got out of the throttle and back into it, I'm talking foot off, foot right back on the throttle, no time for the nose to drop.
    So basically you're saying you "pedaled it"... Hmmmm, how about in the past? Any changes since the last time out? Is the motor "nosing over", like running out of camshaft or vacuum? When you lift and stab it, the only thing you're doing is adding the accelerator pump squirt to the fuel supply, which could grab a few Rs back, but it should be short lived. ???? Any float level changes lately? ... OK, another guess. Is it possible your valve springs are going away? Weak springs could set up a harmonic vibration that could get the springs shaking sideways and could cause the valves to begin to float. Lifting, even for a split second could get the springs back in order for a short time until the process begins all over, and the Rs drop again... Again, do you have a fuel pressure gauge? And/or a vacuum gauge? ... Sloppy/floating valves should cause a drop in vacuum.... F/pressure would be my first investigation...After that, you might look at max ignition advance for any changes since it was set, but that is down my list of possibles. IMO, it could be the springs....
    Ray
    LOUD BOATS SAVE LIVES

  8. #6
    Senior Member Luckie Stiff's Avatar
    Join Date
    Dec 2007
    Location
    Bakersfield
    Posts
    1,189

    Default

    Ray, first off thank you for the ideas as to what it might be. The setup is basically that same as it's been for the last 5 or so years, it's my "go to" setup, you know, the one that never leaves you on the beach. At any rate, my fuel pressure gauge is 5 at idle, 6.5-7 at speeds. Timing hasn't changed, coil is good. I'm going to dig into the spring thing this week and see if that's it, hopefully not.
    "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?"

+ Reply to Thread

Quick Reply Quick Reply

Register Now

Please enter the name by which you would like to log-in and be known on this site.

Please enter a password for your user account. Note that passwords are case-sensitive.

Please enter a valid email address for yourself.

Please select your insurance company (Optional)

Log-in

Tags for this Thread

Digg This Thread

Posting Permissions

  • You may post new threads
  • You may post replies
  • You may not post attachments
  • You may not edit your posts
  •  
 

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90 91 92 93 94 95