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Thread: Low rpm buck

  1. #1
    Madmike1's Avatar
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    Low rpm buck

    Hello

    I have done a bunch of mods to my 2011 rxpx this winter and today was the first day out with it. It runs and sounds great on the trailer, will rev above 6000 very fast and show vacuum and boost on my autometer boost gauge. I put it in the water and went to leave the dock and it wouldnt go above about 3500-4000 rpm before it would make this buck or clunk noise and drop in rpm. The boost gauge shows vacuum but when I start to accelerate and it gets to 0 vaccum this will happen. Any ideas what could be causing it. All of my mods were done this winter and they are located in my sig.

    Thanks!
    Mike


  2. #2
    hero's Avatar
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    have u checked for boost leak??
    check your charger

  3. #3
    Madmike1's Avatar
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    Thats what I was leaning towards also.... I build my own bracket and piping and used t-bolts and silicone couplers. It is hard to tell tight enough vs too tight on the aluminum piping as it will crush the piping if you tighten them too tight. I guess I need to take the piping to a exhaust shop and have them put a bead on them...

    thanks

  4. #4
    Having Fun jp1300r's Avatar
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    Do you have brand new spark plugs in the ski?

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    Madmike1's Avatar
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    I did change out the plugs at the lake just to make sure it wasn't them... It acted fine for about a minute after I replaced them, started to get some small acceleration and then thunk... back to the same symptoms. My AFR gauge is reading really lean when this happens like 16-17.

  6. #6
    Having Fun jp1300r's Avatar
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    Whats your fuel pressure? I know you know the AFR is not right. Don't try and run it hard till its figured out.

  7. #7
    Having Fun jp1300r's Avatar
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    I would pull the valve cover and just make sure everything looks ok with the valvetrain. Prop torque to about 95 ftlbs? What SCer are you running?

  8. #8
    Madmike1's Avatar
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    No FPR yet, I'm not sure I will need it (according to Jerry the Vtec flash is tuned for the 50lb injectors).Im running the 137mm ET charger on the ski. I just did a compression check just in case and I was just under 150psi on all three cylinders. The motor only has 11 hours on it so I think that is fine.

    I have a small leak around the reverse nut (replaced with a aluminum nut) so I have to pull the pump and I will check the prop to make sure its right but when I installed it I really leaned on it!

    Could the fuel pump assembly cause this? I pulled the pump to see what I would need to do to add a walbro and FPR and then reinstalled it... The fuel gauge reads correctly and it fired up so I figured all was good, but the lean condition is really freaking me out... would a boost leak cause a lean AFR or rich? My thinking is it would be rich but I'm not sure.

    What would I be looking for under the valve cover? It revs out fine on the trailer (only rev'd a couple of times hard but could get it to 6000 or so real quick.

    Thanks for all of the trouble shooting tips!

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