Page 1 of 2 1 2 LastLast
Results 1 to 10 of 14

Thread: Low RPMs

  1. #1
    DaveC's Avatar
    Join Date
    Jun 2007
    Location
    Central Oklahoma
    Posts
    2,362
    +1
    41

    Low RPMs

    Here is the story, it has been going on for some time now.
    I have constantly had low RPM issues with this setup for a long time now. Several have given me ideas thru PMs during this time, just have not come up with a solution. The RPMs have been low at the first of the year with 8260. I installed the 15/20 I have that was pitched for similar mods to this except, I had a Rude1 charger. To get the 15/20 to 8520, I had to add roughly 4mm to the impeller and switch from a 81 to a 83mm ring. At 8520 RPM I see right at 78.4 MPH. Previously with these mods, impeller and Rude1 I had a best speed of 84.6 and numerous 84 mph runs.

    The problems started along the time I switched to a Rotax Racing 4224 camshaft for a short time. When I was installing the new cam, I also added a RRFPR and new Delphi 50# injectors and had the bung installed on the Jpipe.
    Along in this time also, I added the new ride plate modified by Jim. Did not care for the way the welded skegs worked and removed them.



    Any ideas ?
    Last edited by DaveC; 07-29-2011 at 09:47 PM.


  2. #2
    shrabber's Avatar
    Join Date
    Apr 2008
    Location
    Jacksonville, FL
    Posts
    5,305
    +1
    376
    All them mods with stock fuel pressure regulator I would start there you have no way to tell whats your base psi wot psi etc. do you have a afr guage? Gets some readings

  3. #3
    DaveC's Avatar
    Join Date
    Jun 2007
    Location
    Central Oklahoma
    Posts
    2,362
    +1
    41
    Generally a stock X charger being used with a Riva ECU and 48# injectors is known to be safe. But guess there is only one way to know for sure.
    Last edited by DaveC; 07-29-2011 at 09:51 PM.

  4. #4
    Moderator Snoman's Avatar
    Join Date
    Apr 2006
    Location
    South Chicagoland
    Posts
    14,688
    +1
    846
    Quote Originally Posted by shrabber View Post
    All them mods with stock fuel pressure regulator I would start there you have no way to tell whats your base psi wot psi etc. do you have a afr guage? Gets some readings
    With a Riva ECU and 50s you shouldnt need to worry about a RRFPR, it is mapped for the OEM one which base pressure is a 58 psi...

    Dave i know you checked BUT i would triple check all your timing components.....If this started acting up when you switched cams ill bet theres something amiss in that area..jumped tooth or something silly..

  5. #5
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    Location
    CT
    Posts
    25,930
    +1
    1,407
    Possible crank gear slip?

  6. #6
    DaveC's Avatar
    Join Date
    Jun 2007
    Location
    Central Oklahoma
    Posts
    2,362
    +1
    41
    Dunno Scott, I used both the cam/crank locking tools. I also verified TDC of the crank with a dial indicator and found the locking tool position to be spot on within the last two days.

  7. #7
    DaveC's Avatar
    Join Date
    Jun 2007
    Location
    Central Oklahoma
    Posts
    2,362
    +1
    41
    Just me thinking here, but would that be noticeable when you confirm the crank locked position ?

    Quote Originally Posted by beerdart View Post
    Possible crank gear slip?

  8. #8
    Moderator Snoman's Avatar
    Join Date
    Apr 2006
    Location
    South Chicagoland
    Posts
    14,688
    +1
    846
    Quote Originally Posted by DaveC View Post
    Dunno Scott, I used both the cam/crank locking tools. I also verified TDC of the crank with a dial indicator and found the locking tool position to be spot on within the last two days.

    hmmmmmm...At a lose..did you try moving the cam advancing and retarding it to see if you picked up any RPM??

  9. #9
    DaveC's Avatar
    Join Date
    Jun 2007
    Location
    Central Oklahoma
    Posts
    2,362
    +1
    41
    With the cam/crank locked, the sprocket sits in a slight retarded position as in, you can just barely see the slot on the left side of the bolt. I tried it with a little more advance, not max but more. Found it to be sort of soft feeling in the mid range RPMs and ended up with about the same 8520 RPM.

  10. #10
    Moderator beerdart's Avatar
    Join Date
    Aug 2006
    Location
    CT
    Posts
    25,930
    +1
    1,407
    No the only way to tell is by the CB shaft alignment marks.

    http://www.greenhulk.net/forums/show...hit&highlight=

    Quote Originally Posted by DaveC View Post
    Just me thinking here, but would that be noticeable when you confirm the crank locked position ?

Page 1 of 2 1 2 LastLast

Thread Information

Users Browsing this Thread

There are currently 1 users browsing this thread. (0 members and 1 guests)

Similar Threads

  1. Low RPM's
    By RedRyderRXP in forum 4-Tec Performance
    Replies: 13
    Last Post: 08-13-2006, 07:48 PM
  2. 06 rxp low rpm
    By rxpenpastu in forum Sea Doo Open Discussion
    Replies: 1
    Last Post: 07-21-2006, 02:25 PM
  3. Low RPM Issue
    By xenonx in forum 4-Tec Performance
    Replies: 11
    Last Post: 06-19-2006, 03:19 PM
  4. fixing my low rpm's
    By MDGPR in forum Yamaha PWC Performance (2-stroke)
    Replies: 4
    Last Post: 06-17-2006, 08:26 PM
  5. New 04 RXP Low RPM & Speed
    By RXP04 in forum 4-Tec Performance
    Replies: 0
    Last Post: 07-02-2005, 09:12 PM

Posting Permissions

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