Results 1 to 5 of 5
  1. #1
    Sly Fox DKFox's Avatar
    Join Date
    Feb 2009
    Location
    Huntsville, Alabama
    Posts
    103

    787 backfiring through flame arrestors at 3/4+ throttle

    1998 SPX with 787 engine. Fairly new machine to me.

    Has MSD ignition enhancer, PROK flame arrestors, and PSI exhaust. It also has a brand new SBT rebuilt engine in it. (I know... I know... lets don't argue that here. Its already bought and in the watercraft.)

    1.) Put the engine in late last year. Don't know if I can trust my pressure gauge totally... but reading 150 psi in both cylinders. (Wish it was slightly higher pressure, but no difference in them which is good.) Broke the engine in at the end of last year with light riding, then parked the watercraft for the winter.
    2.) I'm using the standard MSD dip switch settings.
    3.) I don't remember the exact carb jet sizes I used (because I have 4 other skis I worked on at the time)... but I remember them being larger than normal.
    4.) I rebuilt the carbs with Mikuni parts. Pop off pressure was in spec. Cleaned the whole fuel system. It does not have the grey fuel hoses. I swapped those out early last year before my original engine went belly up. (Cooling hose had popped off.)

    Took it to the river yesterday. It runs great up 3/4 throttle. Anything above that it didn't really rev up any more and ran rougher. Would smooth back out if I left off the throttle and held it to no more than 3/4 open.

    After putting new spark plugs in, I put in on the water hose this evening. Noticed that its backfiring through PTO side carb flame arrestor at any throttle over 3/4 open. (The old plugs were too black. Not wet... but not the good dark brown either.)

    What do I check next?
    Thanks in advance.


  2. #2
    This is how I run a jetski shop in the desert nmpeter's Avatar
    Join Date
    May 2008
    Location
    Elephant Butte New Mexico
    Posts
    6,529
    +1
    1,276
    I'd bet the rv is off a tooth or two

  3. #3
    Sly Fox DKFox's Avatar
    Join Date
    Feb 2009
    Location
    Huntsville, Alabama
    Posts
    103
    Yeah... I was wondering about the RV too and second guessing myself. I used a new RV and checked the degree settings 3 times before I buttoned it all up and installed the engine. I called it "good" all 3 times. (At TDC.) I've done that procedure many times on other skis I own without any problem.

    I'm wondering more about the MSD ignition enhancer being set correctly. I've got really good spark, but the timing is adjustable over a wide range with those dip switches. However, if spark timing was off it would affect it over the whole range of throttle, right? Not just 3/4 +.

  4. #4
    Tool Bag water worx's Avatar
    Join Date
    Aug 2006
    Location
    Sunny Fla
    Posts
    1,925
    +1
    66
    Probally hitting the rev limiter.

  5. #5
    LPG256's Avatar
    Join Date
    May 2009
    Location
    NOBLESVILLE, IN
    Posts
    77
    +1
    6
    Def sounds like timing. Find the directions for msd and start at stock.
    Also, with 1st back fire, possibe it sheared brass gear, r.v. Could be off just enough

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. FS - Parts Aftermarket Flame arrestor for dual carb'd 787/717/657 seadoos
    By thetolleyman in forum Sea Doo Classifieds
    Replies: 1
    Last Post: 11-14-2012, 10:39 AM
  2. FS - Parts FS: Rossier Pipe and Composite Flame arrestor for Seadoo 787/800
    By thetolleyman in forum Sea Doo Classifieds
    Replies: 3
    Last Post: 10-07-2012, 06:43 PM
  3. Jetting Info for 787 with Aftermarket Flame Arrestors
    By Team Bilford in forum 2-Stroke Performance
    Replies: 2
    Last Post: 07-14-2011, 10:32 AM
  4. FS 787/800 R&D Powe Plenum Flame Arrestors
    By ultramaxracing05 in forum Sea Doo Classifieds
    Replies: 1
    Last Post: 05-28-2010, 02:54 AM
  5. F/S 787 Injection pump/stock flame arrestor
    By ultramaxracing05 in forum Sea Doo Classifieds
    Replies: 0
    Last Post: 08-29-2009, 03:58 AM

Posting Permissions

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