Results 1 to 9 of 9
  1. #1
    Buplaux's Avatar
    Join Date
    Feb 2014
    Location
    Zionsville, IN
    Posts
    19
    +1
    2

    Help with Identicle gp1200r skis with same carb setting but different a/f ratios?

    Hello,
    First post i have pair 2000 gp1200r i purchased this winter for a project. 80 hrs on both. One lost oil line with previous owner so i completely rebuilt that one. Both went to premix, both have had carb return mod done, all carbs have been completly rebuilt with mikuni parts, stock air box and jetting and d-plate in both. Compression on both skis was good and even across the board (original one was a little lower than rebuit ski but to be expected). Both skis run flawlessly with no bogging or dead spots anywhere in throttle range. Here is my question.. Why does original engine run leaner (according to the plug chop) than the rebuilt engine with carb settings exactly the same? I realize small crank seal leak could be possible but the plugs are all exactly same for all three cyl. Figured they would be diff according to where leak in relation to cylinder may be if that was the case? I set needle arms correct height and kept original springs in all carbs. I dont know pop off but should be somewhat irrelevant because wot plug chop shows same results. Could it be simply because the compression is lower on this ski the pulse is effecting fuel pressure and also a/f ratio? It isnt lean to where i will melt (very light tan) anything but for sure leaner than the chocolate colored plugs on the rebuilt engine. Thoughts on why the difference?
    Thanks, Jeff
    Last edited by Buplaux; 04-30-2014 at 06:29 PM.


  2. #2

    Join Date
    Sep 2012
    Location
    Medina OH
    Posts
    19
    +1
    1
    Plug chop IMO is a general quick reference. I've never had good results using plug chop method. The carbon build up on top of pistons will tell you everything about how your motor is running. No carbon is to rich. Lots of carbon is to lean. Somewhere in the middle is just right.

  3. #3
    Buplaux's Avatar
    Join Date
    Feb 2014
    Location
    Zionsville, IN
    Posts
    19
    +1
    2
    Nobody?

  4. #4
    Almost's Avatar
    Join Date
    May 2010
    Location
    Cape May, NJ
    Posts
    778
    +1
    73
    Did both sets of carbs get rebuilt at the same time?

  5. #5
    Buplaux's Avatar
    Join Date
    Feb 2014
    Location
    Zionsville, IN
    Posts
    19
    +1
    2
    Yes. Same time. Same settings on both sets. All new mikuni parts. Both start and run flawlessly but I cant figure why the difference in plug color between the two skis. I would rather run on rich side for obvious reasons as long as i dont foul plugs. If it was a crank seal i figured it would effect closest cylinder and not the rest. All are the same and pretty uniform a very light tan but not as tan as i would like while the rebuilt engine is coffee or chocolate across the board.

  6. #6
    Lots of factors effect how lean or how rich a given setup is. You have done everything that I or anyone might do to be safe but at this point, if you are concerned about leanness, open up the highs an 1/16 of a turn or less until you mess up the smoothness of the power band or you get the precise shade you are looking for. While manufacturing tolerances are close, each carb can be slightly different. If the compression on a given engine is lower, then you can assume that the carbs might be delivering less fuel due to lower vacuum and flow at a given rpm. You mentioned that you did not check pop off. I agree, WOT is not really effected but if one engine is "popping off" earlier, it could make the general color darker unless you ran WOT for quite a while. I am guessing that you are comparing the same rpm ranges for both motors. Rarely do two engines with the same carbs adjust out to exactly the same number of turns in my experience. I usually start at the same factory recommendation (or Oside Bill's) for the number of turns but until the engine runs the way I want it, the job is not done right. I think you probably know all this but since you asked, those are my suggestions. "when in doubt, take them out" Good luck.

  7. #7
    Buplaux's Avatar
    Join Date
    Feb 2014
    Location
    Zionsville, IN
    Posts
    19
    +1
    2
    I will be removing stinger today and taking the highs and lows out another 1/3 of a turn and see where that puts me.I guess what Im ultimately trying to get at is, is it common for two identicle engines barring the compression and freshness to have different carb settings?. Or does this fact point to a major problem somewhere? I can pull it out if needed but it runs flawless and everything I can check is good.

  8. #8
    After thinking about this overnight, put a "T" fitting in one of the pulse lines and hook a vacuum gauge to it. Compare it to the other engine to see if there is any significant difference. If there is less vacuum, then at least you will know that one engine is slightly different then the other. You might want to consider getting "T"handled needles for the high sides. It eliminates having to take the stinger off to adjust. 1/3 of a turn on highs is a lot but at least you should notice a difference. I am thinking an 1/8 of a turn would be all that might be needed though.

  9. #9
    Buplaux's Avatar
    Join Date
    Feb 2014
    Location
    Zionsville, IN
    Posts
    19
    +1
    2
    Good idea. Also Im kinda thinking the same in regards to less compression less vaccuum = requiring the idle butterflies to be open slightly more than the fresh engine which in turn requires the low screws to be richer in relation to the fresh engine. Is this thinking correct guys?

Thread Information

Users Browsing this Thread

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

Similar Threads

  1. Replies: 1
    Last Post: 05-01-2014, 05:35 PM
  2. Need Help with SLT780 Carbs
    By toddkageals in forum Polaris Open Discussion
    Replies: 5
    Last Post: 07-25-2010, 09:41 PM
  3. Help with a Carb Rebuild?
    By rlacy916 in forum Polaris How To & FAQs
    Replies: 9
    Last Post: 06-29-2009, 12:53 AM
  4. Need help with a Carb!!!
    By AT_Viper in forum Open Discussion
    Replies: 8
    Last Post: 05-25-2009, 09:17 PM
  5. help with 96xp carb tune!!!
    By flyby9er in forum 2-Stroke Performance
    Replies: 2
    Last Post: 08-04-2007, 10:08 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
  •