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Thread: Carb Help

  1. #1

    Carb Help

    I feel like I'm hounding everyone here with all my problems! Spent 3 hours at the lake shoreline this morning. I was hoping to get my rebuilt, EVERYTHING DONE TO IT '93 650 tuned up and start the break-in! New top end yada yada yada, everthing!! All Compression excellent and even. Problem: Center cyl only firing? MAG and PTO plugs soaked with fuel/oil mix. Used my spark checker and all getting spark. Since center cyl is firing fine, I moved center plug wire to both MAG and then PTO, no fire! Finally came home, ripped carbs off and went thru them again. All pop-offs are good, all holes, jets, pathways clean. All are new parts from OEM Mikuni kit. Before I put it back on, is there any way to check if there are any other problems with the catbs! Reeds are new, I did a leak-down, it was good! Is there anything I can check with the pump hooked up, but carbs not mounted? It will run on just the center, but obviously not real well. If the MAG and PTO plugs were dry, I would be happier, but they are obviously getting fuel, just maybe too much! I do have clear, new fuel lines and I see some bubbles that don't appear to be moving thru the lines very fast as its running or I'm cranking? Also, the clear fuel filter approx 12" before the pump only fills up about halfway up (laying sideways) as it's running! Somebody solve this!


  2. #2
    Click avatar for tech links/info, donation request K447's Avatar
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    If you don't have ignition at PTO and MAG spark plugs but you do have ignition at CEN then something is wrong with the ignition system.

    On a Fuji engine all three spark plugs fire together every time any cylinder needs spark. Recheck the wiring for the ignition stator, coils and the CDI. My guess is that the CDI is only firing for the CEN cylinder and is not getting a signal from the stator for the other two cylinders, or something like that.

  3. #3
    I thought of that, that's why I tried the known working plug wire on the other two cylinders. I also put my spark checker on while at the lake and all 3 fire. I might think that maybe the other two sparks were weak, but if that was the case, either would fire when I put the center plug wire on them!

  4. #4
    Click avatar for tech links/info, donation request K447's Avatar
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    The timing of the spark is important. If the only trigger that is firing the ignition coils is the signal for the center cylinder, then putting that plug wire on the other two cylinders won't work because the spark is not happening during the compression stroke on that cylinder.

    For each cylinder not only do you need spark, you need that spark to happen at the right time. It sounds like the only TIME the plugs are actually sparking is when the center cylinder needs spark. When the other two cylinders need spark it is not happening.

    Or something else very basic is wrong, like no compression or broken reeds.

  5. #5
    I'm under the impression that in these olde machines, each wire fires every time one of the cylinders needs one! In fact, there's an instruction video from one of the major PWC dealer/repair shops where they put one working wire on each cyland they all fire fine when they have the working wire on each plug?

  6. #6
    BlueFishCrisis's Avatar
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    True, but what K447 is getting at is that even though each plug fires every time the CDI tells it to, which is 3 per rotation, if the CDI is only telling the plugs to fire one of the three times, the cen cylinder will fire on all three wires, but the others will not because they will not be in compression ready for spark. You mentioned compression is fine. Have you ohm tested your stator? What is the condition of your flywheel magnets? Finally, may need to test with a known good CDI to see if the CDI is failing.....

  7. #7
    OK..I understand. I have a family deal today so I will start checking tonight! I hope it's not the stator because on my "93, it has the hull support in front of the stator so I'd have to take the entire engine out AGAIN! I checked all the readings when I took it out at the beginning of this overhaul, but since then I have added a fuel gauge and RPM gauge so maybe something was not reconnected properly. First I am going to check the spark jump like in the video on the "what to check" fuji engine site. Judging from my spark checker when it's running on the center cyl, I would say it's firing 3 per cycle, but maybe not?

  8. #8
    Click avatar for tech links/info, donation request K447's Avatar
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    Disconnect that recently installed RPM gauge from inside the electrical box. It is possible that it is interfering with ignition somehow, or that something got disconnected or reconnected incorrectly when it was installed.

    I would not expect the newly added fuel gauge to make a difference to the ignition, but stranger things have happened...

    A timing light can tell you if you are getting three sparks per crank revolution. Put some tape on the PTO coupler and mark TDC for each piston on the tape. Put a unique hash mark next to each cylinder TDC so you can see if all three cylinder marks are getting strobed.

    If you want to be more precise you can measure the correct piston positions for spark advance and mark the tape. Fashion a pointer from wire attached under a nearby nut.

  9. #9
    OK...(++ Note..carbs are off, can't try to run at this point)

    ....did the tape around the PTO coupler! Used 1' blue tape. Put a dot at forward edge of tape when mag was at TDC. Put a mark in center of tape when center cyl at TDC and a makr at rearward edge of tape when PTO at TDC. so I have three dots spaced evenly around the coupler.

    Put timing light on the center plug wire and turned engine over. All 3 dots light up at same time, nice and bright, in a straight row.

    Put timing light on PTO and light is intermittent, with some of the dots appearing, others not and then vise versa. As I manipulate wire, the light is intermittent! Mag cyl gets nothing. If I move the center spark plug to the Mag, I get all three dots!

    Conclusion = need to replace plugs, which are pretty new...AND the wires and then see what happens and go from there!

    Do the plug wires :twist/push into the coils?

    Can I use auto wires and cut to length and if so, what type, size, carbon, wire???
    Last edited by K447; 09-01-2012 at 08:46 PM.

  10. #10

    It's fixed..tnx k447

    After all the work I've done, it's finally fixed, thanks to the suggestions from K447 re: putting tape around the PTO coupler and marking TDC's.

    I then used my timing light and discovered that cyl #1 and 3 were intermittent. When I used my spark tester at the lake shoreline, it showed that I was getting spark on all 3, but after using the suggestion from K447 in my garage, the problem was easily "seen" with the timing light.

    I would see all 3 dots lined up nice and straight and then one or more would disappear, then return etc etc etc.

    I press the starter button now and it starts up immediately and runs like a top! Now I can take it tomorrow morning and actually tune the low screws, then run the first two break-in phases and then check the high screws.

    My initial settings are 1/8th turn higher than spec at all screws. Since the recommended first two break-in procedures involve not more than 20% throttle, I figure I don't have to worry too much about my high speed screws or burning a piston. Any suggestions re: my initial startup/tuning/breakin would be appreciated!

    I've been posting on here for several months and have probably read almost all the polaris threads, plus a lot of the others after searches! I can't say how much I appreciate everyone's help and this forum! Thanx to all.
    Last edited by K447; 09-02-2012 at 01:48 PM.

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