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  1. #1

    Full Circle Crank Project

    I got a few runs in before the season ended and I will describe how it went. The machine I installed it in is a 2000 pro 1200 with triple factory pipes, 48 novis, v-force reeds, and ported msx cylinders. I am running 2 base gaskets and 48 cc heads. The squish was around .068" and compression was 135 psi. I wanted to run more compression but the other heads I had would have had the squish too tight unless I ran a lot of race gas. Initial timing was high on the bottom end and around 13 on top. I also ported the cases while it was apart. First run after a 1/2 tank break in was not good. Ran real rough down low and would only pull 7570 rpms with a stock 707 impeller. Loaded on the trailer and left it in the water. Took the flame arrestors off and the mag. and center carbs. were dribbling really bad at low rpm. Out of time and will continue post later and post pics.

  2. #2
    Rasta Mon Condoms We Be Jammin!!!!! TxPro1200's Avatar
    Join Date
    Aug 2006
    what direction are the carbs facing?? seen guys turn them with the dia.'s pointing out instead of towards the motor

  3. #3
    Connecticut CrazyA's Avatar
    Join Date
    Nov 2005
    Sounds like a nice project. When you say Factory triples, do you mean Factory Pipe Products or Polaris Factory Racing triples? What headcover are you running? Have you tried doubling up the check valves?

  4. #4
    Factory triple pipes and the diaprams are facing forward. Got some timing info. from just pinch it and lugs. Installed a box that had less timing at the bottom and 15 at top. Started on trailer and no dribbling until coming back down from high rpm. Even the middle carb. would do this which it never did before. Then I thought I better check the fuel return pressure. Every year I check it at the beginning of the season and it has always been 2 psi at idle for the last 3 years. Well with no carb. changes it was now at 3 psi. Went from a 125 return jet to a 155 to get it back to around 2 psi at idle and 5 at throttle. Put it in the water and was totally surprised when it was hitting the rev limiter hard at 7700 rpm. Richened jetting up to be safe and thought when the engine was heat soaked it wouldn't bump the rev limiter, but it still did. Couldn't do any carb. tuning that day.

  5. #5
    Installed my original 202 impeller and the rpm was at 7640 so I was then able to do some carb. tuning. Still has a slight dribble on the mag. carb. but better than it ever was before. Initial assessment of full circle crank is that it is smoother in all areas except at 2,000 rpm. At 2,000 rpm it really shakes the handlebars. Next year after more carb. tuning I will be able to compare it to my virage tx for engine smoothness. Topend was 73 mph setup for smooth water and low on gas. This is the fastest it has ever gone and it pulls about 100 rpm more than it did before. When it was stock with that same impeller it ran 62.5 mph at 6650 rpm.

  6. #6
    She likes the bike. But the ski gets her wet!!!! xlint89's Avatar
    Join Date
    Oct 2006
    Cleveland OH
    Nice results.

    Like Crazy mentioned, have you doubled up on the anti siphon check valves? (clear plastic flaps on back side of the jet block)

  7. #7
    I have been running 3 check valves for the last 3 years which definately helped. On the trailer in the water with the mag. flame arrestor off, running in the 2500-3500 rpm range, you will see where it spits fuel back slightly from running too rich from the dribbling. Other carbs. show no sign of this. Just enough to cause it not to run as smooth as it should. Around 4,000 rpm is where the high speed circuit kicks in normally.
    I like running the 707 impeller better than the 202. The 202 loads the engine a little too much right where the pipes just start to come into power. I ran a 7.5 before and it pulled easier in the midrange than the 202. I bent the trailing edge down about 3/16" on the 707. It would slip it off the line and would still bump the rev limiter slightly. Ran 72.4mph at 7700 rpm. At 7700 rpm this engine is still pulling good. I need to get it to bite better down low and run less rpm on top. I'll have to send it somewhere since I don't have the experience to know what to

  8. #8

    Join Date
    Aug 2006
    Homer Glen Il.
    Last edited by 785 lugs; 11-15-2011 at 04:57 PM.

  9. #9
    Sounds cool

  10. #10
    Next summer I will have more time to dial it in and do a direct comparison with my stock virage tx for engine smoothness throughout the rpm range. I had 142 hours on the original crank so I thought it was time for an inspection of the crank anyway. I got to burn 2 tanks of fuel through it and am happy so far. The highlight of my short season was when I was heading back towards the ramp and I saw a jetski coming towards me in the wfo position. I got turned around and got up on plane, waited for him to get closer and hammered it. Passed him up by a good 5 mph in a short distance. When I stopped and he stopped to chat he was amazed at the acceleration of my machine. He asked what it was and what size was it? I said a polaris 1200. He then asked if it had a suzuki engine in it. Asked what it ran and I said low 70's. He had a gpr 1300 that he said ran in the low 70's too, but I had 400 pounds on him and he had a full tank of gas. About that time his friend went by on a stage one gpr that suppossedly went 80. He then went and caught up with his friend and they started chatting. They had to come back by me because of the lock, so I waited for a good 20 minutes for the stage one to come over. Gave up waiting and went over to him. Well he wasn't very talkative and fired up and left. I know gpr's are extremely fast, but I couldn't get this one to make a quick run

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