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No Idle and Occasional backfire on rebuild

H
Jul 18, 2022
5
1
3
Colorado
Finally frustrated enough to swallow my pride and look for some help. We are a family of five and new to sleding (4 years but still sticking to the trails for now). We currently have (2) 2008 Polaris Dragon 800's, (2) 2009 Polaris Dragon 800's and (1) 2006 Polaris RMK 900 (its my "tow truck" :)). When you buy 5 sleds at once to start a new hobby nothing is new or pretty. Last winter I had one of the 2009's go down. Now I am certainly no mechanic, but I love to work with my hands and I figured what better way to get to know my toys then to tear into one and see what makes it tick. That was 4-5 months ago and I have to say for the most part I have had an absolute blast learning about these machines.
OK enough about me!
Started by hooking up a compression gauge to the cylinders and both were less than 30lbs which kind of surprised me because when I purchase it last summer I was told that it had recently been rebuilt and it did have the "Dragon Saver" 1/4" plate between the block and head. But regardless, I pulled the motor out of the 2009 Dragon 800 and both pistons and head was destroyed. I ordered and installed a new Dragon saver kit which included a new plate, pistons, rings, gaskets, injector O rings, and a new head including longer bolts and new stud inserts (pretty standard kit i guess). put it all back together, started it up and the backfire blew dust off my rafters that i am pretty sure had been there since i built the place. I did a lot of research and discovered that i should have checked the TPS reading and also should have changed out the reeds while i was in there...pulled the motor again, still having fun at this point... ordered and installed new reed valves (used the old reed stiffeners from the old reeds), figured since i was this deep i would order a new TPS and a TPS meter from TPS.com. Installed the new TPS, backed off the valves and set to .74, adjusted the valves to .9399 (couldn't get the .94 to happen), cleaned off the orange rubber valves and carbon off the valves, put everything back together and still it will not idle and backfires depending on how i adjust the idle screw. it runs sounds great when it is running. i need to hold the throttle in for it to start. It will not start at all if i do not hold it open. reading this morning i fear that i did not back off the idle screw when setting my TPS (not sure if this makes a huge difference or not??) . anyways if i need to pull the motor again i certainly can (i still have everything taped and labled) but starting to pull the white flag from my pocket. if there is anything that someone can think of that i can check i would love the feed back. if i did something wrong or missed a step please let me know. i am ready to continue to learn but would be great to either figure it out or cough up some $$ to the real mechanic.
thanks for help in advance everyone!
 

retiredpop

Well-known member
Lifetime Membership
Jul 3, 2001
1,350
295
83
Calgary
You need to back off the idle screw for sure to have the throttle plates closed when you start the procedure. If in doubt start the TPS setting procedure again.
Hopefully you did not adjust the synchronizing screw which ensures the throttle plates operate at the exact same time.
It seems some of your voltages are not right. They should be .70V and ,930V respectively, not .74V and .94V.

This is from the increasing your IQ section in the IQ forum.
The baseline calibration IS with the throttle plates closed. This is an independent adjustment of both TB's.

THEN you adjust the TPS to the closed throttle plates at :
900/755 CFi .705 - .715 volts (I shoot for the middle at .710)
600/700/800 CFi 0.70 +/- 0.01 Vdc.

After the baseline is done... THEN you open the throttle plates with the Idle screw to:
2005 900 & 2006 900/755 CFi .930 volts
600/700 CFi .950 volts
2008/09/10 800 CFi .930 volts
All +/- .01 volts
 
H
Jul 18, 2022
5
1
3
Colorado
Thank you for the reply Retiredpop. I misspoke above about the .74. I did adjust to .70 and .94 and i did back off what i now know is the idle screw before setting the .70. At this point I had not touched the synchronizing screw (yes i said at THIS point :mad:). When I reassembled it and tried starting it is when I was getting moderate backfire and no idle. THIS is the point I starting jacking with what i thought was the idle screw and now seeing your reply and looking at page 5.4 - 5.5 in the manual realize that YES I messed with the synchronizing screw (multiple times to be honest ?). looks like I am pulling this beast again and starting over. Ritiredpop is it as simple as steps 9-14 on page 5.5 of the manual as far are removing synchronizing spring, back of the idle screw again then setting to .70, reinsert the synchronizing spring, screw in until i read .710, and then adjust the idle screw to .930 and NOT .940? if that is the case it looks like the first time i tried this with the exception to adjusting to .930 instead of .940 i had it right but still it had backfire and no idle. maybe the idle could have been resolved with the correct idle screw,?, but still had backfire and had to hold down the throttle to get it started. Maybe that is the difference between .930 and .940. any thoughts there? should i put my old TPS back on (only changed it because i figured "since i was elbow deep" at this point)
thanks again for the reply
 

retiredpop

Well-known member
Lifetime Membership
Jul 3, 2001
1,350
295
83
Calgary
Throttle plate synch looks pretty straightforward as per my manual. For some reason I can't attach the file so I will copy and paste the text here.

To adjust throttle plate synchronization, follow these steps: 1. Perform the TPS Baseline Adjustment. The TPS must be set to specification. 2. Carefully back the synchronization screw out so it no longer touches the tab, but do not remove the screw or the spring. 3. Verify the TPS voltage is set to 0.70 +/- 0.01 Vdc. If it is not, re-perform the baseline adjustment. 4. Slowly turn the synchronization screw inwards until the instant the voltage on the multimeter changes. Back the screw out so the voltage reads 0.70 +/- 0.01 Vdc. NOTE: When turning the synchronization screw, do not push the screwdriver with enough force to move the throttle cable cam. Doing so will affect the TPS voltage reading on the multimeter.


As far as the .930 vs .940 voltage my understanding is that setting to a higher voltage reading will increase the idle. I don't think that setting to .940V would cause any problem. I wonder if you are experiencing problems with the throttle safety switch setup. Is your throttle lever free play adjusted to spec.? I have had those little switches act up in the throttle block.
 

retiredpop

Well-known member
Lifetime Membership
Jul 3, 2001
1,350
295
83
Calgary
Finally got my laptop fixed so here is the page from the manual.
 

Attachments

  • TPS Idle and synchronization adjustment.pdf
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H
Jul 18, 2022
5
1
3
Colorado
Thank you retiredpop. I will give this a go. I read another forum and it said to pull out the lower spring below the synchronizing screw and then adjust the TPS to .710 before adjusting the idle screw to .93. I have adjusted my throttlebody to the those parameters but I have not reinstalled it yet so I think I will readjust them to yours first and give it a shot. Thank you for the help.
 
H
Jul 18, 2022
5
1
3
Colorado
Retiredpop, finally got some time to go out in the shop and play a little more. It took me a couple of times but tweaked the synchronizing screw and TPS just right and she fires right up. No backfire, it idles and seems to purr. Going to take it in to a shop for a quick look over before the season starts just for assurance but they should not have to do much. Thanks for the help!
 
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