TPS switch
  • akpd
    Posts: 6
    Joined: Fri Nov 02, 2018 5:54 am

    TPS switch

    by akpd » Sun Nov 04, 2018 5:31 pm

    2008 CRF250R

    What does the TPS control, spark advance ?
    Charlotte NC

    2008 CRF250R, Grandson's bike I'm the repairer/fixer... LOL
    Work in progress,1968 Firebird resto-mod
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    JimDirt
    Posts: 4406
    Joined: Sat Nov 25, 2006 6:31 pm

    Re: TPS switch

    by JimDirt » Mon Nov 05, 2018 9:46 am

    The TPS tells the Ignition Control Module how far the throttle is open and advances or retards the ignition map accordingly , same way as in a old Chevy had a Vacuum Advance in the distributor , when the engine was working and the throttle was opened bringing in more air/fuel , the points plate would be pulled to spark sooner or later depending on the need of the engine from the extra or less vacuum drawn thru the intake , this works the same way with the exception that it is controlled electronically by physical position sensing where it is , rather than the amount of vacuum drawn to position it , since higher rise manifolds in a car engine had less vacuum than a shorter one , it made this system highly inaccurate , due to the variance of vacuum controlling the timing , which is why all EFI and modern carbs whether on a car or a bike have a Throttle Position Sensors now ..... Vacuum timing control is just too unreliable ....hopefully I did not overload you with info , but that is basically the reason they have them and the main function of them ;) :-k 8-[
    2020 CRF450R
    2006 CRF450X
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    Weiser , Idaho
  • akpd
    Posts: 6
    Joined: Fri Nov 02, 2018 5:54 am

    Re: TPS switch

    by akpd » Tue Nov 06, 2018 2:58 am

    Thanks for the info JimDirt, LOL no you did not overload me with information, I totally understand distributor advance curves, cam lobe separation angles (LSA) & cam duration all of which effect vacuum. TPS sensor signal voltage on todays car/trucks going to ECM with addition of Knock sensor signals, cam trigger, crank trigger... etc etc. allow all the newest technology run in perfect harmony.

    Well to get back on track with my CRF250R issue, do you know if on the 250 can the TPS retard the timing enough to cause backfiring through the exhaust.. maybe just to lean. FYI, the exhaust valves are not to tight. A little history, I just purchased the bike for my Grandson & the bike is hard to start (bump starting only), once started it runs fine but does not idle very well at all. I checked the idle circuit, pilot jet , hot start closes, all good, carb is clean. Checked valves, exhaust .012 & .013, intakes are tight .002. I just received a shim kit and will adjust accordingly. I'm just putting a plan B together (ignition) if the valve adjustment does not cure the issue.

    Thanks in advance.
    Charlotte NC

    2008 CRF250R, Grandson's bike I'm the repairer/fixer... LOL
    Work in progress,1968 Firebird resto-mod
  • User avatar
    JimDirt
    Posts: 4406
    Joined: Sat Nov 25, 2006 6:31 pm

    Re: TPS switch

    by JimDirt » Tue Nov 06, 2018 8:29 am

    Yes the TPS can affect how it runs to a point , but judging by your valve specs , I am going to guess that this is the issue , 0.004 would be a minimum I would be comfortable with , and some actually set them at that , but anything below that and you will start getting the popping and hard starting issues your experiencing .... On a related note , once the valves are in need of adjustment like that , they are on their way out and can last 1 or 2 rides , or 1 or 2 months , but they will zero out at some point soon , so you will need to do a valve job , if he is not going to be racing , I would recommend Stainless Intakes to replace the Titanium if your looking for longevity and less maintenance , they won't really affect performance as long as they are matched with springs to compensate for the extra weight of the Stainless valve

    I run them in my 450R and have raced it with no issues , and I ride it pretty much every weekend at the track , I installed the Stainless 3 years ago and have not had to adjust them since , I also have them in my 450X and installed them in 06 and have not had to adjust them since , you can go with Titanium if you wish , as they have new materials that last much longer than OEM did back then ......That part is up to you , but just be warned that once the valves move , time is minimal before they are done

    Back to subject:

    Adjust the valves , and if you still have popping and starting issues , I can give you all the specs and post testing page images for you to follow directly from the Factory Honda Service Manual if need be to confirm the TPS is working properly and in the correct position .... but if you are planning on keeping this bike , I would recommend getting a Factory Service Manual since you seem to be mechanically inclined enough , you would benefit greatly from having it ....and if you still have questions , this is the place to ask

    One other thing , sometimes just cleaning the jets does not clear them , mainly the Pilot jet , I would recommend just replacing the Pilot , as they are only about $6.00 or so, and that way you know it is clear , it does not take much restriction in them to give the issues your experiencing .....Though I think the valve lash is the primary issue since you gave that info ....... Report back with results from the valve adjustment and we can go from there ... ;)
    2020 CRF450R
    2006 CRF450X
    Image
    Weiser , Idaho
  • Back2-2
    Posts: 1148
    Joined: Tue Jan 04, 2011 3:31 pm

    Re: TPS switch

    by Back2-2 » Tue Nov 06, 2018 2:58 pm

    Check and possible replace your seals and gaskets on the entire exhaust. That is many times the popping on deceleration.

    As for the TPS - I have mine connected on my 450. But as many have found when disconnected the bikes many times run far smoother and better acceleration. I found that on my YFZ and YZF and my Triumph. Just info. - do as you wish on that.
    Neil
    Black Hills of SD
    Life without Motorcycles would just be boring, really boring
    Honda 450X. Yamaha Tracer GT900. HD Fat Boy. Triumph Bonneville. Yamaha Majesty 400. Yamaha Grizzly. Yamaha Wolverine. Yamaha TW200
  • akpd
    Posts: 6
    Joined: Fri Nov 02, 2018 5:54 am

    Re: TPS switch

    by akpd » Tue Nov 06, 2018 6:13 pm

    Thanks guys for all the input. Jimdirt, if the valves don't stay in spec. I'll send the head off to Ontario CA to have it completely rebuilt W/all SS valves, while I'm in there a new piston/rings etc. as well. Service manual is also on my shopping list.
    Charlotte NC

    2008 CRF250R, Grandson's bike I'm the repairer/fixer... LOL
    Work in progress,1968 Firebird resto-mod

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