Fuel economy issue - '02 VFR

Discussion in 'Mechanics Garage' started by jb9573, Nov 15, 2009.

  1. jb9573

    jb9573 New Member

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    My bike - '02 VFR ABS - I'm about 208 lbs.
    Brother's bike - '08 VFR non-ABS - he's about 188 lbs.

    His bike is consistently 3-4 mpg better off than mine when we go out on rides together. We thought his riding style (more tucked behind the windscreen in what he calls his "Superman position" while I'm upright in the wind more often) made the difference, but I tried to mimic his style for a 75 mile Interstate ride today and only eeked out an extra mile per gallon versus another freeway only stint yesterday.

    I get about 36 mpg and he gets anywhere from 39 to 40 mpg. I got 36.9 mpg today on that 75 mile ride being very judicious with the throttle and only getting into VTEC 2 different times for maybe a grand total of 45 seconds on an hour ride.

    My bike also runs cooler by 20-30 degrees. And my bike is a harder to start (crank longer before it fires, best case...maybe give it a little throttle to get it to fire, worst case) compared to his. Lastly, we noticed that my bike has a lot more white smoke that smells like gas on first cold start than his.

    So I'm beginning to wonder if my bike is running rich, too rich, or if this sounds normal. Surely a 20 pound weight difference wouldn't case this, would it? That's only about a 3-3.5% increase in the total bike and rider weight.

    Thanks for weighing in...

    -John
     
  2. TOE CUTTER

    TOE CUTTER Mullet Man

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    Thermostat

    If your thermostat is stuck open it will cause your engine to run cooler and if low enough it will run rich in an effort to warm engine as it thinks it is still in a cold mode.
     
  3. jb9573

    jb9573 New Member

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    Good point. My bike will get hot and the fans turn on (220F or something like that). Just had that happen on Wednesday or Thursday after an in town ride, so I'd think it's functioning properly.
     
  4. TOE CUTTER

    TOE CUTTER Mullet Man

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    What temps do you run at during highway speeds?
     
  5. jb9573

    jb9573 New Member

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    In 150s-160s.
     
  6. TOE CUTTER

    TOE CUTTER Mullet Man

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    That does sound like an open thermostat. I think it cracks between 176 and 178 on mine and never runs below 177 at speed in 40 degree weather.
     
  7. jb9573

    jb9573 New Member

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    1) What do you mean that it cracks between 176 and 178?
    2) Would the motor ever get warm if the thermostat was stuck open? Mine gets warmer at times, but only when I'm running around town and it's warm.
    3) My numbers above are in 55-65 degree weather if that adds to the discussion.
    4) Could a rich running motor cause a 20ish degree lower temp?
     
  8. TOE CUTTER

    TOE CUTTER Mullet Man

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    Crack refers to the first opening of the thermostat . As the engine comes operating temps the thermostat will open slightly and allow the coolant to flow and will close again in an effort to maintain desired engine temps.Not all are the same but most will not open fully until well passed operating temps.If your running in the 150's your are near the point of the V-TEC not coming on due to low engine temp.
     
  9. CandyRedRC46

    CandyRedRC46 Member

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    my crack point is at 172 give or take a degree... if that helps...
    that also seems to be the temperature my bike hovers at on cold days on the highway.
     
  10. jb9573

    jb9573 New Member

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    Could a rich fuel mixture cause the significantly lower operating temps as well as (obviously) decreased fuel economy?
     
  11. TOE CUTTER

    TOE CUTTER Mullet Man

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    I would think it more likely it is running in a cold state longer than normal because it is not coming to operating temp as needed and that is the cause of fuel consumption. It is a common failure for cars as well as bikes.
     
  12. jb9573

    jb9573 New Member

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    I see. My cause and effect could be backwards. The cold motor might be causing the poor fuel economy.

    However my bike is tough to start. So could a motor crank rich enough to not readily fire but opening the throttle allows enough extra air to lean the mix enough to fire? I just don't understand fuel injection enough to reason through that.

    Maybe the startup mixture is controlled by the ECU which would make startup issues completely separate from fuel economy.

    Thanks-
    John
     
  13. Action

    Action New Member

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    If your bike is constantly running cold, then your plugs are never burned clean. You are probably not running rich enough to completely foul the plugs but they are most likely dirty enough to make it hard to start. Bad thermostats are not uncommon on VFR's. Mine would stick partially open. Here is a link on how to replace one

    Tstat Replacement

    Action
     
  14. jb9573

    jb9573 New Member

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    Oh, how happy and sad I am at the same time that I started this post. Happy in that this explains the fouled plugs I found a week after buying this bike used, why the bike started great for a couple of days after putting new plugs in then went back to its old ways, why it gets such poor gas mileage and runs so much cooler than my brothers, and so on.

    Sad in that it looks like I'm taking my bike into the shop this week to sink a little more money in it to get it running correctly.

    But I'm just glad to have an explanation. I think you guys are 100% spot on. Thank you, thank you!

    -John
     
  15. TOE CUTTER

    TOE CUTTER Mullet Man

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    Its not that bad......Three beer job tops. Save the money.....Do it yourself.You will get raped at the dealer.Seriously, its not that big a deal.:thumbsup:
     
  16. jb9573

    jb9573 New Member

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    Action, you were absolutely dead on! Thermostat was stuck partially open. Changed it and now the motor stays in a 172-180 degree range. Plugs were fouled (badly) too and I think changing them has fixed a poor starting issue. I appreciate the recommendation and the excellent instructions for changing the Tstat.

    And ToeCutter, you were right. The job wasn't too bad to do. Thank goodness for a brother-in-law who is mechanically inclined and not afraid to try (or too young and dumb to know better).

    Plus doing the work was much more satisfying than cutting a check for the dealership rape.
     
  17. CandyRedRC46

    CandyRedRC46 Member

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    so problem solved? awesome!!! :thumbsup:
     
  18. Meatloaf

    Meatloaf New Member

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    I wish I would have seen this post originally. The stuck thermostat was spot on. I had the same issue back earlier in the year and it was hard to track down. I was actually getting so much gas down the cylinders that it was massively dilluting the oil. I think someone should make a sticky out of this problem for future problems.
     
  19. jasonsmith

    jasonsmith Member

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  20. madtube

    madtube New Member

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    Maybe this will help. The 08 ECU is significantly different than the 02. All the fuel maps have been changed to compensate for the 600 rpm drop in VTEC engagement. You would be surprised to know all of what needs to be remapped changing something like that. The engineers tweaked all the fuel delivery settings starting in 06.
     
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