Slow degradation in fuel economy (5th gen)

Discussion in '5th Generation 1998-2001' started by jtherkel, Jul 16, 2014.

  1. jtherkel

    jtherkel New Member

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    When I bought my 1998 VFR800 with 12,000 miles, I achieved 42-44 MPG, depending on how I rode. Now, at 64,000 miles, I cannot get higher than 36-38 MPG.

    I know from the forums that 36 MPG is not the worst in the world, but I know this specific bike is capable of more. Also, the bike seems slightly down on power, although this is my seat-of-the-pants feeling.

    Here's some background info.

    • Problem slowly got worse between 40K and 64K miles
    • Just replaced all 4 spark plugs with NGK Iridium CR9EHIX-9
    • Just replaced clutch plates & springs (unlikely culprit, but it was starting to slip)
    • Air filter is clean
    • No engine error codes
    • Bike has stock gearing, exhaust, etc.
    • No Power Commander malarky :)

    I thought the spark plugs would do it for me. What would be your next step?

    Here are two ideas I was considering.

    1) Fuel injectors
    I could get the injectors cleaned by someone like http://fuelinjectorconnection.com/. But maybe they would leak like this guy's. http://www.vfrdiscussion.com/forum/index.php/topic/58416-fuel-injector-cleaning/

    This company seems to offer "matched" injectors. It's not clear whether they just clean and guarantee your injectors or send you products from their inventory. Anyone ever used them? http://www.factorypro.com/injector_cleaning and matching/injector_clean_match.html

    For my reference, the Honda part number for 5th gen is 06164-PCA-000 "INJECTOR SET, FUEL." Each one goes for $166 on RonAyers.com.

    2) Spark plug wires
    This seems like a long shot to me.

    What else am I missing?

    TIA,
    John
     
  2. Aimbot9000

    Aimbot9000 New Member

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    put some gumout/seafoam/ any other injector cleaner in and see if that helps. clogged fuel filter, bad fuel pressure regulator, brake pads dragging, gaining weight, riding more aggressively as you got comfortable with the bike. I'm sure if your piston rings are worn or valve clearance is wrong they would also affect mileage.

    A more helpful person should be along shortly.
     
  3. Terry Smith

    Terry Smith Member

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    Not sure if I'm the more helpful person. However if fuel use is rising then either the bike is working harder (you're riding faster, or gearing has changed) or it's running richer. From what I've read here the fuel pressure regulator does seem to give grief as it ages leading to higher pressures and so more fuel injected per stroke. After that the sensors like MAP and temp might cause fuel use changes if they misread.


    Sent from my iPhone using Tapatalk
     
  4. marriedman

    marriedman New Member

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    Is your gas being replaced with ethanol? I know when I go through Illinois my MPG plummets with their shitty fuel.
     
  5. TNRabbit

    TNRabbit New Member

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    This^^^^^^
     
  6. jtherkel

    jtherkel New Member

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    Great suggestions! Here are my initial thoughts.

    Clogged fuel filter
    I've got a few bottles of Sea Foam laying around. I'll give that a try first. If mileage improves a little, this might be the issue.

    Bad fuel pressure regulator
    Will look into it if the Sea Foam does not work.

    Brake pads dragging
    I don't think this is an issue. I can push the bike by hand in the driveway, and the brakes are not especially hot, even after a long ride.

    Riding more aggressively as you got comfortable with the bike
    This is definitely the case, but I even get bad mileage on the highway and when riding behind friends at a tame pace.

    Sensors like MAP and temp might cause fuel use changes if they misread
    Will dig into this if necessary.

    Ethanol fuel
    Really? I had no idea this was such a big factor. The next time I pass by a place that promises Ethanol-free fuel, I will fill up and track my mileage for that tank.

    Gaining weight
    You cheeky bastard. I'm working on it. :)

    Thanks,
    John
     
  7. marriedman

    marriedman New Member

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    Oh yeah it is! I have a Scion xB and I go visit my parents in Iowa frequently. If I fill up in Ohio, Indiana, or Iowa - 32 mpg. If I have to get gas in Illinois, 26 mpg. I fricken hate ethanol!

    Also, don't forget winter blends of fuel. On my VFR, if I am riding in the cooler months, mpg will go down to 35 no problem. Scion goes down to about 28.
     
  8. reg71

    reg71 Poser Staff Member

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    Have even worse case or this issue on my 5th gen. Have had SLOVFR and TOE CUTTER both dig into it and I still have a problem. Some of it is the fact I ride in high RPMs so power is always at hand, but there's more to it than that. I still notice a fair amount of popping from the exhaust especially if I am fuel loading then back off the throttle.

    I'm just about to the point of selling the damn VFR. Anyone want a high mileage VFR with lots of additions and a gluttony problem?
     
  9. jtherkel

    jtherkel New Member

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    Update with a happy ending!

    A friend insisted that my problem was clogged injectors. He described a solution that had worked for him in the past with cars. It involved disconnecting the fuel pump and replacing it temporarily with a cleaning solution that had its own fuel pump.

    Following the advice of Aimbot9000 above, I figured if the injectors were truly the problem, a little Sea Foam might help. This is a fuel system cleaner similar to STP / Lucas / Techron, but people seem to prefer Sea Foam.

    The instructions recommended 1 ounce of Sea Foam Motor Treatment for each gallon of fuel. I dumped an entire 16 ounce bottle (!) into my 5.1 gallon VFR tank. If I noticed a small improvement, like 1 MPG, I would spend the money on the fancier treatment.

    On a good day, I would see 38 MPG, and riding assertively would drop the mileage to 36 MPG. My next tank of gas after the Sea Foam treatment showed a little over 44 MPG. The odometer went all the way to 201 miles! I have not seen that fuel economy in two years. This improvement inspired me to write poetry.

    Oh Sea Foam
    My glee has found a home
    You let my motor run free
    Returning its natural state of 44 MPG​

    -John
     
  10. TNRabbit

    TNRabbit New Member

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    LOL! Congratulations~
     
  11. Terry Smith

    Terry Smith Member

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    Thanks for posting this John. I've ordered up a bottle of Sea Foam and will replicate your procedure and hope for the same results. Currently getting 33 MP US gal. Which sucks!
     
  12. jtherkel

    jtherkel New Member

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    Cadbury64, please post back, and let us know your results.

    I should clarify that my VFR achieved 44+ MPG while I was riding behind some friends who were on slow, farting Harleys.

    I have not been able to check my mileage since then because I threw another 16 ounces of Sea Foam into my last tank (hiding my face in shame now). I figured, if it worked one time, why not use another bottle. :) The mileage seems to have held up. I'll know for sure after my next tank.

    My two big questions are:

    1) Where did the deposits in the fuel system start?

    2) Where did they go?

    For #1, I would like to think that this bottle cleaned the tips of the injectors, but it's likely that the fuel filter inside the tank also contained a bunch of gunk.

    For question #2, it's possible that I moved the deposits from the fuel filter to locations inside the motor. I hope instead that the deposits continued out the exhaust, but who knows?

    Since the bike is 16 years old with 65K miles, I feel ok experimenting a little. I really hope the results stick.
     
  13. red rider

    red rider New Member

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    Sounds like thermostat to me. I had the exact same issue. It was the thermostat. It's a pretty easy fix, just time consuming.
     
  14. Terry Smith

    Terry Smith Member

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    I was hoping the thermostat was my problem too, but I have replaced that (the old one was knackered) with no change to the fuel consumption. I'll try the Sea Foam (this weekend hopefully) as it is a low-cost test, and after that I have a new fuel pressure regulator on order.
     
  15. jtherkel

    jtherkel New Member

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    I did not check my thermostat, but I always keep an eye on the digital thermometer in the gauge cluster.

    Normal operating temp seems to be 180 degrees Fahrenheit.

    In slow traffic on a hot day (> 80F), the temp might climb to 220F. The fan usually kicks in around 215F. This seems to match what others are seeing.

    If your engine is running colder than 180F, then your themostat is probably stuck open. If it's running hotter than 220F, then you want to check the fan and its fuse. The fuse blew on mine, and I saw the temp climb to 230F on a hot day. Yikes!

    -John
     
  16. Terry Smith

    Terry Smith Member

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    So I followed John's lead and dumped a full 16oz can of Sea Foam into a full tank. I then rode for 200 km and refueled. Allowing for the volume of the additive, I got 14 km/L which is about normal for me. So no obvious improvement yet. I'll give it another run soon and see if there's any change.
     
  17. Quattro73

    Quattro73 New Member

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    I added 1/2 bottle STP injection cleaner into a full tank ('99 VFR), rode 340 km and refueled 17 L. Quite happy with 20 km/L. My CBR gets 24 km/L when driving nice (and not slow).
     
  18. jtherkel

    jtherkel New Member

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    Cadbury64, I definitely did not get good mileage on the tank that contained the Sea Foam. I rode three days of curvy roads in a row, maybe 300 miles/day. In the middle of the second day, I noticed better fuel economy. Filling up at the beginning of day three, I saw 42 MPG, and I achieved a little over 44 MPG on the ride home.

    Then I put another 16 ounce bottle of Sea Foam into my tank. That tank only achieved 36 MPG.

    Now I am at home, doing the daily grind, not riding enough to figure out the economy. :(

    I will post an update when I have more data. I know the Sea Foam made an impact, but it did not appear immediately.

    -John
     
  19. TNRabbit

    TNRabbit New Member

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    I dumped two cans of Seafoam over 2 tanks of fuel...last check was 44 mpg. After the current tank & once I'm back to straight fuel, I'll post further results....
     
  20. stoops

    stoops New Member

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    I think a bottle of sea foam is in my future
     
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