Page 1 of 2 12 LastLast
Results 1 to 10 of 11

Thread: Not making it on fuel 2 hr race?

  1. #1
    KTMTalk Member
    Join Date
    Mar 2008
    Userid
    89887
    Location
    Watertown Tennessee
    Posts
    179
    Blog Entries
    2

    Default Not making it on fuel 2 hr race?

    Son ran out of fuel for the first time on my watch. I should have stopped him for fuel but was just one of those days.

    We are running a 2019 TC150, IMS oversized tank, keihn carb.

    Hard to believe there can be such a variation in fuel consumption between riders and similar bikes. Others are finishing with plenty of fuel left. We have ran multiple jetting with stock and now a new keihn. We can do some races on a tank but are on the razor edge of running out.

    Anyway, not looking to change jetting, float levels or an electron carb. But I'm thinking he may be losing a bit fo fuel early on with the ful tank by squeezing it out with his legs. Not sure if it would even be worth the effort but I thought I read somewhere that guys were installing a 1 way valve in the overflow hose to prevent fuel from being pushed out?

    Any thoughts or ideas to save a bit of fuel for those oh-so-close races. Last season, we could afford to stop and fuel, this season, I expect to possibly lose a position for stopping.

  2.    Sponsored Links



    LOGIN AND CLICK THE SHOP ONLINE LINK FOR THE DISCOUNT


  3. #2
    KTMTalk Member 3rdGearPinned's Avatar
    Join Date
    Jan 2006
    Userid
    49315
    Location
    Bend Oregon
    Posts
    3,328

    Default Re: Not making it on fuel 2 hr race?

    Got your overflow hose looped?

    Could add try to slightly inlarge the tank with hot water and a few psi of pressure..

    Sounds like itís time for a dry break.

  4. #3
    KTMTalk Member
    Join Date
    Jul 2002
    Userid
    1162
    Location
    waterford Michigan
    Posts
    3,332

    Default Re: Not making it on fuel 2 hr race?

    Depends on the soil for me
    sand sucks the fuel
    16 150sx
    can normally go 2 hours on 2.6 g xc tank
    gearing 13 50
    2016 ktm 150sx set-up for mx & offroad

  5. #4
    KTMTalk Member
    Join Date
    May 2004
    Userid
    20380
    Location
    Wilmington Delaware
    Posts
    666

    Default Re: Not making it on fuel 2 hr race?

    Real question is what did you loose by not stopping and running out?

  6. #5
    KTMTalk Member
    Join Date
    Jan 2015
    Userid
    164042
    Location
    Albuquerque NM
    Posts
    166

    Default Re: Not making it on fuel 2 hr race?

    Sounds like the Stewart Baylor problem. He has often complained that he cannot get the same fuel economy as his competitors. From him, contributing factors are his size (bigger and heavier), riding style (on/off as opposed to carrying momentum through the corners), and bad starts forcing more consumption to get to the front rather than getting the hole shot and managing the distance to second.

  7. #6
    KTMTalk Member
    Join Date
    Mar 2008
    Userid
    89887
    Location
    Watertown Tennessee
    Posts
    179
    Blog Entries
    2

    Default Re: Not making it on fuel 2 hr race?

    Dry break would be nice, just money, right? Thought about it when we ordered the oversized tank but i got cheap. Not juts the fuel tank, the gas can to go with ain't cheap.

    Haven't head about looping the vent hose? How does that help?

    Only reason I thought about some type of check valve, one time, just before a race, I filled the tank to the brim, he jumped on the bike and was getting ready to take off, I panicked when I saw liquid running down the frame, did not know what it was at first. It was fuel gushing out of the vent hose where he was squeezing the tank with his knees. Not sure how much would actually push out before it got down low enough to stop.

    I had heard about slightly pressurizing a warm tank to get a few more cups of fuel, just haven't tried it out yet.

  8. #7
    KTMTalk Member
    Join Date
    Jun 2014
    Userid
    159601
    Location
    Terre Haute Indiana
    Posts
    375

    Default Re: Not making it on fuel 2 hr race?

    I know you said you have tried different jetting and don't want to mess with that, but on my bike the fuel mileage difference is crazy with different needles. I can finish a 2 hour race without stopping for gas now that I have changed needles. I actually run a bigger pilot and main than I did on the other needle that got the terrible fuel mileage

  9. #8
    KTMTalk Member
    Join Date
    Feb 2019
    Userid
    182075
    Location
    Temecula Ca
    Posts
    599
    Images
    6

    Default Re: Not making it on fuel 2 hr race?

    A check valve in the vent line is cheap and easy, check the ends of the carb vent lines after a hard ride for fuel if your loosing any to overflow it should show, like one of the other people sad ridding style and weight well also make a difference. Heck it could be any of the above or a little of everything. A quick way to tell if heís squeezing it out with his knees is to tape a small bottle to the vent line fill the tank and have him ride a few minutes and check it.

  10. #9
    KTMTalk Member
    Join Date
    Jan 2004
    Userid
    14241
    Location
    Forest Floor
    Posts
    1,032

    Default Re: Not making it on fuel 2 hr race?

    If itís knees then he must go through riding pants often? My guess is the fuels expanding. Two hours should be possible on a stock tank for woods type use. Are you riding WOT desert/sand?

    I agree on the needle having a big influence on fuel use. Thatís where Iíd be looking and the float levels to make sure itís not just pouring out the bottom vent.

  11. #10
    KTMTalk Member JamesDean's Avatar
    Join Date
    Apr 2002
    Userid
    616
    Location
    Olympia Washington
    Posts
    4,798

    Default Re: Not making it on fuel 2 hr race?

    Route the bottom float chamber vent/overflow tube as pictured. Turn the fuel petcock to the OFF position when storing the bike. This vent/overflow hose is not used on the Lectron or Smart Carb, and that contributes to those carbs getting better mileage in situations like this.

    If there has been a significant reduction in mileage , then the float needle isn't holding the fuel back in rougher riding conditions and it may be sticking open. Replace the float needle and lower the float level 1-2mm as a preventative measure. The float should angle slightly away from the chamber's sealing surface at that point, while holding the carb at a 60 degree angle from inverted.



    The Keihin PWK carb float height check is below-



    Mikuni TMX float measurement-

    www.JDJetting.com
    JDJetting support- Tech@JDJetting.com
    '21 KTM 500 EXCF w/JD EKI Tuner
    '18 TE250i TPI, Now a 300i, JD EFI 250/300 Tuner
    '18 300 XCW - Mikuni TMX JDJet Kit (S-4 Needle Jet), Jet Block Gasket Fix
    '17 FE450 w/JD EFI Tuner
    '08 530EXC FCR Carb Kit, Dual Spray Accelerator Pump, Motard Wheels

Page 1 of 2 12 LastLast

Similar Threads

  1. Race fuel? What octane? what kind? (fuel questions)
    By rbozz837 in forum Oil, Gas and Coolant - PreMix, Crankcase, Gearbox oil (2 strokes and 4-strokes) and Coolant
    Replies: 1
    Last Post: 04-16-2010, 05:09 AM
  2. Replies: 22
    Last Post: 02-12-2010, 07:12 PM
  3. Dirtbike Fuel Guage (making one)
    By loghopper200 in forum General Discussion (PUBLIC)
    Replies: 24
    Last Post: 05-20-2009, 05:00 PM
  4. 65 compression/squish and race fuel (when do you NEED race fuel)
    By cr rev in forum KTM 65SX, 85SX and 105 SX
    Replies: 7
    Last Post: 12-28-2007, 06:23 PM
  5. Race fuel vs 93 octane pump fuel in a 2 stroke...
    By RiderX in forum Oil, Gas and Coolant - PreMix, Crankcase, Gearbox oil (2 strokes and 4-strokes) and Coolant
    Replies: 15
    Last Post: 09-12-2006, 12:22 PM

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •