HT mileage and performance comparison

Discussion in '2-Stroke Engines' started by mountain80, Dec 6, 2008.

  1. mountain80

    mountain80 Member

    So for interest sake after taking a stock HT and doing a port and polish, matched manifolds, taper bored carburetor,higher compression, rejetting the carb, cutting the baffle tube changing the gearing from a 40T to a 36T, retapered needle I now have a huge increase in mileage. Granted when I did the first mileage check it had about 600 km and was still a little tight but I now am getting a huge increase. After measuring out a predetermined amount of fuel (4 litres) and having an increased tank size(4l) I ran the tank till she died. Here is the difference:

    Stock 75 miles/Imperial gallon
    improved 114 miles/Imperial gallon

    I ran the tank bone dry and used my electronic bicycle speedometer which I checked against a garmin gps. With my new 4Litre(actually 4.4 litre) tank I ran out of fuel at 160 km or 100.8 miles.

    It has more power AND mileage so one can get their cake and eat it as well.
    Cheers
     

    <
  2. Flapdoodle

    Flapdoodle Member

    Impressive. That is a 52% increase.

    Did you modify the carb, or is it a different one?
    Did you change the needle taper yourself? How is this done?
    Is the bike considerably louder?

    Thanks,
    ~Flap
     
  3. mountain80

    mountain80 Member

    I modified a stock carb. If you look closely at the filter side of the intake you will notice a step or shoulder as it is called. The shoulder is now gone and the bore is tapered inwards for a smooth flow. Yes I changed the needle taper myself. It took a month of weekends polishing and measuring with a digital micrometer as well as testing. I did a lot of throttle chops and marked where the needle position was and marked with a marker while inside th carb bore.Basically from idle to 1/4 throttle it was lean and I have to run it at the leanest needle setting for 1/4 throttle and up for 2 reasons; when you increase compression an engine is more efficient and I live at 4400 ft altitude so I ended up taking the stock.028 jet and dropping it down to .025 thou. Dropping the needle leaned everything out nicely with a tan color on the plug. As far as loud it actualy is respectable, I cut the baffle tube in the cap so it is barely sitting inside the baffle chamber/plates but no more. Another reason I feel for the mileage/power increase is I had custom machined a boost bottle and had carefully include the length of hose to the intake so it matched within 1 cc of the engine displacement. The difference in bottom end torque was huge. Their was a fair amount of porting/polishing as well as the piston skirt being cut to exactly match the intake port. I did not go radical on my porting but made sure everything was matched as perfect as possible. As a last note I used 2 layers of scotchbrite pads for a filter and opened up the filter housing, but soon I may go to an after market filter such as the one from sick bike parts. When I did my mileage test It did include start/stops and full out running for 3/4 of an hour nonstop.
     
  4. Flapdoodle

    Flapdoodle Member

    I am even more impressed. But then we won't get the return unless the effort is put in.

    I would be afraid the Scotchbrite abrasive would come loose and become ingested. I have some furnace filter pad that looks very much like Scotchbrite. For these filters they make a spray that is supposed to make them stickier. The ingredients say it is water and ethylene glycol. Easy enough to make.

    After your success, I will remove about 1/2 of the step on the carb intake and see how that goes.

    Thanks a bunch for sharing all your hard work with us.
     
Loading...