Poor Gas Mileage, Need Advice On Getting It Dialed In

Discussion in 'Rack Mounted Engines' started by LabRat63, Feb 17, 2008.

  1. LabRat63

    LabRat63 New Member

    The install was easy, easier than I expected. No problems at all except that dratted kill switch clamp.

    I mounted a 32cc Tanaka from GEBE on a cheap POS bike from WalMart. The bike is a Roadmaster Mt Sport 5X. It has front suspension and a beefy looking frame with large diameter tubes, but it has real sloppy looking welds. I doubt it will last too long, but as long as it lasts long enough for me to afford something better, it was $60 well spent.

    I have gone through 3 and a half tanks of gas so far, and the gas mileage is nowhere near what I expected. GEBE claims 25-30 miles per tank. I figured I would get maybe 20-25 because I am on the heavy side, about 275-280 Lbs. I went to work today to pick up my check. It is 6 miles there, so 12 miles round trip, and that took 4/5 of a tank of gas. A little math shows about 90 MPG where I was expecting at least 140-150 MPG. I think the idle is high so I'll adjust that today or tomorrow. Can too fast an idle cause that big a drop in mileage? Or is it that it is a new engine and it will improve? How far down should I adjust it? To where the back wheel does not turn at all when the back of the bike is lifted, or is that too low?

    I already know I need to have the wheel trued, there is a tiny bit of wobble in it. I have seen the thread about how to get the drive ring centered and using drops of epoxy to keep it there. What else can I do to tweak the performance?

  2. Skyliner70cc

    Skyliner70cc Active Member

    With the load on the engine, I doubt it will get much better. You should fabricate a larger tank. I'd get a Happy Time tank and then use a small 12 volt electric fuel pump (hobby stores sell fuel pumps that safely pump gasoline) to transfer it to the other tank.
  3. kawasaki999

    kawasaki999 Member

    Its probable your gearing, you could go up 1 tooth and try that but you will loose pick up and hill climbing power. I have a tanaka 47r and a 14 tooth gear and I am getting 160+ mpg. your mpg will increase a little when the motor breaks in. yes adjust idle to where the wheel does not spin. hope this helps.
  4. kawasaki999

    kawasaki999 Member

    tanaka 47r

    this is my set up with 1.5 litre extra tank. I get 60+ miles on this tank.

    Attached Files:

    Last edited: Feb 17, 2008
  5. gone_fishin

    gone_fishin Guest

    there's a 1000-mile projected break-in with the tanaka...i wouldn't recommend gearing it "up" until then...my mileage isn't what i expected either, 13tooth, but it's pushing a heavy bike/rider. i'm at 600 miles, and am anxiously awaiting the day when i can put the boost-bottle on it and bump it to the 14tooth.

    no need for a fuel pump with the diaphragm carby...didn't i link you to the aux-tank topic in yer other thread?
  6. kawasaki999

    kawasaki999 Member

    Augidog, If you r running the 35 I dont think u will like the 14 tooth, I am going to try the 13 and I live in flat Florida. The 14 gears me high with the 2.2x26 tires.
  7. LabRat63

    LabRat63 New Member

    A few more questions (Rats do excel at being pesky ya know :) )

    I got the idle set properly now, But I'm having trouble getting the belt to track down the center of the gear. I tried turning the motor and raising one side as in the how-to on GEBE's site, but it didn't work. The belt is hard up against the left side of the gear (as you look at it from the back of the bike). What size of washers do I need to use to shim the gear out? I want to find out before pulling the gear because I have to go buy them.

    The stock brake pads are already shot. Which ones are the best to get? And since I'm sure I can't afford them right now, what are the lowest cost ones that will last for a while?
  8. kawasaki999

    kawasaki999 Member

    You can shim out the bracket at the axcel with washers and if that does not work shim the gear with stainless steel washers, measure the shaft, I think they r 3/8. Cheap pads r at walmart.
  9. skyl4rk

    skyl4rk Guest

    You might want to check if you have dragging brakes or if you need grease in your wheel bearings. Dragging brakes will affect gas mileage quite a bit.
  10. LabRat63

    LabRat63 New Member

    Getting better. The first time I rode to work from my old house, about 7 miles, I had 1/5 to 1/4 tank left. Yesterday, I rode to work from my new place, 9 miles, and back with a side trip of about a mile and had about an inch left in the tank. Top speed so far was 32.2 MPH on a level stretch. A headwind really slows me down though.
    Last edited: Mar 2, 2008
  11. Esteban

    Esteban Active Member

    Just like mentioned above, put many more miles on it before doing anything drastic. Also, remember that the " claimed MPG " from the dealer, is NOT going to be achieved with anything other than slower cruising speeds. Just like a car.
  12. JemmaUK

    JemmaUK Guest

    Flat out on the GEBE 32cc I get about 30.5 to 32mph depending on conditions and slope etc. Im not particularly heavy but I get the impression that the Schwinn cruisers have been built with spare parts from a Tiger Tank - one thing about them is you'll never hurt the frame lol.

    As far as fuel consumption goes I get about 20-22 miles per tank but then I usually ride the bike flat out (im not really that kind to the hardware lol). I am toying with putting some model aircraft fuel in with the mix, only a small amount, to see what happens to performance and have ordered a tuned pipe for the bike as well which should make alot of difference..

    Hope you enjoy the bike - as regards the reliability of the bike concerned - as long as you dont try and do something like jumping kerbs etc you should be ok - its the shocks that hurt welded joints - avoid that and you should be ok

    Jemma xx
  13. vegaspaddy

    vegaspaddy Member

    i currently have about 100 miles on my bike as i just get a chance to ride at the weekends at the moment, i am not sure about the gas mileage but am still have about half the engines tank left in my 1 gallon red jerry tank.

    Check your brakes when i first set it up i had my own too tight the pads were just catching the rims but a couple of quick adjustments and the bike seems to ride better.
    the speedo shows i have clocked at 33 mph riding the 13 tooth gear, but i backed off as the front suspension forks felt pretty fragile, anyhow i enjoy cruising around at the 20 - 25 mile mark, the bike and engine seem to handle better in that range.

    Breaking in, the elders say it takes close to 1000 miles, thats alot of riding but i am going to follow everyones advice and wait before i start putting add ons to the engine. I might try and add a couple of inchs of silcone hose to help quieten down the engine abit.

    kawaski i like the add on tank setup you have do you have it blogged anywhere, if not where did you get the tank, is it gravity fed all the usual questions that rookie builders ask sorry.
  14. kawasaki999

    kawasaki999 Member

    vegaspaddy, I changed tanks , now have 1 gal gas tank from home depot 2.99, not gravity fed, combination pump from carb and pressure from tank. I got a 2 hole grommet and a 1 way valve from any lawn mower shop 4 an echo weed wacker. 1 hole 4 you fuel line the other 4 your vent line with the 1 way valve. The valve lets air in but not out, so a small amount of pressure is built up. Without the pressure a motor will still run ok but top end will suffer a little.
  15. kawasaki999

    kawasaki999 Member


    new tank

    Attached Files:

  16. If you put the bike on the kickstand, and push downward on the handlebars, keeping the front wheel on the ground, pivot on the kickstand until the back wheel comes off the ground, and spin the rear wheel with your hand...see if she spins freely, or not. Try the same with the front wheel...make sure nothing is rubbing...he he he. And yes, a good headwind is worse than a hill for me....really slows ya down.
    Last edited by a moderator: May 7, 2008

  17. Good Point! I'm sure that if I kept it around 20mph, my milage would improve drastically. GEBE is being quite truthful about it, but under economical running conditions.