GEBE 2-stroke mid-range power loss...


Local time
9:53 AM
Jun 4, 2008
Hi all,

I have a 32cc Tanaka 2 stroke engine... unmodified with about 780 miles on it. I ride almost every day, commuting to work so I've gotten to know its feel and accelleration curves.

In the last couple of days I've noticed that I have a loss of accelleration between 19-22 mph on the flat. Once past this range, accelleration seems normal again up to it's normal 29 - 30mph. Accelleration from 8 mph to 19 mph also seems ok. It's just a "flat" between 19 and 22 mph. Its telling me something is different and needs addressing.

I ride only paved roads. I've checked the plug... looks brown and clean... no oil or excess residue. The gas is the same I have been using over the past week. I've pulled the air filter... nothing especially dirty there. Nothing oily. I run a 50:1 oil mix. I don't bother to prime... just takes two to three pulls with the choke on to get it started and it has never failed to start.

Once this week on the way home, it acted like it was going to cut out on me at a stop light. First time it's ever done that. It sputtered a little bit and I gave it some gas and it kept going. Hasn't done it again that I can remember.

The only thing different is that I have a leaking gas tank. The seam opened below the lower mounting bolt and leaks gas ever so slowly. I've ordered a new tank from GEBE and it should be here in the next couple of days. I put epoxy adhesive over the outside of the tank to quell the leak but it only did a little good. So I only fill the tank with enough gas to get me to work so the level is below the leak when I arrive.

Could this have to do with the level of gas in the tank? I wonder. It is lower than normal. Still... why the flat band in the middle?

It's a puzzlement.

I have not removed the spark arrester... don't know how. Nothing on the engine has been modified.

Any thoughts...

Thank you,

Maybe your fuel lines or filter needs changing. You'll probably get that with the new tank anyway so consider that done. If the spark plug is original you should probably change it out or at least clean the other one really well and check the gap. If that doesn't help try cleaning out the carb, maybe it's bogging in the switch between high and low jets somehow. And scrape out the muffler if it has any build up. I doubt you'll have to do this though if you're running 50:1. Check that arrestor anyway to make sure it's not clogged.
I've had a fuel tank leak as well - from hitting the ground at speed - however it didnt cause any changes to the cycles performance.

It sounds a little odd that its causing problems in the middle band - makes me wonder if it is fuel related since you'd expect power loss in the upper speeds if it was fuel stavation. So far as I know the engine has a very simple carb that is non adjustable and doesnt have multiple jets..

I wonder if its something up with the CDI/Ignition unit on the engine (inside the casing attached to the side of the cylinder)

The fuel tank on the Tanaka isnt that hard to remove, but the fuel line is a bit of a pain to get off, the other one you can pull free, but the fuel line needs to be teased off the carb nub.

Jemma xx
Thanks for your suggests ya'll,

I've been considering other possibilities. I carry a fuel bottle on my bike. Since the tank started leaking I have only put enough gas in the tank to get to work so that the level once there would be below the crack in the tank.

Before going home I would use the fuel bottle to put enough gas in the tank to get home. The fuel in the bottle is not likely the same fuel as I have at home. And this is the first time I have used the fuel in the bottle since I've been carrying it on my bike. I wonder if it is fuel related. I don't know... seems like a long shot.

I'm going to wait a couple more days for the tank to get in and install that before I start taking things apart on my engine. I did pull the arrester off thought it did look clean.

How long are clutch pads supposed to last? They aren't likely the problem but I was curious anyway. I'm a big guy... 250#s plus. I keep about 50psi in the tires.

I don't know enough about carboration on a 2-stroke to recognize a problem if I saw one. But I'll get my feet wet if the problem points in that direction.

Will keep you posted.

Thanks for your feedback.

Sirjakesus, I had a cold ride in on Friday. Are you commuting to work? I look stupid enough without adding a snowsuit. :) I got in to work feeling like Dumb and Dumber did riding their "hog".

Haha, No unfortunately I work too far away from home to use the MB for commuting. They're mostly just a hobby for me as I've always loved biking but in its pure form it just takes way too much out of me. I used to spend a couple hours riding my bike for pleasure then I'd have to chill the rest of the day because all the hills here really beat you up.
Maybe you should check out the battery powered heated clothing that hunters use. They're less bulky and I hear awfully cozy. It may be well worth it if you're commuting in the winter.

My issue seems to have wandered away. It's not clear what happened but I don't have the hesitation any more (or maybe I just got used to it :).

It may have been related to the fuel but nothing jumps out at me as to why. The engine is still running strong and I'm a happy camper!

Thanks for the comments and ideas!