Vintage Dirt Bike Q & A

OK so I go to start my MT 250. It starts in about 3 to 4 kicks. It idles around 3,00 rpms for about 5 seconds then all of a sudden revs to as high as it can. The kill-switch does nothing and when you open the throttle the engine dies.

This is my first motorcycle and everything that I have done to this bike so far is from advice from the internet, some friends and the manuel I ordered. I bought the bike in the beginning of this summer. When I piked it up my dad test rode it for me, he got it to third or forth and then it ran out of gas. It seemed to run fine, I asked my dad how it felt, he said "like an old bike". So we take it home and I stare at it for a day or two and then I decide to take it for a spin. I already put a little gasoline in when I first got it can just to kick start it a couple of time to show my mom and her bf, but for some reason I decided to add a little more and to my surprise I was unknowingly adding pri-mixed fuel for the weed wacker. Then it wouldn't start unless the throttle open when I kick started and it would "idol" only f the throttle was half open. So I drained the fuel and put new fuel in. It ran but there was a terrible lag in the opening and the release of the throttle and had random hiccups that would rev the engine. I took it for my first test run and it almost threw me into a tree! I did some research and, got a carb rebuild kit, cleaned and rebuilt the carb. I was ready to test run again. Everything went smooth, I did a couple of laps then I decided to shut down the bike, I start the bike back up and this time it decides to rev, and not stop. I flick the kill-switch, nothing happens. I shut the fuel, nothing happens. I pull the key out, nothing happens. I pull the wire for the spark plug out, nothing happens and I'm freaking out. Every time you would pull the throttle it would rev at a high rpm. I panic and pull the fuel line, I make the petcock lose in the process, so now fuel is leaking out and my bike idling super high, the bike dies on its own in about a minute. So I refasten the petcock and take at a look at the carb again, it turns out that I messed up the order on the jet needle set and I didn't fasten the jet needle under the valve plate, so it wasn't being forced back down from the closing of the throttle. So with that fixed, and a newly installed fuel filter to the fuel line, and a new air filter I was ready for action. But now I am stuck from where I stand now and I need help.

I've had this bike for too long for it not to be running already, I have made allot of mistakes along the way but I am happy that now I understand much more then I ever would have if everything went perfect. I have take an motorcycle corse and have my license, the bike is registered, all thats left todo is to get this thing running! I want to at least ride this thing in fall. It is a shame to see such a pretty bike just sit there. PLEASE HELP, thank you in advance.

Mason

With a bike that old I would suspect leaking crankshaft seals on the erratic revving. If the kill switch doesn't work, you have electrical problems. Take the time to trace all wiring and make sure each component is working.

Before my bike decided to go crazy, when I was capable of test riding it, the kill switch did work. Do you think it just went then? or do you think this is anther issue?

I don't know if you solved this already or not, but here is my experience/impression.

The bike will run faster leaner that rich. I mean it will rev. If/when you run out of gas some time, you will find it lurching and if you pull in the clutch it will rev like the dickens. Before storing, I will sometimes try to run the motor with the petcock off so that the carb is empty when I turn it off. The thing is, once it is running on fumes, it revs up to the limit, and you can't shut it off. It begins dieseling because the combustion chamber is so hot. You can pull the spark plug wire, turn off the key, etc. It won't matter. If you turn on the gas and flood it, it will die.

So, what you describe sound to me like a motor being starved for gas.

I am not sure why you are stuck now that you have put the carb back together properly.

If I were you, I would first, make sure which way the fuel flows with the petcock positions (just let it drain into a cup), make sure it flows smoothly and shuts off.

Next, grab the shop manual on the honda-elsinore site in the manuals section, and go through the routine maintenance and make sure everything is in good order. Pay particular attention to making sure the oil pump is pumping.