dirtbike help

[808ridaz]

hi, i have 1985 cr125. the problem is when i go to take off in first gear i have to throttle it alot for the bike to start going as if it had no bottom end. but the mid/top end is great. the bike starts fine. it has a new top end and i just cleaned the air filter and carb. please help!

 

[808ridaz]

i for got to say that when im going around 6 mph and open the throttle, it starts to bog. why?

 

[Jaymes]

Nearly the same thing with my 1986 KX80. I haven't tried it in 4 months, so I can't remember the exact pattern, but it would do it randomly in higher gears/rpms too. I have to give it the right amount of gas at the right time or it will engage and die. My bike also starts relatively easily. Also emits a lot of light blue exhaust until it's been running for 5-10 minutes.

 

[rmc_olderthandirt]

Sounds like a carburetor issue.

You say that you just did a top end rebuild. Was it OK before that? Were there any other changes, such as a new pipe or silencer, since it ran properly?

If you have made some sort of change then it is likely that the carburetor jetting needs to change.

If you haven't made a change then it is an indication that something is going wrong. You also said that the carburetor was cleaned, so I would suspect that you didn't get it back together properly. When you cleaned the carburetor, did you remove the throttle slide from the cable? If so, then I would suspect that you didn't get the needle back into the correct position (it will have a clip that holds it and several spots it can go).

If it isn't the carburetor then I would suspect that you have an air leak. Inspect the rubber boot between the carburetor and engine carefully. Perhaps it just isn't up around the carburetor properly or there might be a tear in it.

Take the carburetor and reed plate off and inspect the reed valves.

It is also possible that a crank seal has gone bad and air is leaking in through the crankcase.

A small air leak will make the engine run lean at low RPM but not bother the top end much.

If everything seems to be OK then you can try adjusting the needle jet. Remove the top cap (where the throttle cable attaches). The throttle slide will come out with the cap. Where the cable attaches to the slide there will be an adjustment for the needle jet. Raising the clip lowers the needle, which makes the mixture leaner. Take a guess and move the clip one position then see if the problem gets better or worse.

Most of the time jetting issues can be resolved with the needle position alone. If it needs more than that, and you haven't changed anything, then I would be very concerned that something else is actually causing the problem.

Rod

 

[808ridaz]

i did get the bike for free from my uncle. i did a new top end my self, since i did it to other bikes and they ran like a champ. the wall looks good. it does have a pro circuit pipe and i dont know if thats stock. if i did have an air leak in my crank case, how would that affect the engine? and am i supposed to have a gasket where the fly wheel is?