help with bogging just past idle

[triprop]

pentora 250 with nibbi PE30 that has always run perfect stock. went out and was running great for over 30 minutes and then started to bog real bad just past idle. turned it off waited a couple minutes and started it back up and was running fine, just as i got back to the house it started bogging again. do you think that is more likely a pilot jet or a air/fuel screw thing?

[TominMO]

If it ran fine at first, then later on started bogging, I'm thinking you need to do a valve adjustment. Exhaust valve stem heats up and lengthens, valve doesn't close completely, loss of power. It may be something else, but this would be the first thing to check. Also check the intake valve clearance too of course.

[triprop]

thanks for the reply. i did adjust valves and all seemed fine. did .003" and .004".
i thought maybe i forgot to turn off choke, but no.
i checked plug and its super lean. trying to download pic but not letting me. but very tan tip and white insulator. that needs to be fixed but i dont think that would make it act up or would it? too much air not enough fuel?
whats the first adjustment you think i should do? air screw first then pilot jet then needle, to adjust a lean condition?

[triprop]

a lean condition can be caused by carb not adjusted properly or is it caused mostly by the valves, particularly the exhaust side?

[triprop]

my clamps on air filter were just a tad loose so i retightened them. my concern is theres a general understanding that these chinese machines come from factory running lean. im gonna try adjusting the air screw first.

[ProDigit]

Originally Posted by triprop

my clamps on air filter were just a tad loose so i retightened them. my concern is theres a general understanding that these chinese machines come from factory running lean. im gonna try adjusting the air screw first.

Chinese bikes, like the Vader 150, came way to Rich from the factory. With the stock exhaust that is more restrictive they put a 40 pilot jets in it, which should be a 38 or 35, and the main jet was a 95 which is extremely restrictive.


In most cases having hiccups when your bike warms up, means that your intake valves are adjusted incorrectly. The intake valves should be 0.002" to 0.003".

There is a chance that your pilot or your main jet is too big.
If you don't want to rejet your carburetor, you can lower the needle by one or two clips. Or, you can also close the air fuel screw, giving less fuel to the carburetor. The second option is better if you have a OEM carburetor, that does not have a needle jet adjustment setting.

Your pilot jet will become too big if you remove the restrictive exhaust and replace it with a more open style exhaust. At sea level the pilot should be 38 or 35 at the very minimum. But 40 is quite often too much.