'Hunting' when hot

[R_I_C_H_A_R_D]

Hi

I have just bought a 2001 TXT249. After about 15 or 20 mins of puttering around and the bike is nice an warm, the revs seem to climb and fall, almost as though you are giving it little one second bursts of an eighth of a turn on the throttle. It gets so bad that the bike actually cuts out in the 'dips', and if you give it some throttle as the revs fall, the revs pick up pretty slowly. I am running 100ml oil to 5l petrol - Is this correct? (50:1)? I am not sure if this is related, but even when the bike is hot, I still need to use the choke to get it started. I am new to two strokes, but as I type this I think perhaps I should have replaced the plug as a starting measure, but think possibly it is an air screw setting or something else in the carb - but as I said I am a novice so any (simple)advise would be appreciated.

 

[REVERUP]

Sounds as if it may be a piece of dirt or crud in your carb. Drain your float bowl first see if that helps.
If not pull the carb and clean all the jetting circuits out with a shot of compressed air or a stream of carb cleaner.

Good luck,
Roscoe

 

[RBD]

Richard,

Look for an air leak around the carb to engine and reeds, also check around the base gasket area.

Ron

 

[gasser]

First that's a lot of oil to be running in a trials bike. Most people run synthetic oil at 80 to1 or 100 to 1 in trials motors.
As for your problem my xc300 had much the same symptoms when it was overheating so check your water level and look to see if it's flowing in your radiator (remove the cap before the motor warms up then let it idle till the water is hot and you should see water movement when you rev up the engine - works that way on a car anyway). One last note too much oil in the gas will cause the motor to run lean which will also cause it to run hotter. Hope this helps. - Ken

 

[RBD]

I am not sure if this is related, but even when the bike is hot, I still need to use the choke to get it started.

It still sounds like a lean condition to me.

Ron

 

[R_I_C_H_A_R_D]

Hello

Thanks for all the responses!

REVERUP, I'll give the carb and jets a clean as you suggested(I've just got the bike, so have no idea when last it was cleaned).

RBD, how do I check for an air leak around the carb/inlet manifold. Now that you say that, I did notice the rubber was very slightly perished, so maybe if I look properly I will see something that is visible to the naked eye, but if not how does one detect a leak? Also in your second post, you say running lean, could this be the air screw setting? I checked out some articles on this site on how to set the air screw, so maybe I will play with that too and see what happens?

gasser, the bike has a brand new fan on the radiator, but I never thought of checking the flow of water, so that is definitely something I will check. I stopped riding when the 'dips' in the revs were almost cutting the motor, coz I was worried I was doing damage. Re the oil mix, if I understand what the manual says correctly 1,5% would mean 1.5 to 100 (which if my math is correct, would be about 66:1??? - and this would also mean I am using too much oil) I was given different advice on whether to use synthetic oil or not, so ended up just buying the standard two stoke stuff they had at the Mobil garage. Perhaps not the right thing heah? Also, I don't know if the way one is riding will have an impact, but at the moment I am really just noodling around on the bike getting used to the feel of it, so seldom opening the throttle past 1/4 turn

 

[stay_upright]

I can get something similar on my 2t enduro if the bike is fully hot and too lean on the air screw. Try turning it in 1/2 turn at a time to see if that cures it.