Strange engine behaviour on aprilia rs 125

[ice.shark]

Hi,

The following is happening and I find it a bit strange. In the current weather and on my current 3 mile commute my bike warms up to about 50C. I close the choke and then it idles at around 1200rpm. After some riding, when I stop and let it idle (it idles OK and doesn't die) and then I proceed to take off, the bike cannot gain higher rpm. When I give it throttle rpm goes to 2000 (engine sounds deeper) and if I don't let go of the throttle it will die. I will not go above 2000 rpm whereas normally with that much throttle it would be at 4k-5k. The only way out of this is to open the choke. while idling and then engine works OK.

I have no idea what is causing this. Bike is running OK otherwise (as far as my perception of OK goes) but when I stop, I need to open the choke or when I try to take off, engine will die when I open the throttle.

I found this which looks like a similar problem but I don't know where these throttle hoses are on aprilia rs 125 (2005):

https://www.apriliaforum.com/forums/showthread.php?260503-Engine-dies-while-idling-and-throttle-is-quot-blipped-quot

[Kickstart]

Hi

Sounds like it is lean at low throttle openings. Also, does it die if ridden for a decent distance (ie, 3 miles isn't that far).

Would suggest whipping the carb off an giving it a clean. Check the position of the idle mixture screw (also, which type it is, some have an idle air screw and some an idle mixture screw - both perform the same function but adjust in the opposite direction). Check the carb rubber for cracks. Check the position of the clip on the needle (mounts in the carb slide).

If it dies if ridden for longer distances / higher speeds then possibly a problem with fuel flow to the carb. Blocked fuel filter / blocked fuel tank breather, etc.

All the best

Keith
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[ice.shark]

Thanks. After a bit more riding and testing/probing the problem, I found out that if I open the throttle gently (choke fully off) then the engine wouldn't die. With choke fully open, I could open the throttle quickly and the engine will handle it.

Anyway, I adjusted the tickover rpm to 1900 with the knob on the carb and the problem is gone. The engine also behaves better now and I can take off without having to redline it.