RS125 2 stroke issues/how to remove carb for cleaning

U

unL33T

Well-known member
So I picked myself up an Aprilia RS125 which was kind of in need of service (chain and cables had never been tightened for one).

When I first rode it the choke, clutch and throttle cables were way loose. Tightened them up and the chain and now it rides much nicer. However, after I did the throttle cable, I noticed the bike would idle high (~3-4k RPM) when I stopped at lights for a few seconds before dropping back down to normal (~1.5k).

After I did the choke cable, the bike starts up much nicer when cold (I presume because the choke is actually doing something instead of just tugging on a loose cable) but now the high idle condition happens all the time and it doesn't drop back down. If I release the clutch slowly and let the bike pull the revs down until near ~2k or so and then pull the clutch in again, it will stay down around 1.5k. Also, when it's cold enough that it's not properly warmed up but warm enough that I don't need the choke or to blip the engine to keep it running, it idles at 1.5k fine.

I know the carb could probably use a good breakdown and cleaning but is there anything in particular I should be checking? I can't seem to find a "how to" for removing the cleaning the carb, either. I can find how-tos for just cleaning but nothing that explains how to go about removing the thing. I'm generally alright at doing these things with some decent instructions but I'd rather not go in blind. I've only done things like brake jobs, fairing swaps, swapping out an alternator, replacing generator cover, etc on my own in the past.

Thanks.
 
Idle adjustment screw?

AS for carb removal, once the fairings are off its usually held on by a rubber boot that you loosen then they pop off.

Let me know if you want some help. Im jealous of the 2 stroke
 
I know about the adjustment screw but since I can manage to knock it down to normal without adjusting it and it idles properly when cold, that it wouldn't be the problem.
 
I dont understand excactly when the idle is going high. And is the idle only high for a few seconds then goes to normal?

Cold Engine - Idle Normal

Warm Engine - Idle High

Clutch Trick - Idle Normal?
 
You got it right. The idle stays high unless I do the clutch trick. It used to drop back down after a few seconds the first day but since then it just stays high.
 
To me that sounds like your idle screw. When its cold its open enough that you dont need choke.

If it was set correctly your choke would be on to allow more fuel to get it going. Kind of like when you leave the choke on the bike idles high.

I think the clutch thing was a red herring.
 
It idles low when I leave the choke on. I thought choke cuts off air and therefor more air flows when choke is off and idle is higher. No?
 
Guess I could just try it on my ride home. Just didn't want to muck around with it and then be stalling out on my way to work.
 
unL33T said:
It idles low when I leave the choke on. I thought choke cuts off air and therefor more air flows when choke is off and idle is higher. No?
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You are correct the choke restricts air causing the fuel ratio to be higher. If you leave a bike idling with the choke on the idle will go up after its all warmed up. When you take the choke off it the ratio is normalized and the idle returns.

As I said once its warmed up I would turn down the idle screw then tomorrow when its cold you should be able to turn it on with the choke.
 
gnatwest said:
You are correct the choke restricts air causing the fuel ratio to be higher. If you leave a bike idling with the choke on the idle will go up after its all warmed up. When you take the choke off it the ratio is normalized and the idle returns.

As I said once its warmed up I would turn down the idle screw then tomorrow when its cold you should be able to turn it on with the choke.
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Will test out on my way home today and see what happens. I still have a feeling it will just be stalling out a lot but we'll see.
 
Sounds like gunk in your carb slow speed circuits. Maybe a partial blockage in pilot jet or your air screw circuit causing a lean spot (high idle). I had a similar issue - cleaned my carbs and no problems since. You may get lucky and just need an adjustment on your air screw.

This should help : http://www.carlsalter.com/pdfs/Aprilia_RS125 Repair_manual_2006.pdf

Figure out the minimum amount of stuff you need to remove to access the carb.
For me it's usually :
seat > tank > airbox > carb

Once you've got the carb out, lots of good youtube videos to show you how to clean them.
Just note down the number of times your air screw is turned out and the number of turns for the idle screw.
If you get them out - check for the size of your pilot jet and main jet, and what position your needle is in.
Should help you get a baseline for future jetting on your carb.

Good luck.
 
Hmm thanks for the info. Tried to play with the idle adjustment but found that after it getting stuck at high idle at every light on the way home (and using the clutch trick to knock it back down so I wasn't sitting at 4k RPM for the whole time), in neutral on the stand it would idle normally. I have a copy of that manual but couldn't find much about removing or cleaning the carb. Just about removing the engine (which included some stuff with the carb) and how to adjust certain things.

Also, half way home it decided it no longer wanted to let me know how fast I'm going. Looks like I've got another issue to deal with.

Think I'll be taking the 650R to work tomorrow. Good thing I haven't managed to sell it yet! Lol
 
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Apparently the speedo sensor is on the rear brake somewhere and is common to have fail. Replacement is like $50. Not a big deal.
 
Check the carb slides are not hanging up.
Adjust the slide rest position with the thumb screws on the outsides of the carbs.
Check you have the correct springs above the slides.
 
OH ... and be SURE you have no air leaks around the carbs and boots.
Air leak = squeaked top end
Welcome to the land of two strokes, where valves are for toilets.

Nice bike.
 
Another question... should I be able to push the bike while it's in gear or should the compression of the engine prevent that?
 
I've had a bike where the choke cable was stuck on closed so everytime I use the choke it would revv high when warmed. Got new cable, problem went away immediately

Sent from my tablet using my paws
 
unL33T said:
Another question... should I be able to push the bike while it's in gear or should the compression of the engine prevent that?
Click to expand...

Yes. Its how those of us without starters get our demonic weedwackers going.

Sent from my Nexus S using Tapatalk 2
 
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