RS125 - Starts, rides and 800yds later, stops.

Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

Hi All,

My son has bought an Aprilia RS125. It had been sat in storage for 3 years and has lots of "bits" on it.

Full Arrow Exhaust being the most noticeable mechanical change.

I could not get the bike to start, so replaced the plug, drained the fuel tank, cleaned out the carb and new filter in the airbox. Still no joy. So.... I took it along to a bike mechanic who had to change the jets because of the exhaust apparently.

The bike arrived back and started fine, so insurance and tax now sorted and son goes to ride the bike.

Starts up, waits for the COLD sign to disappear and sets off. Seemed fine for 800yds or so, then cuts out. Each time the bike was in Neutral, it started fine, when when selecting 1st it either cuts out right away, or cut out when you let out the clutch.

I have bypassed the stand switch to be sure it is not that. I did this by removing the multiplug and shorting the two outer pins.

Bike was left to cool and again started, went up the road for about 800yds, maybe a bit more, but stalled and will start in neutral as normal.

I noticed that the bike will drag when you select first, I tried to adjust the cable at the lever, but that seems to make little difference.

My final thought is that the clutch pack is faulty as it has stood for 3 years, but I'm not really sure if that's likely.

Bike has covered 22,787km.

Any help would be much appreciated.

thanks
Pete..

PS: Sorry about the long post..

dobby · Nitrous Nuisance Joined: 09 Mar 2010 Karma :

did you strip and clean the carb

Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Unlikely that the exhaust would make enough difference to the jetting at idle to stop it starting (although quite possible for it to be dangerously lean at speed).

The clutch needs to be adjusted with the adjuster in the middle of the clutch housing. This actually adjusts the clutch rather than just the cable free play.

Depending on how long takes to restart I would suspect that it isn't getting fuel through to the carb as quickly as it is being used. Normally caused by a blocked fuel tank breather pipe, blocked fuel filter or a kinked fuel line.

All the best

Keith
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Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

Hi Keith,

The bike will restart immediately if it's in neutral.

I'd didn't know that the clutch can be adjusted in the way you mentioned, so I'll give that a whirl.

Tank Breather pipes are clear and the fuel line is fine. I'll check the fuel filter. I didn't think to change this, should do it as the bike was stored for 3 years.

thanks for your help.

Pete..

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

There is a filter in the side of the carb. Assume it has the standard 28mm carb, in which case the fuel pipe goes to a banjo shaped cover with a bolt in the middle. Under this cover there is a mesh disk as a filter.

All the best

Keith
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Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

Hi,

The fuel filter is nice and clean, so that's ok. However, I looked at adjusting the clutch at the clutch cover and noticed that the locking nut was hugely tight (but the key here may be LOCKING), but once slack, the centre grub screw was also quite tight.

I backed off the grub screw a couple of turns and as suggested in the manual, I tightened until I could feel resistance, then backed off half a turn.

Does this sound right?

I had also slackened the adjustment of the cable at the lever before doing this.

thanks
Pete..

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

That sounds right, assuming you adjusted the cable free play in the lever after you had done the clutch itself.

The RS125 box is always a bit notchy if you try and change gear when not moving.

All the best

Keith
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Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

dobby · Nitrous Nuisance Joined: 09 Mar 2010 Karma :

good luck

Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

Damn, 800yds is a long way to push a motorcycle. Especially when you are 6ft 2in and the bike is a diddy little 125.

Anyway, adjusting the clutch made no difference. Temp got to 68 and bike lost power, then stalled when I went to change gear.

I have a new thought. I noticed that the cold air ide (choke) thumb lever is quite stiff and will only travel 3/4 of the way along the symbols. If this was poorly adjusted (ie open a bit), I assume that this will change the fuelling when the engine is warm and cause a similar stalling / lack of throttle issue?

Can this be adjusted?

thanks
Pete..

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Not really much adjustment on the choke cable (think there might be a small adjuster on the carb end of the cable), but not that much movement needed. Probably is worth taking the choke plunger out of the carb and checking it is free to move. However it would probably foul the plug up fairly rapidly if the choke was stuck on, and probably not restart that easily.

That it dies after a short while running still suggests to me that it isn't getting enough fuel to keep running. If the filter in the carb is fine and the fuel pipes and breather are fine I would be tempted to take out the fuel tap from the tank and give that a clean.

All the best

Keith
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Frost · World Chat Champion Joined: 26 May 2004 Karma :

Start it up and rev it a bit. Keep the revs above 5000 for 30 seconds and see if it cuts out. Then try restarting it and doing the same. If it cuts out first time after 20 seconds or so, then won't restart or does start but cuts out after 5 seconds or so then its certainly a fuel supply issue.

Try repeating the above with the fuel cap off. If it runs no problems then it's just a blocked tank breather.

bladerunner · World Chat Champion Joined: 09 Sep 2006 Karma :

First off..stop riding 800 yards away from the house!!

then it's a bit hard to tell from what you say it sounds electrical if the bike is only doing it in neutral after a while is odd though....you have wired up the side stand switch..the next line would be to try the neutral switch does removing it stop the problem? it could be a problem somewhere else on the loom?

is the bike not losing power before it dies.....granted it don't sound like you have really had a chance to get to know the bike yet but if it stops pulling well at large throttle openings before stopping then it hints at fuel etc

And yes the clutch adjuster is very different to the usual jap stuff eh..and can take a little fiddling to get right for the first time you do it....maybe change the gearbox oil for the recommended stuff in case it's a thinner type in there at the mo!
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

Ok,

So, the tank breather pipes, there are two. One that I can blow into freely that exits into the tank filler via a small square hole.

The other is a larger diameter and has some back pressure when I blow into it and I can hear pressure released when I stop blowing. This pipe exit at a small valve in the fuel filler area. I did fish out a ball of debris, but the air flow didnt seem to be much affected.

I can start the bike and hold 5000 rpm (although I did get a few whinges from the neighbour) for 30 seconds. I can stop the engine and restart immediately.

If I put the bike in gear, there is a noticeable clunk and the bike feels like it's dragging a bit.

I can pull off with a decent whack of revs and easing the clutch off.

200yds and same symptoms. Around 70 degrees on temp indicator, loss of power and bike comes to a stop. At this point the gears are a pain in the nuts to change. To get into first (then neutral) I have to rock the bike back and forth. I have checked the gearbox has oil and it does, but it is not filled so much that it will overflow when the bung is removed.

Sorry to be a pain, but I'd rather learn how to maintain my lads bike rather than drop it into a mechanic everytime it farts (being 2 stroke it may do that alot).

thanks
Pete..

https://www.pwmcomputers.com/Images/Aprilia_RS125.jpg

Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Frost · World Chat Champion Joined: 26 May 2004 Karma :

Sounds like the clutch is dragging, may be just in need of adjustment or new plates. does the bike die when you come to a stop or change gear?

bladerunner · World Chat Champion Joined: 09 Sep 2006 Karma :

well fair does to you wanting to lean about the little beastie they are quite simple once you are familiar with them. have a go at adjusting the clutch again with say half a turn less adjustment this time it should help. Also going back to the too rich sticking choke option is it 4 stroking before it dies? if it was too rich that's what I'd expect and if your mechanic friend has changed the jetting and it was not doing this before then try fitting the original jet back in and see what happens if the rest of your work does not help.

Keep the fairing off till you have fixed it as at least it's easy to work on then and also the main jet will come out the bottom of the float bowl so you don't need to remove the float bowl to check it..but i guess you knew that already. You can make sure the breather is not the problem if you ride with the tank cap open if that stops the problem then you know it is the breather blocked and if it ain't at least that's that crossed off the list of possible problems.
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Current bikes...cbr929, KDX200's, Rd125lc mk2, RGV250's

Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Hi

Well, that should count the breather out (although still worth taking the fuel tap out of the tank and cleaning it).

I am still inclined to think it is a problem with fueling (the only thing electrical that seems likely to me to strike after a short run would be a faulty coil overheating). If it occurs when braking then that is when you have the throttle shut and it is running on the idle jet. However if I understand you it is idling fine when first started which suggests the idle circuit itself is fine.

If it was running rich I would expect it to foul the plug, and take ages to clear enough to restart.

Out of interest, what is the main jet in the carb? On the PHBH28 carb it is easy to check as it is mounted in the large brass "bolt" that holds the float bowl on.

All the best

Keith
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Computageek · Two Stroke Sniffer Joined: 15 Jun 2010 Karma :

stirlinggaz · World Chat Champion Joined: 22 Jul 2007 Karma :

that size of jet would be too big, i have never used higger than a 128 (+ that bike was heavily modded)
with arrow exhaust you should have a 122-125, if the oem airbox is there, but that wouldnt cause the cutting out.
sounds like the clutch is badly adjusted + a change of gear oil would help.
the grub screw adjustment on the rs is a bit tricky if your not used to it. (after a bit, you learn to adjust by feel usng the special clutch tool or a 12mm socket from a 1/4 inch socket set & a pair of molegrips, with a screwdriver through the middle,lol
the clutch assembly is very easy to remove from the rs & a set of friction plates is not expensive.
have you tried draining out all the old fuel & replacing it, and sticking a new BR9EG plug in?
download yourself a copy of the wsm, a bit comprehensive than the haynes (book of lies)
cheers,
GAZ

Digitalize · Nearly there... Joined: 09 Aug 2009 Karma :

So the bikes cold, you let it warm up until it no longer says COLD, then after 30 secs at 7k, its at 70c? Thats basically 30c in 30 secs. Which sounds very odd for me, my mates used to take an age to get hot (Which was bloody annoying because we had to wait for him!)

Hope you get it sorted, atleast it looks tidy.
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1998 CB600F Hornet

stirlinggaz · World Chat Champion Joined: 22 Jul 2007 Karma :

does sound a bit hot,tbh.
should change from COLD quite quickly at this time of year though & if idling for a couple of minutes it will go to about 50deg then if the revs arnt going above 5000rpm & going slow, then no cool air hitting the rad to cool it down & would reach 70 within 5 or 10mins easly.
might just be needing bled,
cheers,
GAZ