2005 RS125 cutting out!

[Tom_N]

Hi all,
Been so long since I've posted on here. Cringed when I logged in with my user name

Anyway bought myself a 2005 Aprilia Rs125 today which was VERY cheap. Too cheap to miss, problem is that it will run fine for ten or so minutes but then cut out. There looks to be an RS250 pipe modified to fit it and a stupid looking open air filter. Just thought I'd check on here incase it was a common problem. It will save me tearing it down into bits.

Cheers
Tam

[Timmeh]

lol noob

[bikenut]

:karma: hi dude

when it cuts out after 10 mins or so does it loose its ignition?? ( heat related problem perhaps )??

feedback please

[Skudd]

I have found that this issue is usually caused by a problem with the bike or perhaps a fault. You need to check which one it is first to eliminate the other, then that will be the one that needs to be sorted.
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[Tom_N]

Thanks for the quick replies.
Not even sure yet to be honest. I've only just got it home and the battery was flat. Charged battery and tried to get it going tonight but it wouldn't go. Pulled the bowl off the carb and jet sizes are as follows.

Not sure which one is main jet but when I removed the 14mm bolt on the centre of the bowl theres a jet on there which is 115.

Big jet up the centre of the carb is 264.

Pilot is 62.

Any idea what they are meant to be. Theres an rs250 pipe modded to fit and the aforementioned atrocious airfilter.

I have noticed that even with the fuel line disconnected and the fuel switched to 'ON' there is only a slight trickle of petrol. I'd of expected it to really flow out??

Thanks
Tam

[Timmeh]

[Tom_N]

Hi,
No this is a gravity fed fuelling system. Cleaned up plug and jets and got her running briefly then it cut out. Wouldn't start again so let it sit ten minutes and tried again. Seems like its more eager to start when crankin the starter on full throttle and run a second then cut out. also noticed the idle speed is wound fully in! Got a sickening feeling of compression.
*edit* The bike has a good strong spark all the time.

Tam

[jimmyRS]

Had a similar problem before with my RS, but was a matter of a clogged airbox + a carb in need of a clean, have you done both?

Keep the battery topped up too, after you've finished testing to see if it'll fire, pop it back on a quick charge to keep it tip top.

If its sparking fine and its getting fuel, little else it could be except compression, however you said the fuel was 'trickling' out, have you taken the fuel tap off and cleaned out the filter inside the tank?

Hope you fix it buddy!

[Tom_N]

Yep there is a brand new fuel tap on there which I had bought a while ago for another bike but never fitted. This helped fuel flow but still no joy. My theory is that with me cracking the throttle wide there is more fuel getting into the cylinder thus creating compression momentarily as this will create an air tight seal between rings and bore. Think thats Why its briefly firing. Maybe/hopefully thats cobblers though. I'll do a compression check tomorow.

Tam

[jimmyRS]

right now a compression check seems the best way to go about it after all,

hopefully its just the rings if anything at all

[jimmyRS]

btw jus looked at the picture, its unlikely thats a rs250 pipe unless they've bodged it as rs250 pipes both come out on the right hand side of the bike, not the left.

And as for the open air filter, get rid and stick a stock box back on there. If it hasn't been upjetted by 8-10 it'll be running lean as hell, plus them things aren't great when it comes to damp/wet weather. Talking from personal experience

[Tom_N]

Yea, standard airbox is a must. Hoping it isn't compression. Strange how when it does start it runs fine for a few seconds then just cuts out like someones flicked a switch! Maybe fuel starvation. Iv heard there's a filter in the carb on these bikes. Anyone any idea where it is. Maybe its blocked

[Tom_N]

Done a test tonight.90 PSI dry and 100PSI wet. Wonder if i could get away with just doing rings or should I just get a piston kit.
Cheers again guys
Tam

[bikenut]

:karma: hi dude,

so you have good sparks all the time, reasonably good compression ( should run on those figures ) with good ffuel flow to carb?

have you done a fuel flow test ie how long will it take for say 2lites of fuel to fill a clean pop bottle??

blockage in fuel system ( tap may have its own filter/sediment bowl, or even filter sticking up into tank??

check fuel cap vent!

do flow test and time.

feedback please with some pics

[jimmyRS]

them things should be pushing 110psi if fully perfect, but 100 isn't bad at all, definitely shouldn't be the problem making it not fire.

looking more down the lines of fuel starvation than compression, tried popping some fuel down the plug hole then firing up? if it fires, more than likely its a fuelling problem, if it doesn't fire its back to compression/spark

not to doubt you, but are you sure the spark is strong? With my RS50 i was at a loose end like you when trying to fault find, turned out my stator was kicking out enough to spark nicely when outside the barrel, but inside with the compression and fuel it couldn't.

hope you sort it out soon mate

[Tom_N]

Hi, as mentioned I changed the fuel tap. The spark plug is wet and also is putting out a strong blue spark. Noticed the inlet manifold looks a bit perished! So could be drawing in to much air. Read somewhere an average rs should be doing 120 PSI. Anyone got access to a manual? Wander how many turns the airscrew should be out. 1.5? After me trying to fire her up for so long the battery could be getting low so ill put that on the charge tonight again and try from there. We'll not be beat lads!
Tam

[Kickstart]

Hi

If it is failing to start then likely the main jet and needle are irrelevant.

Does it start and run for 10 minutes, and when it dies refuse to restart for a bit, and when it does restart run for far less time?

If so my main guess would be that the fuel filter is blocked, the fuel pipe is kinked (both unlikely given you have already changed the tap, and it dribbles from the pipe) or that the fuel tank breather hose is blocked (in which case running it with the fuel cap open will fix it).

But your compression readings are also low so probably needs new rings as well.

All the best

Keith
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[Tom_N]

Yea now when it starts it just dies straight away even if I try to hold a rev. I don't suppose its that daft airfilter. strange how its really trying to go with the throttle wide open. Defently seems like fuel starvation. q,Reeds maybe? Unless the battery hasn't enough kick to get a good spark. At the minute im only getting about 30 mins at a time to work at it. I'm off Monday so ill get a good look then.

Cheers
Tam

[jimmyRS]

if you've only recently fitted the air filter, then possibly. It might be starving of fuel and/or running lean due to too much air for the air filter and the worn manifold you said earlier.

Unlikely to be the reeds either unless you've done more engine mods, in which case you would need thicker (stiffer) reeds to stop them opening up too much too early and loosing power.

Screw the battery, ask a friend and try and bump start it, them things are generally easy enough to bump, n it'd allow you to see if holding the revs open/closed helps with starting.

n remember, do it in second gear, not first

[Kickstart]

Hi

Try it with the petrol cap removed.

Jetting wise for the filter, not sure much will be required. At idle (where you have the problem now) the difference between the filters will be tiny compared to the air they can flow.

All the best

Keith
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[Tom_N]

Part solved. Cut back a but of the ht lead and now there's a slightly bigger spark. She fires up now. Need to take her a run to see if she's still cutting out. Light at the end of the tunnel

Tam

[jamesrs250]

[hadden]

daft i know but are you sure the coke is in the right position.wont be the cause of the problem but if it ran fine for 10 minutes and then not,i would check that.easily done,my symbols had rubbed off and it took me ages to realise i had left the choke on
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[Kris_taylor1988]

If I was you I would do a top end rebuild as 90-100psi is bad on these bikes anything below 120psi I would do the top end.

You might get away with just rings but take the top of and have a check. Prob end up needing a piston kit and get the cylinder horned.

And that main jet sound to low on that standered engine with a
Decatted exhaust and airbox is about 122