Aprilia RS125 Idle problems

[tommivercetti]

Trying to get my bike sold but it won't idle

The idle screw is all the way in and tried various positions on the mixture screw

The jets are 122, 62, 70

It revs nice and runs perfect at the higher revs but first 1/4 is poor and it idles at 1k then drops below and dies

Bike has recent rebuild (main bearings, seals, replate and new piston) new battery and new plug, but ran same before all this

The bike has never really run right with the current carb a friend gave me when i broke mine but all the jets are same. it used to idle with the current carb but now screw is all the way in. Is there something that can get blocked in the carb, i've stripped and cleaned it many times but nothing

Some bike details: 2005, Full power, full jl exhaust and nearly all standard done about 20k but had rebuild, generally tatty bike

I think it might be a carb problem but i don't have a spare to try, any help appreciated

[stirlinggaz]

hi,
i presume your running the standard dellorto 28mm carb?

with the jim lomas exhaust i used a 128 main jet, cant remember the others though (i'll have a look back at what was best carb set up),,,
them wee carbs are very sensitive to the slightest turn of the air/mixture screw. (which is why i always ditched the 28mm for the vhsb 34mm, works a lot better on the rs, i see the 28mm carb as a restriction.)

have you looked at the obvious/usual rs probs?
try it with a NEW spark plug & dont bother with those fancy iridium plugs, just buy 3 copper ones, you wont notice any difference anyway.
try a new BR9, for now.
are you using standard airbox? (with both trumpets open)
& check all your cables, especially the choke.
theres a good carb guide in the stickies, written by resident expert. (kickstart)

so, to sum up : remove carb from bike, strip it & clean it & refit with air/mixture screw at 2 full turns out.
choke working as it should? no air leaks anywhere?

before you stick the new plug in, this is an ideal time to do a compression test. your looking for over 120psi (its handy to know what figure your starting with, for future services) its one of the 1st questions i ask a seller (i've had a few rs125's )

fit a brand new BR9 & make sure the battery is FULLY charged. (the rs likes over 12.5v to start) & dont rely on the lcd for voltage, its notoriously unreliable. use a multi-meter.
fresh fuel?

post the results please?

cheers,
GAZ

[tommivercetti]

Yes 28mm carb

I have just put a new ngk br10eg plug in

The airbox is standard and both ports are open

The choke spring was broken so i have replaced it, it's definitely returing.

I have removed the carb countless times and cleaned it all with carb cleaner and it stays the same

The battery is brand new fully charged and reads about 12.6 in the bike (not sure about when running but the carb is off at the mo)

The fuel is fresh I just syphened it out of my comuter but even with a fresh tank of vmax it runs the same

I don't have anything to test the compression, but it ran like this before and after a the full rebuild with a brand new wiseco piston and replate of the barrel. So is this still worth checking? I'll see if i can get a compresson tester

Thanks

[stirlinggaz]

hi,
the reason i suggested a new BR9 is because its cheap, rotax recommend it & it wont foul as quick as a 10.
who done rebuild? compression should be around 150psi if top end re-built correctly.
i'd be testing this 1st.
most hard starting is caused by fouled plug,low compression or f*cked battery.
the rs is pretty fickle when it comes to the battery, if its not 100% it can cause all sorts of weird issues.
how many turns out is the air/mixture screw? (the wee screw that needs a screwdriver to turn) this VERY sensitive, so only adjust it when engine warmed up & turn it 1/4 turn at a time.
can you get it to increase idle rpm by using throttle stop screw? (the black plastic screw on side of carb body)

cheers,
GAZ

[tommivercetti]

Still not managed to get hold of a compression tester.

The idle screw is all the way in and the mixture screw doesn't seam to make it increase the tick over at all (i messed about with it when the bike was last on road and fully warm) so I've left it about 2 turns out.

I did the rebuild, I've done about 4. but Firefox Racing in Keighley did the replate and matched it to the piston they supplied so hoping they did it right and the compression should be good

My friend is going to clean the carb in a ultrasonic cleaner, then i just need to get hold of a compression tester but I don't want to keep throwing money at this bike as once its running it's only going to pull about £1000 tops and i've spent maybe £200 so far on getting it to a selling condition

Thanks, Dom

[stirlinggaz]

hi,
if its not idling correctly, have you tried putting the choke on?
& what happens when you do?
most carb problems on the rs are caused by guys messing with air/fuel screw, not realising that the smallest of adjustments can f*ck it up.
i cant remember if the 28mm carb has an air adjustment screw or a fuel mixture adjust screw.....(they both adjust in different ways)
if its near the air filter end of the bike its an air adjust screw & turning it anti-clockwise will make it run leaner.
if the screw is nearer the engine end, its a fuel mixture adjust screw & turning it anti-clockwise will richen the mixture. (iirc lol)

wind the plastic screw out a bit, it shouldnt need to be screwed all the way in.
get the engine warmed up (with the air screw set at 2 full turns out, try & get the bike to idle,regardless of rpm. once you have it idling, turn it in to increase rpm, out to lower rpm.
THEN try & set up the air screw turning 1/4 turns at a time, with a bit of faffing about, it should need choke to start & once warmed up put choke off & it should idle at 1500rpm.

now you know why most rs owners go for the 34mm cab, far easier to set up & completes the de-restriction process,
cheers,
GAZ