RS125 wont run properly

[pits]

Right, well that is it, myself and the guy rebuilding my RS125 are stumped, with my bike it makes no sense what so ever.

*Shorthand for those who can't be arsed to read it, RS125 broken, wont rev between idle and 2krpm ish after the temperature has hit 70 degrees, everything is brand new on the bike and just been rebuilt*


Problem with the bike.
turn it on, press the start button and it instantly starts no fuss, it is instant on the button every time.

Revs freely as it is warming up, you can ride it whilst is warming up, pulls off nicely doesn't stutter or cut out, not sure what it is like above 2krpm the bike is cold and I frankly don't want to take it past that being cold.

Temperature comes up, hits 70 degrees, operating temperature and the moment you touch the throttle it bogs down and dies, press the starter button, fires straight bike up and idles, touch the throttle, bogs down and dies. You can set off, but you need to coax the throttle up to about 5krpm and slip the clutch to get it to move, then it will ride happily past 25mph it is perfect.

Below 25mph bike bogs down and cuts out, again will start instantly on the button each time, but you need to coax the throttle back open.

Now the list of what has been done
Engine rebuilt
New plug
New filter
New carb
Wiring checked

Engine has done 2kmiles if that, all at running in pace for most of it, using Castrol fully synthetic 2t oil, and it ran fine for 1700 miles it had a flat spot half way through and need a final set up and tune.

Dropped it to the garage, final set up done, test ride it was fine, then it bogged down and wouldn't run, more fiddling, still cut out, carb was worn, so we took a carb off another RS125 that was there, slapped it on, bike ran perfect, ok a slight flat spot bottom end and not as quick top end but it didn't bog down.

Bought a brand spanking new carb Dellorto PHBH28BD, took the bike back, fitted the new carb, it ran lovely up untill 70 degrees and bogged down again, same as my old carb was doing.

This of course baffled us, as how does one carb work and 2 don't even though they are set identically, so all the wiring came apart, no faults were found, tried a new CDI thingy on it, didn't change anything, still cut out.

Power Rave Valve, this has been taken apart and cleaned out, put back on, and it still wont run.

Checked the fuel, fuel is good, throttle and choke cable work

Apart from the PRV everything is brand spanking new on the bike engine wise, and the bike runs fine until it hits 70 degrees and then it will not rev past idle upto 2k rpm without cutting out, and you can't set off at anything less than 5krpm.

There is no reason why it shouldn't run and work, taken the jets out and replaced the jets, up jetting, down jetting, making a new pilot jet etc.

Really starting to get on my tits now, everything is brand new, the whole bike has been apart and rebuilt checking everything over, and now it is all being rechecked again.

Any help would be greatly appreciated.

[Syris the Indomitable]

Could be coil related, as coils warm up they become more resistant, thus less resistivity. This would explain you needing to rev the engine to get the electons flowing. A coil is Essentially a high-voltage transformer made up of two coils of wire that act like a fireing capasitor.
Current flows from the battery through the primary winding of the coil so check the rectifier too!

Also RAV valve may faulty.
The rav valve is a solenoid/electric switch and actuator.
You can actually set these up without this, all you do is srew the slide plate permanently open with the screw and locktight.
Also has the 2 stroke feed been set up properly?
I also worry about a 10th milli oversized piston kit being fitted without the your cylinder being re-honed.
____________________
In Greek mythology Ichor is what immortals have in the place of blood
Those that mind, don't matter...Those that matter, don't mind. Do you agree with this?

[stirlinggaz]

50% of rs problems are carb related (& the other 50% being battery related)
to the op : you say you got a new carb, but is it jetted properly?
because you say it ran ok with a borrowed carb.the rs is quite hard to set up & can be a bugger if the jetting is not spot on.
have a look inside the carb & post whats stamped on the jets, &
tell us what exhaust you have also, (phbh28 is fitted to umpteen bikes & has to be jetted to suit)
cheers,
GAZ

[pits]

Carb is for an RS125 jetted for an RS125, tried rejetting from 115 main to a 120 main.

Essentially everything has been done to the carb, upjetting down jetting, tuning with in the manual specifications, the float set, there is nothing on the carb that hasn't been replaced or checked and set to standard.

2 stroke feed is correct.

RAV has been set

Not checked the coil, but it doesn't really make sense that it would be that, as the bike works fine up untill 70 degrees, if you leave the bike to idle to 70 degrees it bogs down and cuts out at 70 degrees, if you ride at 50 degrees the bike is fine, untill it hits 70 degrees.

It hasn't got an oversized piston kit added, the bike has been built to stock, nothing upgraded, standard exhaust with arrow can I think, this was on when I bought it so no idea really, the exhaust has been apart and de-coked



The thing with the carb.
Standard carb was playing up, causing the cut out at 70degree issue after being setup and then wouldn't run when set back to where it was for running in.

Second hand carb was placed on and the bike ran fine apart from a flat spot and lower top end, idled fine and road at 70 degrees and 80 degrees no issues.

Original carb was deemed as faulty, so I ordered a new PHBH28bd with 115 Main Jet, 65 Pilot Jet
(https://www.pjme.co.uk/acatalog/Aprilia_RS125_Air_Filter__Fuel__Carburre.html)

[Kickstart]

Hi

I would be more inclined to worry about the setting for the idle screw and the needle jet (and the position of the clip on the needle jet) than the main jet.

Does almost sound like an air leak giving a weak mixture, most obvious at small throttle openings and revs (maybe leaking main bearing seals). But that doesn't explain the issue at 70 degrees (unless you happen to turn the choke off then which I think you would have mentioned).

All the best

Keith
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Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Syris the Indomitable]

Yeah as said above, upon reflection as the engine warms and the compression rises the mixture is absolutely crucial.

The trouble with the RS sport pro (If your is a sport pro), is that if de-restricted all the following have to be done.

1. Exhaust fine you have an arrow.

2. Check the air box, the nozzles may have a tube blocked up, just remove that blockage.

3. cdi, under the rear seat, is a black box, a resistor need drilling and destroying, silicone needs digging out and the circuit board snapping to destroy it's environmental dip.

4. You want a br10es spark plug for a unrestricted bike.

5. Power valve/rave unit, (You have this sorted)

6. The carburettor set up on these is absolutely crucial and as you know it need up-jetting.

The thing with the70 degrees may just be incidental, coils and rectifiers warm affecting/increasing resistivity.
____________________
In Greek mythology Ichor is what immortals have in the place of blood
Those that mind, don't matter...Those that matter, don't mind. Do you agree with this?

[pits]

[Syris the Indomitable]

K. Good luck.
Check behind the dash too, you may have one of these playing havock.
https://img202.imageshack.us/img202/1871/meninblackalien.jpg
____________________
In Greek mythology Ichor is what immortals have in the place of blood
Those that mind, don't matter...Those that matter, don't mind. Do you agree with this?

[pits]

Luck isn't what I need, I need a new something that will do something to make it work

[pits]

Been down to see it today, mentioned the rec and coil, guess what, he replaced it.

He had another RS125 there a few weeks back and basically he swapped every component electrically to figure it out, CDI, Rectifier, battery, coil, spark plug.

Still no joy, I was thinking maybe a temperature sender has gone, are there any temp senders or any engine sensors, like crank sensors on the bike?

[stirlinggaz]

[pits]

As far as I am aware it is restricted, the rave valve is stock and this was also swapped from another restricted bike, the frame also has a sticker saying it has a power rave valve.

It only does 90mph like a restricted RS

Carb is for a 99 onwards RS125, the bike is a 99 MY RS125

Carb is set for a 99 RS125

Choke cable is fine, and the choke can be turned off at 50 degrees so it isn't running on choke.

Main bearing seals are all brand new, the engine has been fully rebuilt no expense type affair.

The problem is, up to 69 degrees the bike revs freely and doesn't cut out, there is no bogging down, then it hits 70 degrees and it will not run, an air leak I would expect there to be an issue at all temps, but this is above 70 degrees only.

I trust the guy who is doing the work, everyone I know uses him, and everyone reccomends him, and everyone brings their broken RS' to them, he is stumped on what it could be and has even spoken to people who race them.

He is going to take it to a dyno and see if that shows anything.


What I can't understand is.
It has fuel
It has spark
It runs.
Everything electrical has been tested
The engine is brand new essentially
Exhaust isn't leaking, new spring clips on, and no holes in it.
It works as it should up till 70 degrees
70 degrees it doesn't want to run...

Manual choke, so it isn't cold start settings not shutting off


It really makes no sense If the dyno doesn't show anything up, I am going to have to take it to someone else so they can have a head scratch, but it is costing a fortune now in just labour.

[Kickstart]

Hi

Not aware of a feedback of the temp to the ignition which is the only thing that would make such a dramatic cut off at a particular temp.

Might be worth a trawl through the wiring diagram though,

All the best

Keith
____________________
Traxpics, track day and racing photographs - Bimota Forum - Bike performance / thrust graphs for choosing gearing

[Syris the Indomitable]

Arrr! Just had a thought is there a wax operated thermostat in the cooling system, or any thermostat for that matter, it won't be opening to allow fluids around the engine thus shutting it down.
These do break.

Just one more thing I was was thinking, just wondering if the Manual choke is actually shuting the air off when you switch it off.
____________________
In Greek mythology Ichor is what immortals have in the place of blood
Those that mind, don't matter...Those that matter, don't mind. Do you agree with this?

[pits]

I was wondering on a thermostat as well, but I have been told that it isn't that either.


Manual choke is shut off at 50 degrees and the bike works fine up till 70 degrees.

[Syris the Indomitable]

Then if it's shutting down at exactly 70 degrees it must be electrical.

I am guessing yours is a 122 engine and not the 123.

The 122 seems to have a more complicated electrical system.
You have a coolant temperature thermistor (Not thermostat which you will have of course), and diodes on the same circuit which doesn't appear on the 123.
Could be these which are faulty.

Scroll down a bit for the 122 and 123 wiring diagrams.
Loads of good info here.
https://www.apriliaforum.com/forums/showthread.php?t=98428&page=2

This is page one.
https://www.apriliaforum.com/forums/showthread.php?t=98428

It may even be a dodgy connection within that region.
____________________
In Greek mythology Ichor is what immortals have in the place of blood
Those that mind, don't matter...Those that matter, don't mind. Do you agree with this?

[stirlinggaz]

still reckon its carb related.............
ok, first, your bike is not restricted.
a functioning powervalve blade/housing & solenoid is only fitted to full power bikes. (on a restricted or uk learner legal bike there is only a blanking plate though both are fitted with the rave box)
afaik, there is nothng electrical that would shut the engine down at 70deg, so i think that is coincidental.
change your spark plug for a BR9 or 10. (humour me)
you say that it cant be the choke but it can if the brass choke piston is sticking in its hole.(it relies on a correctly adjusted choke cable & the spring working) this is something you cant see & a tight choke cable would cause the choke to be always "slightlly on"......
so remove it at the carb end & give it a clean or remove it at the choke lever end.
then tell me what you have the carb set at please (air screw especially) & what you are doing with the throttle. (ie. are you letting it idle till 70deg? or are you opening up the throttle?)
also, can you hear the carb slide clunking down when you open up the throttle & let it go?
turn the idle adjust screw (it controls slide height) all the way in, this should make it idle higher & then back it off a little at a time until it idles at 1200rpm.
cheers,
GAZ

[Fortuna]

This happened on my NS125R and it turned out to be a slit in the rubber stump that sits between the engine and carb.

[stirlinggaz]

[pits]

Well we have had a look at it, got another RS125 there, swapped bits and bobs over and still no change.

Going to take it for a trip on the dyno to see if throws anything up.

What we can't understand is

My original carb played up, and was worn, so we put someone elses carb of another bike on, this bike was running fine.

The carb of the other persons bike, straight on, and it ran, it didn't cut out once, didn't faulter low down, just at the top end.

So we bought a new carb, which does exactly what the first carb has done.

Going to let the guy dyno it first, if he can't find anything I am going to take it elsewhere as I can't keep paying for him to do the same things over and over.

[stirlinggaz]

[pits]

Well it has been on the dyno, and a problem has been found, it should be fixed and back by Monday.

The problem wasn't carb or plug related, it was infact an intermittent fault with the stator, how the feck that works I don't know, but it should be fixed for Monday now

Cheers for everyone who has helped with info

[thekopite954]

Hi Guys,

This is my first post on here, so apologies for resurrecting a 2 year old thread, but I am currently having the EXACT same issue with my brothers RS, and just wanted to know if changing the stator solved the issue????

Regards
Daz
____________________
'Those who risk nothing, do nothing, acheive nothing, become nothing'

[pits]

Believe so, 2 years ago now near to the day as well, but the bike got completely stripped apart and the whole wiring loom was checked over and there was an intermittent fault with the Stator, but it may have also been an intermittent fault with the loom itself.

Have to be honest it was 2 years ago now so can't really remember what it was exactly, all I do remember is that it involved the whole bike being stripped.


I miss my RS125
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[thekopite954]

I'd have never posted on this, with it being as old as that! But when I searched google, the top result is this thread...... Only because this RS is doing exactly the same thing, after nearly exactly the same work (engine rebuild)...... I couldn't ignore it without trying,

Might just tell him to take it the dyno for some trial and error work!
____________________
'Those who risk nothing, do nothing, acheive nothing, become nothing'