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Aprilia RS125 Backfiring : I have No idea

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saikouslx
Renault 5 Driver



Joined: 06 Apr 2008
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PostPosted: 23:59 - 31 May 2009    Post subject: Aprilia RS125 Backfiring : I have No idea Reply with quote

For my Birthday i got a 1999 RS125. Rode it on my birthday, it was fun, then the next day it seized. It was also making a large kncking noise. Opened it up, powervalve cable had snapped, barrell was scored and piston fucked. So i did a full top end rebuild, new barrel, piston (mitaka) and new powervalve cable and blade. started up the engine it ran fine, except there was a large knocking noise which was the crank bearings. took out the engine opened it up, magneto side bearing is fucked. Replace the pair along with oil seals. sealed it all up and put the engine back in the bike.
Now initially there was no spark, this was a loose connection in the HT lead to the coil. I stared the bike quickly as soon as i got a spark, there was petrol in the carb i wanted to hear it run. It ran and ticked over. Put the tank on and it ran for a little bit then .. bang a backfire. at first it was really loud, i started th bike a few times and it does the same thing, itll tick over, take a little throttle but past 3k it usually goes poof and dies. At first it wasnt ticking over for as long, i think this was cause i was scared the oil pump was failing so i over compensated by putting 2 stroke in the tank. I also checked over the rubber inlet and gave it a coat in silicon so seal any possible cracks.
I have now put fresh petrol in (high octane - excellium from total, i have only used high octane), and i took out the spark plug which was oily and cleaned it, the top of the piston also looks fairly oily. I ran it a couple of times and when the bike started backfiring, i would take out the plug and clean it. It seemed to get a little better, the bike bumps easily (my battery has worn down by now) but the last time the spark plug didnt really seem oily although the top of the piston still is, i managed to eliminate the failure of the oil pump (it working!).
But i still dont know whats causing this. It will idle for a while but it wont reli pull or rev. Im buying a new spark plug tomorrow (just as a hopeful try) BR10EG, but can anyone help me out? I dont think it is timing as it doesnt backfire alot, just after a while then itll cut out.
Im close to giving up, but ive done so much work i would like to fix it my self, also i bought the bike for 1000, and have spent about 400 on it so far, ive only got to ride it for one day really and i dont really want to give it to a shop, Im 17 and have paid for all of this myself (except for 200 which my parents kindly helped with), and i cant afford the 50 per hour +parts. Ive been able to source alot of knowledge through friends , etc, but no one has really been able to pin point it. So please help me out? Smile Any suggestion i will try it out. Cheers.

and sorry this turned into such a long post.
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chrisscott
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PostPosted: 06:41 - 01 Jun 2009    Post subject: Reply with quote

i had one mate, exactly the same problem never found it, ended up getting rid of it.
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bmwsport
Nitrous Nuisance



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PostPosted: 18:43 - 01 Jun 2009    Post subject: Reply with quote

i have a similar fault with mine at the moment, will the bike ride? i can ride mine but will die over 4k...
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Billing
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PostPosted: 20:40 - 01 Jun 2009    Post subject: Reply with quote

rather than cleaning the plug, change it, my tzr keeps fouling plugs, does near enough the same thing, but it fixes with a new plug Thinking
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EnergyInducti...
Crazy Courier



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PostPosted: 20:47 - 01 Jun 2009    Post subject: Reply with quote

Sounds to me like an ignition timing problem.
Have you tried a new CDI unit?
My ignition timing was off before and used to backfire like mad, Sometimes it would kick back, or refuse to start. Ever since it's been sorted, my plugs no longer turn black, and there is no backfiring.
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saikouslx
Renault 5 Driver



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PostPosted: 22:30 - 01 Jun 2009    Post subject: Reply with quote

right, put new spark plug in. Didnt do too much. I wont rev past 3k, however i did find it revved higher (up to 5k) with the choke on. I think i might give up soon and give it in to a shop, anyway of testing CDI? Really dont want to give it in tho but might have to.
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tutton
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PostPosted: 22:39 - 01 Jun 2009    Post subject: Reply with quote

Tryed opening up the carb, and chucking in a +5 jet?
more oil = more fuel needed and all that?
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BenR
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PostPosted: 22:05 - 02 Jun 2009    Post subject: Reply with quote

New CDI time me thinks, change the HT cap/lead whilst you're at it. Thumbs Up
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saikouslx
Renault 5 Driver



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PostPosted: 21:13 - 24 Jun 2009    Post subject: Reply with quote

right, i sent the engine to an ebay service, and it came back and the bike still backfires. I dont think its the seals or gasket as no oil is leaking anywhere (or gearbox oil being burnt), also my magneto side is clean, no petrol residue. Ive cleaned out the carb etc, but i noticed a 115 jet (120 is meant to be standard one) so im getting a bigger jet, but why did it run fine before? Apparently its not the cdi because i took it to a shop and they said they put a spare one in for testing it (they have one at the shop as they had a similar rs 125 in), but maybe they lied so that i would pay them to rebuild my engine? Or would my bike being fullpower affect its performance on a restricted cdi? Any thoughts appreciated.

*I took it to a shop, but they wanted too much for a rebuild so i saved money by going on ebay. I researched the guy before sending the engine and he seemed legit. It was Road and Dirt Performance.
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stirlinggaz
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PostPosted: 21:32 - 24 Jun 2009    Post subject: Reply with quote

Hi,
wouldnt have trhought it was the CDI, & using a "restricted" CDI wont have made any difference.
as there no such thing as a "restricted" or a "de-restricted" CDI, there all the same, just some have the emission dip removed.
does yours have the dip removed? (has the sealant been cut into?)
i'd second the idea of trying out different jets.
perhaps thats why it seized in the first place?
no harm in chopping a bit of the HT lead off.
& try using a BR9 plug, till you get it running ok,
good luck,
cheers,
GAZ
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mad_revs
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Joined: 24 Jun 2009
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PostPosted: 22:25 - 24 Jun 2009    Post subject: Reply with quote

dont no if this is of any help or not but i used to have a mark 3 yamaha rd 125lc and had the excact same problem for about 6 months tried everything and nothing fixed it.in the end just out of luck i was fiddling with the wires one day that connect to the cdi.i unplugged one of the wires and left it unplugged and ever since then it was fine.if its a similiar set up.you should have 3 connectors connecting the cdi to the loom a yellow one a red one and another colour(cant remember)start the bike and try unplugging one wire at a time.two of the wires if you unplug them will make the bike cut out but the 3rd one it will still run perfect with it unplugged.then hopefully it shouldnt backfitre anymore.i dont no why this worked for me but was just fiddling with it one day.and a set up on a rs is probsbly completeley different but its got to be worth a try
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stirlinggaz
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PostPosted: 13:53 - 25 Jun 2009    Post subject: Reply with quote

mad_revs wrote:
dont no if this is of any help or not but i used to have a mark 3 yamaha rd 125lc and had the excact same problem for about 6 months tried everything and nothing fixed it.in the end just out of luck i was fiddling with the wires one day that connect to the cdi.i unplugged one of the wires and left it unplugged and ever since then it was fine.if its a similiar set up.you should have 3 connectors connecting the cdi to the loom a yellow one a red one and another colour(cant remember)start the bike and try unplugging one wire at a time.two of the wires if you unplug them will make the bike cut out but the 3rd one it will still run perfect with it unplugged.then hopefully it shouldnt backfitre anymore.i dont no why this worked for me but was just fiddling with it one day.and a set up on a rs is probsbly completeley different but its got to be worth a try


hi,
sorry mate, but the rs has no such set up.
the only mod that can be done, is cut into the sealant & "cut" the bridge that controls the emissions dip.
which, surprisingly, makes a HUGE difference.
the CDI, has no secondary wiring, it just plugs in. & afaik, is non servicable.
i'd be starting with the basics.
check the manifold for cracks.
check all over for leaks, check the gaskets.
remove the carb, strip it down & clean it, then give it a blow through with an airline.
then return the carb to stock settings.(including checking the float height)
get a couple of different sized main jets.
i dunno what exhaust you have on, but i would think you should be looking at around 120-125 sized main jet.
you do have the stock airbox? & not an open air filter?
get a couple of new plugs. (br9's should only be about 3 quid for standard plugs)
& start again.
check for a spark,
check for fuel,
check compression.
then get it running & see what what part of the rev range the problems are.
good luck,
cheers,
GAZ
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saikouslx
Renault 5 Driver



Joined: 06 Apr 2008
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PostPosted: 22:44 - 25 Jun 2009    Post subject: Reply with quote

stirlinggaz wrote:


hi,
sorry mate, but the rs has no such set up.
the only mod that can be done, is cut into the sealant & "cut" the bridge that controls the emissions dip.
which, surprisingly, makes a HUGE difference.
the CDI, has no secondary wiring, it just plugs in. & afaik, is non servicable.
i'd be starting with the basics.
check the manifold for cracks.n
check all over for leaks, check the gaskets.
remove the carb, strip it down & clean it, then give it a blow through with an airline.
then return the carb to stock settings.(including checking the float height)
get a couple of different sized main jets.
i dunno what exhaust you have on, but i would think you should be looking at around 120-125 sized main jet.
you do have the stock airbox? & not an open air filter?
get a couple of new plugs. (br9's should only be about 3 quid for standard plugs)
& start again.
check for a spark,
check for fuel,
check compression.
then get it running & see what what part of the rev range the problems are.
good luck,
cheers,
GAZ

ive done the first three. Doing the jets tomorrow, and ill look up how to set float height (as the carb is apart). I have the stock airbox with a pipercross panel filter in (said it requires no rejetting), it has spark, ive repalced the fuel twice, waiting for my mate to bring his compression tester round. I have no clue what make my exhaust is but im pretty sure its not standard. I heard running my bike on a br9 could burn a hole in my piston :O Is it worth buying a new pickup or magent and coil (i saw a similar thread where the guy said it was shorting in the magneto) and the shop i sent it to said the pickup wire had cut slightly, but wasntthe problem (maybe they did a shit job?). Cheers for all the help, will let you know how it turns out!
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steo
Nova Slayer



Joined: 08 Jun 2009
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PostPosted: 23:12 - 25 Jun 2009    Post subject: Reply with quote

It does sound like an engine timing issue. if the bike wasn't backfiring before the rebuild & only came into it after it, did you screw the stator plate back in exactly the same position as you took it off?
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bladerunner
World Chat Champion



Joined: 09 Sep 2006
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PostPosted: 23:23 - 25 Jun 2009    Post subject: Reply with quote

OK I'm going to state the obvious...but have you checked the woodruff on the flywheel key ain't sheared? Quite common on a first time build as the taper need to be spot on and the flywheel nut proper tight. Easy enough to make a flywheel holding tool for the RS.


Also if that does not help..try a good battery or jump leads. I know my RGV will not run well with a shot battery so let me know how you get on after these checks.
Wink

EDIT* if the flywheel was catching on the genny has it damaged any of the wires? or hit the pickup coil and has the flywheel rubbed through any of the wires near where they come out of the cover? All worth a look!
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mad_revs
Two Stroke Sniffer



Joined: 24 Jun 2009
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PostPosted: 17:17 - 26 Jun 2009    Post subject: Reply with quote

stirlinggaz wrote:
mad_revs wrote:
dont no if this is of any help or not but i used to have a mark 3 yamaha rd 125lc and had the excact same problem for about 6 months tried everything and nothing fixed it.in the end just out of luck i was fiddling with the wires one day that connect to the cdi.i unplugged one of the wires and left it unplugged and ever since then it was fine.if its a similiar set up.you should have 3 connectors connecting the cdi to the loom a yellow one a red one and another colour(cant remember)start the bike and try unplugging one wire at a time.two of the wires if you unplug them will make the bike cut out but the 3rd one it will still run perfect with it unplugged.then hopefully it shouldnt backfitre anymore.i dont no why this worked for me but was just fiddling with it one day.and a set up on a rs is probsbly completeley different but its got to be worth a try


hi,
sorry mate, but the rs has no such set up.
the only mod that can be done, is cut into the sealant & "cut" the bridge that controls the emissions dip.
which, surprisingly, makes a HUGE difference.
the CDI, has no secondary wiring, it just plugs in. & afaik, is non servicable.
i'd be starting with the basics.
check the manifold for cracks.
check all over for leaks, check the gaskets.
remove the carb, strip it down & clean it, then give it a blow through with an airline.
then return the carb to stock settings.(including checking the float height)
get a couple of different sized main jets.
i dunno what exhaust you have on, but i would think you should be looking at around 120-125 sized main jet.
you do have the stock airbox? & not an open air filter?
get a couple of new plugs. (br9's should only be about 3 quid for standard plugs)
& start again.
check for a spark,
check for fuel,
check compression.
then get it running & see what what part of the rev range the problems are.
good luck,
cheers,
GAZ


didnt think it would be the same set up but worth a go
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Kickstart
The Oracle



Joined: 04 Feb 2002
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PostPosted: 17:55 - 26 Jun 2009    Post subject: Reply with quote

Hi

By backfire do you mean through the exhaust or back through the carb? Through the exhaust suggests it is dumping a load of excess fuel into the exhaust and then igniting it (is it a catalysed version with the original exhaust?). Through the carb would suggest timing issues, but the reed valve should really stop that unless they are damaged.

I would doubt the jetting or the oil is the issue. Oil might make it a tad lean on fuel, but assuming you didn't drown it I doubt it would make a relevant difference. The main jet might be slightly small (might well be correct. Aprilia did vary the main jet a bit depending on year) that should only be relevant at large throttle openings (3/4 or more).

Cdis mostly either work or don't. The cdi restriction makes no difference at all outiside the 4750~6000rpm range (massive ignition retard from 5000 to 5750 for the environmental dip).

One thing that might be worth checking (easy to check, but would doubt it is the issue) is the clearance between the crankshaft igition pickup and the flywheel.

All the best

Keith
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Hutchysrs50
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PostPosted: 13:44 - 27 Jun 2009    Post subject: Reply with quote

i havnt read all the posts so sorry if its been said.

i would think its the timing out, could of been the problem in the first place putting extra force on the engine doing the crank/bearings in.

i had a problem with my old tzr 50 after it has been started for a while it wouldnt rev past 3k either, that was due to the jetting being to low once it was fully warmed up, but the problem only went away after i re-built everything!
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saikouslx
Renault 5 Driver



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PostPosted: 15:24 - 27 Jun 2009    Post subject: Reply with quote

hi, up jetted it today, now the bike behaves slightly differently. It seemed to rev out abit better up to 5k, sounded abit better still with choke on, but once it gets past 50 degrees it refuses to start. I also opened up the magneto sde to find a pretty paterrn of what i assume is rust swirling out form the cventre. It looks as tho the rust was displaced by moisture, and it seemed moist but i wasnt too sure, i cudnt smeel petrol but the swirls wiped away on my finger, therefore i reckon this is petrol residue, so the crank seal has gone? When we first took out the seal i made a scartch into the housing abit, but then smoothed it to avoid it catching the seal, could this be the problem? Although a mechanic told me that the seal should seal it up. i was at the most 1mm deep. Cheers for all the replies, what do you guys reckon?


Also if anyone is interested in buying this bike i wouldnt say no for the right price, its looks in mint condition apart form the fact it backfires, its a rossi rep.
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tutton
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PostPosted: 15:32 - 27 Jun 2009    Post subject: Reply with quote

Whats the right price? Wink
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Timmeh
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PostPosted: 17:58 - 27 Jun 2009    Post subject: Reply with quote

For a '99 model with an engine that's previously been subjected to some major abuse, been seized at least once and now got major issues I wouldn't pay more than 400, depending on how clean the bodywork was.
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tutton
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PostPosted: 17:59 - 27 Jun 2009    Post subject: Reply with quote

I sold mine with no engine for 410, with cacked fairings and no speedo drive, do i win a cookie?
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tutton
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PostPosted: 18:04 - 27 Jun 2009    Post subject: Reply with quote

Nothing son, doing training for test again,
im going to fucking pass this time Laughing
then as soon as i pass im going out and buying a J1.
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