Aprilia RS125 Issues

[R6R6R6]

Hello guys.

Recently purchased a Aprilia RS125 2005. I am not sure if it is restricted or not but it does have a non standard exhaust system.

The Problem:

- The bike quite often drops revs and then dies and is a bitch to get started again.
- The bike will not rev past 5000 rpm unless I use the clutch to get it into powerband and release (and then its speed daemon) which makes it a pain for driving in the city.
- Can sometimes be hard to start

I have recently had the main bearing replaced as on my first run (after letting it warm up and taking it easy) the engine seized and back wheel locked. The guy at the garage told me the previous owner filled it with the wrong oil and the main bearing wasn't being lubricated causing it to fail.

I am looking to pass my full DA in the next few months so i wont have it for long but it would be nice to have it running properly till then. I am assuming something is wrong with it atm or am I just riding it like a noob? I had a Hyosung GT125R 4 stroke and although it had in comparison no power it did at least rev all the way up the rev range.. albeit slowly.

[P.]

Would get a compression test done on that engine.

What spark plug are you using, is the bike derestricted at all? Any mods?

When was the last piston/ring change?

What oil are you currently running.

Nothing wrong with the GT125R

[R6R6R6]

No no the GTR was a great bike, just wanted something a little nippier .

The guy who fixed my bike (he is well recommended) told me that the piston/ring was fine. I have not changed the spark plug as of yet but will probably do so just to rule that out.

I am running top quality fully synthetic oil and as far as I am aware there are no mods except the exhaust system.

[Kickstart]

Hi

Not sure on the first point. First thing I would check would be the fuel filters (including the one in the carb) and fuel tank breather. On the basis that these being a bit blocked would result in it taking a while for fuel to get through to restart (but I would also expect the bike to cut out if running for any reasonable length of time).

2nd point sounds like it just hasn't had the cdi unit mod done. The RS125 has a deliberate massive flat spot between 5000 and 6000 rpm caused by large amount of ignition retard. The cdi is designed so it can be easily modified to use a different ignition map to remove the flat spot. There is a particular point that you dig into the cdi unit to find a metal bridge that you cut.

As to hard to start, could be anything. But with a 2 stroke a new spark plug is a regular item so I would try that first.

All the best

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

[R6R6R6]

Do you think the flat spot in additional to the filters being clogged would stop it from going past 5000RPM? I understand that there is a flat spot but at the same time I would still expect it to be able to pull through it into the powerband at least slowly. It literally just stops and refuses to go past. If I pull in the clutch I can get it past drop the clutch and i'm away!

[Kickstart]

Hi

The flat spot is so bad that in most gears it will not just go through it. Get it past 6000rpm and it should be fine.

Filters being blocked will stop the fuel flowing / slow down the fuel flow. Until the fuel level drops a bit it will have no effect, and how long that takes will depend on how blocked the filter is and how much fuel you are using

All the best

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

[R6R6R6]

Cheers Keith.

As long as its an intended 'feature' and not a problem that may be linked to something blowing up next time I ride it I am quite happy. I am not keeping it for long and will be selling it in the next month or so after my DA.

I would do the CDI-de restriction but as I am looking to getting a new bike shortly ill just put up with it for the time being.

The next rider can do as he/she wishes.

Thanks again

Scott

[Kickstart]

Hi

The cdis are commonly modified even before the bikes are picked up by their first owners.

There are plenty of online guides as to how to modify it.

If it is full power it should really wake up around 8000rpm and then rev out to about 11000rpm.

One thing some people do as a cheap derestriction is to modify the power valve blanking plate to be like the power valve in the high revs position. If this is done you will have stuff all low down power and the power will kick in fairly hard at 7k~8k.

All the best

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

[demon9374]

[Kickstart]

Hi

The power valve works by lowering the top of the exhaust port. Effectively variable valve timing on the exhaust side.

At low revs it is down and at high revs it is up. This is to get decent top end performance and salvage a bit of bottom end power. While you might be able to get more bottom end power with other mods I suspect that they would cost you a load of top end power.

The exception to this is that the power valve is open in the high revs position below 2500rpm. This is so around town it opens and closes regularly to try and stop it sticking. Also means that below 2500rpm it is really pathetically powerless.

The blanking plate is just like a longer power valve blade turned over (ie the bottom end is vertical in line with the side of the piston, rather than horizontal in line with the top of the exhaust port). If might give a touch more power at lower revs (and a load more below 2500rpm), but will kill top end performance.

All the best

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

[demon9374]

Cheers Keith.

I've got the blanking plate you see, just wondered if it could be modded or whatnot to give me some low end, not really bothered about top end too much, it's not like it'd make it hard to get past 40mph lol

Plus.. Speeding is illegals!