Question:

I have upgraded my bike with a 180cc kit, malossi fuel injection and a sports exhaust.

I seem to have real problems with the starter being under powered to start the bike.

I have burnt out standard starter motors and also (although it lasts longer) a heavy duty racing starter.

Is there a starter upgrade I could get? Or is there a more powerful starter that I could modify to fit in the YZFR 125?

My reply:

When you say ‘malossi kit’ did you also fit the malossi camshaft? Do you happen to have a picture of the kit and/or the camshaft you installed?
I’m asking because some aftermarket cams don’t let you install the decompression mechanism, which would give you the sort of starting issues you describe.

Their reply:

Yes I installed a racing camshaft also. 
I’m not aware of any decompression mechanism. 
Only the advance/retard mechanism bolted to the end it the camshaft. 
Is the decompression mechanism a further addition? Or is there on on the bike as standard? 

Answer:

the decompression mechanism is part of the stock upper timing gear, see the pic below. There’s a little lever which gets activated by centrifugal force (once the engine is getting turned over) and that operates a cam which opens one of the valves slightly which means the cylinder doesn’t seal off properly, and makes it easier to start.

They do this because it means they can have a smaller (lighter) starter motor, smaller cables, smaller battery etc.

more details here:
https://www.motorcyclespareparts.eu/en/yamaha-parts/2008-yzf-r125-motorcycles/camshaft-chain
IIt sounds like you’ve got a vernier/adjustable cam gear (for adjusting the valve timing) which doesn’t have the decomp mechanism, and hence you’re having trouble starting.

If you look at the camshafts below the left one does not have the decomp hole, just a little indent where the whole would be. The right one (difficult to see i know) has a hole where that indent is, which goes right through to the cam lobes, and   where the decomp lever (part 6 here: https://www.motorcyclespareparts.eu/en/yamaha-parts/2008-yzf-r125-motorcycles/camshaft-chain )  slides into.

There are cams with and without the decomp mechanism because this engine is used in a bunch of bikes.. and for example the R15 which is very popular in asia has a kickstart so then i don’t think you don’t need the decomp mechanism. Hence also an R15 would be able to run the adjustable top timing gear with no problems.

What you probably need is one of these (“stage 2” version):https://sxparts.com/performance-camshaft-yzf-r125-r15-wr125/

In the first pic you’ll notice it has a little cutout just to the left of where the cam bearing sits.. that’s for the little decomp lever. 

If you get one of those cams, the stock top timing gear will fit, as will the decomp mechanism and then you won’t be burning out starter motors anymore. I run the same cam in mine, for the same reason, also 180cc, no starting problems…I think it worked out about $90/£~60 delivered

btw idk if the malossi cam has the decomp hole.. if it does then you can just bolt the stock top timing gear + decomp mechanism back on and you should be good.