RS125 2008 not starting

mwr_allen · L Plate Warrior Joined: 23 Mar 2016 Karma :

Hi All,
I have an RS125 2008 model with a stock VSHT28 Dellorto carb and stock Rotax Reed Valve and after stopping for 5 minutes yesterday and trying to start it up again it just doesn't want to start. The battery is fine, the plug is sparking, there is compression from the piston, the fuel pipe is flowing. When hitting the ignition it's just turning with no ignition in the cylinder, just spinning and not biting. When riding it just before I stopped it did sound quite grumbly, also, I have recently had problems with the water pump which I still need to replace the seals and O-Rings as it was slightly leaking coolant from the weep hole when running.
Not sure if this is enough to go on but any help would be much appreciated.
Thanks.

andy_uk · World Chat Champion Joined: 13 Aug 2011 Karma :

mwr_allen · L Plate Warrior Joined: 23 Mar 2016 Karma :

Ok so I've taken the plug out and checked compression and it's good, I've put a new plug in, I've taken out the carb, cleaned and blown through all jets and inlets, taken out the reed block and checked reeds which seem to be clean and fine, after talking to my local mechanic on the phone while everything was in place I removed the main jet from the bottom of the carb and tried turning over the engine with the main jet bolt removed and its dry, no fuel coming into the float bowl at all so it would seem that there's no fuel getting into the carb although the fuel pipe is fine and pumps out fuel when disconnected from the carb and try to turn over.
The old plug was a bit dirty and oily when I removed it yesterday.
I'm at a complete loss as to what the problem is.

P.addy · Red Rocket Joined: 14 Feb 2008 Karma :

Compression is registered in psi. Not on a 'good' rating Wink

What actual pressure is it at. If it was grumbling and it's not had a rebuild in a few thousand or its sat for months best get your wallet out.

mwr_allen · L Plate Warrior Joined: 23 Mar 2016 Karma :

Unfortunately I do not have a compression tester although when I put my thumb on the spark plug hole and try to turn it over it blasted my thumb off with some force.
Just on the carb float bowl side of things, it should be getting fuel into it correct? As at the moment it's not getting fuel in there at all.

P.addy · Red Rocket Joined: 14 Feb 2008 Karma :

Yes, fuel should go into the carb.

I'd suggest getting a tester, its key on an RS.

I'd probably suggest checking the fuel is actually coming out of the tank, then cleaning the carb and making sure all is clean.

mwr_allen · L Plate Warrior Joined: 23 Mar 2016 Karma :

Ok thanks, I will get a tester soon.
I have had the carb apart and cleaned, the vacuum seems to be working as I took the fuel pipe off the carb and when I turn the bike over a little it pumps fresh fuel straight out.
Where the fuel pipe goes into the carb, when I blow on the inlet I can't blow through it unless I push the floats up on the bottom of the carb, the mechanic I spoke to on the phone suggested getting a syringe with some fuel in and forcing some fuel into that inlet while the carb is intact and on the bike to get some fuel into the float bowl and at least try to get it to bite when turning it over and it might clear any unseen blockage.

P.addy · Red Rocket Joined: 14 Feb 2008 Karma :

Sounds like hope and dreams.

Fuel goes into the carb with ease, when it gets to the maximum, the needle closes up the hole.

I'd suggest whipping it off again and checking that the whole for fuel is clear and the needle is seated correctly.