honda fes 125 s-wing pantheon not starting help plz

[Andym]

No. Electronic ignition is generally very reliable and it's unlikely anything like a cam sprocket would jump a tooth on any modern engine, but given you have petrol, compression and a spark it can only be the combination of these that's the issue.

Andy

[amebb]

No. Electronic ignition is generally very reliable and it's unlikely anything like a cam sprocket would jump a tooth on any modern engine, but given you have petrol, compression and a spark it can only be the combination of these that's the issue.

Andy

hi Andy
I just had a look at the compression on the motor bike. I cranked it a few times and the compression is 25psi. I have had a look online and i think that may be too low.

What are your thoughts ?

Thanks

[Argyll]

That sounds way too low. I would expect well over 100psi although I don't know the engine in question. Are you sure you did it correctly? Did you have the throttle wide open?

[roadster]

Yes that pressure is very low but are you sure that the scooter doesn't have a centrifugal decompression device on the end of the camshaft? These generally keep an exhaust valve open at cranking speed so you need to turn the engine over at about 1000 rpm to get a true reading. For example you could rig up an electric drill running at low speed or perhaps use a car battery to boost starter performance. ... and of course decompressors can themselves stick and prevent the engine starting much as if the exhaust valve was stuck open.

[amebb]

That sounds way too low. I would expect well over 100psi although I don't know the engine in question. Are you sure you did it correctly? Did you have the throttle wide open?

Yes even with the throttle full open or closed i am still getting no more than 25 psi.

What would cause this compression presure to be so low ??

[Argyll]

There are several reasons but you'll find plenty of specific info online, for example, https://everbiker.com/how-to-fix-low-co ... otorcycle/

[Andym]

25 PSI is indeed too low. Should be tested throttle held open, crank spinning fast enough.

All good advice above.

I'd start with what you can do with the head on.

Pour a tablespoon of oil into the plug hole and repeat the test. If you suddenly have compression it's the piston rings.

Adjust the valve clearances, checking for anything odd and watching them move. Make sure TDC makes the Mark's on the cam etc. line up. Make sure any timing chain tensioner is free and working, if it wasn't, can the timing chain jump?

Turn it over and listen for any hissing out of the head gasket.

At that point if you are still none the wiser it's time to take the head off and have a proper look.

Andy

[amebb]

25 PSI is indeed too low. Should be tested throttle held open, crank spinning fast enough.

All good advice above.

I'd start with what you can do with the head on.

Pour a tablespoon of oil into the plug hole and repeat the test. If you suddenly have compression it's the piston rings.

Adjust the valve clearances, checking for anything odd and watching them move. Make sure TDC makes the Mark's on the cam etc. line up. Make sure any timing chain tensioner is free and working, if it wasn't, can the timing chain jump?

Turn it over and listen for any hissing out of the head gasket.

At that point if you are still none the wiser it's time to take the head off and have a proper look.

Andy

UPDATE

Yesterday i took the engine cover off and noticed that the valves were stuck. This was the reason why, i think nothing was happening.

After a few minutes i cleaned up the valves from the top and slightly loosened them.
The work i did was not perfect but it was just to locate and isolate the issue.

I tried starting the moped again and this time it wanted to start, there were a few back fires (Blue Flame) from the intake manifold that were not there before.

So, i think i have made some progress here.

Todays question is.... can i remove the head to check and fix the valves or can this be done without removing the head?

Thank you

[Andym]

I wouldn't mess, take the head off.

Why have the valves stuck? This isn't an every day failure. Something bent? Head inserts loose? Oil starvation? Corrosion from long term lack of use? Something come loose and jammed?

If I was in a hotel car park with a ferry waiting I might use loosening spray to get going, but I would doubt it as a long term repair.

Andy

[amebb]

I wouldn't mess, take the head off.

Why have the valves stuck? This isn't an every day failure. Something bent? Head inserts loose? Oil starvation? Corrosion from long term lack of use? Something come loose and jammed?

If I was in a hotel car park with a ferry waiting I might use loosening spray to get going, but I would doubt it as a long term repair.

Andy

Hi Andy

I have no clue why the valves are not opening correctly.

Like i said originally, my friend purchased this moped and when it arrived it would not start.

Slowly, we have ruled out so many possibilities and now face the valves not opening etc.
There was no oil in the engine, well very low and we did fill the engine with oil but over a few days the oil leaked out.

The oil leak is a problem but nothing major at this stage as we need to get the moped working again.

So, today i will have a look at the bike again and see what we can do on it and if the head needs to be removed then we can do that and see what is going on inside.

Will keep you all updated.

Thank you