Piston Travel???

[Architecten]

After my GP gave up in St Bees I've rebuilt the stator but once back together the engine was running a bit racy. I've played around with the jetting but this had little effect. So I finally got round to checking the timing last night. It was around 2-3degs out so adjusted the plate and fired her up. The timing then looked about right but it was still ticking over too fast.

I let it run for around 5 minutes while checked the timing, adjusted the air screw etc but it didn't help. I was starting to suspect it may be an air leak when it started over revving. I cut the engine and pulled the ht lead off but had to turn the choke on to kill it. The over revving lasted no more than 10 seconds. I then twisted the throttle a few times to get some fuel in it to cool it down and tried to kick it over but it was stuck.

I can turn the flywheel backwards and forwards and see the piston traveling up and down but as it reaches TDC it is like it hits something??!! I know I need to strip it down but has anyone any idea what it could be?? I was thinking it may be a ring or maybe the crank has twisted but the over revving seemed to be such a short time I'm surprised something so bad has happened..... help....!!!

[Chris in Margate]

Pre-ignition. The piston gets white hot and ignites the fuel like a diesel. Mostly always down to excessively weak mixture caused by air leak. Can also be down to overly advanced ignition but 2-3 degrees won't really make that muh difference.
Got to strip it to assess any damage.
Happened to me once on a garage forecourt. Alarming to say the least !

[mick1]

I wonder if part of the stator has come loose/broke ? that could cause the jamming and also explain the over reving (timing slipped).

[Architecten]

It's not the stator. I had the flywheel on and off as I was check the timing etc. I suspect it's an air leak as it took a while to start but the plug was wet with petrol... it was flooding but once started it was weak... if that makes sense! But I'm surprised if it is an air leak, it's an RT so the head is held down with 8 nuts...

Just a bit gutted, I've not been riding the scooter, just been methodically going through things to get it right...

[mick1]

I've pressure tested a few engines lately and 2 had an initial leak at the barrel base, leaking air up the barrel stud and coming out around the cylinder head nut. Might be an idea to pressure test before stripping it down.

[drunkmunkey6969]

Post a pic of what you find when you strip

[Architecten]

Where's best for a leak test kit?

I will check the stator again as well. It's odd that it only stops as it reaches the head. It just clunks like it's hitting something...?!

[Chris in Margate]

Probably a detached ring.

[mick1]

My first pressure tester was a push bike inner tube connected (Jubilee clips) to the inlet manifold and the exhaust stud. I pumped it up and sprayed soapy water over the barrel, and manifolds. Bubbles soon appeared !! Once I had sealed the leaks I pumped it up again, tried the soapy water (no bubbles) then left it a couple of hours to see if it deflated.....all ok.

[Yanker]

Post a pic of what you find when you strip

Is your interest in 'size' or 'specfic content' when the 'Architect is performing his/her stage act? In certain circumstances an assistant may be required: if there is not space for a selfie stick. Perhaps someone in the audience could volunteer?

But if you mean taking a look at the reaction when he/she or she/he strips, I am sure ammusement is guaranteed.......