Just when it was going well

[Tractorman]

Went to Peterborough a little over 50 miles I thought this would nicely finish off my running in. I done almost 900 miles with a rapido classic with no problems. Going to Peterborough I was keeping an eye on the temp gauge because it was a side to head wind but the scooter went well. Coming back stopped at the big M for lunch just outside Peterborough and then filled up at the nearby esso garage. No head wind now so I was away cruising along at 50mph and less than two miles down the road the thing nipped up, WHY?? Same amount of oil, engine warmed up but not overheated I put down to the fuel at the garage. I put extra oil in and no more problems on the way home. The piston does not look to good but the cylinder has cleaned up fairly well.

[Warkton Tornado No.1]

I know this wasn't the cause of your issue but, extra oil means a weaker mix in fuel/air, if you think about it.

I know a lot of you still do it, but, be aware that it is the amount of neat fuel that is used in combustion that is critical in the mix that the carburettor achieves, not the amount of 'petroil.'

That's why you should rejet if you go from, say, 50:1 down to 33:1. Adding oil weakens the 'mix' of fuel/air.

I hope to have helped, not score points!

[Tractorman]

Thanks, but I put the extra oil after the seizure.

[coaster]

Thanks, but I put the extra oil after the seizure.

That's the point he was trying to make, if it HAD been a weak mixture that had caused it you would have made the problem worse by putting more oil in. It could be that without the head wind you were using a different throttle position and maybe you have a weak spot in the progression. Did you check the plug colour when it nipped up?

[Raveydavey]

If mixture was the issue wouldn't that have shown in the temperature gauge? Could it be the temp had risen but went unnoticed? Was that the longest ride it's done since you started running it in?

[Tractorman]

If mixture was the issue wouldn't that have shown in the temperature gauge? Could it be the temp had risen but went unnoticed? Was that the longest ride it's done since you started running it in?

Since starting this session of running in one eye is never away from the gauge and it was around 60c. York rally would have been the longest but not as hard as the run to Peterborough.
Coaster you may be right throttle position would not be the same with the following wind but I never thought to check the plug.

[Swat]

1st posting for me on here & a relatively unscientific one at that !!

My setup is a 225 Rapido classic (+LTH reed) i had similar sutuation transitioning from running in to normal usage. As AF's had built engine, I took bike back & had dore honed & jeeting adjusted to I think 55 pilot & 138 main) Since been generally ok (probably a bit rich at bottom end) I've had a further near seize experience early this yearwhen head temp rose suddenly & i got the 'pinking' noise. Occurred in simialr speed/weather circumstances to your description. I try to steer clear of that no mans land of around 50 mph when bike almost runs on closed throttle in 4th.
Ride at 55 to 60 & it's happy as Larry.

[coaster]

....... I try to steer clear of that no mans land of around 50 mph when bike almost runs on closed throttle in 4th.

I'm also a bit wary in situations like that and I'm constantly backing off the throttle so that it 4 strokes for a few seconds and therefore cool the piston (weather it needs it or not (gauges not currently working )

[Warkton Tornado No.1]

This might just add to confusion, but here goes.

There are rarely absolutely still conditions but does anybody wonder what happens to that 'stack' of petrol/air mist that hovers around the bell mouth of the carburettor in certain conditions?

If both examples here are running through filters or beneath panels with no cut-out, then take no notice.

However, my own belief is that if the wind is in a certain direction & dependent on throttle position, there can be times when the conditions for a safe burn are no longer at an optimum. The 'stack' gets blown away, to the detriment of the carburetion. To some extent, that's why some racers (piston ported, Rapido or Mugello) use carb bell mouth rubbers. Power increases probably due to consistency of 'charge.'

Now, before some prat suggests getting a wind vane or some such, I would suggest most of us have felt a little nervous in windy conditions whilst rolling on & off the throttle with everything else to contend with.

It’s just a suggestion that came to mind......I’ll get my coat.

[Adam_Winstone]

A 'new' throttle position could be the simple answer for this, remembering that 900 miles at half throttle equals zero miles at 3/4 throttle. I've seen a number of my pals run in at a certain throttle position and have no issues during the whole running in period, a great plug colour from the 0 to 1/2 range, then come to me asking why they've seized the first time they hold it open at 3/4, confused because 'I've run it in for 900 miles!' Ask what testing and checking they've done at this 'new' throttle position and the answer is none.

This may not be the case here but I just wonder if we're not looking beyond the obvious?

Adam

[Warkton Tornado No.1]

Adam, you are surely correct, but presumably everybody knows to 'stay on the gas' especially with tuned engines?

Perhaps they don't, & nowadays rider/tuners are more commonplace & seeking further refinement so settings are perhaps less forgiving than umpteen years ago......

[Tractorman]

Thanks for all your posts. I got it back together and took it out again today similar conditions but perhaps stronger wind. Did a 20 mile run into the wind and back with a tail wind with no problems, but I did take your advise and opened it up more with the wind behind me. ILC rally on Saturday will be the final test before I put the sidecar back on.