Intermittent rough running - stator?

[alanscottj]

Now my scooter is jetted ok (but not perfect, a tad rich) every now and then it runs pants, a bit stuttery but right through the rev range. Then it clears itself and runs spot on again. Did a plug chop yesterday when it was running good and the plug was a nice dark colour, maybe a tad rich. Later in the day when experiencing the stuttery running I did another plug chop and the plug was very light/greyish colour. Every now and then when riding there is a bit of a blip like it is rich. Plug I have in is a BR8ES. Ignition is a varitronic set at 24 degrees. Recently had to replace the regulator as it had died so hoping the stator isn't on the way out? Any thought guys?

Many thanks.

Scott

[Adam_Winstone]

Watch out that this is not a throttle position issue! Plug colour will only ever give you a poor average of jetting, unless you hold it at a specific and constant throttle position for a couple of miles, then cut the ignition and coast over to check how plug colour relates to that specific throttle position. You would then need to do that for 1/4, 1/2, 3/4 and full throttle, otherwise plug colour will tell you very little.

Have a search for info on 'choke tests' which can give you instant feedback on the jetting at all individual throttle settings.

NB: 1000 miles at 1/4 to 1/2 throttle equates to ZERO miles at 3/4 to full and may people seize the first time they try to hold a bike at 3/4 on a long straight road! Plug colour is very important and will inform you of how a bike is running/jetted, however, it often lulls people into a false sense of security; nice and brown around town and then ZIP!!!! on the open road.

Adam

[alanscottj]

Watch out that this is not a throttle position issue! Plug colour will only ever give you a poor average of jetting, unless you hold it at a specific and constant throttle position for a couple of miles, then cut the ignition and coast over to check how plug colour relates to that specific throttle position. You would then need to do that for 1/4, 1/2, 3/4 and full throttle, otherwise plug colour will tell you very little.

Have a search for info on 'choke tests' which can give you instant feedback on the jetting at all individual throttle settings.

NB: 1000 miles at 1/4 to 1/2 throttle equates to ZERO miles at 3/4 to full and may people seize the first time they try to hold a bike at 3/4 on a long straight road! Plug colour is very important and will inform you of how a bike is running/jetted, however, it often lulls people into a false sense of security; nice and brown around town and then ZIP!!!! on the open road.

Adam

Thank Adam - I just can't understand why the poor running is intermitent and then runs great again. But I do agree that i have to do a proper chop for a couple of miles. Can't wait for dyne

[Adam_Winstone]

Intermittent poor running is very common with a faulty stator, typically because of a failing LT coil but also possibly because of loose earth rivets, poor soldered joints or hairline fracture of the LT coils earthed end wire. A good pal of mine had this on his TS1, which was running an Indian stator that gave perfect readings, and for weeks he played with his jetting, with the bike running fine for a couple of days, then being rubbish for a couple, then fine again, then rubbish again, all the time continuing to give perfect readings. I finally convinced him to let me rob a different LT coil off one of his original PX stators, modified the laminates on the Indian stator to accept the Vespa LT, and he has not had any repeat issue in the years since (c.a. 5 years or more!).

This may be jetting or ignition related. Best of luck getting it sorted.

Adam

[Daggs]

Air leak ..........

[alanscottj]

Air leak ..........

I did do a leak down test when I rebuilt the engine but will do another just to rule it out

[alanscottj]

Intermittent poor running is very common with a faulty stator, typically because of a failing LT coil but also possibly because of loose earth rivets, poor soldered joints or hairline fracture of the LT coils earthed end wire. A good pal of mine had this on his TS1, which was running an Indian stator that gave perfect readings, and for weeks he played with his jetting, with the bike running fine for a couple of days, then being rubbish for a couple, then fine again, then rubbish again, all the time continuing to give perfect readings. I finally convinced him to let me rob a different LT coil off one of his original PX stators, modified the laminates on the Indian stator to accept the Vespa LT, and he has not had any repeat issue in the years since (c.a. 5 years or more!).

This may be jetting or ignition related. Best of luck getting it sorted.

Adam

When I posted a graph of my most recent dyno, someone on here (Dan maybe?) commented that the way the line on the graph went down (lost poser after max bhp) it looked like there could be an issue with my ignition. This could be another clue that there could be something wrong with it?

[alanscottj]

Found the culprit! Found an earth cable that goes to my frame dangling down - the nut and bolt holding it to the frame has obviously worked loose over the past few days. Reconnected nice and tight and engine running as it should be. Happy days