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Post by lshigham on Feb 15, 2011 9:03:52 GMT -5
Try dropping the needle one notch or a smaller main jet.A partially clogged air filter will give these symptoms too.I think other than the kill switch circuit,you've covered the ignition system.. I'm trying to leave the jetting alone, as I know that it was fine in the past. It was done on the dyno. I'm now certain that my problems lie in the ignition system, I got hold of a spark tester that lights up when there's spark. It goes out when it bogs and stutters. New CDI/Coil arrived today, now fitted. I shall report back  |
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Post by lshigham on Feb 15, 2011 11:35:13 GMT -5
:swear: :banghead: :doh: :bfg: :rant: Still broken  |
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Post by 90GTVert on Feb 15, 2011 12:15:37 GMT -5
Have you checked all the connections in the kill switch circuit as 190 suggested?
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Post by lshigham on Feb 15, 2011 12:47:27 GMT -5
Have you checked all the connections in the kill switch circuit as 190 suggested? Sorry. Yes, kill switch is behaving itself, grounded when off and open when on. I can get it up on a dyno for a 30 second diagnosis, but not until the weekend. I live 10 miles from civilization, and don't even have a bus service, this is my only form of transportation. I did try dropping the needle, in desperation. No change, but I think you might be on the right lines. I just need to figure out what's causing the richness. |
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Post by troy1896 on Feb 15, 2011 13:20:49 GMT -5
Wasn't it a brand new cylinder that was dynoed? Could it be, and I'm just guessing here, that it was set up a little rich because of extra heat developed from the tighter tolerances, and now that it is more worn in it needs leaner jetting?
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Post by stepthrutuner on Feb 15, 2011 14:35:04 GMT -5
Try dropping the needle one notch or a smaller main jet.A partially clogged air filter will give these symptoms too.I think other than the kill switch circuit,you've covered the ignition system.. I'm trying to leave the jetting alone, as I know that it was fine in the past. It was done on the dyno. I'm now certain that my problems lie in the ignition system, I got hold of a spark tester that lights up when there's spark. It goes out when it bogs and stutters. New CDI/Coil arrived today, now fitted. I shall report back I have been following your troubles with a lot of interest since I have the same Piaggio motor on my Derbi. I've been experiencing a cut-like stutter at around 9300-9500 and have tried everything fuel wise including upjetting to a 120 MJ to no avail. I've practically decided that the CDI is to blame so I am awaiting your outcome. |
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Post by lshigham on Feb 15, 2011 14:39:01 GMT -5
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Post by lshigham on Feb 15, 2011 14:40:56 GMT -5
Wasn't it a brand new cylinder that was dynoed? Could it be, and I'm just guessing here, that it was set up a little rich because of extra heat developed from the tighter tolerances, and now that it is more worn in it needs leaner jetting? An interesting theory for sure, and certainly not something I would have thought of. However, the cylinder was set up with 13.5:1 AF ratio for max power (fairly lean, I wouldn't like to go any leaner). |
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Post by 190mech on Feb 15, 2011 15:13:38 GMT -5
I wonder if it is a stator or pickup coil that is shorting under high RPM vibration???
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Post by stepthrutuner on Feb 15, 2011 15:14:13 GMT -5
Thanks for the heads up on diagnosing my ignition. Right after posting my last reply I happened to think of a possible problem with my trigger or the air gap. I'll be checking it all out. Thanks again!
Reg
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Post by lshigham on Feb 15, 2011 15:21:10 GMT -5
I wonder if it is a stator or pickup coil that is shorting under high RPM vibration??? It's possible, they're fine when idling. The stator output is fine to the coil (110v, min 50v) and the pickup resistance is within range. Not sure how I'd test it at 13k, and I'd hate to throw more money at it. I'm thinking that although there is a spark issue, it's caused by the plug fouling due to an excessive rich mixture :stumped: |
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Post by troy1896 on Feb 15, 2011 15:23:02 GMT -5
I'll throw out some more guesses if you like. They are basic things that you probably have checked already, but maybe haven't listed.
I see that you have Malossi rollers in your sig. I have had those rollers show flat spots after 400 miles. Might be worth a check.
Does your new carb have a power jet? I have seen that give tuning troubles.
Is the plug a "B" or "BR"? I have seen that make a difference on some CDI's as well.
I had a similar high speed miss before, and the problem was that at certain RPM's, a vibrational resonance was created, and caused some contact problems between the spark plug boot and the plug.
I really like your idea about the spark jumping the insulator. I know that the plug wire is probably new, but the insulation could be bad or have a thin spot.
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Post by lshigham on Feb 15, 2011 16:41:48 GMT -5
I'll throw out some more guesses if you like. They are basic things that you probably have checked already, but maybe haven't listed. Thanks, every little helps  I see that you have Malossi rollers in your sig. I have had those rollers show flat spots after 400 miles. Might be worth a check.I needed to have a shufti in the CVT anyway, thanks for reminding me. Does your new carb have a power jet? I have seen that give tuning troubles.Nope Is the plug a "B" or "BR"? I have seen that make a difference on some CDI's as well.I've tried all the combinations of resistor and none resistor plugs and HT caps, just to cover all bases. I had a similar high speed miss before, and the problem was that at certain RPM's, a vibrational resonance was created, and caused some contact problems between the spark plug boot and the plug. New plug and boot came with the CDI installed today, and there's no way in hell that it's jumping off. It was a pig to get over the plug  I really like your idea about the spark jumping the insulator. I know that the plug wire is probably new, but the insulation could be bad or have a thin spot.A good theory, but the CDI/coil came with a new HT lead as well. I've discovered that my reeds weren't sealing very well at all to the cage (stray threebond on the mating surface), so I've rectified that, cleaned the carb and checked the gubbins for holes, leaks, blockages and anything untoward. We shall see in the morning. In the meantime, any ideas, no matter how wacky, will be gratefully received. |
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Post by stepthrutuner on Feb 15, 2011 19:38:50 GMT -5
When I checked the ac voltage from the stator ignition coil I only read 38v (the troubleshooting guide said it should be 50-80vac). That could be the problem. When the problem occurs at speed, however, I seem to be hearing detonation. I've also wondered if I might have a coked piston/head?
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Post by lshigham on Feb 16, 2011 2:40:43 GMT -5
It's not a bad theory, especially as it occurs round the RPM range where there should be maximum compression.
If you need a new stator (probably, I was getting over 100v AC in that test) I know of a cheap one in the UK that they should be able to send over.
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