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Power loss when in 3rd and 4th gear

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Re: Power loss when in 3rd and 4th gear

Postby Fast n Furious » Mon May 18, 2020 2:05 am

Does it rev out fully in first and second gear?
or has it developed a magic rev limiter situation?
This situation can happen and is usually caused by:-

A duff pickup coil (which will show as ok with a resistance check :shock: ) You need an oscilloscope to see if these are working properly or not.

An excessively worn mag bearing.

Twisted crank webs.

Intermittent continuity of the LT coil:-
This is a notorious fault that is well discussed on this forum. To test for this:- connect a multimeter set on the 200V+AC range across the green wire connection and ground (moving coil meters are preferred to digital here but not essential).
Start engine and get it warmed up good: At tick over expect a reading of 60-75v which should rise to around 200v as you rev it out. If the reading flattens out early then this is typical of a failed LT coil.
These poorly connected LT coils suffer badly from engine vibration and temperature changes resulting in a fractured earth tail wire which only connects when the vibration and coil temperature is low enough. It's this intermittent connection of a bit of copper wire, about the diameter of a hair, that causes the rev limitation. A lot fail within the first 100 miles.
It's an easy test to do..... for peace of mind if now't else.
Good luck.
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Re: Power loss when in 3rd and 4th gear

Postby dave81 » Mon May 18, 2020 9:08 pm

Had a similar problem years ago. Silencer was blocked.
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Re: Power loss when in 3rd and 4th gear

Postby Gsparky » Thu May 21, 2020 10:14 am

Hi, I’m going to have a good look in to it later today or tomorrow, just to answer a question yes it does rev out fully in 1st and 2nd gears, but once I’m in to 3rd then 4th it can fail in either of those gears, it seems to have progressed from an issue that I have had with it for some time,for a good while now on a 20/30 mile run, in top gear, nearing top speed, it would stutter and I had to drop the revs to stop it cutting out, I used to think it was a fuel or air issue, thanks all for your help.
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Re: Power loss when in 3rd and 4th gear

Postby Gsparky » Fri May 22, 2020 4:28 pm

Hi all, I have just tested the stator wires, I have 75 ohms between green and white wire, and >200 ohms (open circuit) between the red and white wire, sticky’s book says I should have 95 ohms between green and white wires and between 450-540 ohms between the red and white wires, so I would say I have a faulty stator!, I haven’t got any flywheel tools, but sticky’s book says you can shock the 17mm nut free with an impact screwdriver, has anyone tried this method ? (Reverse thread I know)
Many thanks Gary.
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Re: Power loss when in 3rd and 4th gear

Postby MickYork » Fri May 22, 2020 4:53 pm

Once you have the nut free you still have to extract the flywheel off the tapered shaft...….A flywheel extractor for under £5 might be a worthwhile investment.....flywheel holder for £15 would certainly make life easier.....
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Re: Power loss when in 3rd and 4th gear

Postby Gsparky » Fri May 22, 2020 5:24 pm

Yes I will probably get a flywheel holder too, thanks Mick and all for all the advice
Regards Gary
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Re: Power loss when in 3rd and 4th gear

Postby Gsparky » Sun May 24, 2020 5:46 pm

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Re: Power loss when in 3rd and 4th gear

Postby Gsparky » Sun May 24, 2020 5:47 pm

Sorry was struggling to submit photo and it’s gone through upside down!
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Re: Power loss when in 3rd and 4th gear

Postby Gsparky » Sun May 31, 2020 1:14 pm

Hi all, just been out on my scooter after replacing the stator plate, but I’m still having the same problem!
All fine until half a mile cuts out in either 3rd or 4th gear, pull over and after a few kicks starts up again then limp home in 2nd gear
Pissed off now! Anyone any thoughts on where to go next ?, on the plus side I have a spare stator plate!
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Re: Power loss when in 3rd and 4th gear

Postby Scooterdude » Sun May 31, 2020 1:48 pm

CDI
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Re: Power loss when in 3rd and 4th gear

Postby roli150lam » Sun May 31, 2020 3:12 pm

Take the air hose off,see if any different
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Re: Power loss when in 3rd and 4th gear

Postby Gsparky » Sun May 31, 2020 5:45 pm

I will get a new cdi, and try that, I did go for a run with no air filter before I replaced the stator and it was no different.
Thanks for your help
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Re: Power loss when in 3rd and 4th gear

Postby Fast n Furious » Thu Jun 04, 2020 2:08 pm

Probably not relevant in this case but engines with carbs on the right hand side can suffer from fuel starvation if the fuel pipe is routed in such a way that it gets crushed between the bump stop and frame. All's fine until you put weight on the bike and ride down the road. :o :roll:
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Re: Power loss when in 3rd and 4th gear

Postby Gsparky » Sun Jun 28, 2020 6:23 pm

Hi all, just tried my scooter again after previously replacing the stator and now after replacing the CDI unit, used a red Ducati one but I’m still having the same issue, engine dies when I get in to high rev in 3rd or 4th, pull over 2/3 kicks then limp home in low revs, I get about 1/2 a mile when this happens, I haven’t changed the lead between spark plug and CDI unit so thinking of doing so, someone mentioned a partial seize so thinking that way, tried with petrol in reserve to see maybe fuel tap issue , pissed off again was hoping it would be ok! any thoughts?
Regards Gary
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Re: Power loss when in 3rd and 4th gear

Postby MickYork » Sun Jun 28, 2020 6:54 pm

I'ld still measure the fuel flow as I suggested earlier.

That's a fair old loop you have on the fuel pipe, might be worth shortening it as well.
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Re: Power loss when in 3rd and 4th gear

Postby missing lynx » Sun Jun 28, 2020 7:53 pm

You say you've changed the stator did you check the timing and the timing marks also what number plug are you using?
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Re: Power loss when in 3rd and 4th gear

Postby Gsparky » Sun Aug 23, 2020 7:10 pm

A friend of mine is sorting through the scooter now, he suspects a fuel issue but I will post the final outcome soon hopefully!
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Re: Power loss when in 3rd and 4th gear

Postby Paul Slack » Mon Aug 31, 2020 11:11 am

Main Jet?
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