Scooterotica

Hi Guys
I'm losing my sanity with engine misfire/splutter in 4th gear after 1/3 throttle. It revs ok in 1st, 2nd & 3rd gear but in 4th it wont run correctly. Engine is tuned 225cc TS1, these are things I've tried below:-
Changed Plug
Changed plug Cap
Changed HT lead
Tried 3 CDI units
Cleaned out carb, jets etc
Flushed out fuel tank
Petrol flow exceeding 1 pint in 60 seconds
Taken green wire out of CDI to eliminate any failure in the wiring
Changed reed petals
Replace old Mikuni carb with new Mikuni carb. jetting the same as one taken off
Old stator changed to new BGM stator with pick up height packed and checked and strobed
Old flywheel magnets loose, so replaced with new flywheel. Re-timed and strobed.
Any help is most appreciated

What pipe are you running? I found something similar with a 'flat spot' on a Fran Race around 5,500rpm. Lower gears could power through it but in 4th I'd get a stutter. Lowered main jet to solve it.

GeorgeS wrote: ↑Sun Dec 03, 2017 7:00 pm What pipe are you running? I found something similar with a 'flat spot' on a Fran Race around 5,500rpm. Lower gears could power through it but in 4th I'd get a stutter. Lowered main jet to solve it.

JL3 Scooter run fine in the past. It is a problem that has developed which I can't fathom out. So I would discount the exhaust

if your running it in this weather and it was ok before i would do a plug chop at were your getting the splutter and see whats happening i always go richer in winter go up 2/3 jets on the main or go up on clip to richen and try that

garry inglis wrote: ↑Sun Dec 03, 2017 7:17 pm if your running it in this weather and it was ok before i would do a plug chop at were your getting the splutter and see whats happening i always go richer in winter go up 2/3 jets on the main or go up on clip to richen and try that

I will try a plug chop, but problem has existed foe some time. My attempts of rectifying the issue have been over months

usually a misfire is stator and splutter is carb related what is the timing set at if its 18 try 17 and stator check earth tabs and low tension coil also is the pick up height spot on with the fly wheel because either side of centre can cause misfire

celt wrote:

GeorgeS wrote: ↑Sun Dec 03, 2017 7:00 pm What pipe are you running? I found something similar with a 'flat spot' on a Fran Race around 5,500rpm. Lower gears could power through it but in 4th I'd get a stutter. Lowered main jet to solve it.

JL3 Scooter run fine in the past. It is a problem that has developed which I can't fathom out. So I would discount the exhaust

I'd agree with you there, as I think the JL3 gives quite a continuous delivery with no Noticeable power band.

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What grade of plug are you running? I’ve known people suffer similar when trying to run NGK 10, sometimes even with a 9... but rarely with a 9. You could certainly try a different grade and see if it helps. Some odd ‘special’ types of plug, which others may recommend, can also cause such an issue. This can result from a plug not getting hot enough to ignite the mix correctly, resulting in a misfire.

Fuel starvation is a good shout from others. Are you running a rear exit tap? If not, just make sure that your hose is not squashing against the top of the flywheel cowling under suspension movement. A tap and hose can flow perfectly on the stand but then become heavily restricted when you sit on the bike to ride it, causing starvation. Get off to check and all is Ok again!

Good luck sorting it.

Adam

When did you last change your rings? a compression check could be an idea especially if this has come on over a period of time.

When you say ‘jetting same as one taken off’ ...did you use the old jets or replace with new, like for like?

If this is a new problem which has developed, and the scooter previously ran ok....then my advice is that you should have fitted NEW jetting to the OLD carb...rather than the other way round.

It’s possible that your needle/atomiser combo has worn...thus running richer, and creating a midrange misfire at that point. Replacing the atomiser/needle should tighten things back up.

Ignore this post if you used new atomiser/needle...