Spark plug too light after dyno

[Thackers]

Hi. I had my scoot dynoed by a highly skilled reputable 2 stroke tuner earlier in the year after running in. The scoot ran fine It took me various places inc up to Ayr for the euro. The final drive was slightly out, and whilst experimenting on this to find my current setting I thought I'd do a plug chop. The plug is way too lean!! So I had it re dynoed on Sat and the jetting was spot on, with the fueling a little on the rich side but the plug is still too lean.
I've checked all that that should be tight and it was, replaced the carb rubber but it was ok, checked fuel flow, cap breather, changed petrol pipe for increased int bore . I've checked the flywheel, woodruff key and stator which are all in the same position so the timing position hasn't altered (varitronic)
Could this lean plug be down to a fault with the CDI mapping going haywire?
I welcome any thoughts or advice.
Sorry for the long ramble.
Thank you

[Fast n Furious]

You might just need to run a colder plug? Worth a try!

[Thackers]

You might just need to run a colder plug? Worth a try!

Thank you that's something I'd not considered I was using a NGK 8 so I'll try a 9.

[Rich Oswald]

You might just need to run a colder plug? Worth a try!

Thank you that's something I'd not considered I was using a NGK 8 so I'll try a 9.

Dave, Unless you are doing some long and fast motorway type runs, then a 9 will carbon up and eventually fail on you imo. TBH I hate NGK plugs, only Champion or Nippon Denso for me.

Rich'

[Binny]

Dave, Unless you are doing some long and fast motorway type runs, then a 9 will carbon up and eventually fail on you imo. TBH I hate NGK plugs, only Champion or Nippon Denso for me.

+1

[Fast n Furious]

Yes.. An 8 plug is cold enough assuming that you are not running some ridiculously high compression ratio.

[Thackers]

Thanks for the advice fellas
The kit is the casa ss225, with LI150 gears and a 46 x 15 crown wheel/ sprocket . 30mm dellorto TSR EVO pipe. All fairly common I would think.
Point taken regards plug brand and number, I'll go back to the 8 and look into changing brands for the equivalent.
Thanks again.

[Fast n Furious]

Dave... can you be certain that your NGK plug is genuine? NGK is the most counterfeited plug brand out there!!!! Counterfeiters tend not to bother copying Champion or Denso.
Try using a Chamion N3 and see what difference it makes before pulling your hair out changing anything else.

[Rich Oswald]

Thanks for the advice fellas
The kit is the casa ss225, with LI150 gears and a 46 x 15 crown wheel/ sprocket . 30mm dellorto TSR EVO pipe. All fairly common I would think.
Point taken regards plug brand and number, I'll go back to the 8 and look into changing brands for the equivalent.
Thanks again.

Champion N3 or Nippon Denso 24

Rich'

[Thackers]

Dave... can you be certain that your NGK plug is genuine? NGK is the most counterfeited plug brand out there!!!! Counterfeiters tend not to bother copying Champion or Denso.
Try using a Chamion N3 and see what difference it makes before pulling your hair out changing anything else.

That is a very good point indeed, I can't remember where I got them but it was online. I thought the fake ngk plug thing was a thing of the past!! But I'm obviously mistaken.
I'm not saying mine are fake but changing the brand is easy enough and makes sense not to be ignored .

[alex_hughes]

I’ll be interested in how this pans out, please let us know.

For what it’s worth a club mate is suffering the same problem, my first thought was fake plug, but changing from NGK to Champion didn’t help him at all.

[Thackers]

I’ll be interested in how this pans out, please let us know.

For what it’s worth a club mate is suffering the same problem, my first thought was fake plug, but changing from NGK to Champion didn’t help him at all.

I will of course, I'll try post some pics up of the plug chops. Or anything I change or alter

[Thackers]

Hi Alex, I have sent you a P.M

[alex_hughes]

Well, an update on friends bike.

The first thought was fuel starvation and its turned out to be a longer than normal float needle getting wedged as the float bowl emptied on full throttle, and so not letting enough fuel flow. At less than full throttle the bike rode fine, witnessed by a medium/slow ride to the 5N rally in Northern Ireland. (great rally, BTW)

Thanks must go to Adam Winstone, our club mate with the determination to get to the bottom of this one. Top man, as always.

[Thackers]

Well, an update on friends bike.

The first thought was fuel starvation and its turned out to be a longer than normal float needle getting wedged as the float bowl emptied on full throttle, and so not letting enough fuel flow. At less than full throttle the bike rode fine, witnessed by a medium/slow ride to the 5N rally in Northern Ireland. (great rally, BTW)

Thanks must go to Adam Winstone, our club mate with the determination to get to the bottom of this one. Top man, as always.

Good result and great detective work

[hullygully]

Well, an update on friends bike.

The first thought was fuel starvation and its turned out to be a longer than normal float needle getting wedged as the float bowl emptied on full throttle, and so not letting enough fuel flow. At less than full throttle the bike rode fine, witnessed by a medium/slow ride to the 5N rally in Northern Ireland. (great rally, BTW)

Thanks must go to Adam Winstone, our club mate with the determination to get to the bottom of this one. Top man, as always.

Good result and great detective work

+1

[gaz_powell]

How do we end of with stuff like this.... A new one on me!!

Top work from Mr Winstone and other one to put in the bank of what could it be...

Glad you got sorted

[Covboy]

I’m wondering if this type of event was the cause of my GT240 mishap
On the suggestion of NSaints I’ve upped the inlet valve to a 3.5 and I’ve also cross drilled the holes to a larger diameter

I’ll now measure the needle…

[hullygully]

is that why when you install any new fuel jet you get a fuel needle with it? are these bespoke to the fuel jet size?

[Warkton Tornado No.1]

I’m still trying to get my head around the problem stated to have caused the issue

I have no doubt in the excellent detective work in resolving the problem - being fuel starvation - but float needles are not only sprung (which obviously varies their length whilst functioning) but they are ‘sided’ to only fit the float needle jet at point contacts & to allow for flow.

Fuel flow issues within the bowl normally occur due to the float & pin issues, though if the tangs - that engage with the float needle - are somehow distorted, that can cause sticking.

Yet another reminder that the complete carburettor & fuel taps should always be dismantled fully & checked to ensure correct function, even when brand new