Lammy running sh*te

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soullad
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Sat Aug 15, 2009 9:30 pm

Having a mare with my normally super reliable Imola

I changed to a JL4 from a ScootRS pipe and found the midrange fourstroking. It also needed new clutch plates and the gearing altering so decided to bring it indoors n kill 2 birds with one stone.
changed clutch n gearing but then scoot wouldn't pull over 1/4 ish throttle, really spluttery.
Thought this might be electrical so bit by bit changed the CDI, plug, ht lead, plug cap and still no different.
Then thought it might be rings or reed petals so took top end apart. Reeds fine and fitted new rings just for measure whilst I had it in bits. Still ran crap.
Then thinking it could be carb bought a second 28mm phbh carb and fitted jets as below

choke 70
idle 60
av264
x13 second clip down (already tried x2)
130 main
airscrew 1 1/2 out
300 float needle valve

still ran poor so tried 125 main - no difference. Today swapped out the stator for a new bgm one and still seems like its fourstroking above 1/3 throttle. It does not rev out, in fact barely makes 35mph !!! With the above I might have been slightly out but surely not that far that it won't run?
tried running with no fuel cap on in case its a vacuum thing. Tried turning on choke - at low throtlle it wants to die, at full throttle - makes no difference.
Am now really really curious what is causing this. Any help fellas?

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Andy Pickering
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Sat Aug 15, 2009 9:44 pm

Could it be something simple like a dodgy JL4..? seems everything was fine until the change of exhaust,maybe try scootrs back on and see what happens..had this problem on a car and the baffle was blocked and the car wouldnt pull much over 30mph..changed the exhaust and it was back to normal..just a thought.
Ricspeed, gone but never forgotten RIP my friend #59

soullad
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Sat Aug 15, 2009 9:51 pm

when i changed it initially it did 4 stroke in the midrange but would clear and then pull fine.....then I didall of the above and now it doesn't clear at all

andyC
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Sat Aug 15, 2009 11:17 pm

pilot/idle too big! try

50 pilot
Av268 atomiser
X7 needle top clip
40 slide
130 main should be fine
70 choke
1 1/2 to 2 turns out
always works for me.
imola/30mm/jl/dyno'd

soullad
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Sun Aug 16, 2009 8:16 am

Thanks Andy
Before i try, this I'm curious as to why you think the pilot could be causing this, and also your atomiser is 2 sizes bigger (and therefore richer ) in the midrange where my problems seem to begin?

Daggs
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Sun Aug 16, 2009 8:39 pm

Soullad: You've dug a firkin great hole and fell in it! :shock:
You changed the exhaust and a side effect of that is the jetting requirement changed.
Interfering with the previously O/K electrics, top-end, reed valve etc. was not necessary. :?
You need to concentrate on jetting.

Remember this basic principle:

Pilot jet/air screw affects tickover/ pulling away.
Needle/atomiser " mid-range running.
Main jet " Full throttle.

soullad
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Mon Aug 17, 2009 12:06 pm

Yep, you are probably right, but I've tried an X2 and an X13 neeedle .........should i go as low as an X7 with an av264 atomiser - its a tuned kit too, additional base transfer, 110 rod, packing plate etc etc ?
I've also tried a 120 main - which is usually Clubman sized range, not a jl4 and it won't clear when turning the throttle back to wot.
Why is this so critical though. surely it would run better than this albeit a tad rough not the 30mph im getting at the mo?
Anyone run an Imola with 28mm dellorto and jl4?
Cheers

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Diablo
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Mon Aug 17, 2009 12:22 pm

Daggs wrote:Soullad: You've dug a firkin great hole and fell in it! :shock:
You changed the exhaust and a side effect of that is the jetting requirement changed.
Interfering with the previously O/K electrics, top-end, reed valve etc. was not necessary. :?
You need to concentrate on jetting.

Remember this basic principle:

Pilot jet/air screw affects tickover/ pulling away.
Needle/atomiser " mid-range running.
Main jet " Full throttle.

Not quite. The mixture screw as it will be on the PHBH effects the whole range right the way through although the effect is more noticable from tickover and just over. The needle and atomisor do mainly affect the mid range but I've been surprised to see just how much the needle affects full throttle openings. This applys especially to Mikunis but also dellortos as well.
I'm quite surprised that changing to the JL4 has had such an effect so wouldn't nessecarily concentrate solely on jetting.

The ones set up here usually use AV266 with an X7 needle and a 120 to 125 MJ.
You will find it hard to get the mid range bang on and unless you dyno it you may not be aware that it will run weaker at some point. For that reason er on the side of caution and set it up slightly rich low down. This is one of the downsides of fitting a race exhaust. Just thrash it everywhere and you'll be fine :D

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teamsequipe
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Mon Aug 17, 2009 2:38 pm

Have you fitted the exhaust gasket correctly ?
Old Lambrettas Never die ..................... they just go Faster !

Ron Moss says "Supertune it !"

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sean brady scooters
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Mon Aug 17, 2009 3:37 pm

is the needle secured in the slide properly........?
and not moving independantly.............only mention this as i,ve seen it done before producing similar results.........
Sean Brady Scooters - 01765 690 698

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