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Juddering at closed throttle

Technical help for all early models, A, B, C, LC, D, LD, E & F models

Juddering at closed throttle

Postby Myerscough180947 » Tue Oct 29, 2019 3:40 pm

Can anyone shed light on a problem with my Mark 2 LD150 please ?
After fitting the Variotronic Ignition System the scooter judders harshly on deceleration with a closed or almost closed throttle. Its as though it isnt getting fuel. I have changed the main jet from a 73 to an 80,and raised the needle to its lowest groove but the problem has only marginally improved.
Good acceleration, cruises fine at 40 mph but on deceleration at 30mph in 3rd or at 20mph in second there is harsh juddering.
Difficult to drive through town.
Didnt have this problem before fitting Variotronic.
HELP !!!!!!!!!!!!!!!!!
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Re: Juddering at closed throttle

Postby Rich Oswald » Tue Oct 29, 2019 10:03 pm

Post moved to this section from Forum help.

Rich'
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Re: Juddering at closed throttle

Postby mm man » Wed Oct 30, 2019 12:11 am

Rich Oswald wrote:Post moved to this section from Forum help.

Rich'


Why has this been moved to the forum help section “not for scooters?”
Most of the pre 57 page is for technical help with scooters ?? That what it’s titled as.
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Re: Juddering at closed throttle

Postby Rich Oswald » Wed Oct 30, 2019 11:17 am

mm man wrote:
Rich Oswald wrote:Post moved to this section from Forum help.

Rich'


Why has this been moved to the forum help section “not for scooters?”
Most of the pre 57 page is for technical help with scooters ?? That what it’s titled as.


Read my post again my friend. It says moved "from" forum help not "to" forum help.

Cheers,

Rich'
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Re: Juddering at closed throttle

Postby jbcollier » Wed Oct 30, 2019 3:25 pm

What did you set the timing to?
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Re: Juddering at closed throttle

Postby mm man » Wed Oct 30, 2019 8:50 pm

Rich Oswald wrote:
mm man wrote:
Rich Oswald wrote:Post moved to this section from Forum help.

Rich'


Why has this been moved to the forum help section “not for scooters?”
Most of the pre 57 page is for technical help with scooters ?? That what it’s titled as.


Read my post again my friend. It says moved "from" forum help not "to" forum help.

Cheers,

Rich'



My apologies....note to self .....read twice comment once :oops:
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Re: Juddering at closed throttle

Postby Fast n Furious » Wed Oct 30, 2019 9:49 pm

Suggest that you use a strobe light to see what the timing of the spark is doing. Are you sure that the stator plate is fastened down properly?
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Re: Juddering at closed throttle

Postby Myerscough180947 » Tue May 12, 2020 7:22 pm

Timed at 26 BTDC
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Re: Juddering at closed throttle

Postby Myerscough180947 » Tue May 12, 2020 7:24 pm

Timed at 26 BTDC
I was told it was 26 BTDC but just checked with my strobe and its 32 !
Could this be a problem ?
Plus, should the Spark Plug have a bigger gap than 0.020 if using a Varitronic ?
Last edited by Myerscough180947 on Fri May 22, 2020 6:19 pm, edited 1 time in total.
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Re: Juddering at closed throttle

Postby Fast n Furious » Tue May 12, 2020 8:20 pm

It may not be ignition related.
Check your carburettor fuel bowl for signs of water contamination. These old carbs will work ok with some water in them until you brake which then pulls this water up through the jets.
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Re: Juddering at closed throttle

Postby Myerscough180947 » Fri May 22, 2020 6:22 pm

Fast n Furious wrote:Suggest that you use a strobe light to see what the timing of the spark is doing. Are you sure that the stator plate is fastened down properly?

Just used my strobe and its 32 BTDC ! Is this too much?
What should Spark Plug gap be using a Varitronic ?
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Re: Juddering at closed throttle

Postby Fast n Furious » Fri May 22, 2020 10:08 pm

I think so... If memory serves.... I think the original timing was 26 degrees BTDC.
I wouldn't worry too much about retarding the timing below 26 because the compression ratio on these old engines was very low anyway.
Suggest you re-time it to 26 and see what difference it makes.
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Re: Juddering at closed throttle

Postby jbcollier » Sat May 23, 2020 2:46 pm

+1, set the timing correctly and go from there.
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Re: Juddering at closed throttle

Postby Myerscough180947 » Sat May 23, 2020 7:26 pm

jbcollier wrote:What did you set the timing to?

its at 32
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Re: Juddering at closed throttle

Postby Myerscough180947 » Sat May 23, 2020 7:28 pm

jbcollier wrote:+1, set the timing correctly and go from there.

Thanks will do
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Re: Juddering at closed throttle

Postby Myerscough180947 » Sat May 23, 2020 7:29 pm

jbcollier wrote:+1, set the timing correctly and go from there.

Thanks will do
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