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125 3rd gear jerking/stopping starting/shudder

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ollieroache
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PostPosted: 15:19 - 27 Aug 2017    Post subject: 125 3rd gear jerking/stopping starting/shudder Reply with quote

My lexmoto venom 125 has done 750 miles and in 3rd gear at around 35mph sometimes the bike will jerk, almost like ive very quickly shut the throttle and applied again. Never has happened in any other gear. No clutch is being applied when it happens. Just opening the throttle.

Any ideas as to what is causing this? Fixes?[/u]
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Teflon-Mike
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PostPosted: 15:49 - 27 Aug 2017    Post subject: Reply with quote

The rider? - Has to be top of the list, on a learner bike, before blaming the bike.

Common newb error is short-shiftng; it only takes about 3bhp to go 30mph, your lexmoto probably has near nine.... at the red-line.... so, easy to cog p almost as soon as moving, then again, then again, a-n-d.. what? judder-judder-judder... 'cos needs all that 3bhp... power is torque x revs, and its aproximatly liniar so on a 9bhp CG copy motor, with max power of 9bhp made at 'about' 9ooo revs, you have aprox 1bhp per 1000rpm... so, 1st... 0-20 and gears give you maybe 20 times the torque multiplication, thing revs out easy, with 9bhp being delivered before it runs out of puff, and you only need maybe 1, to go 15mph.. 2nd... again, maybe 10x torque multiplication from gears, and you still only need 3bhp, and you have 3x that when it runs out of revs... B-U-T ow you shift up.... torque multiplication from gears drops to maybe 5x, and the revs fall back, to maybe 18oo, where you only have maybe 2bhp... and you need 3, to go 30.... result, the bike 'bogs', because it barely has the power to hold the speed you are doing, let alone any spare to offer acceleration....

Solution.. RAG IT! Little bikes need to be thrashed, and you should be using revs not gears, and not short shifting up the box so soon.... bike will be smoother, more responsive, WONT blow up unless its fcuked to start with, regardless of how tortured it sounds, and you will ride far 'better' not making so many upshifts begging so many downshifts, none of them needing to be rushed, you'll have more time to do everything else that needs doing, like watch for SMIDSY's, and other hazards, and have a generally easier time of it NOT making more work for yourself than you need to, and all will become smoother and more comfy for all....

THAT is 'one' possibility.

Other is... 750 miles, on I assume a new bike? Has it ever been serviced? Its about due an oil change and tappet tickle, as 'run in'miles see things loose off.....

Add A+B, and you have almost certain answer to the phenomena....

Quite likely not a lot wrong with the bike, other than it being a generic Chink, that likes lots of loving care and attention, few ever get.
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Pete.
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PostPosted: 16:34 - 27 Aug 2017    Post subject: Re: 125 3rd gear jerking/stopping starting/shudder Reply with quote

ollieroache wrote:
My lexmoto venom 125 has done 750 miles and in 3rd gear at around 35mph sometimes the bike will jerk, almost like ive very quickly shut the throttle and applied again. Never has happened in any other gear. No clutch is being applied when it happens. Just opening the throttle.

Any ideas as to what is causing this? Fixes?[/u]


It's jumping the 3rd gear dog. Get it back to the vendor for warranty work.
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ollieroache
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PostPosted: 16:35 - 27 Aug 2017    Post subject: Reply with quote

Teflon-Mike wrote:
The rider? - Has to be top of the list, on a learner bike, before blaming the bike.

Common newb error is short-shiftng; it only takes about 3bhp to go 30mph, your lexmoto probably has near nine.... at the red-line.... so, easy to cog p almost as soon as moving, then again, then again, a-n-d.. what? judder-judder-judder... 'cos needs all that 3bhp... power is torque x revs, and its aproximatly liniar so on a 9bhp CG copy motor, with max power of 9bhp made at 'about' 9ooo revs, you have aprox 1bhp per 1000rpm... so, 1st... 0-20 and gears give you maybe 20 times the torque multiplication, thing revs out easy, with 9bhp being delivered before it runs out of puff, and you only need maybe 1, to go 15mph.. 2nd... again, maybe 10x torque multiplication from gears, and you still only need 3bhp, and you have 3x that when it runs out of revs... B-U-T ow you shift up.... torque multiplication from gears drops to maybe 5x, and the revs fall back, to maybe 18oo, where you only have maybe 2bhp... and you need 3, to go 30.... result, the bike 'bogs', because it barely has the power to hold the speed you are doing, let alone any spare to offer acceleration....

Solution.. RAG IT! Little bikes need to be thrashed, and you should be using revs not gears, and not short shifting up the box so soon.... bike will be smoother, more responsive, WONT blow up unless its fcuked to start with, regardless of how tortured it sounds, and you will ride far 'better' not making so many upshifts begging so many downshifts, none of them needing to be rushed, you'll have more time to do everything else that needs doing, like watch for SMIDSY's, and other hazards, and have a generally easier time of it NOT making more work for yourself than you need to, and all will become smoother and more comfy for all....

THAT is 'one' possibility.

Other is... 750 miles, on I assume a new bike? Has it ever been serviced? Its about due an oil change and tappet tickle, as 'run in'miles see things loose off.....

Add A+B, and you have almost certain answer to the phenomena....

Quite likely not a lot wrong with the bike, other than it being a generic Chink, that likes lots of loving care and attention, few ever get.


Thanks for the reply.
I shift to 3rd at around 30mph, i have short shifted before and felt the shudder and unresponsiveness, however, this jerk is happening when the bike is at about 8000rpm, its not like im shifting up at 4000rpm. This is an odd jerk that only ever happens in third gear, im worried that this will happen while im cornering and i'll come off.
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ollieroache
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PostPosted: 16:37 - 27 Aug 2017    Post subject: Re: 125 3rd gear jerking/stopping starting/shudder Reply with quote

Pete. wrote:
ollieroache wrote:
My lexmoto venom 125 has done 750 miles and in 3rd gear at around 35mph sometimes the bike will jerk, almost like ive very quickly shut the throttle and applied again. Never has happened in any other gear. No clutch is being applied when it happens. Just opening the throttle.

Any ideas as to what is causing this? Fixes?[/u]


It's jumping the 3rd gear dog. Get it back to the vendor for warranty work.


What does that actually mean? Jumping. It's had its first service.
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ollieroache
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PostPosted: 16:58 - 27 Aug 2017    Post subject: Reply with quote

Oh and its had an oil change
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Teflon-Mike
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PostPosted: 17:56 - 27 Aug 2017    Post subject: Reply with quote

ollieroache wrote:
Oh and its had an oil change

It has a slide carb, the slide opens the 'door' letting air into the engine in direct responde tou you twisting the throttle; you crack throttle open, doors open wide, air-speed through the carb drops, vacuu over the jets falls, engine goes 'lean' when it needs to go ricth to allow acceleration, motor 'bogs'. Make sense?
Almost all simple slide carb engine will do this; CV carbed engines wont 'so-much' as the slde is lifted by vacuum not the twist grip, so air speed through them is kept at 'Constant Velocity.. hence CV...
Fuel injected engines, 'may' do it to some degree, the throttle boddy opening quick letting air-speed drop, but a sensor in the syststem 'should' compensate to some degree, though some do still give a little lag and flutter...

NOW... your motor is probably a CG GS dervative, not that it makes huge dfference; in either case they were designed around forty years ago, when bikes weren't even subject to exhaust noise regulations in the UK! To get such old designs to achieve the 'emissions' requirements of current times, they have seriously de-tuned them.. which is why what were 10-11bhp motors at best, made in chna make around 9bhp; but on top of that, they also significantly leaned the carburation; engines need to go 'rich' for best power, or acceleration; hence the last of the line Honda CG's have 'pumper' carbs... they have been seriousely down-jetted to provide as 'lean' a mixture as they can get away wth, wthout the motor melting under 'detonation', then they have a little piston and jet system, so that when you open th throttle a bit fast, it 'squirts' some extra furl into the carb to make the mixture rich, briefly.. very ineeficient, but means that in the dynamic state that emmisions tsts are done, the things beat the system...

B-U-T... if you have such a de-tuned engine, then it s very likely that you will get such acceleration 'judder' as the over-leaned carb sorts itself out, and a puper carb may actually make matters worse, over enichening the mixture when first activated...

Such anomolies are not uncommon, and as said, a more experienced rider will 'ride around' such woolliness, compensating by either clogging down and making motor scream a bit to get some go, or opening the throttle a lot more gently, or predicting the lag and opening the throttle a little earlier to allow for it...

But.. may be annoying, and WILL get more pronounced if your motor is more out of tune.....

As said, these Generic-Chnky bikes are built down to a very low quality, for 3rd world markets where labour costs are low, and anticipated maintenance a lot higher....

750 miles, and you say its had an oil change!?!?!?!? THAT is NOT a 'service'!!!!

It probably aught to have had a new spark plug at the very least by now, as early miles have burned off all assembly lube, and bedding in of bits of metal that rub on metal make smooth oil tight surfaces, so until then oil will be getting down the valve stems and past the rings and 'fouling' the spark plug. Metal rubbing on metal, will see things like the cam-shaft 'wear' and loose any high-spots where the followers run on them, and clearances between such parts find their natural groove; hence the tappets should have early re-adjustment.

Any mew bike should similarly suffer; one made down to a very low standard of original quality control, likely with low quality metal and more questionable part hardenng, and not made to teh same exacting tolerances on worn out old machinary inherited from Brazil or Tiwan, is going to suffer even more...

Th extra wear and tear of the bed-in miles, will thanks to exhaust-gas-recirculation systems and cran case extraction vents puttng oil vapour from the crank-case and smoke from the exhaust into the air-box to be recycled through the engine for a second 'burn' , taking extra 'burn-off' crap with them will hammer the air-flter and spark-plug some more... and quite possible a new filter is needed at first servce.

Like I sad, serving is a heck of a lot more than 'just' changing the oil, and on a new engine first service intervals come up short as the motor beds in....

Now, could be that you have any number of faults.. BUT first rule of diagnostics is you eliminate the easy and obvious first.... and new rider is top of the list, and a proper service right under it.... and before wasting any time hunting for mystery anomalies, you do a full and proper servise to eliminate silly questions!!

So.. back to top... 750 miles is just eough for a new rider to start getting a little bit blase with the thing and putting t under greater stress, and noting when its not 'quite' responding, it is also when bed-in starts to see stuff fall out of service limits and need proper adjustment, not just an oil change... SO.. back to top.... do a full ad proper service... that means new plug and tappets, check, clean, replace filters and anything else, then return to top, test ride, double-check rider numtpess, and do you 'really' have a 'problem' worth chasing with the spanners?
____________________
My Webby'Tef's-tQ, loads of stuff about my bikes, my Land-Rovers, and the stuff I do with them!
Current Bikes:'Honda VF1000F' ;'CB750F2N' ;'CB125TD ( 6 3 of em!)'; 'Montesa Cota 248'. Learner FAQ's:= 'U want to Ride a Motorbike! Where Do U start?'
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ollieroache
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PostPosted: 18:19 - 27 Aug 2017    Post subject: Reply with quote

Teflon-Mike wrote:
ollieroache wrote:
Oh and its had an oil change

It has a slide carb, the slide opens the 'door' letting air into the engine in direct responde tou you twisting the throttle; you crack throttle open, doors open wide, air-speed through the carb drops, vacuu over the jets falls, engine goes 'lean' when it needs to go ricth to allow acceleration, motor 'bogs'. Make sense?
Almost all simple slide carb engine will do this; CV carbed engines wont 'so-much' as the slde is lifted by vacuum not the twist grip, so air speed through them is kept at 'Constant Velocity.. hence CV...
Fuel injected engines, 'may' do it to some degree, the throttle boddy opening quick letting air-speed drop, but a sensor in the syststem 'should' compensate to some degree, though some do still give a little lag and flutter...

NOW... your motor is probably a CG GS dervative, not that it makes huge dfference; in either case they were designed around forty years ago, when bikes weren't even subject to exhaust noise regulations in the UK! To get such old designs to achieve the 'emissions' requirements of current times, they have seriously de-tuned them.. which is why what were 10-11bhp motors at best, made in chna make around 9bhp; but on top of that, they also significantly leaned the carburation; engines need to go 'rich' for best power, or acceleration; hence the last of the line Honda CG's have 'pumper' carbs... they have been seriousely down-jetted to provide as 'lean' a mixture as they can get away wth, wthout the motor melting under 'detonation', then they have a little piston and jet system, so that when you open th throttle a bit fast, it 'squirts' some extra furl into the carb to make the mixture rich, briefly.. very ineeficient, but means that in the dynamic state that emmisions tsts are done, the things beat the system...

B-U-T... if you have such a de-tuned engine, then it s very likely that you will get such acceleration 'judder' as the over-leaned carb sorts itself out, and a puper carb may actually make matters worse, over enichening the mixture when first activated...

Such anomolies are not uncommon, and as said, a more experienced rider will 'ride around' such woolliness, compensating by either clogging down and making motor scream a bit to get some go, or opening the throttle a lot more gently, or predicting the lag and opening the throttle a little earlier to allow for it...

But.. may be annoying, and WILL get more pronounced if your motor is more out of tune.....

As said, these Generic-Chnky bikes are built down to a very low quality, for 3rd world markets where labour costs are low, and anticipated maintenance a lot higher....

750 miles, and you say its had an oil change!?!?!?!? THAT is NOT a 'service'!!!!

It probably aught to have had a new spark plug at the very least by now, as early miles have burned off all assembly lube, and bedding in of bits of metal that rub on metal make smooth oil tight surfaces, so until then oil will be getting down the valve stems and past the rings and 'fouling' the spark plug. Metal rubbing on metal, will see things like the cam-shaft 'wear' and loose any high-spots where the followers run on them, and clearances between such parts find their natural groove; hence the tappets should have early re-adjustment.

Any mew bike should similarly suffer; one made down to a very low standard of original quality control, likely with low quality metal and more questionable part hardenng, and not made to teh same exacting tolerances on worn out old machinary inherited from Brazil or Tiwan, is going to suffer even more...

Th extra wear and tear of the bed-in miles, will thanks to exhaust-gas-recirculation systems and cran case extraction vents puttng oil vapour from the crank-case and smoke from the exhaust into the air-box to be recycled through the engine for a second 'burn' , taking extra 'burn-off' crap with them will hammer the air-flter and spark-plug some more... and quite possible a new filter is needed at first servce.

Like I sad, serving is a heck of a lot more than 'just' changing the oil, and on a new engine first service intervals come up short as the motor beds in....

Now, could be that you have any number of faults.. BUT first rule of diagnostics is you eliminate the easy and obvious first.... and new rider is top of the list, and a proper service right under it.... and before wasting any time hunting for mystery anomalies, you do a full and proper servise to eliminate silly questions!!

So.. back to top... 750 miles is just eough for a new rider to start getting a little bit blase with the thing and putting t under greater stress, and noting when its not 'quite' responding, it is also when bed-in starts to see stuff fall out of service limits and need proper adjustment, not just an oil change... SO.. back to top.... do a full ad proper service... that means new plug and tappets, check, clean, replace filters and anything else, then return to top, test ride, double-check rider numtpess, and do you 'really' have a 'problem' worth chasing with the spanners?


I paid 80 pounds for a full first service, i expect they did more than just change the oil, but im just explaining that the oil had been changed because I thought that would affect the judgement.
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NJD
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PostPosted: 18:21 - 27 Aug 2017    Post subject: Re: 125 3rd gear jerking/stopping starting/shudder Reply with quote

Pete. wrote:
Get it back to the vendor for warranty work.


x1000.

One LM Venom I saw long ago was on the bench and the mechanic claimed the gearbox's were the worst out of the bunch. Amazed me since the LM Arrow I had was poor as awt.

Wouldn't even bother attempting to spanner on it if warranty exists. Crack on with making it someone else problem and enjoy the trouble free days in-between this and the next issue once you get it back.
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ollieroache
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PostPosted: 18:22 - 27 Aug 2017    Post subject: Reply with quote

Its also less of a judder. Its one jerk.
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Pete.
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PostPosted: 19:15 - 27 Aug 2017    Post subject: Reply with quote

ollieroache wrote:
Its also less of a judder. Its one jerk.


One jerk accompanied by a clack from the engine and a small lunge. Only does it under power and the more power the more often. Only does it in one gear?

Gearbox dog. Nothing you can do about it get it back to the dealer.
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132.9mph off and walked away. Gear is good, gear is good, gear is very very good Very Happy
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Rogerborg
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PostPosted: 21:14 - 27 Aug 2017    Post subject: Reply with quote

Teflon-Mike wrote:
It has a slide carb

Does it? OP bought it in July 2017 after ordering it in June and having to wait a month, so I'd stick my neck out and assume that it's a Euro 4 EFI model.
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ollieroache
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PostPosted: 21:46 - 27 Aug 2017    Post subject: Reply with quote

Pete. wrote:
ollieroache wrote:
Its also less of a judder. Its one jerk.


One jerk accompanied by a clack from the engine and a small lunge. Only does it under power and the more power the more often. Only does it in one gear?

Gearbox dog. Nothing you can do about it get it back to the dealer.


Okay thanks, I'll give them a call soon and see whats happening
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ollieroache
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PostPosted: 21:47 - 27 Aug 2017    Post subject: Reply with quote

Rogerborg wrote:
Teflon-Mike wrote:
It has a slide carb

Does it? OP bought it in July 2017 after ordering it in June and having to wait a month, so I'd stick my neck out and assume that it's a Euro 4 EFI model.


It's just a venom se 2016
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