SM 125 Gangsta loses power in 6th gear

SM, SX, RT, FunX, and models re-branded as ATK in U.S.

Moderators: DAVID THOMPSON, phlat65

SM 125 Gangsta loses power in 6th gear

Postby LeftaSALTYtaste » Sun Apr 16, 2017 1:37 pm

Hello all,

This is my first post but have been lurking on here trying to find a couple of questions answering.

First is.. My SM 125 will reach 60mph in 5th gear but as soon as I change up in to 6th, she will loose power and drop to 55 and then some. Can anyone give me any pointers to resolve this problem?

Second is .. She's totally standard engine, drive train and exhaust wise. I'd like to get a little bit more out of the top end and maybe some decent acceleration. I'm used to mainly off road crossers like Honda CR250 (I know ithey're a 2 stroke and quick) or the CRF450 I've also had an XR400 but as I'm only able to ride a 125 on the road. Can I gain any more out of this little bike? Maybe up jetting, Big bore, Upsizing sprockets or exhaust? Funds aren't a problem and I'm handy with a spanner 8)

I'm in the Highlands of Scotland so plenty of hills and I'm 14 stone. Am I comparing the speed of a crosser and this somewhat tame but superb little bike too much?

Cheers in advance.

Salty

P.S. Shes a 2006 model.
LeftaSALTYtaste
 
Posts: 6
Joined: Fri Sep 16, 2016 11:41 am

Re: SM 125 Gangsta loses power in 6th gear

Postby DAVID THOMPSON » Sun Apr 16, 2017 4:51 pm

follow this link
viewtopic.php?f=4&t=49

and give your carb a good clean

these 125 models were tuned to the max to begain with so most mods do not help and the one for a smaller front sprockets
is a bad one
read about my sprocket mod and go for one that gives about 55 or 60 mph
55 or 56 teeth on rear 52 if its 17 inch wheel

mine runs at 69mph WFO and it is very hilly where i live with 60 or less sppeed limits
and i weigh 230lb i am in the usa and stones are what we put on a country road to get the mud under control :D

dave
Dave 2002 MZ RT125 +1995 Saxon Tour (rotax500cc)
1997 MZ Skorpion Traveller added 6/13/09
Located in WV USA
"I like the road less traveled if it's PAVED!"
E mail wd8cyv at yahoo dot com
User avatar
DAVID THOMPSON
Moderator
 
Posts: 4487
Joined: Sun Nov 23, 2003 11:01 am
Location: Parkersburg, West Virginia USA .questions answered MZ 95 up, BMW 1953 to 1979 and ham radio WD8CYV

Re: SM 125 Gangsta loses power in 6th gear

Postby breakwellmz » Mon Apr 17, 2017 2:17 am

I agree that i sounds like a case of it being overgeared for a 14 stone bloke in hilly country, sounds like you need a top gear ratio somewhere between the current top and fifth gear.
It`s a BIG step down in torque and power from what you are used to, get that test out the way and move on to something bigger for the road eh?

Edit- 6 speed?
breakwellmz
 
Posts: 379
Joined: Sun Dec 16, 2007 7:11 am
Location: SW England

Re: SM 125 Gangsta loses power in 6th gear

Postby DAVID THOMPSON » Mon Apr 17, 2017 9:50 am

i do not count the gears i just use them
and the BIKES less than 350cc are just big mopeds
pass the test and use the 125 for short trips and as a back up

my bike from 4000 miles to 12,000 miles would run 70 and cruise at 60 to 65

as it got past 15,000 it lost a bunch of top end now at 23,000 thousand it suffers and complains to do 60mph
with the posted speed limits where i live it seldom goes over 55mph
like i said if its smaller than 350cc it's just a moped
and hop up kits are a waste of money

but i love the little thing and will keep it tunning as long as i can
:smt023 Dave
Dave 2002 MZ RT125 +1995 Saxon Tour (rotax500cc)
1997 MZ Skorpion Traveller added 6/13/09
Located in WV USA
"I like the road less traveled if it's PAVED!"
E mail wd8cyv at yahoo dot com
User avatar
DAVID THOMPSON
Moderator
 
Posts: 4487
Joined: Sun Nov 23, 2003 11:01 am
Location: Parkersburg, West Virginia USA .questions answered MZ 95 up, BMW 1953 to 1979 and ham radio WD8CYV

Re: SM 125 Gangsta loses power in 6th gear

Postby LeftaSALTYtaste » Mon Apr 17, 2017 12:24 pm

Hi David.

Cheers for your advice and I've read that link and the first thing I done was to clean my carb .Any other ideas?
I was thinking of a 52 tooth rear sprocket as have the standard 49 on 17" spoked rims so guess I'll order one now if I can find one.

As to passing my test @breakwellmz ...Erm I'd like to but don't have a spare grand (£1000 to you David :wink: ) and as I'm in the far north ; we don't have many summer days for riding so drive a Subaru Forester STi and use the crosser off road for fun.

Cheers lads

Salty

P.S. 14 stone = 196 lb so I'm guessing I should be able to get somewhere near your figures.
LeftaSALTYtaste
 
Posts: 6
Joined: Fri Sep 16, 2016 11:41 am

Re: SM 125 Gangsta loses power in 6th gear

Postby breakwellmz » Mon Apr 17, 2017 12:45 pm

If it revs to the red line (i assume it has a rev counter) in the lower gears but not top there not anything wrong with it apart from too high a top gear, if that`s the case that 52 tooth rear sprocket will be a good starting and maybe finishing point.
Sorry about the comment about getting a full licence, i had no idea that it was that sort of money. :shock: Next year it will be 40 years since i passed mine.
Is it a 5 or 6 speed box then?
breakwellmz
 
Posts: 379
Joined: Sun Dec 16, 2007 7:11 am
Location: SW England

Re: SM 125 Gangsta loses power in 5th gear

Postby LeftaSALTYtaste » Tue Apr 18, 2017 1:56 am

breakwellmz wrote:If it revs to the red line (i assume it has a rev counter) in the lower gears but not top there not anything wrong with it apart from too high a top gear, if that`s the case that 52 tooth rear sprocket will be a good starting and maybe finishing point.
Sorry about the comment about getting a full licence, i had no idea that it was that sort of money. :shock: Next year it will be 40 years since i passed mine.
Is it a 5 or 6 speed box then?


Cheers bud and guess I don't count my gears either as it's a 5 speed and not a 6 speed box according to specs online. Paha :oops: No rev counter though, not even a fuel gauge.

I just purchased a 52 tooth on fleabay for under £30 delivered, so we'll see what the outcome is. http://www.ebay.co.uk/itm/401152215950?_trksid=p2057872.m2749.l2649&ssPageName=STRK%3AMEBIDX%3AIT

I wish I'd passed my test when I was a young lad but was happy riding Vespa's with 150 Malossi kits and Lambretta's before heading down the car route and using the Honda range of crossers (dirt bikes) for the flying feeling when hitting 30 foot kickers :D . I did have a GP 125 Lambretta with a 38 mm dellorto, 190 Suzuki head and piston and a PM tuning upswept pipe with a YPVS (she was a mishmash of parts) that hit 105 mph and soaked my leg in petrol with the open side draft carb , Thinking back thats scarey on those small wheels but the joys of having no fear at 17 ay?
I remember the test to be in 2 parts ; the first to allow you to ride up to a 350 with a restriction on bhp of sorts , now it costs the best part of a thousand pounds.... Gutted and not to mention the CBT :roll: .

Anyway thanks for your advice lads and will update when I fit the larger chain ring.

Salty

EDIT: Nope she definitely has 6 gears as I've just checked :?
LeftaSALTYtaste
 
Posts: 6
Joined: Fri Sep 16, 2016 11:41 am

Re: SM 125 Gangsta loses power in 6th gear

Postby DAVID THOMPSON » Tue Apr 18, 2017 9:46 am

too bad they do not have 30hp then you could use number 6
dave
if the oem sprocket is dished cut the center out to make a spacer to make the chain line up

again here viewtopic.php?f=4&t=49
Dave 2002 MZ RT125 +1995 Saxon Tour (rotax500cc)
1997 MZ Skorpion Traveller added 6/13/09
Located in WV USA
"I like the road less traveled if it's PAVED!"
E mail wd8cyv at yahoo dot com
User avatar
DAVID THOMPSON
Moderator
 
Posts: 4487
Joined: Sun Nov 23, 2003 11:01 am
Location: Parkersburg, West Virginia USA .questions answered MZ 95 up, BMW 1953 to 1979 and ham radio WD8CYV

Re: SM 125 Gangsta loses power in 6th gear

Postby LeftaSALTYtaste » Tue Apr 18, 2017 1:06 pm

DAVID THOMPSON wrote:too bad they do not have 30hp then you could use number 6
dave
if the oem sprocket is dished cut the center out to make a spacer to make the chain line up

again here viewtopic.php?f=4&t=49


Yeah true dat :roll:

No the oem sprocket luckily enough is not dished, so the one I bought will be a straight swap. Just hope my chain is long enough, mind you I've got a fair bit of my tensioners left. :D
LeftaSALTYtaste
 
Posts: 6
Joined: Fri Sep 16, 2016 11:41 am

Re: SM 125 Gangsta loses power in 6th gear

Postby DAVID THOMPSON » Tue Apr 18, 2017 2:17 pm

i had to use the center out of the old sprocket to make my chain line up straight to the front
and longer bolts
my bike sold new july 2002
dave
Dave 2002 MZ RT125 +1995 Saxon Tour (rotax500cc)
1997 MZ Skorpion Traveller added 6/13/09
Located in WV USA
"I like the road less traveled if it's PAVED!"
E mail wd8cyv at yahoo dot com
User avatar
DAVID THOMPSON
Moderator
 
Posts: 4487
Joined: Sun Nov 23, 2003 11:01 am
Location: Parkersburg, West Virginia USA .questions answered MZ 95 up, BMW 1953 to 1979 and ham radio WD8CYV

Re: SM 125 Gangsta loses power in 6th gear

Postby LeftaSALTYtaste » Mon Apr 24, 2017 1:56 am

Well after fitting the 52 tooth sprocket she's a wee bit better at pulling up through the gears, she even lifts the front wheel 8) .
I don't have to rag her neck in 5th either to keep the speed up before changing to 6th and she'll even do 70 mph.

Happy days and thanks for your help lads.

Cheers
Salty
LeftaSALTYtaste
 
Posts: 6
Joined: Fri Sep 16, 2016 11:41 am

Re: SM 125 Gangsta loses power in 6th gear

Postby DAVID THOMPSON » Mon Apr 24, 2017 9:59 am

if there is no tachometer on it at 70mph its wfo if you want it to last keep it below 65mph
the ignition cuts out at 10,000 rpm or 10,500
they made a tuff motor but wfo all the time will kill any thing
dave
Dave 2002 MZ RT125 +1995 Saxon Tour (rotax500cc)
1997 MZ Skorpion Traveller added 6/13/09
Located in WV USA
"I like the road less traveled if it's PAVED!"
E mail wd8cyv at yahoo dot com
User avatar
DAVID THOMPSON
Moderator
 
Posts: 4487
Joined: Sun Nov 23, 2003 11:01 am
Location: Parkersburg, West Virginia USA .questions answered MZ 95 up, BMW 1953 to 1979 and ham radio WD8CYV

Re: SM 125 Gangsta loses power in 6th gear

Postby LeftaSALTYtaste » Sat Apr 29, 2017 2:18 am

DAVID THOMPSON wrote:if there is no tachometer on it at 70mph its wfo if you want it to last keep it below 65mph
the ignition cuts out at 10,000 rpm or 10,500
they made a tuff motor but wfo all the time will kill any thing
dave

Aye I do realise this and don't keep it at WFO for long, the roads are extremely winding where I live, so I'd be mad to :roll: , It means that I don't have to change in to sixth gear most runs unless there is a long straight as fifth will cruise at 60 no problem now. I even had around 75-78 out of her on a small decline but as I wear a peaked helmet the wind was catching it a felt like my head was going to be ripped off ahaha, so I soon slowed down.

I did have ignition cut out a couple of times before the sprocket change as was having to throttle her neck before changing to top gear.
I have heard there is a CDI box that will allow for higher revs but don't think i'll bother as she has become a lot more fun with the larger sprocket . She pulls better , especially up hill and sometimes I'll even get the front wheel to lift. :twisted:

Cheers again for your help and insight Dave.

Salty
LeftaSALTYtaste
 
Posts: 6
Joined: Fri Sep 16, 2016 11:41 am


Return to 125 cc

Who is online

Users browsing this forum: No registered users and 1 guest

cron