RD125LC - they can't be this bad?!

Yonder · L Plate Warrior Joined: 04 Jan 2016 Karma :

I've inherited a Yamaha RD125LC from my dad, which I've just taken out for a spin. Choke open or closed, hot or cold, it's absolutely useless to the point of being dangerous!

On a flat road it has huge difficulty pulling up to 30mph, opening the first 1/2 of the throttle actually bogs and slows the bike down. Pinning the throttle to the stop it will creep up by 1mph every 5 seconds or so. This is with between 3 and 5k RPM showing on the dial. Over 7k it will pull pretty hard. It's not modified in any way.

I know it's a 125cc 2t, but I've just come back from Thailand riding 100-125cc 4t's and they have a HUGE amount more pull at 1.5k RPM than this RD does at 5k. Surely they can't be this bad as to be actively dangerous? Honestly a push bike would be significantly quicker. It must be broken in some way?

Pjay · World Chat Champion Joined: 18 Jan 2016 Karma :

It's a 2 stroke, it will be terrible at 3k, keep the revs up, as like you said, it pulls at 8k, this means it works as intended.

af1 · Borekit Bruiser Joined: 09 Mar 2016 Karma :

You need to look back at the history of the bike , why did they stop using it ?

What have you done to the bike before riding it ?

You need to check the engine over, clean carb, change 2 stroke oil filter.
clean power valve, change crank seals (they will have probably started leaking.
This can cause a lean mixture and seizure)
Did you change the gear oil ?

The carb jets could be blocked ? Unrestricted these bikes will do 85 to 90 mph.

Somethings wrong ! The piston by not being used could have gummed up.
Take the head and barrel off , clean rings , check clearance The piston may be worn.

A bike with long storage will have many problems. Seized chain will reduce power,
brakes stuck on etc

These are worth a few quid. Sell it before you break it. It's not like a pile of
shit 4 stroke.....

Other tests are compression test , looking for worn piston rings etc
leak down test, paticularly looking for air leak , which will kill the engine, crank , pistons....

Other 2 stroke problems can be that the exhaust has gummed up, causing back pressure, lack of performance.....

Pictures would be nice btw

Yonder · L Plate Warrior Joined: 04 Jan 2016 Karma :

Fair enough comment, I know small 2t's aren't about low rev torque but this just seems ridiculous. I probably should have mentioned I've ridden a 110 semi-auto 2t before and it was quite happy pulling along flatly but steadily, keeping up with traffic, at low revs...

I was hoping to use this bike to commute through the city a couple of days a week, if I have to have it screaming at 8k just to cruise along with 30-40mph traffic it'll be up for sale!

Yonder · L Plate Warrior Joined: 04 Jan 2016 Karma :

redeem ouzzer · World Chat Champion Joined: 06 Oct 2015 Karma :

They have cock all bottom end when derestricted but shouldn't bog down. Clean the carb, paying special attention to the emulsion tube and air circuit which should be spotless.
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af1 · Borekit Bruiser Joined: 09 Mar 2016 Karma :

Has the bike got a power valve, they got one after 1983 I think
they always seize , and cause poor performance .....

I love 2 stroke 125's , top speed of 105 officer....

https://i945.photobucket.com/albums/ad293/fatterhatter/Aprilia%20AF1%20resto/CNV000131_zps42a77497.jpg

They are very reliable , if maintained, if it's not working properly , it will seem slow, but twice the power has higher gearing. https://i945.photobucket.com/albums/ad293/fatterhatter/sprort_zpsu5m6lfgx.jpg

Yonder · L Plate Warrior Joined: 04 Jan 2016 Karma :

As requested, here is the dusty beast:

https://i64.tinypic.com/106kk6x.jpg

https://i68.tinypic.com/bl7aq.jpg

https://i66.tinypic.com/if1nbb.jpg

https://i64.tinypic.com/335cemh.jpg

As you can see no YPVS on this engine, apparently they only came in from mk2 onwards (the round barrel engine) and this is a mk1.

My dad actually had the carb cleaned ultrasonically by a garage a few months ago, so it shouldn't be that. I took the carb apart and the jet is on the bottom clip which is richer than spec, yet the bike still feels lean - it does actually run slightly better (more low rev power) with the choke open, particularly when cold...

Nice pics btw! Some spotless classic 2t's there.

redeem ouzzer · World Chat Champion Joined: 06 Oct 2015 Karma :

Pipe is wrong, it's off a mk3 or TZR. Break it, the clocks will do a couple of hundred quid.
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Alawson68 · Renault 5 Driver Joined: 26 Jan 2013 Karma :

if you pull the choke out and it likes it, it's jetted wrong. Looks like he's changed the pipe and left the jetting as standard which means it's running lean and you're heading for a sieze. This generally happens north of 70mph on a country lane.
The crankcase seals may have gone as well. I had one of these 31 years ago to the day (im 48 tomorrow) and it was phenomenal but had to be kept in the power band 8k - 12k. To realise the 'cult of elsie' you need to give it the beans, but not until you've sorted the jetting out, or you'll bin it in a hedge.
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Yonder · L Plate Warrior Joined: 04 Jan 2016 Karma :

I'm aware the pipe is from a later model, should be an all black number without a seperate end can but there you go. I wonder if could be a significant cause of low rev issues in that the pipe is designed for a YPVS engine, which in this case it isn't attached to. As far as I know it's had that pipe on for years, certainly since before my dad had it.

Good point about the jetting Alawson. I'll either get that looked at or source an original pipe.

Kickstart · The Oracle Joined: 04 Feb 2002 Karma :

Ariel Badger · Super Spammer Joined: 02 Dec 2006 Karma :

Lovely little bike, please do not break it.
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Enduro Numpty · Could Be A Chat Bot Joined: 31 Oct 2012 Karma :

Alawson68 · Renault 5 Driver Joined: 26 Jan 2013 Karma :

spnorm · Crazy Courier Joined: 18 Aug 2007 Karma :

That's a lovely little bike and just wants the engine sorting. I couldn't quite afford one when I was a 17 year old learner in 1986, so bought a 125 Superdream instead Embarassed

They weren't that pesky when restricted, but could be if they'd been tuned. I know a lad local to me had one which was virtually as fast as my RD250LC

Yonder · L Plate Warrior Joined: 04 Jan 2016 Karma :

Don't worry, the bike won't be getting broken by me. It might get sold in one piece in a worse case scenario, but definately not broken.

Looks like the thing to do now is source a mk1 exhaust, which having a scan around the internet seems easier said than done - couldn't find any!

redeem ouzzer · World Chat Champion Joined: 06 Oct 2015 Karma :

If you can't find a stock pipe then a Micron will do, however the later big can ones benefit from surgery.
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Alawson68 · Renault 5 Driver Joined: 26 Jan 2013 Karma :

Wednesday Biker · Spanner Monkey Joined: 11 Sep 2014 Karma :

Its not running right.
I had one and the wheel comes up on acceleration in first and second.
The powerband was about 7 or 8k if I remember and are a bit depressing under that.
Probably not as fast as I remember but they were pretty pokey, so yours just doesn't sound right.
There might be a washer thingy that needs chiselling out at the front of the pipe. Was on mine.