1978 yamaha rd125dx twin

[paulierd125dx...]

hello ,bikers -

iam new here , and new to being a biker or learner biker -

I own a 1978 Yamaha rd125dx twin - standard -

QUESTION-
can anyone here give me any info on performance mods ?

[redeem ouzzer]

These bikes aren’t restricted in any way so you’re into old school tuning I’m afraid. I would say stick an RD200 engine in it but you need most of the 200 to do this and it’s not the late 80’s / early 90’s anymore where bits are cheap and easily available.
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Be a REAL MAN!

[Teflon-Mike]

It used to be that ANY 125 built and registered before 1982 was exempt from the 12bhp learner restriction. This 'grandad right' was dropped when they changes licence regs and upped Learner Legal power to 14.5bhp. So good odds that if you dont have a full licence, an old aircooled RD125 would make more power than your licence allows any-way. ISTR that they claimed about 17bhp.

Which rather makes the tuning question somewhat mute. If you have a licence to ride that bike as is, you have a licence to get a bigger one, which is almost certainly cheaper as well as more reliable that muggering about with that antique....

That particular perversion IS likely for nutters only; and I know of a few pretty highly tuned RD-twin motors that have been used in old TZ frames, sometimes with similar era TZ barels and stuff, for more reliable track-bikes... for the road? It's old school tuning, for more than they make stock, and how much reliability do you want need? These things have been 'Kart-Tuned' for ultimate power, and I seem to recall claims of around 25bhp not being out of order, with the ports widened and lifted and a decent pair of expansion chambers, BUT piston life drops exponentially and you are looking at 500 mile rebuilds and rebores with big risks of siezures... it may be 'fun' to see how quick it will go, but not when you have to push the fekker home!

Is there a real plan here, or just a nieve hope?
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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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That bike won't be learner legal.

Any performance mods will be quite expensive and not that effective as these bikes are already full power. There isn't 15 bhp just sitting there waiting to be unrestrcited.

If it has standard exhausts, swap them for spannies, such as Gibson (Still in business) or Micron, but this will be £500+ for a pair. The carbs will then need upjetting a little to match. Any further improvements will need porting work or a head skim, which won't be cheap either. Even fitting an RD200 motor will need all the ancillaries like carbs and pipes and won't be cheap either.

You're not going to get much value for money from any of this. You might be better off just getting it running better to start with. Maybe a rebore and new pistons/rings/small ends, plus a proper carb strip and clean.
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[Diggs]

Those old RDs were pretty nippy if I recall. I remember going from a 50 to an unrestricted KH125 and it was like riding a rocket in comparison, and that was about 14bhp when running right.

My advice - keep it standard and retain its value. 'Tuning' unless its done properly will lead to tears... When you pass your test, ride it for a bit then sell it for a bigger bike.
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Now - Speed Triple, old ratty GS550, GSXR750M
Gone (in order of ownership) - Raleigh Runabout, AP50, KH125, GP125, KH250, CBX550, Z400, CB750FII, 250LC, GS550, ZXR750H1, Guzzi Targa, GSX750F, KH250 x2, Bimota SB6R and counting...

[redeem ouzzer]

All off the shelf expansion chambers are utter dogshit, no exceptions.
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[Pete.]

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[redeem ouzzer]

Jolly Motos are old tech in YPM now, very revvy pipe but tech has moved on and there’s things like the Martin Johnson pipes that give the same or more bhp than Jollys but with much more torque and drive. Allspeeds and Microns were always shit and modern copies won’t be any better (which I believe the Gibson pipes are). I spent £700 on a set of Lomas pipes which were gorgeous to look at but complete shit. Poor ground clearance and all revs with a hole at 5.5k that was impossible to tune out. With custom pipes I’m getting the same peak but more grunt than most tuned YPVS’s. Pipe design has come a long way in the past few years.
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Be a REAL MAN!

[paulierd125dx...]

Hello guys
Thankyou very much for all your comments I will keep
My rd125dx twin as standard and just only give carbs clean up
And install new pistons rings change carb jets maybe -
Kind regards Paulie

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