DT125R ARCHIVE

this is what i found on here

http://www.125ccsportsbikes.com/forums/index.php?showtopic=84425

Please bear in mind i do not know the sachs, only from what i've read above, i'm only going on personal experiences, i have had 9 4hw tzr's and three 4dl tzr's and 3 2rk tzr's through my door in the last year, all bought, reconditioned, and sold on, i only have my personal experiences to tell you.

firstly to clarify, the 4fu barrel, is not from the tzr-RR, it's from the uk/european spec from the 4hw/4fl
model which is a tzr-R

it's ported slightly different to the 4dl tzr's and dt's, and it's a nicosil plated barrel, with flat top piston, it has slightly different compression to the others, and doesnt produce more peak bhp than the others, actually less, not by a lot, but enough for you to notice, HOWEVER it is ported for functionality, rather than aggressiveness, so it is more useable power, but when on it's standard bottom end, it is less powerfull than the tzr-RR
(please note, if you seize the 4fu barrel it's £100 to £150 for a decent replate, it cannot be rebored!)

next the 3mb barrel and head, nice peice of kit, capable of 33bhp, at the rear wheel, WITH WORK used on the DT-R and the TZR125-RR series 1 and 3 4dl, the italian import model, higher compression, better power, better performance, but higher in the rev range due to the more aggressive porting, the engine casings/crank areas were developed by moto minarelli, for the extra power, and belgarda did all the frame and cosmetic and changing brakes etc.

then you have the holy grail, i'll pay a lot of money to anyone who gets one of these, the actual 4DL sp barrel, it has 4DL stamped on the side of it, and some italian name. and is a massive step up from what we're used to, you cant re-port a 3mb barrel to this level, no matter who you take it to! it is very aggressicely ported, but it's as smooth as a baby's bum from 1000 to 13500 rpm! the engine that had this barrel on it will produce an accliamed 35 bhp, at the wheel. (remember it's acclaimed!)

right, my opinion, do you want a brilliant reading on a dyno, or a good fistfull of useable power, think about this, as tuning options depend on it, i mean why go get it re-ported to produce more power, it your peak power is over the redline, you'd not be able to use it without risking blowing it up!?

if you have the 3mb bottom and top end, then well done, you're onto a winner, i'd recommend just doing exactly what yamaha intended. go for the tzr125rr set up: 32mm dellorto, change the reeds and inlet manifold, and stick a 4dl exhaust on it, but be carefull which you go for, the series 1 and 3 are different, one looks fat, and one has a long stinger, one produces max power at around 10,000 rpm, the other at 11,500rpm, guess which one is more useable!

if you have the uk spec bottom end, be carefull,they look the same/similar as the 3mb, but the flwheel is different, as are the casings, and crank, and an interesting fact, the uk spec (4hw/4fl) tzr125r uses the 2rk con rod from the 1987-1992 model, (not made to handle masses of power) i've had no end of engines come through where people have tried to stick this and that on it, it's gone splat and i've bought it to recondition it. i'd go as yamaha intended, grab the 28mm mikuni carb off a 4hw tzr, and the inlet and reeds to match (if that isnt what yours is running at the moment) IN MY OPINION, DO NOT RUN A HIGH COMPRESSION KIT ON THIS BOTTOM END, IT WILL NOT HANDLE THE POWER, AND IT WILL SH*T ITSELF UNDER STRESS, IT JUST CANT HANDLE IT.

the ram air filters may sound great (that great sucking noise!), but can damage reliability due to the lack of controll of airflow, ideally you'd need to rejet from summer to winter and visa versa due to changes in air density and temperature through the seasons, NOT FORGETTING THEY GET SODDEN WHEN IT RAINS IF ITS NOT PROTECTED! (which isnt the case as much with a standard airbox) but it's a long debate that'll never end, airbox or not airbox or not..... each person prefers their own, but the gp's all use airboxes....... lol

for both engines, tzr125r, and tzr125rr, the best thing you can spend your money on is the exhaust system, and carb, maximum power gains, in the rev range you want it, with only the time consuming task of re-jetting to suit.
that or send the barrel to a well recommended 2t engineer, and tell him what you want from it!

dont know if this helps, but i fancied a ramble on about something, and seeing as the sachs uses the yamaha engine, i thought this seemed a good place to do it!
let me know if i'm wrong on anything, i'm still learning, but after stripping a lot of tzr engines this year, i'm getting there!



last but not least, a little note on bhp, this whole 33bhp marker that everyone chases, it's a very challenging target to find, seeing as even a rs 125, only produces 27-29 at the wheel, the 33bhp claim is the reading taken from the crank! power is lost throught the transmision and the drive gears/chain, and then the tyres, i've seen three brand new bikes from aprillia, straight onto a dyno out of the box, they ranged from 26-28.2 bhp at the rear wheel. and that was back in the day when they were the fastest thing a crazy teenager could buy!

the very very best and top flight of the superteen 125 bikes are only running at 35 bhp, and the top flight only make one race before needing a full rebuild, if they went past arond 35 bhp, the bikes wouldn't even finish the race before falling apart through the strain.

anyone who claims 33bhp at the wheel, show me/everyone the dyno readout, if you got the 33bhp, you've worked hard, tuned very well, spent a lot of money, and got a very fast bike, be proud!