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folks,

i have fitted a new old stock tzr125 barrel to a project of mine, so, standard size bore. however the power valve came from a barrel that was bored to max 2mm over and had been machined back for clearance from the piston.

the bike struggles to get to where the power valve begins to open and then rips your arms off. i am wondering if this hole in the power could be due to excessive power valve clearance (as in the valve is effectively "open").

any thoughts anybody?

les.

a couple of ideas.
i am working on a project involving a dt250mx engine in a better rolling chassis and had the idea to graft on a yz250e cylinder for more poke. the cylinder i bought was 2mm over, and i discovered that there are very few pistons available, all of the forged pistons are expensive and skirt-less so life was not going to be long. so i had the idea to have it re-lined with a bridged inlet port and use an IT250 piston which has the full windowed skirt. the job came back from PJME in the UK and is superb, blasted barrel, relined and bored to 1.5 thou for 250 euros including postage.
another advantage seems to be that standard genuine pistons are very cheap (i paid 25 euros) because i suppose no-one has standard cylinders any more, so this relieved some of the re-line cost.
i suppose this could be done if someone was fitting tz cylinders to an rd, and improve piston/cylinder life.

good day folks,

to anybodys knowledge, has a piston ring been tried, fitted below the piston pin but above the raised skirt sides, to help with piston slap? i had a barrel and piston in my hands the other day and played about a while and i believe it could be made to work.
it would obsiously not want to come out of the bottom of the cylinder sleeve but it looked do-able.
wondered if it had ever been tried.
just saw a porsche engine being stripped on tv, and they had exactly this on the piston, obviously 4 stroke so easier.

cheers
les.

hi again,

has anybody on here used a race cylinder on a road bike, say a tz barrel on an rd, and opted to use rd pistons with the full skirt to save on high wear rates?

i have a couple of questions. i am using a yz250 cylinder on a dt250 bottom end and want to use the skirted dt piston, however there is enough rocking at bdc into the inlet port to allow the skirt to catch on the bottom of the inlet port, even with some chamfering i dont like the look of it. the bore clearance measures good.

were the race pistons without skirts used only for added inlet? or possibly also because with a wide port this skirt catching problem occurs? if is so i would obviously be better off using the race yz piston, which leads to my next question, where on the piston is the bore clearance measured? from the top of the piston inlet port?? at this position surely there is already some tapering of the piston?

any advice/previous experience of this issue is greatly appreciated, i want this project to work!

cheers
les.

folks,

hoping someone may have some ideas.
out riding my lovely tzr125 when, one by one, components started burning out.
first the koso digital speedo/rev counter, then the digital temp. gauge. (separate component). then the power valve controller.
the bike still runs, so got home, but anything wired to the battery burned. i have tested them separately with a power supply and they are dead. does anyone think that the regulator/rectifier faulted and overcharged? the battery after all this only read 10.5 volts and now wont hold charge, so i may have cooked that.

any ideas anyone (please!)
cheers
les.

Dudes,

what does small end noise sound like please? i have a marble in a tin type rattle ONLY on tickover, nothing at any revs or on the over-run. the bore is fresh and measureably tight so i am wondering.

many thanks
les.

folks,
couple of pics of a recently finished project. Chassis is a TDR125 with a DT400 engine shoehorned in there. the chassis, wheels, brakes are far superior to the original DT versions, and the dt400 engine is one of my favourite 2strokes. it runs sweet to 7k rpm, it would pull a stump out. the carb is an OKO 34mm flat slide power jet, foam air filter, the exhaust is an adaptation of the original TDR.
cheers
les.

folks,
my daughter and myself are recently diagnosed on the autism spectrum she is 16. so to make the most of it as we share an interest in motorcycle building we decided to do a joint project, what a great bonding experience. she built the purple one, she built the engine on her own and did all of the spray job. honda NSR75/80s were very popular in europe and were modified for racing a lot. if anyone is interested in these engines (very similar to cr80) below is a good resource for tuning them, which i did use. The purple bike has a standard engine that is derestricted fully (they were restricted over here) and the repsol one has a malossi big bore kit, large carb and reeds.

https://honda80ccracing.weebly.com/build-your-own-racer.html

cheers again
les.

folks,
new build just finished, its a Honda NSR75 rolling chassis with a TZR125 powervalve engine fitted. bodywork is Honda RS125 GP bike and ONLY JUST fits on the chassis (1/2 inch clearance to the front wheel).
cheers
les.

good day folks,
i am fitting a yz250 cylinder on my dt250 engine for extra fun. this is a straight swap apart from having to move the stud holes 2mm. bore and stroke etc. is all the same.
the whole top end will basically by yz250, however i was intending using a dt250 piston for added life, the only difference is that this piston has the rear skirt intact, however i find that with the extra width of the yz inlet port that the dt piston skirt appears to "catch" on the bottom of the inlet port on the way down.
has anyone had any experience with this type of thing. i always thought that the removal of the rear skirt for the race set up would be to increase induction, however could it  be that it avoids this "catching"?
any thoughts welcome, before i fire her up!
cheers
les.

Good day folks,

does anyone out there have any idea about comparable jet sizes from mikuni to keihin? there is a conversion chart going around online that seems to be miles out, showing only around a 15percent difference.
from the jets that i have at home the hole in the keihin seems to be approx twice the size as mikuni for the same jet size, if that makes sense.
i am building bikes and replacing knackered old mikuni carbs with new oko's and would like a rough start point.
anyone have any solid information?

cheers
les.

folks,

i have a tzr 125 with powervalve.
from the cdi to power valve controller there is a wire that sends the rev. signal so as the controller knows when to start opening the power valve. the bike starts and runs perfectly and i am very pleased with it. however i am wiring a digital rev counter and following instructions to take the signal from the said wire.

upon disconnecting the said wire with the bike running i got a shock equally as strong as holding the ht lead to the plug.

there is no short/connection from the ht lead to the frame etc. the bike runs perfectly.

does anyone know why this should be, i do not want it to be a fault that will burn out a rather expensive power valve control box.

cheers
les.

hi all,

i have just finished building a tzr125 engine to install in a honda nsr80 chassis for a bit of fun. my question is this, it is rebored to 2mm over and i was wondering whether anyone would advise increasing the combustion chamber size for this bore, to avoid possible problems with detonation? by my calculations the engine has increased in size from 125 to 133cc.

cheers
les.

Good day folks,

i have just installed a refurbed crankshaft on a single cylinder tzr125 with new koyo crank bearings. all went together very well with a little heat here and a little deep freeze work there.

after assembly i can feel a VERY slight play up and down on the crank bearings, and it seems that the crankshaft is a less than tight fit on the inner bearing races. the inner races rotate with the crank when i spin it, so it is the bearing doing the work,  however if i hold the inner race with a screwdriver it is possible to rotate the crank by hand in the inner race.

the detectible up and down play wobbling the crankshaft is very slight indeed.

what is the general opinion here, start again and try to improve or leave as is, or any other suggestions?

could the crankshaft be worn and a smaller diameter than the inner bearing race??

any help really appreciated.

cheers folks
les.

Folks,

This may be a wild stab in the dark, but, would it be possible to re-spoke a wheel by replacing one of the original spokes at a time and making sure that the tension is the same as the original in every case?

cheers
les.

Hi folks,

i have a DT400 full recon engine, sweet as a nut, with a pwk 34mm carb (new) and to start with, standard size jetting.
question is, the bike refused to rev thru a midrange splutter, so i lowered the needle (clip now on the top setting) and it is greatly improved but not gone completely. so where do i go from here?? smaller idle jet? or smaller main jet?

any ideas welcomed.

cheers
les

good day folks,

just finished a rebuild and after a couple of teething problems with getting it running now it is fired up and sweet as a nut. Except!! i seem to only have first gear. it snicks down into first lovely and rides fine and comes back up into neutral fine, but nothing from second gear up. gear lever just lifts and stops.

is this something that might be cured by taking the clutch cover and clutch off only?? or is it definately an engine out job.

any suggestions appreciated.

many thanks
les

Folks,

question. will a coil from a 12volt bike work on a 6v bike? or would i only get "half a spark"?
seems a daft question however the bike still wont start!

it is a dt400mx, with a completely recond. engine, great compression, brand new carb. excellent cdi ignition with a new cdi unit from rexs speed shop. however it refuses to fire at all and i just realised that the coil is from a tdr125 12v. so maybe the spark is weak (there is a spark when i hang the plug on the engine).

any advice appreciated.
cheers
les

folks,

does anybody know if the kickstart spline is the same diameter on the dt250/400 as the rd250/400? 18mm i think?

thanks in advance
les.

folks,
solve one problem and......
rd/lc hybrid engine. starts on right hand cylinder only. nothing at all from the left. swapped the orange coil wires over and the plug leads and the problem stays on the same side.
I assume that this test absolutely rules anything electrical out, I have swapped the plugs over as well.
so I am thinking to start looking at the carb, however the plug is always wet.
any ideas??
thanks
les