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there is no tuning done. i will order and try a new valve, wont hurt to have a standard size one anyway.

cheers
les.

M in sc,

very quick reply!

it is controlled by the standard yamaha set up (servo etc.) however i have the modified programmable power control box, which i would highly recommend. however it does not matter where i programme the valve to open, it makes no difference to the power before it opens.

les.

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.

i hope so!
the dt250mx (i think dt250e/f in usa) only makes 17hp, as opposed to 38 for the yz250, so should be fun!

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.

Hi,
my experience in my younger years when k+ns were very popular was that you could not jet big enough to stop it running weak, i seized an engine before i learnt. all went away upon removing them. now i use soft filter pods and no problem. so fully agree with your post.
cheers
les.
happy holidays!

another old hack for these heads in the uk where they were REALLY common, was to scrap the head gasket, lap the surfaces together and then assemble with heat resistant silicon, it gets the squish just right. i tried it on mine and it worked.

les.

hi,
one "cheat" that i used, that people will probably hate me for, was to buy a metre (yard and a bit) of high tensile threaded bar from the local hardware shop and cut studs of appropriate length for the cost of about 5 euro. they never failed once.
les.

Hi,
done this conversion before, they do indeed fit straight on any earlier model, however the stud lengths will need to be longer, and the liner tangs on the 350cc barrels i believe touch the flywheels so they need to be taken down a bit. i used a bosch 12v coolant pump from a volkswagon golf, about 50 euros. never had a problem.
cheers
les.

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.

teazer,

yep, i always thought it should be the other way round. i was a bit concerned because of the blown components with the previous reg/rect. that just cost me a couple o hundred or so. didnt want to blow them again.

cheers
les.

thanks folks,
good to go then so.
les.

yup, i will do, but what would cause the voltage to DROP  when revving the bike??

les

Guys,

i have replaced the burned components including a refurbed ypvs controller. also replaced are the battery with a new one and the regulator/rectifier.
however, when running i get 14.7 at tickover across the battery, dropping to 14.2 when revved, what goes???

the only difference from standard yamaha is the battery which is 3.5amp AGM instead of 5amp lead/acid. could it be that?

thanks for any help/advice.
cheers
les.