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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.

teazer,

actually, its the other way round, the aircooled runs hotter, so the clearance can be less, as the barrel and the piston are expanding at roughly similar rates so the clearance remains predictable.
watercooled barrels run cooler so the piston expands more in comparison and reduces the clearance more, i believe that to be the reason that recommended clearances for water cooled pistons become debatable when the piston is going in an aircooled barrel.

even the above quoted pro x paper states that the manufacturers recommendation supercedes all of that information.

just my 2 euros worth.

les.

than;ks for that guys, i feel a bit better now. wont be licking it any time soon tho.

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,

just had the same problem exactly with a brand new master cylinder.

i could feel just a tiny bit of pressure occasionally, but then it would release and go to the handlebar, as if fluid was slipping by the seal. i kept on pumping and pumping until i got some pressure and then cable tied it back under pressure and it improved in no time.

i think the new seal was "dry" and under pressure it lubed and expanded up, works a treat now.

les.

greaser greg,

yup, that would suggest that it is slightly too rich on WOT, so, as above.

les.

hi all,

years (and years) ago a certain Terry Beckett in the uk helped me jet an rd400 that i was working on. he told me to jet big enough to get it to splutter and cough at WOT and then back down on the jets just until it cleans up. much like you would do when adjusting the high jet on your chainsaw.

it worked for me every time and marked the point in my motorcycle career when i stopped blowing up engines!!.

hope this may help.
cheers
les.

hi,

m in sc.

both of those i will do. many thanks.

les.

hi again,

i can measure the squish in the next couple of days but it will be standard, i was thinking that if i did not reduce the squish and left it as standard then at lease the compression would be on the "good" side??

the head gasket is a multi-sandwiched alloy type that holds water as well, so it is not easy to modify for increased size. on top of that they actually sell big-bore kits for these that use the standard head??

whats the thinking out there?

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.

Folks,

ive seen a mystery like t his before but on DT'S,  are you sure you have the correct dipstick??

cheers
les.

folks,

thanks for all the replies, new crank on the way!

cheers
les.

guys,

right, upon stripping, it seems that there may be some wear on the crank bearing faces, maybe it has spun the bearings up before in the past. not too easy to detect, as the bearings have to go into the crank cases before the crank goes in, so you only find out on assembly.

what would be a plan of action if, say, this was an irreplaceable crankshaft?? slightly knurl the faces? anyone come across this problem before.

i would like to try and use the crank i have if poss, especially as i assembled it with new rod etc. and it is very difficult on my press to get it apart without grinding the pin in half, as i did with the knackered one.

probably floggin' a deadun' here but worth a small shot.

cheers
les.

folks

thanks. yup, already started. think ill order some more bearings from a different supplier and try them on the crank. i dont think that the correct width of the crank bearing face is available, so its suck it and see.

any other ideas are very welcome

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.