Messages

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.

hi,
looking at the very nice way that you fabricated the engine mounts it would be a shame to rip them apart to move the engine over 10mm. but would it be possible to machine 10mm off of the engine mounts on the engine and then slide the engine over on the bolts and use spacers in the other side?
i have built half a dozen hybrids and have always found that it is best to get the engine to line up rather than start spacing everything else. even if it means offsetting the engine by a small amount.
cheers
les.

RDFL
Ireland
cheers, 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.

50gary,

i have bought 5 of these for single cylinder two strokes and i find them brilliant, you can set the wheel size for speed, the number of cylinders for revs. etc. it even has a battery voltage meter. i have the tacho connected to the feed signal from the cdi box, which if you dont have it would need to come from the coil feed which i have not tried.
the chinese translated instructions are pretty straightforward to "interpret" but if you have any problem let me know.

https://www.ebay.co.uk/itm/233919950698

cheers
les.

M in SC,

yep, done.

les.

1976rd400c,
cheers for that, i am much happier now!
les

1976rd400c
thats exactly the type of thing that i am looking at.
when you say "banging away", do you mean that you can hear it loud?
mind you, 4 thou is a huge clearance!
cheers
les.

folks,
thanks for the feedback, feeling more confident that i wasnt putting the wrong piston in wrong barrel, i honed a bit more today, and am much happier with it now, there is also a good radius on the port and a chamfer on the piston skirt just to be sure.
i will post how the initial start up goes!
cheers
les.

Dvsrd,
there is 5-6mm overlap to the side of the inlet, increasing as the skirt reaches the bottom of the port (as the port curves in).
les.

Dvsrd,
hi again.
yes, just rebored and the ports are chamfered. it doesnt catch solid, more seems to "ride up" onto the bottom of the port. clearance is tight so i will hone slightly tomorrow and if that helps.

M in SC, are you saying that by taking a few mm off the bottom of the piston that it wont reach the bottom of the port?

cheers
les.

M in SC
ill do more work on it tomorrow, at the moment the rebore is on the tight side and it may be "pushing out" into the inlet port.
i have researched since posting and the IT250 barrels have pretty similar ports but with skirted pistons so it should work.
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.

Ive taken all that in. i will dial each bike in in the usual way, was just looking for a better stab at a "start point"  as i had begun to think that a similar stamped jet from one to the other might be waaay off. i know more  now.
thanks again
les.

hi,
yup, i am using OKO with keihin long hex jets.
So we could say that similar marked keihin jets are roughly double the flow of hex mikuni.
cheers
les.