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Topics - John Orchard

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General Discussion / Just checking in .....
« on: January 11, 2024, 10:15:44 AM »
2 weeks no posts, just keeping things active :-) Come on Chaps, just talk anything VMX, I need my fix ;-)

Tech Talk / CR250M inlet port height different, why?
« on: September 08, 2023, 05:32:25 PM »
So here is another useless rambling post from me :-)

I've known for many years of the odd inlet port of the Honda CR250M, but I only just now wonder why? I guess I look at employing such trickery on another bike. With the top of the two inlet port windows at different heights, below is a link to the cylinder liner. I guess at a couple of the following reasons ....

* Added crankcase turbulence?

* Flow from each port directed in a different direction?

* With one port starting to close before the other, could it give a mild supercharging effect to the later closing window?

By all reports the CR250M was the fastest 250 in its time, the inlet port being the only thing that seems to stand out from the 250's, makes me wonder, hmmm.

Feel free to offer your own crazy ideas :-)

Hey Guy's, I want to purchase some parts from the US, the company that sells them does not ship to Australia, is there a company, or rider, that I could pay to purchase the required parts and post to me in Australia?

System problems? / Is security certificate going to be updated?
« on: August 08, 2023, 02:04:48 PM »
See above :-)

Tech Talk / RM125S Piston rings without notch for pin, eh?!
« on: July 15, 2023, 09:06:13 PM »
I have some NOS pistons & rings to suit '75 Suz RM125S, the rings (the .60mm thick ones) do not have a notch where they end at the pins, with the standard size rings fitted into a new 56mm bore, there is a 1.4mm end-gap. I think that when fitted to the piston, and slipped into the cylinder, a minimum of 1.2mm gap is required for the pin thickness, so the 1.4 would allow them to not jam hard against the pin when hot.

What are your thoughts of running such a wide end-gap? I was thinking of running .25 over rings, and grinding an angle at the ring end, to minimise the end-gap, but I worry that a .6mm think ring does not leave much metal to handle the heat?

Has this matter ever arisen for RM125S owners before?

I was wondering if anyone has used a 1980 Honda CR125 copper head gasket, 12251-466-000, on a Suz TS125? Could anyone advise me of the distance from stud centre to stud centre? TIA

EDIT; Yes it is the same :-)

Tech Talk / Mikuni hex main jet thread !!!
« on: May 24, 2023, 08:06:41 PM »
Hello Chaps, I was looking for a thread-tap to suit Mikuni hex main-jets, according to the Mikunioz website the thread is 5.3mm diameter by .9mm pitch, what tha! After a bit of searching I am not having any luck finding a tap, anyone got any ideas? Me not having a clue about anything imperial, would there be an imperial measurement that would come close?

Tech Talk / Where can buy jet reamers 2.0mm to 3.0mm?
« on: April 30, 2023, 04:51:11 PM »
Anyone know where I can buy tapered jet reamers, maybe a set of 5 or 6 that range between from 2.00mm to 3.00mm (yes to open needle-jets :-) ), style as per the ones in this link:  But up to 3.00mm, or maybe 2.80mm

Tech Talk / Needle jet still works with a closed throttle !
« on: April 28, 2023, 06:33:02 PM »
I thought I'd run something past you guys (what again!), trying to get my TS125/VM32 jetting fine tuned, I think (?) umm how do I put this into type .... ok I'll start somewhere.....

In neutral, rev the bike up, chop the throttle, rpm's hang up (probably around 1500 rpms?) like too lean (which it is), after aprox 20 seconds the idle comes down to aprox 800 rpm (nice idle), then finally conks-out.

I think, as the rpm is quite highish, with a closed throttle, just after closing the throttle, the engine is drawing fuel from both the pilot/airscrew AND the needle-jet, once the idle rpm can creep down, fuel stops being supplied by the needle-jet and then the pilot/airscrew has sole control.

So, in all my years I have never had a bike with this kind of issue, probably because I am basically starting from scratch, rather than someone else (the manufacturer) doing the hard work. I never considered that the straight section of the needle/needle-jet can be drawing fuel with a closed throttle! I guess only while the rpm is high enough to have air speed to do so.

While confusing myself, I had the pilot jet too rich and the needle-jet to lean, bike revs its tits off above normal idle rpm (lean), conks-out at normal idle rpm range (too rich) ..... all rpm affected, with a closed throttle !

Ok I'll work on my theory tomorrow, hopefully I am correct :-)

General Discussion / Ideas for carb jet holder?
« on: April 23, 2023, 08:42:57 PM »
Anyone got a good idea for holding a range of main & pilot jets, I really couldn't be stuffed drilling & tapping 100 holes.

Tech Talk / Mikuni needle jet bore sizes, 159 type
« on: April 16, 2023, 07:05:46 PM »
I'll post this here, it took me long enough to find it, sure there is someone out there that has a more complete listing. These are for the 159 type needle jet for Mikuni VM30, 32 & 34, not sure if the sizing correlates to other models.

Description codes & bore sizes.

O-4 = 2.620mm
O-6 = 2.630
O-8 = 2.640
P-0 = 2.650
P-2 = 2.660
P-4 = 2.670
P-5 = 2.675 (half size)
P-6 = 2.680
P-8 = 2.690
Q-0 = 2.700
Q-2 = 2.710
Q-4 = 2.720
Q-5 = 2.725 (half size)
Q-8 = 2.740
R-5 = 2.775 (half size)

I thought I'd have a play drilling out some needle jets but I don't own any equipment exact enough :-) I guess I just wanted to know if the bore size was the only specification that changed with the description code. In a pinch, if I needed a richer 1/4 throttle (the point where the needle jet bore size and needle straight section are in play) I'd consider reaming out the needle jet ID with some tapered jet reamers I have. Being the butcher that I am ;-)

Tech Talk / My TS125B jetting specs, eh?
« on: April 11, 2023, 08:13:29 PM »
*EDITED* I just thought I'd bounce my jetting specs off you guys, they seem all over the place to me, after comparing to other 125's.


RM125A port timing
RM125A pipe
VM32 carb
External flywheel
TS185 electronic ignition, standard TS125B ignition timing.
TS125B head with 1.2mm off the face, head gasket 1.2mm thinner, .8mm squish ....... It's got high comp, maybe too high?

Main jet: 195
Needle: 6DP17 #4 groove
Needle jet: P-8
Pilot jet: 55
Slide: 2.5

It seems to go ok, plug is chocolate brown safe, I just expected a much larger main jet (about 230?) and much smaller pilot jet (about a 35?). I guess I just need to stop second-guessing myself?

RM100 N, T, X ('79 ~ '81) cylinder, excellent condition, bore 50.5mm good to use, no stripped threads, good studs, unmolested ports, Crankshaft, big-end feels nice, $200 the pair, Can email pics.

I was wondering if there is anyone on here that lives in New Zealand, that could buy a part for me from over there and post it too me here in Victoria, Australia?

I wanted two of part number 9052-106, which are 35cc gas bags for shock absorbers, from this company: they will fit in a small cardboard box, happy to pay in advance for items and all postage costs.

I have checked with them, they have stock, they are $10 NZ each.

Or I can order them on-line and have them delivered to an address in NZ. To get them sent by DHL to Australia is $250 !

For Sale / JT V2000 junior armour.
« on: March 03, 2023, 12:40:19 PM »
For sale, JT V2000 armour, junior size, has one broken clip, $100

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