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Wanted / Re: WANTED: damper rod extenders Yam DT1,2,3 RT1,2,3.
« on: November 03, 2024, 06:02:21 pm »We will be anxiously awaiting the outcome. Do you have the specs for Damper rod mod"back in the day?
No but I can easily design it :-)
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No but I can easily design it :-)
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Wanted / Re: WANTED: damper rod extenders Yam DT1,2,3 RT1,2,3.
« on: November 03, 2024, 03:30:16 pm »
We'll see :-)
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Wanted / Re: WANTED: damper rod extenders Yam DT1,2,3 RT1,2,3.
« on: November 02, 2024, 12:53:43 pm »
I bought myself a Chinese mini lathe, let's see how I go :-)
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Wanted / Anyone got something for sale? Hit me up.
« on: November 02, 2024, 12:52:44 pm »
I sell one bike, now have a need to fill the void ;-) Got anything of interest, feel free to dangle the carrot :-)
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For Sale / Pre 70 Yam 250 for sale, SOLD
« on: October 23, 2024, 09:02:23 am »
OK now has come the time to sell my Pre 70 racebike, it is a 1972 DT2 converted to run in the Pre 70 class, following are details ....
GYT cylinder head.
DT1MX ported cylinder, .50 over.
New '77 TS250 piston & rings.
WEBCO lowered engine cradle frame.
VM38 carb.
PVL ignition.
Recent engine build with bearings & seals.
CZ replica plastic airbox.
Custom down-pipe, repackable muffler.
Heavier fork springs.
NOS Redwing steering damper.
Rear shocks have S&W freon-cell conversion.
RM125 seat, custom Yam cover.
GSXR600 clutch rod push assembly.
TX500 kickstart lever.
Dual-clamp front axle.
Braced triple-clamps.
Wider footpegs.
Custom paddock-stand.
Smattering of ti bolts.
Recent new parts:
Quality 520 chain, DC Plastics alloy rear.
F & R brake shoes.
Wheel bearings.
Brass swingarm bushes.
Headstem bearings.
Fork seals.
$4500 Located Central Victoria.
Comes with plenty of spares.
GYT cylinder head.
DT1MX ported cylinder, .50 over.
New '77 TS250 piston & rings.
WEBCO lowered engine cradle frame.
VM38 carb.
PVL ignition.
Recent engine build with bearings & seals.
CZ replica plastic airbox.
Custom down-pipe, repackable muffler.
Heavier fork springs.
NOS Redwing steering damper.
Rear shocks have S&W freon-cell conversion.
RM125 seat, custom Yam cover.
GSXR600 clutch rod push assembly.
TX500 kickstart lever.
Dual-clamp front axle.
Braced triple-clamps.
Wider footpegs.
Custom paddock-stand.
Smattering of ti bolts.
Recent new parts:
Quality 520 chain, DC Plastics alloy rear.
F & R brake shoes.
Wheel bearings.
Brass swingarm bushes.
Headstem bearings.
Fork seals.
$4500 Located Central Victoria.
Comes with plenty of spares.
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General Discussion / Re: Moto Des Nations
« on: October 09, 2024, 10:44:42 pm »
Yes, race 3 is a bloody classic, will go down in history.
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CZ / Re: CZ 1973 front forks set up
« on: October 04, 2024, 11:48:31 am »Just making a record of my attempts to improve the soft front end on my 73 380.
Forks appear standard except for the addition of `top hats' at the end of the springs. The top hats where an upgrade from back in the day apparently.
30 weight oil. 170 ml per leg. And 10mm spacer at the top of the spring, under the cap.
Feels much better in the garage tests.
Pete
A lot of guys laugh at using such thick oil in suspension, in my '84 CR500 forks I would run 30wt (ISO 100 hydraulic oil) in Winter, and 40wt (ISO 150) in Summer.
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Tech Talk / Re: Are Yam DT1 head bolts/nuts available in alloy?
« on: October 03, 2024, 03:52:31 pm »I have them in Titanium, if that would help.
Thanks but I'm too old to get a bank loan ;-)
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Tech Talk / Are Yam DT1 head bolts/nuts available in alloy?
« on: October 02, 2024, 10:15:39 am »
The cylinder head bolts/nuts on Yam DT1/2/3 & RT1/2/3, anyone know, or have for sale, aluminium versions, or know whether another model has alloy and will fit? Someone had suggested maybe YZ250/360B has alloy and might fit? TIA
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Wanted / WANTED: damper rod extenders Yam DT1,2,3 RT1,2,3.
« on: September 18, 2024, 08:13:08 pm »
Anyone have some bottoming cones, that extend the damper-rod on alloy-slider Yam DT1~3 or RT1~3's. Or even some damper-rods that have been made that are a touch longer?
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Tech Talk / Re: Mikuni needle, part 2, taper start.
« on: September 03, 2024, 04:38:10 pm »I got a company in Brisbane to make me some overzize blanks for my 750 triple. I then linished them down , till I hit the sweet spot.
On my Honda VTR1000F, I used stock needles in the 48 CV's, but I turned-down the bottom half (from 1/2 throttle on) to match Dynojet needles, love it !
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Tech Talk / Mikuni needle, part 2, taper start.
« on: September 03, 2024, 01:35:55 pm »
Regarding Mikuni 6-series needles, I have always wondered, " how much of the needle straight section is still available after the idle position of the slide" so I measured it. Mikuni quote a distance to the start of the taper for all their needles, but, how does that relate to throttle application?
These measurements were taken on my VM38 with right side idle adjuster (my left side idle adjuster measures differently, turns out it's an OEM Kawa slide.) I guess there is a bit of variation between the various models of VM carbs, especially when it comes to Chinese carbs, my Chinese carbs measured way different.
I took the measurements with the slide at 1.00mm from totally bottomed-out, my bike had the idle running sweet at .9mm but I've had some bikes that had the slide raised about 2.0mm at idle, although I think the idle mixture too rich and necessitated the extra air from a higher slide?
These measurements were taken on my VM38 with right side idle adjuster (my left side idle adjuster measures differently, turns out it's an OEM Kawa slide.) I guess there is a bit of variation between the various models of VM carbs, especially when it comes to Chinese carbs, my Chinese carbs measured way different.
I took the measurements with the slide at 1.00mm from totally bottomed-out, my bike had the idle running sweet at .9mm but I've had some bikes that had the slide raised about 2.0mm at idle, although I think the idle mixture too rich and necessitated the extra air from a higher slide?
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Tech Talk / Mikuni 6 series needle comparison graph
« on: August 31, 2024, 11:17:03 pm »
Hey Chaps, I have, in a semi accurate process, created a couple of Mikuni 6 series needle graphs, I only used the details of the needles that I carry, only because it would have been too busy a graph to have more info. I find these graphs easier for a quick comparison between needles.
I am not familiar with creating online graphs using Excel, Microsoft or Google-sheets, so I drew the graphs in Excel then joined the dots, I am sure there would be someone among us that could create a professional looking job? Ian Williams Tuning had an even rougher looking chart on his website, I figured I could make something a little more legible. It was difficult to squeeze in needle diameters of .01mm increments (but I did it) in a graph, I also did one in .02mm increments but it wasn't any clearer.
I hope some find it helpful, regards, John.
My quoted 6FL14 specs do not match the MikuniOz, or any other Mikuni seller's website, as after measuring, their dimensions are wrong, I did find a website listing that does quote, what looks to be correct dimensions, this website even has all the specs for OEM fitment needles!
I am not familiar with creating online graphs using Excel, Microsoft or Google-sheets, so I drew the graphs in Excel then joined the dots, I am sure there would be someone among us that could create a professional looking job? Ian Williams Tuning had an even rougher looking chart on his website, I figured I could make something a little more legible. It was difficult to squeeze in needle diameters of .01mm increments (but I did it) in a graph, I also did one in .02mm increments but it wasn't any clearer.
I hope some find it helpful, regards, John.
My quoted 6FL14 specs do not match the MikuniOz, or any other Mikuni seller's website, as after measuring, their dimensions are wrong, I did find a website listing that does quote, what looks to be correct dimensions, this website even has all the specs for OEM fitment needles!
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General Discussion / Re: Welcome back. Log in issues.
« on: August 30, 2024, 08:31:11 am »i had trouble too....i thought it was just old timers setting in
I think 'welcome back Al' :-)
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Tech Talk / Re: Twostroke VM jetting, just want to think out loud.
« on: August 26, 2024, 10:32:40 pm »Well John,
I think this opens the door for you to share your knowledge. Perhaps you would be so kind as to post your thoughts on jetting the Mikuni VM carburettor i a series of articles.
The Mikuni VM series may be old technology but I enjoy the ease of obtaining new stock and parts. I find them easy to work on, compared to other model Mikunis.
Yeh it would be a 'War & Peace' story :-) I have learned a bit more recently, but it makes me realize that there is so much more to learn? I'll break-down my recent 'realizations' .....
On my wildly ported, high compression (probably too high), VM38 carb'd Yam DT1;
My throttle slide has had numerous attacks with the file to open, or close, the cutaway, my current cutaway equals a 1.5, but due to the many times I have modified it, the 'needle retaining floor of the slide' is now 2mm lower, I had to make a small relief to the under side of the slide, so for it not to bottom-out on the needle-jet shroud, and also make sure the needle does not protrude so far as to hit the main-jet (which it doesn't).
The 2mm lower needle capture means that, with the needle in groove number one (top), it is really -2, heaps leaner, but, because I dropped from 2.5 cutaway to 1.5, the richer cutaway means the needle is not as lean as it might normally be. Plus the filed bottom of the slide has reduced the size of the cavity under the slide, further reducing air pressure (or increasing air-speed and hence vacuum) above the needle-jet, giving a rise to the enrichment, further limiting how much leaner the needle had become.
Now, the many fuel circuit maps of VM carbs are correct but incorrect, they are not as clear-cut as they appear, there is so much overlap (at times) with 'slide-cutaway', 'needle-straight-section' and 'needle-jet'. The many offerings of Mikuni needles, give very little range in diameters of the straight portion of the needle (2.50mm to 2.538), so, to get the air/fuel ratio correct at 'JUST off idle, you have to select the right size needle-jet, but, if your engine needs plenty of fuel at that point, and you go big with a needle-jet, it can also give a lot of fuel all through the needle effected range (half & three quarter throttle), in many instances, it is hard to find a useable needle taper to deal with the amount of fuel the big needle-jet is giving, once off the needle-straight-section.
Reducing the slide cutaway can richen; idle and part throttle mixtures, so if you need a richer mixture at 'just off idle', less cutaway can get you the richness without going to a large needle-jet (that could spoil things once off the straight-section), but, less cutaway will richen idle, so a smaller pilot-jet will be needed.
To a lesser extent, raising & lowering float level can have a small effect on idle & part throttle, but there is only so far you can adjust before you're spilling out fuel, or draining the bowl on those long main straights.
In capping-off this 'just off idle' point; pick a needle-jet that won't send the half & three quarter throttle out of range, then use the slide cutaway to get the 'just off idle' where you want, then match the pilot-jet to the slide-cutaway.
I have read many times; "start your jetting from the main-jet downwards", never really understood that but maybe I do now?
As I fully understand (or think I do) other points, I'll share my thoughts.