Messages

1

Tech Talk / Re: NGK B10E & B10ES

« on: April 01, 2024, 11:49:39 AM »

Now we need to see the results from testing of the 2 types to see if in fact the "S" type is Super as NGK suggests. I recall years ago in a former life dyno tuning a turbo 750 Yamaha engine in a speedway car and being asked to try different types and brands of sparkplugs only to find the basic old NGK cheapies seemed to work best and the expensive Splitfire made less power despite the owner complaining that there must be something wrong with the dyno because the guy at shop told him they made more power.

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Tech Talk / Re: NGK B10E & B10ES

« on: March 29, 2024, 06:23:32 PM »

The "S" means 'Copper core centre electrode (Super)' according to an old NGK book I have so the B10E would not have a Copper core and in theory would be an inferior design. Probably wouldn't be able to notice any difference in the way they work.

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Other Makes (CanAms, Coopers, etc) / Re: Canam 400 piston

« on: February 11, 2024, 04:31:15 PM »

I think I have worked out they have a 36mm compression height but haven't been able to find a skirt length. If you stumble across it an accurate measurement would confirm things for me but thanks for looking. If your shed is anything like mine you will find it when your not looking for it.

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Other Makes (CanAms, Coopers, etc) / Re: Canam 400 piston

« on: February 08, 2024, 10:26:23 AM »

Thanks that will be very helpful. At this point we are going to try an RM465 piston but will need a barrel lift around 6mm but that will depend on finding out what the stock dimension are. The RM piston works out to be 2mm oversize which will make the sleeve pretty thin but the current is a worn 85mm and there is nothing in Rotax pistons that could be used.
An overall skirt length would help as well thanks.

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Other Makes (CanAms, Coopers, etc) / Canam 400 piston

« on: February 07, 2024, 04:03:17 PM »

Anyone out there got a 400 Canam Rotax piston they could measure for us? Need to know the compression height and also a center to center conrod length would be handy as well. The piston in the one I'm looking at is out of a Polaris ATV and I suspect it isn't correct as it sticks out the top of the barrel by almost 2mm.

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Suzuki / Re: RL250 forks - are they 35mm or 1.3/8inch ?

« on: January 22, 2024, 05:02:21 PM »

Honing is ok, example is Mower cylinders with Alloy bores. You just have to clean them properly. Boiling soapy water and a scrubbing brush just like cleaning a cylinder after re-boring. Also need a good hone with parallel stones not the crappy spring loaded things. I've done Maico forks PE Suzuki stanchions as they are meant to be 36mm but the Maico is just under and the Suzy was on size.

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Tech Talk / Re: CR250M inlet port height different, why?

« on: September 13, 2023, 05:29:25 PM »

I go with the piston ring support with piston at the bottom. Question is how much difference would there be if the high cut side was lowered to match the other side. My answer would be SFA as that part of the port is only uncovered by the piston for a very short time and would have zero effect on flow angle or anything like that. The bottom of the transfer port would be in the same category as the piston edge is masking the port for most of it duration. 

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System problems? / Re: Is security certificate going to be updated?

« on: August 08, 2023, 06:38:57 PM »

The warning isn't coming up anymore. Just did an update of Firefox so maybe that was the problem.

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Tech Talk / Re: RM125S Piston rings without notch for pin, eh?!

« on: July 16, 2023, 05:06:16 PM »

Not sure I've seen that on RM125S before but it is common on most Ossa's. The ring peg in the piston is flush with the outer diameter of the piston and the ring gap is around 2mm. First time I sore it I was convinced the rings were stuffed with such a big gap but with the new rings in the bore it looked the same so I looked a bit closer.
Just dug out a new RM piston that has been sitting here for many years and yes it has very narrow ring grooves and a pin the comes very close to the top so that's normal as it seems. Not enough room to file the rings to fit over it unless you take the peg down a bit first but all a bit tricky to do. Just run with it as is, it seemed to work back then.

10

Tech Talk / Re: Needle jet still works with a closed throttle !

« on: May 30, 2023, 10:24:23 AM »

All good info and it shows getting a good running bike isn't always that simple. I often get scared when I hear of someone say I got a new Mikuni for my restored bike as the original carb was worn out only to find that even with the same Jet spec as factory installed they run like crap and often seize that nice new piston they had fitted. The differences between carb bodies old and new can be quite marked with Air jets fitted or not and different idle passage sizes ect.

11

Tech Talk / Re: Mikuni hex main jet thread !!!

« on: May 25, 2023, 09:46:32 AM »

I think the thread is a carry over from Mikuni being licensed copy of Amal. I have a set of #12 UNF 28TPI taps and die and it is very close, the diameter is 5.4mm and 28 TPI works out as .907mm pitch.
Funny a while back there was a Chinese site selling Mikuni jets in what looked to be common sizes but unfortunatley they had a 6mm thread and the jets sizes were mm and not flow rates. Maybe they fitted the Chinese Mikuni or was that Nikuni or whatever knock off they were peddling. I got some and used the #12unf die on them and they screw in ok and the sizes didn't matter for methanol as every time I drill a jet for meth I engrave the MM size on them. Without looking it up what they supplied as a 200 was 2.00mm and probably around a 450 mikuni.

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Tech Talk / Re: Needle jet still works with a closed throttle !

« on: May 09, 2023, 05:32:25 PM »

Fixed - With WFO slide optimiser I have dropped the pilot jet from 57.5 to 15, yes that's right, and I've ordered a 12.5 & 10, dropped the needle-jet from an R-6 to an R-2, seems pretty good now. Ticks along at a nice low idle, playing with the air-screw, now I am 2 turns out (that's why I ordered some smaller). Without the WFO slide thingo, the pilot-jet was right on the money, me being greedy, I wanted more off the bottom-end (I shouldn't keep comparing the ported 125 to my modern 450 4-stroke ;-)

I guess when I had a larger pilot-jet, I had to have the slide higher to keep it idling, that extra slide height allowed enough air to go through to get the needle-jet involved. With a leaner pilot keeping the rpm higher, it allows me to drop the slide down further, separating the introduction of the needle-jet circuit, me earlier thinking it was rpm introducing the needle circuit, but no, slide height ....... 1 turn of the idle adjuster!

The only issue I have now is, from a cold start, even with the choke on, I can't get fuel to flow into the venturi (Start ya Bastard or hand choke required), I think that is more my 'expert' porting ;-) I think that combining my 'non reed-valve porting' with the crankcase reed has softened the intake vacuum pulse from the piston up-stroke (because vacuum starts as soon as the reed opens, and the inlet port is still open while the piston is well back down the bore), next mod is to JB Weld the reed passage, take out the TM piston, put the RM-S back in, and make good use of the regained intake port inertia (it kinda works in my mind). :-D

With the cold start issue try and drill out the cold start jet in the float bowl. Memory tells me they are around .75mm and from there go up to something like .9mm.

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Tech Talk / Re: Where can buy jet reamers 2.0mm to 3.0mm?

« on: May 02, 2023, 04:42:01 PM »

I use drills. I have 0.3mm to 2.5mm in .05mm steps and bigger sizes in "Number" drills. Number drill sizes https://littlemachineshop.com/reference/numberdrillsize.php
I like the drills as they are a fixed size where the tapered reamers will open things out but difficult to control the size.
The mm sizes match Mikuni pilot jets as they are in mm's, meaning a #35 pilot is .35mm etc. Main jet are more difficult as they are in flow rate but most of the jet drilling I do is for Methanol so the .05mm steps are more than close enough.

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Tech Talk / Re: Needle jet still works with a closed throttle !

« on: April 29, 2023, 03:59:57 PM »

Had a 74 CR125 here for an engine rebuild last year and he had a new TM32 on it and the thing was a pig to ride down low. Blubbery at idle even with the air screw out and lean up to about 1/4 throttle. You had to keep it screaming to get away in 1st gear but once moving it would pull down to about 1/4. I put in a smaller pilot and backed the air screw in a heap and then a richer slide( could have been a 2) and the thing was a different bike, he recons it has never gone so well and been so easy to ride.

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Tech Talk / Re: Needle jet still works with a closed throttle !

« on: April 28, 2023, 07:19:45 PM »

Remember the slide cutaway has a big effect on the starting point of the main system and if the pilot is to big you have to have the throttle open further to overcome the rich mixture. Have fun. Did the opening out of the main air jet help?