2 Strokes Down Under

I also found an old piston ring inside the collar. I went with the suggestion of a coat hanger and also left the ring in there. Seemed to work ok with the initial test. Took it for a test run and found it doesn't pull smoothly through the rev range. It splutters a bit around 4K up. I'm absolutely sure the carbs and jets are clean though. Haven't got a compression tester on hand so might try that next or find a two stroke tuner in Sydney to leave it with. Any other suggestions?


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the carb cleaning thing... people drill the brass balls out and then US then again, then refit new balls. You can mess with the jets or even fit some 6mm spacers, but sometimes these bikes do splutter a bit yet nothing like the LCs... the ball drilling is said to be the way tho.

Interesting, I'll look for some info on the brass balls mod. I wasn't sure what they did and why they were there. As always - thanks. Once the brake lines show up I'll be almost ready to have it inspected for club rego. I thought the spluttering was the ypvs not turning quick enough to tune the exhaust when it was passing through that rev range. When I rebuilt the ypvs, I used a grease which seemed to slow the turning speed of the valve.


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The brake lines finally arrived after 6 weeks and a short disappearing act in transit. As always, I was just glad to be getting back to almost finishing the bike, again. So I fit the lines and master cylinder only to find the exact same problem that I couldn't bleed the system, so that was a waste of time and money. I've pulled the master cylinder apart again and am looking at that seal in the middle of the plunger that I couldn't get to fit right. I've put it next to the OEM one and took pics. You can see there's a lip on the new one that stops it from seating in the groove on the shaft. I suspect the seals are different from the 31k to the ypvs but if anyone can offer a better explanation I'm all ears. I'm using a vacuum bleeder but it seems to suck more air in than actual brake fluid which was why I thought the lines were blocked.





The brake clam shells were split and new rubber washers fitted, but I didn't check the interior canal from the bleed nipple to the brake piston. Strange, as the rear brake went back together perfectly.



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Those seals look very different, but they might work I dont know the master youre rebuilding so dont know.

Have you tried plumbers tape on the threads of the bleed nipples? and that the nipples are clear?

and failing that try reverse bleeding with a big syringe or even your vac unit in push mode.

JonW wrote:... people drill the brass balls out and then US then again, then refit new balls...

I've removed the brass balls on a few Mikuni carbs in the past (mostly TM28 and TM28SS). In most cases, this was done to convert the atomiser air supply from "external" to "internal". However, if I need to plug the holes again, I drill and tap to suit short stainless steel grub screws (M5 from memory), which are much easier to remove later if necessary. If you carry out this modification, make sure that the hole is not tapped too deep so that the air passage becomes blocked when the grub screw is inserted!

This modification is also useful if you want to change the size of the main air jet. Once the ball is drilled out, the pressed-in air jet can be removed carefully with a pin punch. The hole can then be tapped to suit the standard Mikuni BS30/97 air jet, which is available in many sizes.

Regards,
James

Some good info, thanks guys. I did find a helpful pic worth adding here. The grub screw is a good idea. I'll try that mod. Would a tapered rubber bung do the same job or too risky in case it gets sucked into the engine?








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So I did the mod. All went without a hitch, but I used some hex grub screws instead of the slotted ones, as my Allen keys can undo at a right angle easier. One side was blocked, the other had some gunk in. Now all clean and back on the bike.



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After standing for 6 weeks over Xmas, I finally went back to have another look at why I couldn't get any pressure in the front brakes. For the record, and anyone else who ends up down this rabbits hole, I had changed the hoses as I thought the old original ones might've been blocked. I purchased a set of braided black covered ones to look original but in adding an updated feel. I was at the stage pre-Xmas where I could suck pure fluid and no air, down through the vacuum hose out of the bleed nipples. So I figured if there's no air, maybe I've screwed up the master cylinder rebuild. Off that thing came as I double checked everything and rebuilt it again. Finally, in late January a friend came over and had a look. He tapped the master cylinder a few times a wiggled the brake lever back and forth about 2 - 4mm. We both witnessed a few micro bubbles come up into the MC. He repeated this for about fifteen minutes until the brakes firmed up. When I was trying to pump the brake lever, I was grabbing handfuls as if attempting stoppies. Clearly there is a knack to the art of brake lever wiggling, that gets passed down through the ages. Maybe being sat there for 6 weeks was actually allowing the bubbles to rise. Who cares, that was my last real hurdle. I'm now off to book an inspection for historical rego.


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And just for posterity, here's a before and after pic.


There's still some tweaking and polishing to do, but it should pass the inspection as is now. Once I have the rego, I won't have to run up and down the back lane annoying the neighbours. One last thank you to all on here for your endless patience and knowledge.

I'll start a new thread for the 500 - Ha Ha!


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Nice job Gavin, great looking bike and this thread has inspired me to get serious about restoring my 1WT 350F2, as that will be a real rocket ship!

Enjoy riding your lovely RZ.

Rgds
Ozhammer

Ozhammer wrote:Nice job Gavin, great looking bike and this thread has inspired me to get serious about restoring my 1WT 350F2, as that will be a real rocket ship!

Enjoy riding your lovely RZ.

Rgds
Ozhammer

Thanks Ozhammer. Originally I wanted the 350 F2 but found the 250 and 500 came up first. One day I'll pick up the 350 for the full house.


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Good effort Gavin, she's lookin' beaut..
& here's a tip which I have found works for those annoying post-bleed soft brakes.

Wrap a cable tie around the brake lever to the bar, & pull it tight... leave it overnight..
This continuous pressure will force any bubbles back up to the master cyl',
& the lever will be firm, when you've cut the tie, & released it.

+1 to the cable tie. I do it on all my bikes even if they bleed up ok now, it always works.

Looks great btw Gavin, great bike now.

I did try that trick after reading about it. I used a quick grip but it didn't work. I left it for 24hrs. Maybe the air was stuck? I don't recommend my method though. 6 weeks is simply too long to wait.


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