Rebuilt BS200RS one cylinder overheating

[skiri251]

My rebuilt BS200RS engine started okay but left cylinder was overheating with blued exhaust pipe.
Idling for couple of seconds after the start, I can feel the temperature difference in left/right headers.

I double-checked ignition timing.
Then swapped left/right carbs and overheating moved to the right cylinder.
So it appears to be carb issue.

The carbs are just cleaned original items. All the parts are original.
They are not yet sync'ed (waiting for the sync tool off eBay.)

Turning in the idle mixture screw (one turn so now it's only half turn open from seated) appears to help.

I will take the carb apart again but any advices?

I see Mikuni sell VM18-144 carbs which are clamp on but regular idle adjust mechanism.
Does any one know internal parts will fit VM17-18?
Or for that matter, can I replace VM17-18 with VM18-144?

[slawsonb]

I would disassemble the carb and make sure none of the internal passages or jets are plugged. It may need an ultrasonic cleaning to really get deep down in there, but if you use a fine copper wire (copper so as not to damage the carb body) you may be able to get it opened up. Compressed air is your friend too. Steve Reed who is a long time member on here has a carb cleaning business and usually gives members good deals (not to speak for you, Steve). You can get his contact info on CarbWorx.com if the noodling with the wire, air, and, of course, carb cleaner don't do the trick.
...bert

[skiri251]

Thanks for the info.
I did clean it as I do with other carbs including a use of fine wire (I use steel though).
So maybe ultrasonic cleaning is needed.

BTW, now the engine won't start. Turned out to be a broken idler timing gear.. (sigh)
I hope Richard has it..

[slawsonb]

Good luck as the project continues!
...bert

[disc_valve]

Well, if the idler gear is going to fail, I guess the workshop is the best place for it to happen. The gear on my Dual Twin failed a few years ago and it meant phone calls and rescue by van and trailer! Ruined the evening's ride-out.

The good news is that the idler gear is quite easy to swap, but you'll need tom line up the dots in the generator drive tgear train to make sure the ignition timing is still OK, and there will be a fair bit of fibre debris lurking around inside the case from the failed gear. Make sure you clean it all out from the primary drive chamber.

The idler gear is a wear point on this engine, but I'm sure a spare should be obtainable from a fellow site member, even if Richard is out of stock.

Graham

[skiri251]

Well, if the idler gear is going to fail, I guess the workshop is the best place for it to happen. The gear on my Dual Twin failed a few years ago and it meant phone calls and rescue by van and trailer! Ruined the evening's ride-out.

Yes I realized that. I was lucky I should say.

The good news is that the idler gear is quite easy to swap, but you'll need tom line up the dots in the generator drive tgear train to make sure the ignition timing is still OK, and there will be a fair bit of fibre debris lurking around inside the case from the failed gear. Make sure you clean it all out from the primary drive chamber.

The idler gear is a wear point on this engine, but I'm sure a spare should be obtainable from a fellow site member, even if Richard is out of stock.

Graham

Richard does not have it at the moment..
Mine was okay-looking one I bought off eBay. The original was worse with chipped teeth.

I don't understand why BS used non-metal gear while stuff like airbox and toolbox were made of sheet metal. (sigh)

It must be too expensive to have a one-off metal one made..
May attempt to make one by myself with JBWeld steelstik thing..

[bsracer]

What gear do you need? Maybe post a pic. If it's the idle gear with two bearings the sits on the post with a spring washer and circlip, I'm sure I have plenty of them. Must be a reason it broke? I don't think I've ever taken a motor apart that had a broken one. I've taken apart plenty of motors with the teeth stripped off some of the main gears and the cases broken where the shift fork post is.


paul

p.s. I run the idle gear on my racer and haven't had any problems even rev'n in the 12k-13.5k range

[skiri251]

Yes, it's idle gear.
Richard found me one so I am okay (hopefully)

Could it be that I reversed left/right ignition coil wiring and the engine back fired a little?
I just followed the wire color (black and white) but for some reason the NOS coil I bought had reversed connection..(?)

Is there a reason why BS used non-metal gear there?

[slawsonb]

Noise reduction fix?
...bert

[disc_valve]

Yes, I would agree with Bert that id was probably done that way to avoid a whine when the engine was running. Your pic looks familiar, though with stripped teeth.

The problem is that the fibre teeth wear over extended use. If you spin the generator by hand, you'll feel the poles alternatively attracting and repelling each other so the shaft feels notchy at low speed. At idle that makes the gears chatter quite noticeably and it produces a distinctive "coffee grinder" noise. Raise the engine speed to a fast idle and the noise disappears unless the gear has worn excessively. Ultimately, you'll notice the chatter at low revs when riding the bike and that's the point when you should think about fitting another gear before it fails.

Presumably a chattering steel gear would have made a lot more noise. The 350 used a steel gears throughout the gen drive train, but without an intermediate idler gear, so presumably there wasn't such a pronounced noise problem.

Graham

[skiri251]

Thanks for the info.

Right before the engine stopped running, I heard loud noise at low rpm which went away once I rev'ed it a little more.
So that was it.

Has any one had metal idle gears made for replacement?
I googled and contacted one transmission repair company and I got a quote of $800. Obviously too expensive.

Are there enough NOS parts available so I don't have to worry about?
Richard didn't have it in stock and he asked one of his friends to get it for me.

[bsracer]

Let me know if Richards friend doesn't come up with one. I'm sure I have a few.

paul