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Jeff
PostPosted: Sun Jun 19, 2005 5:44 pm  Reply with quote
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Wow, that's an experience I'll never forget.

I was about 50 miles into a all highway ride on my Stella and aside from occasional tests of the upper end I had been sticking to 1/2 throttle. I just about laid the damn thing down before I realized what was happening and grabbed the clutch. I slowed her down and I bump started it to free the piston. I let the bike cool a bit and continued on to my destination. I was 60 miles from home though and no tools or parts so I ended up trucking it back. I'm going to pull the top end tomorrow.

Anyone know a good machine shop?


Last edited by Jeff on Sun Jun 19, 2005 7:50 pm; edited 1 time in total
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Derrick
PostPosted: Sun Jun 19, 2005 7:21 pm  Reply with quote
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There is one on University under GT paints. Bob and Jeremy L. use the guy.
I know of a good shop way out west by me if you want to drive.

Sorry to hear about your seize. Sometimes you get one freebie without major damage. If your lucky!

I really recommend starting WAY rich on the main jet. Get it to four stroke at wide open throttle. Then come down in steps until it just stops four stroking. Then you should be O.K.

Two stroke engines will make the most power when they are lean. However, as you know they will self destruct. So, jetting is really a compromise. I jet rich even though I know if I stepped down a couple jet sizes I would be faster.

Sorry, I don't mean to lecture.
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Jeff
PostPosted: Sun Jun 19, 2005 7:45 pm  Reply with quote
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Dude you should see my plug, it's practically black, I thought I was too rich to begin with.
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LOREMipsum
PostPosted: Sun Jun 19, 2005 11:18 pm  Reply with quote
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This is the machine shop under GT paints Derrick referred to:

Aaron's Precision Machine
651.776.2956

He charged me either $35 or $45 for a rebore.
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Tom Lindsay
PostPosted: Mon Jun 20, 2005 7:28 am  Reply with quote
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Jeff,
A hard seize is something I've been concerned about with the Stella - it sounds like they're surprisingly not uncommon. Obviously, if you'd only gone 50 miles, you must not have been going 60 for an hour yet. Is your Stella completely stock? What oil do you use in it, and how long have you had it? I'm new to all this but thinking of doing some long-distance riding in the future. I had been under the impression that seizes were very uncommon on stock stellas if you used good full-synth oil and let it cool for a few minutes every hour. Maybe we all should just always keep a finger on the clutch?

By the way, what happens when a twist-n-go seizes? THere's no clutch to pull in...

Thanks!

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Matty
PostPosted: Mon Jun 20, 2005 7:43 am  Reply with quote
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What were you jetted at Jeff?


Tom, Jeff recently added a DR kit. If you leave it bone stock I doubt you'd ever seize. It's usually when adding some performance parts or messing around with the carb and oil injector, that it happens.

-Matt
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Jeff
PostPosted: Mon Jun 20, 2005 8:26 am  Reply with quote
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A stock stella wouldn't even go 60, but it wouldn't have seized either. That's all Bajaj propaganda.



It's a 2002 Stella, synth oil (ipone), DR177 Kit, 24/24G Carb, stock px125 pipe. The carb is jetted with a 100 main and the idle jet is 30:140 (stock stella)

My plug (B7) is basically black, just a hint of brown on plug chops at 1/2 throttle and above and the plug will foul after a few minutes at idle.

I was thinking for a long ride on a hot day I could have put in a B8 to reduce temp. Also I have about 800 miles on the kit but I have been running full synth since day one. It could be that it was not fully broken in yet too.
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jsyx
PostPosted: Mon Jun 20, 2005 9:08 am  Reply with quote
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really sorry to hear about yer seize, J.
with that big carb and the 177 kit, 100 main sounds awful lean to me despite the plug chops. I know it's different for every bike but i'm curious, did you try something richer first? i.e.-did you work your way down to 100 cos' it wasn't winding out?

p.s.-I KNOW ITS DIFFERENT FOR EVERYONE, but im running a 107 main on just a pinasco exhaust and after drilling a little hole in my air filter to let the main stack breathe, i think i'm still pretty lean... scary.

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Jeff
PostPosted: Mon Jun 20, 2005 9:27 am  Reply with quote
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There is a huge difference in our pipes. I started at 116 and have been working my way down, when I switched to the stock pipe I dropped from 102 to 100 and the chop still looked very rich. It could be that I am way too rich down low and that is obsureing some leanness at higher RPMs.
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Derrick
PostPosted: Mon Jun 20, 2005 9:36 am  Reply with quote
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Sounds like you are very rich low in the rpms. (if you plug loads up at idle) This might be giving you false plug chops. You probably need a new carb if the idle mixture screw threads are crossed, as idle mixture would be too rich and uncontrolable.

When you pull the top end make sure to check the big and small end bearings for scoring and play. It sounds like you had a "heat" seizure, which happens when the piston gets to hot and expands too much for the cylinder. But make sure you didn't damage the crank bearings if there were other issues - like loss of lubication.

Other then replacing the carb you might try a smaller air correction jet or a leaner mixing tube. The smaller air correction jet would richen the top rpms and the leaner mixing tube would lean out the middle. If you had a "heat" seizure at high speed it seems like you are too lean at the top. Also, make sure the idle jet is not too big as this would cause the plug to foul at idle as well.

SI carbs a very hard to tune. I don't like them and convert to side drafts whenever possible.

This is my understand of how the SI carbs work.

Idle jet controls gross idle mixture. The right idle jet will make the mixture screw about 1 1/2 - 2 turns out. If more turns are needed go to a large idle jet and vice-versa. The idle jet effects drop off very fast when throttle is opened.

The main jet controls over all fuel amount at top but also effects middle rpms. A larger main jet will richen from the middle rpms up to the top.

The mixing tube controls the middle mostly. It works like an air brake. Air is sucked in through the air correction jet on the top and then bubbles through the gas from the main jet on the bottom. It slows down the flow of gas into the ventura.

The air correction jet controls the over all amount of air that gets mixed in the mixer tube. A big air jet slows gas flow into the carb at high rpms. A small air jet allows more gas at high rpms.

Tuning SI carb or any carb that uses mixing tubes and air correction jets is a black art.

One last thing you could do to help. Run an added 1% mix in the tank. It won't "lean" you too much and lubrication would be greatly enhanced. Modern oils are great and leave very little carbon crud in your engine. I've done this on all my "kitted" bikes and it works.
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Jeff
PostPosted: Mon Jun 20, 2005 9:46 am  Reply with quote
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Great info Derrick!

Thanks!
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jsyx
PostPosted: Mon Jun 20, 2005 9:49 am  Reply with quote
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Quote:
idle jet controls gross idle mixture. The right idle jet will make the mixture screw about 1 1/2 - 2 turns out. If more turns are needed go to a large idle jet and vice-versa.


Derrick-
Stephen told me that the stock setting for the mixture screw is 3 turns out.
in your opinion, do you think the stock idle jet (30:140), is too small for the carb on the Stella?

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Derrick
PostPosted: Mon Jun 20, 2005 10:13 am  Reply with quote
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One more turn out is not that big of a deal.

Most brand new engines require a slightly richer mixture until run in.

Don't mess with the mixture screw too much. It only controls IDLE and just off idle mixture. If your scooter idles well - leave it alone.

Adjusting idle mixture screw will not make much difference in over all performance. I don't want people obsessing over it.
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nate
PostPosted: Mon Jun 20, 2005 10:20 am  Reply with quote
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Quote:
By the way, what happens when a twist-n-go seizes? THere's no clutch to pull in...


I'm not even going to pretend to know the answers to this- but I'm curious as well.

First, the drive pulley will stop rotating, so it should migrate as close as possible to a closed position- no more centrifugal force, the drive will get as small as possible. At this point the tranny should be no different than when the scooter is powered off- which doesn't produce any issues, as you can roll a stopped TnG without having to do anything special. I'm not sure how the belt 'disengages' from the pulleys at rest- if it's just that the drive is small enough that the pulley doesn't grab, or if there's some other 'rest position' for the belt.

Even if the belt was to stay engaged, I'd think that the torque you're suddenly trying to apply into the tranny in the wrong direction would produce enough slippage to keep the bike rolling.

Yea? Nay? I've never popped open a CVT.
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jsyx
PostPosted: Mon Jun 20, 2005 10:26 am  Reply with quote
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Quote:
Sounds like you are very rich low in the rpms. (if you plug loads up at idle) This might be giving you false plug chops. You probably need a new carb if the idle mixture screw threads are crossed, as idle mixture would be too rich and uncontrolable.


thanks for the info Derrick, but in light of this quote, it seems that it's not a bad thing to keep an eye on after all. Good things to know.

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