Stella Poor Performance

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toigo
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Stella Poor Performance

Postby toigo » Fri Jun 20, 2014 8:08 pm

I'm trying to get the turnbull raffle bike squared away which is a 2003 2T stella. The previous owner seems to have done a number on it. It starts and runs but makes terrible power and probably wouldn't do above 30mph. I cleaned the carb out, checked the spark, checked the compression, checked the reed valve, and have also tried jetting it with everything from a 100 to a 138 main and it's still really bad. Doesn't look to be leaking anywhere around the cylinder and sprayed carb cleaner to look for air leaks and couldn't find anything. The bike idles alright, but isn't making the power it should when you open up the throttle.

It barely runs at all with a 100 and it runs better with a 138, but that seems way too rich for this bike if it was setup properly.

It's got a sito plus and according to the owner a hotreed and a cylinder kit. So I pulled the cylinder off and it's a Pinasco with the bore measuring 63mm. I'm guessing it's a 177cc kit I've seen around. Some scrape marks on it, but nothing major and the cylinder look pretty good.

The ports on the kit seem a good deal off from the ports on the stock stella engine cases. I'd say they're about 1/4" of overlap on the top and the bottom. Could this be responsible for the bike running terribly? I know you're supposed to match the ports on a kit like this, but do these symptoms sound like the result of not properly matching the ports? You can also see from wear on the cylinder base gasket that they are fairly off. A photo of the case ports + piston is below. The cylinder ports (not pictured) line up with the piston ports shown so you can get an idea of how far off they are.

Image

I'm pretty sure this is what's causing the issue, but just wanted some more expert advice. And if this is the issue, then I'll gladly swap someone this kit for a stock stella 2T top end.

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Zeets
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Re: Stella Poor Performance

Postby Zeets » Sat Jun 21, 2014 9:06 pm

Piston in the correct way? It should have a an arrow marking its orientation. Also, timing.
Zayretow

70' Vespa Sprint (2009 LML power)
74' Yamaha RD350 (pinger)
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toigo
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Re: Stella Poor Performance

Postby toigo » Sun Jun 22, 2014 2:10 pm

Yup. Piston is in correct with the extra port facing up and the arrow pointing down towards the exhaust. The timing looks to be right at around 20 degrees before TDC. Kind of thinking that it might be an issue of pressure not getting created properly below the piston maybe due to the reed not sealing correctly.

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imjuanpablo
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Re: Stella Poor Performance

Postby imjuanpablo » Mon Jun 23, 2014 9:35 am

How is the compression? Got a tester? Easy/hard to kick?
John F.

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toigo
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Re: Stella Poor Performance

Postby toigo » Mon Jun 23, 2014 9:51 am

Felt alright to me when kicking it and also just holding my finger over the spark plug hole. I was going to go pick one up potentially. What should the pressure on it read?

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imjuanpablo
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Re: Stella Poor Performance

Postby imjuanpablo » Mon Jun 23, 2014 11:41 am

toigo wrote:Felt alright to me when kicking it and also just holding my finger over the spark plug hole. I was going to go pick one up potentially. What should the pressure on it read?


Should definitely be above 100psi (minimal), preferably 120psi or above...up to 145ish.......
John F.

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Zeets
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Re: Stella Poor Performance

Postby Zeets » Mon Jun 23, 2014 2:51 pm

Check ring gaps too, not sure what they are for a stella or for the oversize kit, but if the gaps are too open it'll blow by like crazy. You should be able to see excessive blow by on the sides of the piston in general though.

If the reed isn't sealing, you'll notice blow back at the carb mouth, you'll feel a huge pluse when it's running. Unless the reed is damaged, or the reed block, it's unlikely a reed problem. You can try flipping the reed over, sometimes people will bend the reed stops to allow them to open further, but what happens is the reeds bend to much and get damaged. You can flip them and that'll usually fix them, but beware, if they're allowed to bend too far the opposite direction, they'll begin to work harden, and that'll cause them to get brittle and break off, then they get sucked into the crankcase and ruin the entire motor. If the reed is installed onto the reed block, it should be closed fairly snugly. If it hangs open any more than a couple thousandanths, it's likely not sealing well. Fiber reeds are the way to go.

Is the throttle traveling the full range?

Muffler clogged with coke?

Intake restriction?

Was the base gasket covering the ports?

I have a compression gauge if you need to borrow it.
Zayretow

70' Vespa Sprint (2009 LML power)
74' Yamaha RD350 (pinger)
2008 Suzuki DRZ-400SM (thumper)

dirtyhandslopez
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Re: Stella Poor Performance

Postby dirtyhandslopez » Mon Jun 23, 2014 5:11 pm

Gas tank about to flip onto reserve? Reserve not working?
That's not going anywhere

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toigo
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Re: Stella Poor Performance

Postby toigo » Tue Jun 24, 2014 9:57 am

Thanks for the help everyone. Fuel flow to the carb looks good and the compression was 135psi. Carb is nearly opening up the whole way, but this is something else for sure. I honestly feel like it the ports being as far off as they are on the cases vs kit. If anyone has a stock stella top end out there I would be extremely grateful if I could buy it from them ASAP. Checking to see if the muffler is clogged is a good thought that I hadn't tried yet.

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Mikeh
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Re: Stella Poor Performance

Postby Mikeh » Tue Jun 24, 2014 12:53 pm

Sorry you're having issues with the scoot Toigo. I thought it would be an easy clean it up and auction it off type thing. Before going too crazy with stuff you may want to check the timing with a gun to see if it's consistent at higher RPMs. I realize that you're have to put the cylinder back on to test it.

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toigo
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Re: Stella Poor Performance

Postby toigo » Tue Jun 24, 2014 3:01 pm

Thanks Mike. No worries. I'll get it squared away. The timing looked pretty spot on at around 20 degrees BTDC. I tested a new coil, but will also test a new CDI on it as well when I get a chance. The stator also looked kind of hammered from something banging around on that side as well unfortunately.

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Mikeh
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Re: Stella Poor Performance

Postby Mikeh » Tue Jun 24, 2014 3:30 pm

I think I have a spare stella stator if you need it.

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toigo
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Re: Stella Poor Performance

Postby toigo » Tue Jun 24, 2014 3:36 pm

Thanks Mike. I'll let you know and really appreciate it.

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Zeets
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Re: Stella Poor Performance

Postby Zeets » Tue Jun 24, 2014 3:44 pm

Does it free rev? (No engine load applied?)

How old is the gas in the tank? It seems like it would be nearly impossible to start if the gas was truly bad... but I dunno, the shit gas the ply us with these days...

I had an old TnG Yamaha that had a combination of bad gas and bad 2T oil. That thing would start, but barely and then ran like complete shit when once it did. I wouldn't go over 20 no matter what I did. I put fresh fuel and 2T in it, cleaned the carb (again) and suddenly it ran fine. It's hard to discount poor fuel quality. May be worth a try to clean everything out and put fresh in it.
Zayretow

70' Vespa Sprint (2009 LML power)
74' Yamaha RD350 (pinger)
2008 Suzuki DRZ-400SM (thumper)

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toigo
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Re: Stella Poor Performance

Postby toigo » Tue Jun 24, 2014 3:56 pm

It does not free rev and shit do I know what that feels like because of the air leak on my smallframe. That thing spins up to 6000 rpm all on its own in neutral.

If you rev it in neutral it will spin up to higher RPMs just like it should, but has no power once you throw it in gear.

A little of the gas was old, maybe 1/3 the tank, but it's since been topped off with fresh gas and premixed in at 2% with motul. The previous owner removed the oil injection. I cleaned out the carb as well. I'll completely drain the tank though. Good thought.


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