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 Chinese 4-Stroke - Powertrain & Drivetrain
 2006 Baja SC50 piston rings/vacuum/idling issues
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drewkuch
St George, KS

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USA
13 Posts

Topic started on 08/06/2008 at 12:12:56 PM  Member Profile  Click to see drewkuch's MSN Messenger address  Send drewkuch a Yahoo! Message  Reply with Quote
2006 Baja SC50 Scooter - 5000 miles
New rear tire, replaced plugs, fuse, and light blubs...that's it!

Bad news...hard to find parts, hard starting in winter, poor acceleration.

My problem....Will not run good. Replaced the fuel vacuum pump to solve the problem, but ended up with the same situation. I believe the piston rings are bad and not sealing and supplying little vacuum out the intake, and then to the fuel vacuum pump. I replaced the pump, put a bigger intake vacuum hose on, and cleaned out the carb, as well as tried a new intake and carb. NO LUCK.

****It pumps gas to the carb. Take a lot of cranking to get it turned over, and it will only run for about 10 seconds. It fills up the float and runs off that until its gone. IS MY FLOAT BAD? WHY WOULD IT DO THE SAME THING WITH A DIFFERENT CARB?

*****Anyone know the stock compression specs for the SC50 motor? Any advice will be appriciated! thanks, drew

-----------------------------------------------------------

p.s.- Cheap modification I found myself. Take the plastic diaphram out of the top of the carburetor. This is the circular part that holds the needle. Place a zip tie on the top of the base, just under the rubber seal. This allows the needle to lift about 1/16 to 1/8 out of its' seat, which allows a little more air to pass.
I'm not responsible for damage, but i've put 3000 miles on my engine this way, helping it out with about 10 miles per hour and more acceleration. :)

2006 Baja SC50 Scooter

rogersj
Twillingate, Nfd

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Canada
861 Posts

Posted on 08/06/2008 at 5:05:41 PM  Member Profile  Visit rogersj's Homepage  Click to see rogersj's MSN Messenger address  Reply with Quote
is it burning oil?

07 DR650SE - K&N air filter air box mod, Dynojet kit, DRZ 250 tail light, and supertrapp racing series slip-on exhaust.

drewkuch
St George, KS

drewkuch has no Avatar

USA
13 Posts

Posted on 08/06/2008 at 11:53:36 PM  Member Profile  Click to see drewkuch's MSN Messenger address  Send drewkuch a Yahoo! Message  Reply with Quote
thanks for the reply....it's hard to tell if its burning oil when it doesn't run. I've changed the oil every 500 miles, using castrol 5w 50. always maintained the engine, becuase its cheap, good oil and replaced the plugs more than often.

***i tried it again today, ran for a bit after i cleaned the carb..not luck. thinking about taking apart the engine for dianostics...but dont want to yet, seeing the problem is hopefully in front of my face...any advice?

anyone know about these baja's? im sure i'm looking at something simple...it's getting spark to the plug, getting gas to the carb, tried 2 carbs on the engine, seems like more of a gas and vacuum problem than anything...hooked up a vacuum guage to it, it read 0-10 fluctuating while cranking. seemed to still have good compression while putting my finger over the chamber. where's the good advice>? :) thanks....drew

2006 Baja SC50 Scooter

rogersj
Twillingate, Nfd

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Canada
861 Posts

Posted on 08/07/2008 at 07:13:36 AM  Member Profile  Visit rogersj's Homepage  Click to see rogersj's MSN Messenger address  Reply with Quote
maybe theres a leak somewhere and air is getting in did any smoke come out while the engine was running? is the plug wet with gas after kicking about 3 million times?

07 DR650SE - K&N air filter air box mod, Dynojet kit, DRZ 250 tail light, and supertrapp racing series slip-on exhaust.

drewkuch
St George, KS

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USA
13 Posts

Posted on 08/08/2008 at 8:54:09 PM  Member Profile  Click to see drewkuch's MSN Messenger address  Send drewkuch a Yahoo! Message  Reply with Quote
well, i waited a day to let everything settle in the engine. Drained the oil and put heavy oil (80/90) and 10-30 mix back in, maybe to help seal the rings a bit more. No luck....

The engine wants to fire, and does a little bit, so the plug is obviously getting fuel. The plug is firing spark good as well. It's just not getting enough fuel and has little vacuum.

I placed my finger over the combustion chamber and had compression, but seemed like there could be and should be more. What's the specs for compression for these engines? anyone? any other advice before i disassemble the head and look for gasket and valve problems?

2006 Baja SC50 Scooter

Smokin101
Panama City, FL

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USA
333 Posts

Posted on 08/08/2008 at 11:14:49 PM  Member Profile  Reply with Quote
Well I generally stay away from these scooters, but if you're having compression problems, you may want to check your valve clearance. Should be 0.05mm metric. I think 0.002" standard. Compression should be around 8-1 or 9-1.

I had a neighbor who had one of these, same problem, I think, like you, that the vacuum valve for the fuel-in was the problem. Unfortunately, my neighbor never ordered any parts, so I never got to find out if that was really the problem. It would run though, just couldn't touch the throttle at all, carb would empty faster than the vacuum valve could allow fuel through.

Pit Bikes

drewkuch
St George, KS

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USA
13 Posts

Posted on 08/09/2008 at 12:34:09 PM  Member Profile  Click to see drewkuch's MSN Messenger address  Send drewkuch a Yahoo! Message  Reply with Quote
thanks for your response...

I did try and replace the vacuum fuel valve and im' having the same problems. maybe i got another one that doesn't work, becuase to me unless the problem is internal in the engine, this part would be the fix.

How do i check valve clearance, as far as do i have to take the whole head off or is there a simpler way without dissassembling too much. 8:1 or 9:1, but do you know the compression specs as far as psi?

any other advice?

2006 Baja SC50 Scooter

Smokin101
Panama City, FL

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USA
333 Posts

Posted on 08/09/2008 at 5:14:22 PM  Member Profile  Reply with Quote
Ok to check the valve clearance, first you need a feeler guage. Next you take the head cover off the head, and remove the flywheel cover, so you can turn the motor over by hand. Next is the trickiest part, putting the motor at Top Dead Center(TDC) on the compression stroke. Turn the motor by hand until you see the intake valve open and close, when the piston is on the compression stroke, the exhaust valve will not move, and neither will the intake.

Here just so you know, and this will help you figure out the strokes: 1st stroke= intake valve opens allowing fuel/air in the motor/also the piston is traveling down at this point. 2nd stroke= the intake valve closes, and the piston travels upwards, this is TDC. 3rd stroke= the spark plug would fire now, igniting the fuel, and creating the power stroke, forcing the piston downwards. 4th stroke= the exhaust valve will open, and the momentum created by the power stroke forces the piston all the way back to TDC, starting the 4 stroke cycle all over again.

There thats about as simple as I can put it. Now as far as adjusting the valve clearance, under the head cover, there is a gear w/ a chain, the timing chain. This gear is connected to the camshaft, which has rocker arms resting against it, these rockers push against the valves causing them to open and close, this is the clearance you must check. The clearance between the rockers and the tip of the valves, there is supposed to be 0.05mm at least for it to operate properly.

Now as far as the 8.1, 9.1 compression ratio, its been a while since I've done this calculation, but I beleive it should b in the neighborhood of 104psi or higher. I'm not absolute on this, but I know the .1 stands for atmosperic air pressure(which I believe is something like 13psi), and the 8 is the multiple to multiply by.

I know its a lot to read, but it's simplest way I can explain it. Hope this helps. Any questions, don't be afraid to ask.

P.S. When turning the motor by hand, make sure you turn the flywheel towards the front of the motor, so as not to turn the engine backwards.

Pit Bikes

drewkuch
St George, KS

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USA
13 Posts

Posted on 08/10/2008 at 5:36:18 PM  Member Profile  Click to see drewkuch's MSN Messenger address  Send drewkuch a Yahoo! Message  Reply with Quote
hey smokin...

Thanks for the advice. Ya, i'm a mechanic, i know all about the 4 cycles. Good stuff to know! are you a mechanic as well?

Well, i checked the valve clearance...had to adjust the top valve. It wasn't open enough. Still, everything in the rotating assembly looked okay. I had no luck getting it to run.

Fuel isn't getting into the cylinder now, just pumps to the float bowl and stays there. doesn't pump when i pull the throttle. To me that tells me the vacuum pump is bad and or the carburetor. I replaced both of them though. no luck. I might try buying a new carburetor.

My compression guage was too big for the moped threads (my adaptor) so i didn't get a reading. It seems low though. Are there bigger kits for ths engine that run well? dependable kits like an 80cc?

I have a gy6 150cc engine. The motor mounts are different and i dont know how to weld, but it's sitting in my garage waiting for this frame. Would it fit and work with my electronics from my 50cc?

Thanks! drew

2006 Baja SC50 Scooter

Smokin101
Panama City, FL

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USA
333 Posts

Posted on 08/11/2008 at 9:31:10 PM  Member Profile  Reply with Quote
Um, well technically I can't call myself a mechanic. I took some mechanics courses in high school, and been hooked on engines ever since. Really comes in handy, having a motorcycle hobby and all.

Well since we're troubleshooting the fuel inlet, and carb. Check out the crankcase breather tube. If it's pinched and the compression is low, getting blow-by, it could cause the vacuum valve to not function properly. Maybe. But since you're getting fuel into the bowl of the carb, I doubt that is the problem. You should be able to crank it with the little gas in the bowl.

Does it have a auto-choke, or manual choke? Check the fuel filter screens in the gas tank maybe. I'm sure you have already though.

As far as the gy6 150, I know some of the electrical you should be able to use, if not all of it. Some plugs may differ. If you can mount it, and get it lined up with the rear sprocket, you should be good. Long as you have some room around the frame for everything to fit in there.

If you can pull the head and cylinder off, not that hard, you can check the piston rings. They don't cost too much. They should overlap the piston when compressed against it. If not, then they're bad.

Other than that stuff, I can't think of any other reason for it not to run. Besides a clogged carb jet.

Pit Bikes

drewkuch
St George, KS

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USA
13 Posts

Posted on 10/15/2008 at 5:35:59 PM  Member Profile  Click to see drewkuch's MSN Messenger address  Send drewkuch a Yahoo! Message  Reply with Quote
can someone tell me how to set the timing on a 2006 baja sc50.

**I also have a 1985 2stroke honda spree im having these problems with. Not enough fuel to the carb and low vacuum somewhere. Reeds? crankseals? bad float? any advice?

2006 Baja SC50 Scooter
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