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PostPosted: Thu Aug 24, 2017 5:50 pm 
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n00b
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To prevent spam, enter the year 'modern' scooters were first sold in North America (hint: 1982): 1982
Hi everyone, just looking for a little advice or direction with an issue. Just picked up a 1987 CH150 that was in good condition and only about 2000 miles on it. I am down to about 1 remaining issue that I am trying to sort out.

Scooter starts great, has good acceleration, no stumbling or misfires. It can cruise at 45 mph no problem, and can accelerate up to 50-55 mph without any issues. But, if I try to cruise at 50-55 mph for more than about 30 seconds the engine starts to surge like it is running out of gas. It won't die though if I let it slow down to about 30 mph or so; and then I can re-accelerate back up to 45 mph no problem.

Spark plug, air filter, and gas cap have been replaced. I have tested the fuel petcock, and the vacuum function is working normally. Although I am wondering if the engine isn't providing enough vacuum at high RPM to keep the petcock open; thus the reason why it doesn't start to surge for several seconds at that speed. Also I have verified that the fuel screen appears clear, and has no debris restricting flow.

I appreciate anyone's thoughts on what might be causing this. To me it feels like a fuel issue, and the petcock/vacuum seems like a possibility. Other than this issue, the scooter runs great.


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PostPosted: Sat Aug 26, 2017 3:55 am 
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Rim Kicker
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Joined: Sun Aug 21, 2016 1:02 pm
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To prevent spam, enter the year 'modern' scooters were first sold in North America (hint: 1982): 1982
Location: Indianapolis, IN
Sounds like the carburetor main and slow jet need to be cleaned. If you have already cleaned them and it is still running rough you need to adjust the air/fuel screw. Take a look at your spark plug and if it is black you need to lean it out. If gray or tan the mixture is good.


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PostPosted: Sat Aug 26, 2017 9:34 pm 
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Throttle Master
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To prevent spam, enter the year 'modern' scooters were first sold in North America (hint: 1982): 1982
Location: Sparta Michigan
A very simple way to verify if the petcock is closing due to low vacuum, is to disconnect and plug the petcock vacuum hose, then attach a handheld mityvac and pump it until the mityvac opens the petcock, then go for a long drive over 55. if the problem is gone, then your lack of vacuum theory is correct.
My 85 CH150 had no problems doing over 60 even with a windscreen.

_________________
The Thrill of Speed overcomes the fear of death.
I have a Ninja powered Grom and a GSXR 1000.


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PostPosted: Sat Sep 02, 2017 9:39 am 
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n00b
n00b

Joined: Thu Aug 24, 2017 5:40 pm
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To prevent spam, enter the year 'modern' scooters were first sold in North America (hint: 1982): 1982
Just a quick update, got the air cutoff valve assembly removed. The assembly looked warped on the top assembly, and was leaking vacuum. Replaced it with a new assembly. After a quick test run, the scooter appears to be running normally at 50+ mph. No issues, hopefully it stays that way. Thanks for the ideas for repair.


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