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Post by scooter on Jan 12, 2015 6:23:03 GMT -5
Thanks, Jersey! I need to test my new scooter like this. I am "jerking" at top end wide open throttle and I suspect either a vacuum leak or a bad fuel pump. I think I'll try propane testing around the vacuum lines and, if I find nothing, I'll pull the pump and clean it. I think the electric is okay. It only jerks on the road, not on the stand and I think it's a fuel issue. I need to learn about doing compression tests. I like what you were saying about leakdown testing. That sounds like a very useful tool. Only jerking under load could be fuel or spark related..a weak coil or CDI issue could cause this as well as fuel. Ive seen motors run fine under no or light load when only small amounts of fuel need to be burned to spin the motor,,then when a load is present with obviously more fuel added,,the spark is not strong enough to burn the added fuel properly. I guess I'll have to learn how to check the ignition system now. |
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Post by jerseyboy on Jan 12, 2015 7:51:31 GMT -5
Only jerking under load could be fuel or spark related..a weak coil or CDI issue could cause this as well as fuel. Ive seen motors run fine under no or light load when only small amounts of fuel need to be burned to spin the motor,,then when a load is present with obviously more fuel added,,the spark is not strong enough to burn the added fuel properly. I guess I'll have to learn how to check the ignition system now. There is some great info in the back of this manual,,plus the video here is all you will need to know about it...Pg 50-56 in this manual. You can tell the manual was translated but its still has some very good info...I went to staples and had it printed out then spiral bound for the shop. www.familygokarts.com/manuals/ace/arrow150_engine_service_manual.pdfAnd this video is good..taught me a ton about the GY6 ignition system. |
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Post by dmartin95 on Jan 12, 2015 10:56:53 GMT -5
dmartin: I was just going back over the old comment where you had a photo of your gauges. 1 question; where the heck is the boost gauge? It's a Boost/Vacuum gauge (Dual purpose)... You just tap into a vacuum line and it will tell you the vacuum, but obviously it would never go into the boost... It was part of a three pack for like 18 Bucks or something... I could've purchased one more suited for these scooters, but for my purposes it should just work fine. |
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Post by scooter on Jan 12, 2015 18:41:08 GMT -5
I guess I'll have to learn how to check the ignition system now. There is some great info in the back of this manual,,plus the video here is all you will need to know about it...Pg 50-56 in this manual. You can tell the manual was translated but its still has some very good info...I went to staples and had it printed out then spiral bound for the shop. www.familygokarts.com/manuals/ace/arrow150_engine_service_manual.pdfAnd this video is good..taught me a ton about the GY6 ignition system. Thanks, Jersey! I will check it out! |
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Post by scooter on Jan 14, 2015 0:45:07 GMT -5
Okay, I took some new readings, this time from a 2008 Qlink Commuter 250 Helix clone, and the results are interesting because this bike runs like crap at WOT. I will post videos and/or pictures when I can, but for now here is a list of vacuum and fuel pressure readings. These readings are on the stand. Fuel Pressure: 1.2 PSIG @ 2000 RPM 1.6 PSIG @ 3000 RPM 1.7 PSIG @ 4000 RPM 1.7 PSIG @ 5000 RPM 1.6 PSIG @ 6000 RPM 1.4 PSIG @ 7000 RPM 1.5 PSIG @ 8000 RPM When I open the throttle any more, the readings drop drastically until I let of the gas some and let it back down in RPMS, then it recovers and goes back up. Vacuum: 1 -5 INCHES Hg @ 1800 RPM Idling. Steady oscillation. 3 INCHES Hg @ 3000 RPM 3 INCHES Hg @ 4000 RPM 3 INCHES Hg @ 5000 RPM 3 INCHES Hg @ 6000 RPM 2.9 INCHES Hg @ 7000 RPM 2.9 INCHES Hg @ 8000 RPM 1-5 oscillating to 10 INCHES Hg and back, Goosing from idle to full throttle After hitting 8000 RPM on the stand, when I open the throttle any more the readings go to about 1 INCH Hg and the "jerking" begins with RPMS jumping up and down, as though the gas is coming on and off rapidly. I will note that I have not yet done a valve adjustment on this bike. I will also note that I seem to be getting poor gas mileage, about 45-50 mpg. I do not know what is standard for this fat and heavy 250 scooter. A cursory propane vacuum leak test revealed no leaks, however I was not thorough in testing. Now compare these readings with the readings below from my very good running gy6 150 scooter. fuel pressure 1.5 PSIG @ 1500 RPM 2.6 PSIG @ 5000 RPM 4.0 PSIG @ 7000 RPM 3.5 PSIG @ 8000 RPM vacuum(IN) rpm 11-15 INCHES Hg @ 1750 RPM steady oscillating between 11 and 15 inches 11 INCHES Hg @ 4500 RPM 6 INCHES Hg @ 5500 RPM 4.5 INCHES Hg @ 6500 RPM 3 INCHES Hg @ 7000 RPM 1.5 INCHES Hg @ 7500 RPM 1 INCHES Hg @ 8000 RPM 0-20 goosing. goosing the throttle at idle makes vac go from 0 to 20 then back to 11-15 oscillation Here is the video. |
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Post by scooter on Jan 14, 2015 17:11:23 GMT -5
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Post by rcq92130 on Jan 14, 2015 17:26:59 GMT -5
The WOT sag you describe is typical of an incorrect A/F setting. AllleyOop has a great tutorial on how to diagnose. Think you may just need a different et.
Not positive, but I seem to recall from last summer the vacuum I was reading was more in the range of 8-10psi.
BTW: the quite low vacuum the GY6 produces compared to a normal (auto or larger motorcycle) engine is one of the reasons I decided to NOT rely on a vacuum driven fuel pump, but go modern (electric).
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Post by scooter on Jan 14, 2015 17:54:12 GMT -5
The WOT sag you describe is typical of an incorrect A/F setting. AllleyOop has a great tutorial on how to diagnose. Think you may just need a different et. Not positive, but I seem to recall from last summer the vacuum I was reading was more in the range of 8-10psi. BTW: the quite low vacuum the GY6 produces compared to a normal (auto or larger motorcycle) engine is one of the reasons I decided to NOT rely on a vacuum driven fuel pump, but go modern (electric). Thanks RCQ. I think your electric pump is a good idea, and while I may put one on in the future, right now my goal is to learn to use instruments to tell me what is wrong with scooters, especially ones I may not be able to take out and drive under a load. I would like to see the pumps you and Shannon bought. I think I'll get one for diagnostics. I can use it to bypass the vacuum pump system to see how scoots operate with a known "good" pressure. If the engine works fine with the electric pump, I'll know for sure it's a vacuum or pump problem. It's not what I'd call a sag though. I get the feeling that the fuel level is going below the jet and then back up again, over and over. I am preparing to upload a video to YouTube right now. |
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Post by jerseyboy on Jan 14, 2015 20:40:20 GMT -5
Wow awesome video!
I think it was starving for more fuel when it was cutting out..just my guess..I would try a better pump or electric pump,,the stock pets are junk if your running one,,also just gravity feeding can get iffy especially at those R's.
I want to get an electric pump and also a better tach than the stock one..
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Post by JoeyBee on Jan 14, 2015 21:04:23 GMT -5
scooter Thank you for the video. Very interesting results and great example of what is happening in the vacuum system. jerseyboy I was thinking the same thing. The reason I haven't switched to a gravity feed system yet is the task of remembering to turn on the fuel before every ride. But with an electric pump I could also install a toggle switch. But once you start down the road of gauges and switch, how far is too far? 
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Post by scooter on Jan 14, 2015 21:15:02 GMT -5
scooter Thank you for the video. Very interesting results and great example of what is happening in the vacuum system. jerseyboy I was thinking the same thing. The reason I haven't switched to a gravity feed system yet is the task of remembering to turn on the fuel before every ride. But with an electric pump I could also install a toggle switch. But once you start down the road of gauges and switch, how far is too far? I'm just using my gauge at the shop but that's cool! I think a vacuum activated relay might be nice for an electric scooter fuel pump but the ones I have found are not cheap, except for the ones made for furnaces, and they may work. That would mean a simple circuit from the battery or ignition, to the vacuum switch, to the pump, to ground. RCQ's pump comes on via relay when his key is turned on. |
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Post by scooter on Jan 14, 2015 21:18:17 GMT -5
Wow awesome video! I think it was starving for more fuel when it was cutting out..just my guess..I would try a better pump or electric pump,,the stock pets are junk if your running one,,also just gravity feeding can get iffy especially at those R's. I want to get an electric pump and also a better tach than the stock one.. Thank you. I think it's fuel starvation too. I went ahead and ordered an electric pump. RCQ twisted my arm. It was cheaper than a vacuum pump of this size anyway. |
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Post by scooter on Jan 14, 2015 21:20:48 GMT -5
Mega dittos from me also. This is a really good thread. Any updated numbers? Not for that scoot, but I just uploaded a new video and readings for a scoot that is not running well. It looks like the vacuum and fuel pressure are low. I wonder if the pump is leaking vacuum. |
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Post by JoeyBee on Jan 14, 2015 22:01:41 GMT -5
I was thinking a rocker switch would be more useful than a vacuum switch. Then I could wire it to a circuit that's activated with the key to prevent it pump when the scoot is off.  But with installing an electric pump, I'll worry about drawing to much current from the battery. Next a voltmeter to monitor the battery.  |
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Post by scooter on Jan 14, 2015 23:16:27 GMT -5
I was thinking a rocker switch would be more useful than a vacuum switch. Then I could wire it to a circuit that's activated with the key to prevent it pump when the scoot is off. But with installing an electric pump, I'll worry about drawing to much current from the battery. Next a voltmeter to monitor the battery. The one I ordered is about 1.2 amps. I don't know how my system will deal with it yet. |
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