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razor mx350 help

 Any help is appreciated.   When engaging the throttle the wheel spinds fast but as soon as any weight is put on the scooter it only goes a couple miles per hour.   The scooter is rated for over 100lbs, but it wont go with my 50lb 6yr old.   Batteries are new and measuring 24v under load.   Chain seems ok, not too loose or tight although i don't really know how much play there should be.  i would guess i can move it by hand up and down a 1/2'' or so.  Any ideas? 


From your description the problem is pointing towards either the battery charger, charger port, or battery pack.

After the battery pack is fully charged it should be at 27.6 Volts, and when under load the Voltage should only drop between 1/2 to 1 Volt. If the battery pack is at 24 Volts under load then most likely the battery charger is not charging it or is not charging it up to the Voltage that it needs to be at, or one or more of the batteries is not working properly and dropping too much Voltage under load.

There is also a very low likelihood that the motor has some burned out windings however that is not very common so I would start with looking at the battery charger, charger port, and battery pack first.

Performing tests on the charger, charger port, and batteries would be necessary to pinpoint the problem.

Test 1: Test the battery charger. When the charger is plugged into the wall and not plugged into the dirt bike its output Voltage should be between 27.6 and 29 Volts. If it is outputting less Voltage than this then it should suspected as a faulty part.

Test 2: Test the charger port. The charger port should have Voltage present at its. If it does not have any Voltage at its pins then it needs to be replaced. Be very careful when testing the charger port to prevent a short circuit.


Test 3:
Since you have already load tested the battery pack I would load test the Voltage of the individual batteries in the pack next. This is done the same way as load testing the battery pack however the multimeter probes would be contacting the terminals of each individual battery during the test. With this test you might find that one of the batteries only drops 1/2 Volt under load and the other battery drops 3.5 Volts under load which would point towards the battery with the largest Voltage drop as being faulty.

Please let us know how it goes.

thanks for your help.  See my results below and let me know what you think the next steps are.

Test1 - Battery charger plugged into the wall - 28.2

Test 2 - Battery charger port - i tested this with the scooter powered on and the multimeter probes on the ports where the charger plug would go - only 2.1.  I realize this is an issue, but my batteries are new and were charged externally before being installed into the bike.  In my feeble mind, while this is an issue, it is not the current cause of low speed when my little one tries to ride it.  See battery measurements below

Test 3
battery 1 - 13.3

battery 2 - 13.1
across both batteries with scooter power switch off - 26.5

across both batteries with scooter power switch ON - 26.5

across both batteries with load (load being tire raised off ground and full throttle - 25.8/25.9

Let me know your thoughts.  Once i get my little one to sleep i'll look at the connections on the charger port and see if anything is loose or corroded.  So wanting to get this going.


rethinking the charging port and that 2v is a good charge rate,   Not sure what i was thinking.   I think it might be the motor.  See attached video.  i can stop the wheel might a little pressure and not sure if i should be able to.   What are your thoughts?  if i need a motor, what part do you recommend.  i don't want to add any speed as i have a feeling this is going to be too fast for my 6 yr old as is.   he'll figure it out though,

the bar code of the bike is 121520-36-14070001147
serial number 07/03/14

ignore my toes in the video and thanks for the help


(2.12 MB)
The 2.1 Volt reading at the charger port is an unusual reading. Most commonly a charger port will read either zero Volts or the full Voltage of the battery pack. That is definitely something to look into, however I agree that the charger port can be overlooked for now since the batteries were charged outside of the bike.

Load testing the batteries with the rear wheel off of the ground is not putting enough of a load on the batteries to truly determine their condition.

I recommend performing the battery load test again with the rear wheel on the ground and the bike being held still in case it wants to move (I usually out the front wheel against a wall to keep the bike from moving for this test). This will put the maximum load on the batteries that can be placed with them with the battery pack installed in the bike.

I am looking forward to seeing the load test results with the wheel on the ground.
thanks,  i performed the load test and this time i sat on the bike (190lbs) and with the throttle full open and the lowest v reading i could got was 24.3.  it was typically 24.9 or 24.7.  BTW - please look at the attachment i uploaded earlier.  Maybe it shows something.  Anyway, I will recharge the batteries again.  Should I bite the bullet and just buy 2 new batteries?  I happen to also be troubleshooting a crazy cart issue, i think you may be helping me with that fourm post as well.   Thanks again.  Todays my birthday and it would be a great present to get either of these resolved but I dont think that is happening.   We are making progress though


Since the battery pack is at 24.3 Volts under load its a tough call whether it is causing the problem or not. I am leaning towards the battery pack not being the problem because 24.3 Volts is a pretty good readings under load and many battery packs will run the dirt bike with a lot of power when they are at 24 Volts under load.

The next step that I would take, if the MX350 is a version 1-8, is to test the throttle to see if its signal output is within specifications. If the throttles signal output is low that would cause the motor to not have enough power. If the MX350 is a version 9 or higher then it has a single speed throttle which either works or doesn't so it does not need to be tested.

If the MX350 is a version 1 through 8 then if you could let me know exactly which version it is then I could provide directions for testing the throttle's output signal.

If it is a version 9 or higher then please let me know and I will recommend the next step to take for troubleshooting the problem.
thanks.  The bar code is 121520-36-14070001147 so i believe it is version 36.  Also has a date code of 07/03/14.  i did upload a video of what the motor sounds like if that is helpful.  I am not sure if you saw that. 

thanks again

The MX350 version 36 has a single speed throttle which either works or doesn't, and it is working since the wheel does turn when it is twisted. So we can rule out the throttle as being the problem.

That leaves the batteries, controller, and motor to look at. The load test results for the battery pack point towards the problem not being the batteries.

The next test I would perform is connecting the motor directly to the battery pack to see if it runs at full power then. If the motor runs at full power when connected directly to the battery pack that points towards the controller being faulty, and if the motor runs at low power during this test that points towards the motor being faulty. I would monitor the battery pack Voltage during this test to make sure it stays above 24 Volts just to confirm that it still passes the load test.

Jumper wires can be made to connect between the battery pack connector and motor connector. These connectors have 1/4" push on terminals inside them which common 1/4" push-on wire connectors will attach to.

         1/4" Push-On Terminals

When making the final wire connection for this test make sure that the rear wheel is off of the ground because it will immediately turn on when the final connection is made. Also push on the final connector quickly to minimize the spark that will be made when it is attached.

During this test the rear brake can be applied of the rear wheel tried to stop on the ground to determine if the motor is now receiving more power than it did when attached to the controller.

Please let us know how it goes.

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