91 Marathon, not up to full performance?

ab46501

Hello all, been lurking here a while and just joined today. I have searched this topic but can't find my answer.

I have a 91 Marathon 36v that I got a few years ago. It was all original and well kept. I now have a lift kit with 22inch tires, new trojan 105s (pack charges to 38.4 volts), HD soleniod (its the brown one that is supposed to be able to handle 1000 amps peak), new HD FNR, new 2/0 gauge cables (yes 2/0 is overkill but the wire and lugs were free to me), 4 year old remanufactured Curtis 500 amp controller and a brand new reworked EMP 2 speed motor.

My problem is my top speed. According to my GPS and also my son riding along on his ATV my torque mode gets 12mph and my speed mode gets 16mph. According to Chuck over at EMP I should be getting about 16 with torque and 20 with speed with my setup. I have had the EMP for a couple of years but just got it back from being reworked due to another issue which I will ask in another thread. In my conversation with them my speed came up and they said I should be seeing more. It had been that way for the whole time I had it and I just thought it was what I was going to get.

The cart does not seem to lack for power as far as I can tell. It pulls well up hills and will spin the tires on loose ground off the start.

At this point my best guess is that it is either a controller or potentiometer problem. Last night I checked the controller per the Curtis manual. It seems to be working correctly starts at 0 and puts out 37.1 volts at high pedal off the M- and B+ terminals to the motor.

The original potentiometer is in question. I checked with my meter and at high pedal it was at 5930 ohms. It reads 0 with no pedal and as the pedal is depressed goes up smoothly. There is no hesitation in the motor and it also runs smoothly during operation. Could the high ohms be causing my cart not to reach top speed?

The only other original parts are the microswitches but they seem to be fine and I don't thing that is the problem.

Sorry for the long post but I wanted to get all the info out there. Thanks for your help!

BGW

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pggroves

Welcome.

Adjust the pot and let us know what happens. Seems just a tad high to me.

Paxdad

Make sure the brakes are not dragging. I have seen this many times.....

e-z-go1988

I was having performance issues with my resistor cart. Run the total voltage of the pack directly to the A1 terminal of the motor. As a troubleshooting aid, I installed a Czonka 500A contactor between the +36v terminal of the battery pack and the A1 terminal of the motor, bypassing the speed board, the solenoid and the FNR switch. The contactor coil was connected to the fast, pedal down position on the speed board. I found no change in performance but did eliminate all of the components that might cause performance issues.
Is there some way to verify the peak RPM of the motor to eliminate that as the cause?

ab46501

Thanks for the suggestions. I am going to try adjusting the pot this weekend. I don't believe the brakes are dragging I can push the cart fairly easy by hand on a flat surface. I have wondered about checking motor RPM but I have not been able to think of a way to do it?

ab46501

I adjusted the pot box by adjusting the linkage. The carts top speed slowed by about 1 mph was all I noticed. I may go ahead and replace it anyway and see if that makes a difference. At this point I think it either has to be it or the controller and the pot is the older of the two.