J head MK5 MKV 0.4 mm/3 mm hotend PLA Jam

Dear Friends,
I am clearly a noob to this forum, building my first 3D printer. I assembled a kit for prusa i3. I am trying to get my first print, however running in to hotend jamming issues. My setup is as follows -
Electronics- Arduino Mega 2560, RAMPS 1.4
Firmware - Marlin
Ponterface and Slic3r
Extruder max acceleration - 2 (default was 3333)
Extruder feed rate - 5 (I guess default was 45 or higher)
Extruder motor is 1.8 deg/step, NEMA 17, V Ref - ( I have tried 0.4 to 0.7V in efforts to increase the torque).

Trying to print PLA without hotend fan.
After 2-4 min into the print (at 185 Deg C, Bed Temp 60 deg C), my extruder motor starts trying really hard, without actually extruding anything. When I use by hands, I am able to extrude but with considerable amount of manual force. I tried playing with the firmware numbers as well as with the Vref. I am thinking more about absence of fan causing PLA to heat up at level above it should, inside the hotend- leading to jamming.
I have ordered ABS and will see if that makes a difference. Any thoughts will be greatly appreciated.

It is almost impossible successfully print pla with a j-head without a fan pointing at the plastic barrel. In fact its almost impossible with most hotends.

So, add a fan and try again.

Extruder max acceleration - 2 (default was 3333)
Extruder feed rate - 5 (I guess default was 45 or higher)

Put those back to the defaults,

Put a fan on the hotend to cool the PEEK.

Since you are trying to cram 3mm filament through 0.4mm (I use 0.5) Raise you temperature from 185 to 195

If you are using a GREG WADES EXTRUDER

Make sure your IDLE bearing is not bottoming out, and preventing it from spinning
Image of area I had to file down to allow bearing to turn

Edited 1 time(s). Last edit at 01/16/2014 12:17PM by ShadowRam.

@lazzymonk and @Shadowram- immediate problem of 3.0 mm PLA jamming my J head MKV hotend with 0.4 mm extrusion hole fixed by taking apart my Greg's extruder, adjusting the hobbed bolt a little bit so that it's centered and making sure that the idler isn't jammed and then pointing a table fan to my hotend/bed while printing at 195 deg C. my V ref is down to 0.38 and extruder stepper seems to have sufficient torque now.
Thank you so much for your help. I changed the Marlin extruder settings to default numbers and so far it is working great.