Gx390 bogging

Clubcar98

New member
The motor will idle fine, but as soon as you give it throttle it bogs, even if you tried to slowly open the throttle. The motor was running fine and all of a sudden started acting up. Maybe has an hour of run time on complete motor build. Motor is a standard bore gx390 with a .100 longer billet rod, .060 shaved flat top piston, stock head with #35 springs, champion 1.1 to 1 rockers, mild torque cam, 6 degree timing key, arc billet flywheel and 24mm bored 3 circuit carb from NR racing. I believe the main jet is a .45.

The motor is actual in a club car golf cart, so it has a pulse fuel pump. I have tried changing the spark plug, putting a different carb on, readjusting the valves, new fuel, new fuel filter, cleaned and blew out the 24mm bored carb and I reset the coil gap to .060. I originally set the gap to .030 and after doing some researching realized I needed to open it up. Non of this made any difference.

Could I have fried the coil and that is my issue? Fuel pump seems to be pumping well, could it be sucking air and I’m not realizing it? These are the only two things I haven’t swapped out. What could my problem be?
 

Clubcar98

New member
Tried switching the coil with another one I have and still no change. Could the timing have changed, somehow? Really at a loss, any help is appreciated.
 

alvin l nunley

Site Supporter
You put in a .100" rod and shaved the head .060", did you change the jetting in the carburetor? If you did, how much did you increase the size of the jets? Both low-speed and high-speed?
 

Clubcar98

New member
The carb that is on it is a 24mm bored carb. Came with a #114 high speed and #48 low speed. Ran great for probably a total of an hour run time and then started bogging down and wouldn’t run to high rpm and slowly got worse and worse to the point that it would bog as soon as you hit the throttle. I pulled the flywheel and checked the key and it’s perfectly fine. I tried factory carb that’s jetted and it ran the same. I’m thinking both carbs are crap and thinking about buying a new one to try.
 

Clubcar98

New member
I pulled the valve cover and spun the motor over, the intake valve moves much faster and more than the exhaust valve. Is this normal or does it sound like a messed up cam?
 

flattop1

Dawg 89
Didn't watch video but if its noticable to the naked eye it done .
Use a mchinist rule to get a much more accurate picture or something more or less accurate .
Lubrication failure is #1 the hardness of the lobe and spring pressue .
A dab of molly lube helps , not idling alot right away after start up .
 

Clubcar98

New member
Looks like I’ll be pulling it apart. It has 35# springs and chromoly push rods. I’ve got it set up to start off the pedal, so there is very little idle time. Shuts off when it comes to a complete stop and starts again when I go. Lubed everything well when I put it together. At this point it is what it is and I’ll tear it apart and get it back together with some new parts and hope for the best. Thanks for all the help.
 

flattop1

Dawg 89
Use 400-1000 grit emery / sand paper to round off the lifter and cam , sharp edges .
A good Hard Arkansas stone will work as well .
 
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