If it turns over fast it is not the battery or charging system. If it turns over fast but does not like to start when motor is warm it is probably running rich. If it ran good before and the carb has not been messed with i would check the air filter. It needs to be nice and clean.
if the o2 sensor is still in the pipes , it is ok
if not have the adaptor fitted to the pipes and it will be ok
the sensor reports the gas composition to the ECM to adjust the air/fuel mixture
if the new pipes are pollution control compliant the adaptor should be already there
if they are not then you are achieving nothing with the different pipes but are actually decreasing fuel economy
Try taking a look at the starter and flywheel while attempting to start the engine. Does the small gear at the end of the starter move forward and engage the flywheel when you try to start the engine? Could it be stuck? The small gear must move forward to engage the flywheel. Keep your fingers away from the moving parts.
Your 4 wheel drive may be working, but it is a torque-sensing front
differential for reduced steering effort, that supposedly sends power to the wheel with the most traction. Many owners have found that just the opposite is true. Your problem may mean that the differential is working, but because it doesn't lock up both tires in the front and only one tire is getting all the traction you can't see it work as advertised. The link to the video is great for showing what may be happening. The front differential may be worn out and need to be fixed or it may just be that it is not working as you expected: https://www.youtube.com/watch?v=KF-iD4pmmoA
If you have a Honda Rubicon, you must place the transmission in Neutral, then pull in Left Hand brake and push down Reverse knob that will remove the reverse lockout and allow you to shift it into reverse. If that doesn't work your reverse lockout knob might be defective or out of adjustment. The adjuster, depending on which model you have, will be on one end of the reverse lockout cable.
I purchased a 2000 Honda Foreman 4x4 and changed all fluids. I put synthetic differential oil in the front and rear differentials.
The problem I am have after about 6 months is the front wheels are not pulling like they use to.
Before I changed the fluids with the front wheels jacked up I could not turn the front wheels but now with very little effort I can turn the front wheels.
Did I make a mistake in using the synthetic oil and if so what is my recourse?
You can try to adjust the linkage below the shifter should be 2 rods there one is low gear other is forward and backwards if that's doesn't do it then you have to pull trans out and sleeve the shift heads hope you can just adjust it
Take the float bowl off the carb. Pull the pin that holds the float on. The needle is attached to the float. The needle just came out of the needle seat. The needle seat can now be pulled out. This is the fun part. Are you really sure it need replaced? If it is needing a good cleaning, take some Mother's aluminum polish and a cotton swab and put it in the seat and spin the heck out of it. It will polish up nice. Be sure to clean with carb cleaner to get any extra polish out before use.. reassemble.