jeepwm69

Sounds like a low battery, out of adjustment clutch, or shift motor going south. Don't put that new angle sensor on it yet. First thing you need to do is the battery. Clean connections and top the battery off. Then try adjusting the clutch. Nut on the front cover. Loosen it, then turn the screw in the middle counter-closckwise till you feel resistance, then back to the right 1/4 turn and lock the nut back down. If the adjustment screw doesn't turn easily, it might be seized. Don't force it, just leave it for now and come back to it. Here's Retro's ES thread. Your shift motor might be going south, or it could just be gunk in the gears under the shift motor. If you do replace the motor, OEM only, even if you buy used. No aftermarket crap.

I actually was going to find your post and tag @Melatv and @retro and @AKATV since they seem to love electrical puzzles so much. Sounds like you need a new TPS either way. I have an extra carb with a good TPS if you want to try it, but if it measures out of spec you probably need one anyway. I don't THINK that the TPS has anything to do with spark, as my machine ran fine while running with a TPS error, BUT then again, my TPS wasn't actually bad, it was just an error code. We did have someone here who had a Hondamatic with a TPS code and it threw the machine into limp mode, so I guess it's possible that it could be causing spark issues.

That's what I did with the wife's. I actually had a 420 footshift with a cracked cylinder, so I had the wife's 420 cylinder bored and used it on that footshift, and bought a new 500 cylinder for the wife's. I wonder what the 520 would do? Looking at the chart @Melatv posted, the HP difference in the EFI 500 and 420 is negligible, but you're only actually going to a 475. A 520 would be almost double the CC increase of the 500 cylinder.

If it's an angle sensor, should be throwing a code. Are you getting any blinking lights or gear position on the meter?

If I had a 420 cylinder that couldn't be bored, sure I'd go bigger. Why not if you're having to buy a new jug and piston anyway. 500 jug costs the same as a new 420 jug. But if your 420 jug hasn't been bored yet and can simply be bored, save your money and just bore it OS with a new piston. After doing it, and looking at the $$$ I spent doing it, minuscule bang for my bucks.

Yep, I had a Rubicon and an aftermarket top end gasket set. Gave me fits trying to get the valve cover on as the aftermarket gasket wasn't stiff enough to hold up the push rods. The OEM gasket make it MUCH easier to do.

Welcome aboard. Post up a pic of your meter on with the headlights on so we can see what you have. @AKATV will be along shortly.

Try without first. If it acts like it's running lean get a programmer. I did one on my wife's 09 DCT Rancher. I put a Weisco programmer on with the top end, but I honestly think it would have run fine without it. Didn't make much of a difference at all over the stock 420 cylinder. Not worth doing unless your original 420 cylinder is gone too far to be bored oversize again. I was curious as to the 520 top end, but you have to either turn down the outside of the bottom of the cylinder (Reduction Boss sells those ready to bolt on) or grind the cases a little to clear the bigger jug. I've gotten away from 420's and am sticking with the older machines, so never got around to the 520 swap.

It does look like a warm coil might point to a bad ECU on these EFI machines, as that Foreman was doing the same thing.

@Mach 1, mine was a bad ECU as well. The track records for ECU's on these new EFI machines doesn't look great for the long term. I've replaced one on a 420FA, and one on that 2012 500FE now. Thanks for reporting back with what you found. Buying a new ECU is always a little scary since they're pricey and not returnable if it turns out to not be the problem.

When you have the machine in a specific gear, the wire associated with that gear should be grounded if you check the wire. Troubleshooting info on the GPS in the factory service manual

Hard to tell without seeing things. You should have a ground wire from frame to back of engine, and another from starter bolt to battery negative. # 8 and 9 here https://www.partzilla.com/catalog/honda/atv/2000/trx450es-a-fourtrax-forman-es/battery You have an N showing on the meter and a strong green light on the N indicator on the meter?

No adjustments that I'm aware of. @toodeep you have any ideas on this one?

Ok, that actually makes sense. You have two clutches in that machine (DCT, Dual Clutch Transmission). One is for 1,3,5, and the other is for reverse, 2, 4 So, given that you started having this problem when you disassembled and reassembled the engine, I would guess you didn't get something back together right on the 2nd clutch. That said, first I'd do some testing and make sure that the solenoid on the front of the engine is working properly. The DCT's run off of oil pressure to engage the clutches. Go to the toolbar at the top of the page, click on the "service manuals" button, and download the factory service manual for your machine. We don't have one for a DCT Rubicon, but for your engine troubleshooting the one for the 2014-2019 420 DCT should work fine. Look in section 13, which will show you how the system operates, and then you'll have to try to figure out what exactly isn't like it should be. The DCT's are complicated, and a PITA to work on, which is why I got rid of the wife's DCT Rancher when she decided she liked my 05 Rubicon better.

This a true ES machine or a DCT?