oldmxrider

You can not imagine, How nice it is at least for Me ! I am 68 and been playing with these toys since I was 15 !

Just a thought, If it was not that load before ! Maybe Your wrong on top dead center. Easy way for top dead center on the compression stroke ! Turn motor slowly in the proper direction, watch intake valve go down and start to come up, next T You see on the flywheel is where You adjust the valves.

I work on a LOT of powersports toys, had a homemade lift for race bikes, but nothing for street or atv's got tired of being on the ground, recessed and modified a Harbor Freight motorcycle lift, have side extension that just slip on when the need is there ! Been using the ! out of it for five years, always something on it !

Just My opinion! if the thing runs and idles correctly after it has started, I would first check valve clearance !

I know it is a long shot but have You checked the SENSOR ASSY., AIR TEMPERATURE Part# 37880-RE1-Z01 Had a race bike last year that was having crazy start and run problems after too much time spent found the air sensor was causing the problems.

That is super cool ! How the heck did You end up with it ?

Thanks ! SlammedRanger ! It was needed ! To the OP I would have bought that thing in a heartbeat for $500 if it had a title that came with it !

It's great dealing with the people sometimes isn't it ! They have NO CLUE ?? I order a couple of thousand of parts a month and They are usually needed fast so the bikes are ready for a race the next weekend. Sometimes that does NOT HAPPEN and it is NOT the sellers fault, I can see They shipped it !

You bought an oem identical carb off eBay ! China carb, correct ? Then put a rebuild kit in it ? Only asking because in My experience if a China carb does not run correct out of the box they are junk and not worth trying too save. The different parts in the carb do not play well with ANY replacement parts !

Yes, I agree ! The ! wires to the plug were not correct ! Took way too many hours to figure it out and drove Me nuts ! I know it is a long shot ! But one I will NEVER forget, been at it longer than You and still always learning !

On the exact same year machine had no spark ! With what sounds like the same mix of parts ! Two wires were switched in the aftermarket ( china ) VR , DROVE ME NUTS ! Cut them changed them around and instant spark ! Do not trust the colors of the China wires for Your VR tests. Darn thing is still running great to the best of My knowledge . I know this could be a long shot, but just something I have run into.

My thoughts are it is not the weight of the tire, it is the outside circumference of the tire, You changed gearing a bit and the computer can not see this ! From Jeeps link that He shared and I found very useful Years ago ! " In “ESP” mode, the ECM tells the swash motor to position the swash plate to five different predetermined “gear” locations when you push the thumb shift buttons up or down. You can use this fact to diagnose a slipping clutch. In Auto mode, when the centrifugal clutch begins to slip, the ECM senses the faster engine RPM, and positions the swash to a higher “gear ratio”. But because the clutch is slipping, the actual power output to the drivetrain is not as great as the ECM expected (and thus "geared" for), and the bike bogs down. By switching into ESP mode, the ECM no longer cares what the engine RPM is and moves the swash plate to a preset position – and everything works normally. So, if your bike acts like it hasn’t shifted down, but then works fine in ESP mode, chances are your clutch is slipping. " I take it You seemed to have no problems before the tire size change ? If You have another 400 AT with the stock wheel and tire size, do a quick swap and see how it shifts ? Does it seem back to more normal ?

I will agree with shrade on this one. Sounds like a clutch problem the new larger tires just brought it to light ! If it works kind of normal in the ESP mode but not in the auto ! The expensive tranny is good ! I brought a beat on severely neglected '05 400 AT back from the dead ran and worked like a new one ! Loved the auto mode ! Now just have a old ES model. Not everyone wants a foot shift model !

Still stop by everyday, motocross racing opened back up so been very busy !

I have repaired quite a few small two stroke engines used in leaf blowers and lawn equipment, if Your fuel lines are good ! Check to see if Your cylinder bolts are tight the darn things seem to vibrate loose and they start sucking air at base of the cylinder sometimes it has blown the base gasket and that will need replaced . Just a thought and it is definitely something that I have run into many times with these engines.

50/50 Acetone and ATF !

In My humble opinion, the motor has a VERY bad air leak if the shot of starter fluid killed the motor, without a doubt ! Fix that first. As far as the oil in the air box I might suspect the china top end kit that was installed even though, You do not see it smoke ! If it was in My small garage, I would do a leak down test on the motor before tearing anything down. Again just My opinion.

Have a few things I am working on in My small space, a 2001 YZ125 tear down selling usable parts on eBay, a 2001 300ex engine that just came in torn down but with some parts to make live again,, a 2001 400ex engine stuffed on a side bench waiting for parts, a 2016 CRF450R for a few small repairs !

If Your tank DOES need lined with a coating ? Red Kote is the way to go, been using it for years, NEVER had a problem, just follow the directions. I use a bag of different sized nuts to shake around the inside of the tank for rust removal and a telescoping magnet makes for easy removal !

Just a thought ! Not an expert on this machine, just asking, what is Your idle rpm ?

Trust Me jeepwm69 it does not look like that all the time !

Tools You can never own enough ! My favorites would be the modified HF lift table that is recessed in My garage floor it will accommodate atv's with the side extensions and My china made modified 20 ton press repowered to 35 ton . I rebuild My own MX crankshafts and 20 ton will not do it ! Have a suspension bench for and shocks and forks It is only 12' x 21' Try to make the most out of it !

OH ! ! Looks sweet to Me !

I am old and slow ! How do I post images that are saved on My pc ? Thanks !

Found this forum from another site, I am days away from 67 years old, usually do race bikes MOTOCROSS motors and suspension, crankshaft rebuilds etc., but the racers also own atv's and side by sides and I make them work ! Been a passion for about 50 years ! GOD I am old ! Hope to be able to help someone one day ! Do NOT know everything and never will always learning !