mxu 300r big problem please help

[djtasos1]

hello to all,i bought a mxu 300r 2016 model before few months but only now i start repairing it,from the beggining it had a proplem that after pass 45 kmh the atv start like breaking it self for every 2-3 seconds like i put a break for a second and imidietly let free again,but this problem doesnt affect the top speed,still it runs till 85 kmh but with this problem from 45kmh till the max speed,so far my mechanic clean the carb,put new jets,new variator belt and rollers,clutch service,new fuel filter,new fuel Cock Valve Switch,new oils and anti freeze,new sparg plug-cap and cable,new rear differential axle and new final drive gear and pinion and new rear differential bearings,after all this  still no results,i also try new cdi and Voltage regulator with no results,can anyone maybe have knowlege about this problem so i will now what to search next?thanks in advice and happy holidays to all!

[Ruffus]

Welcome here!
Since all the usual culprits are ruled out already, I would check the fuelpump, relays (all) and ignition coil.
Brake discs are really free?
Wheel bearings in good running order?

[djtasos1]

thank you!this model dont have fuel pump,i replace already releys and ignition coil with no result,wheel bearings also,breake disk are fine,the atv run normal till reach 45-50 kmh with no problems,after the 45 kmh start this problem,thanks for your advices!

[djtasos1]

the only electrical part i didnt replace yet is the 'emi filter',some with electrician knowledge could answer maybe if this could be responsible for my problem?thank again!

[Ruffus]

Well, from distance then 🤔
..but your runner should have a vacuum fuel pump, grey/silverish square with tubes fro and to..
Maybe do the carb again, and see what happens.

IMHO, EMI filter is just a relay to regulate your fans input and speed.

One one straw: does your rectifier/ regolatur produce 14-14.5 VDC on red/green towards battery?

You say "clutch service", really good shoes and spring coils?
When you shift gears, any changes in sound or feeling?
Cardan system in good order?

[djtasos1]

thanks for your reply,yes i know from distance is not possible to find a problem,im just trying to find a solution before i will decide to send it to kymco official service because is far from my place and it will cost me a lot of money,my mechanic here is not specialist to atv's anyway but hes trying also to find the problem,the mxu 300r dont have fuel pump,it have only a fuel switch valve that i replace already,i dont know if the rectifier produce 14-14.5 V i just use another one from same atv and didnt fix my problem,also i use another ignition coil and cdi unit from the other atv with no result,in the clutch service i replace all the springs inside main and 3 smaller,the clutch shoes are well,before few days start another problem when i try to put reverse from high its very difficult,i need to go to low first and then it will move all the way back to reverse,the atv was abandon for a year before i bought it if that helps you also..thanks again for your help!

[Ruffus]

Well in this case I would suspect my gear and start searching there.
Right spring coils for the clutch?

[djtasos1]

yes,i replace all the spring coils for the clutch with original parts,also the variator belt and rollers,i think its time to say to my mechanic to open the gearbox to check inside..i want to ask you something else now,before 2 days i remove from inside the intake manifold a round metal adaptor i believe it was a air restrictor,but yesterday my exhaust pipe right in corner after the cylinder head it crack and broke,i notice some overheating to exhaust pipe,my exhaust pipe was rusty anyway since i bought it,you believe that was just a coincidence or happens because i remove this restrictor from the intake manifold boot?should i put it back maybe?thanks again!

[Ruffus]

Sorry, I have NOT seen such a air restrictor at KYMCO motors, only in BMW and HONDA motors to adapt to local law of restricted power.

Yes, try to put it back again, maybe it causes kind of distortion.

[djtasos1]

this part in the picture,i will put it back ok

[Ruffus]

Ah ok, try. Nothing bad can happen. Maybe give a feedback then?

[djtasos1]

i will ok when i will put the new exhaust pipe!

[djtasos1]

Happy new year to all!finally i put back this part that i removed from the carb because i found out that this part is there to reduce the  heat from cylinder going to exhaust system,i didnt notice any better performace of the atv whith out it,just overheat the exhaust pipe thats why i put it back ..

[djtasos1]

hello again!before i put my mechanic to open the gearbox can someone with knowlege tell me if my problem have to do with the valves or ground clearenece adjustment maybe  so to start with this first or valves has nothing to do with my main problem?thanks again