Need Help RC 390 hesitation during quick acceleration, rough engine, backfiring, uneven idling

[dhynz]

Hello knowledgeable people.,

To begin, some info about my bike and I'm the second owner had this bike at 24000 km
- 2015 model
- ~25000 km
- Had a full service at ~24000 km


The problem:
While giving quick throttle, the engine would "cut out" of sorts, similar to the sensation if you find yourself running out of fuel.

This is most evident when revving hard and I approach 5000 - 6000 rpm. like there is a hesitation for 1 or 2 seconds during quick acceleration and starts to accelerate well after 6k rpm and also backfiring during deceleration and uneven idling and sometimes shut off during cold start. Now most i feel is the engine is running so much ROUGH like when i give throttle the engine is accelerating rougher couldn’t feel much of a power only the engine revving harder.

My bike has never had valve clearance check till now Maybe that could be a issue? (but i don't have no starting issues).

Things i changed
fuel pump
airbox
fuel injector
ignition coil
spark plug
check the spark plug wire and rubber cap
cleaned the throttle body and all the sensors

still these problem occurs what could be the issue?

SOMEONE PLS HELP!

Thanks!

 

[1JZSupra]

Do you have a video by chance?

 

[B7ACKTHORN]

Did you replace you inline fuel filter? If the fuel filter and everything else you've mentioned has been replaced, start off by inspecting the ECM . A faulty ECM itself will manifest these symptoms with no error whatsoever on the dashboard. But before that I would strongly recommend you to carry your valve clearance procedure. An out of whack valve clearances could and would cause cold and hot engine issues, especially missing, poor top whack and overall poor performance. Start off by inspecting valve clearance, followed by ECM.

Good luck. Keep us updated.

Cheers!

 

[RickCrespo]

If it is, you have the same problem I did with my 15 rc390. I did the same as you and swapped out a bunch of parts that could have been causing the issues, but what finally solved it was changing from those shitty plastic hard accordion type fuel lines within the tank to a basic rubber fuel hose that is rated over 50 psi, and good clamps that aren't oval but round and don't cut into the hose. Your fuel pressure should be around 50 psi at full throttle from what I can remember, I'm possibly wrong about that, but it's an easy enough test to see if this is indeed what is going wrong with your bike.

The test:

Install a fuel gauge inline from tank going to injector. Once you flip the switch on, and don't start just yet, the gauge should go up, and stay steady. Give it about 5-10 mins and leave it in this state, and the pressure should be the same, if it isn't you have an internal leak of some sort.

If it is holding pressure, get the rear wheel off the ground using a rear stand and start the bike and slowly rev the engine in gear and allow the rear wheel to spin, the pressure should also stay within limits, if it doesn't then again, there is a problem with losing pressure within the tank. I did this but on a friends dyno so we could put the bike under load to really test the fueling fixes.

The popping under deceleration is the engine running lean, and the hard starting or stalling all together are also symptoms of a lean problem.

Hope this helps.

Rick