[Cevans7]

New here, first post. Working on my 2013 CRF450R which is backfiring out the exhaust. It started out when riding after 3 min warm up in my backyard. Backfired and then the idle was horrible and it kept backfiring out the exhaust at low and mid RPMs. It ran like a plugged pilot jet (but it is fuel injected) or like I torched a valve.
I checked valves which were spot on. I boroscoped the cylinder and looked at valves which looked good, nothing burnt or missing. Good spark, and gave it a new plug in case. Timing is on exactly. Compression is great. I changed the fuel filter in the tank (which looked dirty). I also have a 2015 CRF450R so I started steeling parts. Swapping the injector helped it (I think). Now the bike idles fine but backfires out the exhaust at high RPMs. I swapped the entire fuel tank and fuel line (Incase I had low pressure or bad gas) but runs exactly the same.
I was thinking maybe the TPS next, but the OBD is not giving any codes. I have not taken off the throttle body yet.
I need an expert to diagnose. Did I fix my first problem and create a new problem? The bike runs great now just has a high rpm backfire. What am I missing?

[JimDirt]

Welcome to the site !!

I would guess the kill switch might have water in it , if they get water in them the bike can run crappy or not at all , and they are known to get water inside , also check all your grounds ... the bikes will either run crappy or not run at all if a ground is bad or if the switch gets water inside ..... That would be my first guess .... , Are you getting any codes on the MAP switch ?? (error flashes) , sounds like you covered most everything else .... Also check the power wire to the coil , see if its loose , as just the vibration from running could cause intermittent power issues , or if you have the manual , check the oHms resistance of the coil , I think it should be between 2.6 and 3.0 , keep us posted on what you find , if it was not those let us know ........ , I don't have a 13 manual , but I have the Service Manual for 09-11 , so most of the reading should be the same ..... I can post up testing procedure pages from the manual if needed .....

[Cevans7]

I have checked resistance across the coil and found it to be exactly the same as the ‘15 model I have next to it (2.6 ohms). Also measured resistance through the plug wire and found 14.26kohms (exactly the same as the bike next to it. I looked at wiring for the kill switch. Everything looks perfect. I don’t remember the last time this bike got wet...ever. It all looks brand new. The kill switch it not giving any codes either. I have disconnected an air box wire and it started giving codes so I know it works, but everything plugged in there are no flashing lights. I also checked timing chain tensioner and it is working perfectly. Any other thoughts?

[JimDirt]

Hmmmmm

How about (sounds dumb but it does cause your symptoms) checking the header gasket at the head (the brass ring) and at the mid pipe connection , a air leak will cause the symptoms , but not be a physical lean condition at the plug , but the pipe sucking in air ..... That is one area to check ..... It still could be a weak fuel pump , it may be working , but not working hard enough to pump under a load .... if you have one , or another tank to swap to try , that will eliminate that ....it is possible that even though you cleaned the filter , that some minute particles got thru and are restricting something in the throttle body , since the injector did not seem to be the issue , or at least not all of the issue ........ The Throttle Position Sensor may not be changing the timing when needed , if its is faulting , or out of spec for some reason , it might cause a issue , and would not necessarily send a fault code

Try giving leardriver a PM (Private Message) , he is the resident fuel system guru around here , if anyone has run across this , it would be him ... go to where it says "PM: Send Private Message" and click on it https://www.crfsonly.com/forum/memberli ... le&u=14707

[Cevans7]

Figured it out. Original problem was solved by replacing that fuel injector. Low idle backfires were gone.

2nd problem was a high rev backfire. After deciding everything was correct on the bike, I wondered if that high rev backfire was just normal while sitting on a stand, near redline, while not under a load, and not completely warmed up. Maybe I just had a hyper sensitive ear. I put my 2015 back together and noticed it did the exact same thing. I put my 2013 all together and went and rode it. It runs perfect. Simple fuel injector was the issue only issue. Thanks for the help.

[JimDirt]

Oh .... Well you did not mention the high RPM backfire was doing that while on the stand , that is "normal" , I thought it was while riding , as you had mentioned with the low RPM backfiring....... Glad you got it sorted out !!!