[cartracer20]

I picked up a new to me 2008 CRF150R about 2 months ago. The seller stated that it didn't idle right and it was too fast for him to ride around with his kids. I bought the bike for what (i thought) was a good deal thinking the carb just needed some help. Fast forward to now, I'm absolutely baffled and I'm looking to see if ANYONE has ever experienced an issue like this before.

Here is the symptom I'm trying to diagnose. I start the bike with the choke on when its dead cold. It runs and idles just fine and once it warms up i can shut the choke off and the bike will idle down and rev clean for about 30-45 seconds. After the 30-45 seconds time period up it starts to burble and run like what i would describe as "muddy", It doesn't rev clean and gets progressively worse until i cant keep it running with the throttle and then it dies. Once it dies i can immediately start the bike back up and it runs clean for another 30-45 seconds. It runs flawlessly for the initial 30-45 seconds once its warm, and then begins to run muddy again. I can repeat this process over and over and the issue is persistent and consistently the same every time. Nothing i have done has helped resolve this issue.

I started with pulling the carb and cleaning it myself, twice. This didn't fix my issue so i moved to checking the valves. While i was checking the valves i noticed cam timing was off 1 tooth. This explained why the bike was harder to start when i initially purchased it. I fixed the timing issue and at this point, the bike was easier to start and ran better until it ran for 30-45 seconds and the issue still persisted. I did not recheck the valves after i adjusted the cam timing, which i may need to do but it was perfectly in spec when i checked it before adjusting the timing. At this point i still thought i was having a carb issue so i sent the carb out to tokyo mods for a complete overhaul. The carb came back, looking brand new. I bolted it on and now the bike runs like a scalded ape for 30-45 seconds. It runs SO GOOD until it doesn't. At this point, since my issue still persisted i decided to start checking electronic components. I bought a used ecm off of eBay and swapped them, this made no change and didn't resolve my issue. I then swapped my coil with another used coil i had laying around, this made no change and didn't resolve my issue. After doing A TON of research on forums and scowering YouTube I convinced myself it was a bad stator so i bought a new OEM stator and installed it. This made no change and the issue STILL persists. I'm stumped and out of ideas to try. I know the carb is good and it isn't a stuck float, I've pulled the float bowl nut after the bike dies and fuel flows out like it should. I know my timing is correct. The bike has good compression and spark and runs fantastic for 30-45 seconds once its warm. This seems like a time or heat related issue, but more so time than heat. If it was solely a heat related issue, i would think the bike wouldn't run flawlessly after it was warmed up and restarted. Does ANYONE have any ideas as to what my issue could be? I've never experienced an issue like this, and I'm fairly new to the Honda R world.

Thanks for your time!!

[Back2-2]

From what you described I would be looking into a fuel flow problem. Either venting and or clogged/ restriction from the petcock. Also, check the carb vent tubes to be certain they are clear and not blocked.

[cartracer20]

The fuel line and filter are brand new. I also cleaned the tank before attempting to start the bike for the first time. With the fuel line pulled off of the carb and the petcock open, it flows what seems like - plenty of fuel. I'm running VP fuel in the bike as well. Another reason I'm having a hard time believing its a fuel issue is, when the bike sputters out and eventually dies - the filter stays fuel. If i shut the petcock off immediately after the bike dies and loosen the float bowl nut, the bowl has quite a bit of fuel in it indicating its flowing fuel well. The vent lines are brand new and routed exactly to factory spec, tokyomods installed them when they built the carb and this issue has occurred before and after those lines were replaced. Any other ideas? Thanks in advance!!

[Back2-2]

I agree - it sounds like a good fuel supply and flow. I would try it with the fuel tank cap removed to just verify there is not a venting issue. One thing at a time.
You did not mention the air filter or inlet for restriction, That would be another thing to check for the sake of eliminating things.
It still does not sound electrical because electrical does not usually "sputter" to a stop, then fire right back up.
I would suggest checking flow float level and things in the carb but it was redone by a repeatable outfit so it's pretty unlikely to not be correct.