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Hello friends, I have a 2017 CRF250L rally with 20,000 miles on it. It will not idle or run below 2000 RPM. I've attempted a lot of diagnostics and part replacements but can't identify the issue. Looking for suggestions before I finally give up. Thanks in advance.

The bike always starts instantly when cold, and correctly runs above 2000 RPM by itself briefly while it warms up. But as soon as conditions start sending the bike below 2,000 RPM towards its normal target warm idle, it quits. If held at higher RPM by throttle it will happily continue running, and can actually be ridden nicely indefinitely if you never try to idle.

When I bought it it had the full FMF exhaust, EJK fuel controller, and a modified air box. This issue existed then, too. I have since installed a stock pipe and stock tail pipe / Muffler, and sealed up the air box lid.

In trying to diagnose this issue, I have replaced the spark plug, air filter, fuel filter, fuel line, O2 sensor, the entire throttle body (complete with never-touched TPS amd IACV, and fuel injector) (and reset the TPS), checked valve clearances and valve timing, bypassed the fuel evap system (to avoid any vacuum leak at manifold), and tried plugging the exhaust port air injection system (though this should not affect idle).

While it feels like a fuel issue, I don't understand why it works fine at speed, and I've replaced the whole throttle body,

While it feels like a fuel issue, I have tried disconnecting the tip-over sensoR. ALSO, I feel like the coolant temperature sensor is working right as the bike knows when it is doing a cold start, and correctly triggers the fan when hot.

I haven't yet done a compression test, but again the valve clearances are good and the bike seems to make fine power.

Any suggestions? I am at my wits end.

Cheers,
Peter

Welcome to the site !! \"D/

I am wondering if it is possibly a issue with the fuel pump itself , maybe it is weak and not pumping at lower rpm for some reason , you mentioned changing just about everything except the pump itself and the ECM .... The only other thing I can think of , is some kind of Mapping issue , you know how the 21 CRF450R has that bog at the bottom and everyone (including a buddy of mine) has had to have it re-mapped by Honda or Tokyo Mods , but it runs fine otherwise except on bottom end , but everywhere else it has no issues , it might be the same kind of thing , and it might need a re-flash or complete different remap ... maybe contact Tokyo Mods and see what they think ....

Thank you very much for the speedy reply. Yes, fuel pump might be next. I wonder if it maintains a constant power signal in all conditions or if it varies? Anyway, I will probably try that next.

Leardriver would know the answer to that one , hopefully he will chime in and can enlighten us on how the pump actually functions as far as pressure vs throttle input , or if it changes at all , or how would the symptoms you describe fit in with the pump ...

The fuel pump is a constant pressure and electrical signal. ECU regulates the fuel delivery.

FYI, replacing the fuel pump (complete factory unit with sender, filter, etc.) did not solve my idle issue. Maybe the ECU is bad.

Have you been in contact with Honda directly ??? (not the dealer , but Honda itself) , there might be some issue that they are aware of , that the dealers are not .... I know with the re-flash of the 21 CRF450R Honda released statements , the dirt bike magazines released statements about getting it re-flashed for FREE at Honda Dealers , and the Dealers knew nothing about it , or at least claimed they didn't know , my friend struggled for a couple months till he was able to get his re-flashed at the dealer , and he had to drive to Oregon to get it done , because the dealer in Boise was dragging their feet on it ....... So maybe there is a issue with the ECU and if it is something Honda has been made aware of , you might get it replaced for free ..... worth a try ...

did you ever solve the issue? mine started doing the exact same thing just a few weeks ago

I had this issue in 2018 on my 2016 CRF250L - spent 3 months trying to fix. Likewise full FMF/EJK/Airbox mods. Tried TPS resets, new sensor assy, even new ECU, checked compression, function tested IACV. Spent weeks thinking it was temperature related & resorted to adjusting the throttle-stop just to keep the bike running.

Eventually got back to the IACV & throttle body - bought a new IACV and before fitting stripped the throttle body - found that the porting for the IACV air flow was blocked with black gunk which I removed with aerosol carburettor cleaner. The old IACV despite function testing OK was sticking when fitted in the throttle body, maybe worn-out? Did IACV fail causing blockage of ports or ports block up causing IACV to fail - who knows. Is this a problem exacerbated by the power upgrade mods?

Anyway, it has been perfect ever since and still has the FMF/EJK/Airbox mods - just recently completed its 24,000 mile service.

I'm a bit surprised at pabarlow's 'replaced entire throttle body' as that would have cured mine - however my advice at first & cheapest diagnostic would be to pull the throttle body, remove IACV & clean both it and the porting with carb cleaner - if that fails then buy a new IACV.

Rog

No, I haven't solved it. I appreciate the post regarding the IACV. Can't hurt to clean out the port there, so I will, but in fact I have bought a new IACV and, as you saw, changed throttle bodies too.

I made a video of my troublesome CRF:

I took it to the local dealer (in Bremerton, WA) and allowed them to do a full-service on it and investigate the issue. They happily did a $700 24,000 mile service (on a single, without a valve adjustment, so funny), and then lightly looked at the idle issue. They diagnosed a kinked fuel line so I let them replace it for the second time. They told me all was great and handed it back once they got my $1000. Unfortunately, there is no improvement at all.

The person I sold this bike to (with full disclosure of the issue) has since told me the issue was with the spark plug connector shorting when hot.

Live and learn, I guess.

Thanks for the update pabarlow.

I am sure that will help someone out in the future.
The fact it only did it when hot would have made it very difficult to find.