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We have had a 2006 CRF450R for about 18 months which we don't use every week as its just for occasional practice track usage. After initially having a couple of faults to sort out it has been faultless for a few outings.

A few weeks ago before winter set in it began stalling occasionally when going into corners but would start back up ok. My 27yr old son who rides it most noticed it was nice and steady at start-up/tickover and at WOT but would not hold a midrange throttle without misfiring and backfiring through the exhaust pipe.

I tried replacing a few items after reading posts and searching on the usual forums but each time I swopped something out the misfire remained. After a few hours working on it today I am getting to the end of my patience with the bike and would like your thoughts on my next attempt in a few days time when this other stuff turns up by post.

I have sent for a new header to silencer seal and clamp along with exhaust repacking materials after a friend came around and noted straight away that it was excessively noisy considering it sports a STD can. He reckons it might be an air leak in the exhaust somewhere that is causing it to stutter at mid throttle openings, could this be the cause?

So far in order of replacement/testing:-

Valve clearance checked (spot on)
Fresh fuel
Iridium spark plug x twice
Disconnect kill switch
Coil, plug cap/lead etc
Sent stator away for testing, resulted in rewind
ICM and harness swop
TPS tested as per manual (4.9K ohms) so tried it unplugged
Carb stripped (again) new main and pilot jets fitted (and AP squirt checked)
Carb connector boot checked for cracks/leaks

The engine is mechanically spot on and has only done a few hours since piston kit, clutch pack, steel inlets/recut seats, all valves checked and lapped in again (all steels now). Engine has been taken apart again since and everything checked again and all OK.

Have I missed something really obvious?

This episode has knocked my confidence a little as I am usually the 'friends dad who is good at fixing crossers'

All comments welcome and I have a thick skin so weigh in if I'm well off the mark with my efforts so far

Thanks guys

Ian

PS. I have 5 Hondas in the garage

You did not mention if you checked the slide plate O-ring/seal , as it can cause some issues , for the Exhaust , try holding a match next to the mid joint and at the head connection and see if it blows the match out , if it does that would be your source of air leak , for the sake of asking , if you have another 450 to swap parts to/from have you tried putting YOUR parts on another bike to confirm there is no issue with those parts , or just put parts from other bikes on yours ??

JimDirt wrote:You did not mention if you checked the slide plate O-ring/seal , as it can cause some issues , for the Exhaust , try holding a match next to the mid joint and at the head connection and see if it blows the match out , if it does that would be your source of air leak , for the sake of asking , if you have another 450 to swap parts to/from have you tried putting YOUR parts on another bike to confirm there is no issue with those parts , or just put parts from other bikes on yours ??

Hi Jim, I bought the parts from a 'known good' running bike as I don't know anyone with a 450r to utilise as a testbed

If I go anywhere near the bike with a match in my hand I might just get tempted to torch the bloody thing!!!

I haven't checked the slide plate seal recently but did so last time I had the carb apart. It was in perfect condition and re-installed properly (the bike has ran fine since then anyway until the recent problems)

thanks for your response

Ian

Yea , if you have ruled out electronics , then you are back to a carb issue or a exhaust leak

Also , since being winter , have you ruled out water in the new gas ??

I emptied the tank and carb bowl out yesterday Jim, no sign of water etc.

I personally didn't realise an exhaust air leak would be able to have such a profound effect on the running of the engine though (still learning at 59)

Ian

I have some more questions about the carb , you said , now that winter is setting in , how cold is it there , and what is your elevation ??

In below 50 degree F weather , the engine will run leaner , as the temps rise the engine will become richer

List your carb settings:

Main Jet:
Pilot Jet:
Needle Clip Position (from top):
Fuel Screw Turns out:
Any other Carb Mods:

Also , a alternative to a match is using stick Incense , lighting it , then holding it near the exhaust joints at the mid pipe and the head will tell you if there is a leak by watching the smoke and if and how it reacts

This is a basic guideline of jetting for your bike

Sea level... 165
2000 ft..... 162
4000 ft..... 160
6000 ft..... 158
8000 ft..... 155

one main jet size for every 2,000 feet or 25 degrees in temp from that baseline

I am far from a carb expert , but these are things i have learned , and do hold value

Main Jet: 168
Pilot Jet: 45
Needle Clip Position (from top): 5th groove
Fuel Screw Turns out: 1.5 turns
Any other Carb Mods: extended fuel screw (zip-ty?)

I am not much above sea level and the temps are not that cold really ranging between maybe 2 and 10 degrees C it is more rainy than cold in the north west of England at the moment

"Also , a alternative to a match is using stick Incense , lighting it , then holding it near the exhaust joints at the mid pipe and the head will tell you if there is a leak by watching the smoke and if and how it reacts"

The exhaust is apart ready for repacking when materials arrive but I will do a 'leak test' when refitted at the weekend (I work in Scotland so I'm away from home now for a few days)

Thanks

Ian

You are right about where you need to be on the carb , you did not mention if you checked/changed the Needle/Seat or checked the float level

Other than that i'm kinda stumped , you might try giving Ken a PM and direct him to your post here , and see if he has run across anything like this , the stalling could also be caused by the clutch hanging , but its not going to make it sputter or backfiring thru the pipe , that is usually a lean condition or a ignition breakdown , so your back to fuel or ignition on that , and it seems you have covered most of that with the exception of ruling out the exhaust

When you had it running did the header glow red quickly when sitting for a couple of minutes ?? if so , thats definitely a lean condition

I dont know what else to suggest

I did notice a glowing header a couple of weeks ago. Maybe I should just wait until I have made the exhaust system leakproof?

Thanks

Ian

Yea you should eliminate it before moving on , do 1 thing at a time so you know what actually makes a change for better or worse and what does not

I'm going home tomorrow and my son has re-packed the silencer and installed the new mid-pipe seal and clamp ready for refitting to the bike.


I will try the re-sealed exhaust firstly


then I will try lifting the needle by one more groove(it ran fine before this misfire arrived though so I don't expect this to work TBH)


Cam timing is spot on and all 4 x s/steel valves were lapped in only a handful of hours ago during an inspection



I think I am going to try and borrow a 'known good' carb just to eliminate having an internal problem that I can't test/see, would a 450x carb work ok?


Thanks again


Ian :uk:

Yea you should be able to swap the carb , just check the jetting/needle clip position/Fuel Screw turns ,etc before swapping so you are working with consistency in specs

The exhaust has made no difference, lost interest for now ...............

OK , the Stator out for rewind , did they say what was wrong with it , and if any other components could be at risk because of whatever was wrong with it ???

JimDirt wrote:OK , the Stator out for rewind , did they say what was wrong with it , and if any other components could be at risk because of whatever was wrong with it ???

When the stator was removed I inspected it very thoroughly and the oil was spotless as were the flywheel and pickup. The stator was inside the parameters of the basic tests but was sent away for checking at west country windings in the south of England (where everybody goes in the UK). They supposedly tested its output and I was told it was LOW and would need a rewind, on re-fitting it made no difference at all to the misfire




I am left with the feeling it MUST be a carb issue even though I have been through most of it. I really need to borrow a carb before I lose my mind!!!

Thanks

Ian