WR 450F (03) Misfire/splutter

Hi there!

This is my first enduro bike and I've not had it very long. The previous owner was the second owner and the bike was previously a standby machine for the UK Yamaha Supermoto team. The reason I'm mentioning that is that the bike has been modified in some ways, some no doubt I'm yet to discover.

Anyway the problem is, is that the bike starts fine and appears to idle without fault. However when under way the engine develops an intermittent misfire/splutter throughout the rev range. It doesn't appear to happen when under heavy or moderate acceleration but does when retarding the throttle or at closed throttle whilst on the move.

The first thing I checked was all the obvious electrical connectors to make sure they were made. I then removed the spark plug. The spark plug wasn't the correct type (a CR9E was fitted) and it showed signs of poor combustion. I fitted a CR8EIX plug and took it for another run without any noticeable improvement. The problem appears to worsen with time. I have changed the fuel in the tank and got it from a different supplier.

The previous owner was shocked to find a problem with it. He claimed that he never noticed a problem that I described whether riding on or off road. He did say that it was characeristically lumpy because it was a single pot engine.

My previous bikes have been in-line four sports bikes so my experience in troubleshooting thumpers is sadly lacking.

Any help would be gratefully appreciated.

Bogieknight

:applause:

Just a jetting problem mate, nothing to worry about.

sounds like you are rich on the needle.

Drop it 1 clip position and adjust the fuel screw.

the cr9e plug is just a hotter plug. it sits closer to the middle of the explosion.

Changing the plug won't make much difference unless it is shagged out.

If you got a manual, it has some good info on carb tuning - problems and how to fix it.

Single potters won't be half as smooth as an inline 4!

Normal for a properly jetted bike, don't worry about it...

the cr9e plug is just a hotter plug. it sits closer to the middle of the explosion.

i agree with trying to drop the needle to lean it. and matty i'm kinda confused on your explanation of a hotter plug; a cr9e is actually a colder plug. a colder plug just transfers more heat from combustion process to the cylinder head, better for high rpms,hotter cams,and higher compression than stock. some of your stuff is way off :applause:

If the jetting changes don't solve your problem, try disconnecting the electrical connector from the carburetor (or TPS - "Throttle Position Sensor").

In some cases, the WR450 will have a stutter while holding a steady throttle and speed while riding on roads. The symptom is more common on WR450F's than other models.

James

Hello All,

Thanks for your replies.

Matty, I found the section in the manual that you mentioned, thanks. I have tried dropping the needle from groove #4 to groove #3; it seemed to make the problem worse. So I'm wondering whether it's worth going past this to #2 or trying the other way to #5? Any opinions?

James, at the time I was changing the needle position I noticed that the TPS connector was filthy. I cleaned this out and remade before I tried out the changes on the road. If I were to disconnect the TPS wouldn't this create problems for the ignition advancement?

I'll have another look in the manual and play about a little further. I'll post back once I've found something else.

Thanks again.

Bogieknight

:applause:

My friend had the same problem with his wr450 until we got him to shift up a gear and cruise around at a lower rpm when cruising. He was riding it like his old wr250.

Disconnecting will change the timing, but it will answer the question as to whether the ignition has an effect.

--Try it... One of the easiest things to do.

James

How about posting your jetting setup, fuel screw position, main jet,pilot jet etc.. I might give a clue to where you need to fine tune it. check my sig for my setup, my bike runs very clean and very strong.

Don't know if I agree about disconnecting the TPS, I have heard it can cause more problems than fix, something about being set at the factory and such and once you disconnect it, it will never be the same, even if you connect it back up. I may be wrong on this. just my opinion

Disconnecting the TPS wont hurt it. In fact, on my FZ1 it's required to disconnect in order to check for the associated computer error code read out on the tach (tells you if orientation is off). Slight rotations in the TPS cause the rpms to rise/fall so you dont want to mess with that aspect unless you know your exact rpm's when adjusting.

I had a similar complaint.

I sealed off the ACV system on the carb.

The way it was explained to me is that the little spring inside

the ACV system controls a diaphram that adjusts the mixture , I think richer,under decel to reduce back-fires.

The problem is that the spring lets the diaphram vibrate under mild

throttle setings which is what causes the "missing" sensation.

I removed the spring and placed a gasket in there to close off the passage.

Sounds like ignition timing "bounce" as a result of the input from the TPS vs engine rpm and is normal. Disconnecting the TPS will eliminate it, but you lose the advantage of ignition timing/mapping and power. Drive around it would be my answer.

Hello All again!

Nothing further to report as I've not had time to work on the bike. But I did want to say that it's a UK bike, so Math Prof I don't think the AIS is an issue.

Having read a bit further on this, concensus either points to a fueling problem or I'm being far too sensitive.

Thing is, I can't beleive that Yamaha would produce a machine that has such an irregular power delivery. As I was overtaking a row of cars recently, one of the cars in question didn't see me and decided to pull out on me. All I needed to get out of the way was a gentle steady throttle response.

Instead it popped and hesitated a little and the revs eventually started to climb until I now felt the need to gun it and wound the throttle open 100% and off we flew. It's where you need a sensitive metered but instantaneous power delivery that it's most noticeable. You can't go around on full throttle all the time!

That's why I think there is a problem and I'm not being anal. (least I hope not!)

Any further feedback much appreciated.

Bogieknight

:applause:

I had a similar complaint.

I sealed off the AIS system on the carb.

The way it was explained to me is that the little spring inside

the AIS system controls a diaphram that adjusts the mixture , I think richer,under decel to reduce back-fires.

The problem is that the spring lets the diaphram vibrate under mild

throttle setings which is what causes the "missing" sensation.

I removed the spring and placed a gasket in there to close off the passage.

Sounds like the ACV(air cutoff valve), especially since the 04 didn't have AIS...

It also sounds like she isn't jetted right...and the accel pump may need adjustment too. RTFM, it's in there...

I think the problem you are talking about on the road is more than the TPS issue. The TPS removal should take care of the slight surges, etc. you get at constant throttle--not the problems you stated on the road and the line of cars

This thread and links to some other threads which you will find in this one might help.

http://www.thumpertalk.com/forum/showthread.php?t=296401&highlight=ACV

As JD said, just disconnect your TPS connector and see if it makes a difference. Quick and easy way to see if it is your jetting or if it is the famous constant throttle stutter.

Also, as Mathprof said, it could be the ACV, but it appears that the only consistant way to get rid of the stutter at constant throttle (small throttle openings) is to disconnect the TPS. Personally, I run with the TPS disconnected and the ACV dissabled (as Mathprof suggested) and I don't have any stutter, and I know for a fact that my jetting is very rich.

Here another one:

http://www.thumpertalk.com/forum/showthread.php?t=159518&highlight=stutter

i agree with trying to drop the needle to lean it. and matty i'm kinda confused on your explanation of a hotter plug; a cr9e is actually a colder plug. a colder plug just transfers more heat from combustion process to the cylinder head, better for high rpms,hotter cams,and higher compression than stock. some of your stuff is way off :applause:

oopsy.... not all manufacturers use same heatrange numbering system.

I have been mistaken by length of insulator leg.

If it's still the original ignition, the keyed one they come stock with (in Oz anyway)

If it is, I bet you a chook and 2 wombats that's the problem.

Is still the original ignition, the keyed one they come stock with (in Oz anyway)

If it is, I bet you a chook and 2 wombats that's the problem.

i kinda know what a wombat is (some mean little furry creature?) i've actually ridden a combat wombat! but what in tarnation is a chook :applause:

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!


Register a new account

Sign in

Already have an account? Sign in here.


Sign In Now