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striaghtarrow
50cc nipper
Joined: 08 Jun 2006
Posts: 12
Location: Perth WA
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 Posted: Thu Jan 17, 2008 9:59 am Post subject: Engine cuts out |
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Looking for some advice please
I have a 04 YFZ 450 and it runs sweet when cold but gets uglier as it gets hotter......runs like a hairy goat especially when you are pushing it hard WOT in 4th and 5th....coughs , farts and back fires.......the problem wasnt there at the start of the day and the bike has run fine on the same jets for 2 yrs....We changed nothing, added nothing....went to the same riding spot we had been at the week before (with no dramas) ....The only thing that was different was the ambient air temp was maybe 4 degrees hotter.
The jetting is fine, ALWAYs run with the lights on
I have already taken a punt that the stator is on the way out and pulled it out to have it tested......i have just heard back from the sparkie and he tells me that the stator is OK.....
back to the drawing board!!!!
Any info that you folk think may help would be appreciated....
Thanks
Ian |
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The Day Starts With OZATV !
Joined: 09 Sep 2006
Posts: 1518
Location: Middleton SA
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| Posted: Thu Jan 17, 2008 10:50 am Post subject: |
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If it coughs and splutters at WOT when hot, i'd be thinking lean, but if it is better when cold then that rules out lean all together.
I'd stay on the electrical path.
It could be stator, coil, CDI or any component that gets hot and works harder at higher revs.
If it is worse with higher engine loads it will more likely be on the high tension side. (High voltage - coil, plug etc) Even a plug breaking down.
To take some load off the high tension side... maybe try running a smaller plug gap. Close it up to about two thirds of the original gap and give it a guick test under the same conditions and see if it fires better.
This should basically make it easier for a weaker spark to jump a smaller gap under load. I would not leave it this way, but this test might confirm you are on the right trail with a high tension fault.
Be careful to only deal with one suspect at a time to track it down. You could accidently / temporarily get it running fine and you won't know which bit was at fault until the wrong wire gets wriggled again and it plays up again.
hope that helps
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greenhuman
Roostin Away
Joined: 12 Feb 2006
Posts: 980
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| Posted: Thu Jan 17, 2008 6:21 pm Post subject: |
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| I'd check the valve clearances. |
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bigjon
Moderator
Joined: 17 Feb 2006
Posts: 1279
Location: Dubbo
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| Posted: Thu Jan 17, 2008 8:21 pm Post subject: |
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| greenhuman wrote: | | I'd check the valve clearances. |
That's where I would start as well.
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Don't close your eyes during the crash, you'll miss the best part |
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PeteW
Moderator
Joined: 09 Feb 2006
Posts: 1877
Location: Doreen, Vic
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| Posted: Thu Jan 17, 2008 9:42 pm Post subject: |
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I'd be starting with the Valves too, an 04 that has done a lot of work the left inlet will have closed up a bit, when it gets hot and the clearances close up it will cause some minor de-comression.
Another common problem with older Yamaha's is the plug cap/coil pack combo, very hard to fault find but it may have a fracture in it that is opening up when the engine heats up around it.
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The Day Starts With OZATV !
Joined: 09 Sep 2006
Posts: 1518
Location: Middleton SA
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| Posted: Sun Jan 20, 2008 1:46 am Post subject: |
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Lot's of credit on the Inlet valve theory....
I've seen that happen when they get dangerously hot.
So... Let us know... What was it?
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striaghtarrow
50cc nipper
Joined: 08 Jun 2006
Posts: 12
Location: Perth WA
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| Posted: Mon Jan 21, 2008 9:31 am Post subject: |
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Gents thanks for all the advise, Heres the story for those that are interested.
i have checked EVERY single inch of every wire, All the plugs and joints, found a few minor dramas but nothing that i felt would cause this. Then i decided to take Petes advice and checked all the valve clearance's and they are on the mid to high (Loose) side of spec so i left them like that, while i was there in went a new plug.
So i decided that Sunday i would take the boy (son) and his bike minus all the plastic and a arm load of bits and pieces from my bike (07) out to where we ride and we would work through every single switch, plug coil or stator until we found the drama.
We rode till the bike got hot and the problem started so first on the list to swap was the coil as per Petes suggestion, ran the bike with the newer coil and what do you know ....no problems at all!!!!....put the old coil back in .....problem came straight back......New coil back in and problem gone again.....
New coil/plug cap being ordered today.
Thanks again for all you help and a big thanks to PeteW for his advise
Oh and i then spent an hour or so putting all the parts back onto my bike
Ian |
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The Day Starts With OZATV !
Joined: 09 Sep 2006
Posts: 1518
Location: Middleton SA
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| Posted: Mon Jan 21, 2008 4:52 pm Post subject: |
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Glad to here you found it relatively easily.
High tension stuff can be a real struggle unless you have the parts to play swappies.
Good work.
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PeteW
Moderator
Joined: 09 Feb 2006
Posts: 1877
Location: Doreen, Vic
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| Posted: Mon Jan 21, 2008 6:26 pm Post subject: |
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| bullet wrote: | Glad to here you found it relatively easily.
High tension stuff can be a real struggle unless you have the parts to play swappies.
Good work. |
Its easy with the Yammie combo plug cap/coil pack one, no choice but to replace the whole thing to find out.
Glad to hear you got it sorted Ian.
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