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450R stutter/miss

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Hi guys,

My 2010 450R has developed a hesitation or a miss whilst riding.

I was about 3/4 way through a session when the problem began, at first it felt like I tagged the rev limiter, but when I got back on the throttle it was there again. Its not affected by throttle %, just has a 'miss' in it which can be described as a jerky feel as it cuts in and out.

I have gone through and checked as much as I can, I have replaced the spark plug. The fuel filter in the tank I did about 5 hours ago. I filter my fuel and have never had this problem. The bike has around 65 hours on it. Unsure if its still the original top end.

The bike starts fine and idles fine. I took it out to test it after I changed the plug and it was fine for about 1minute, then it had the same problem. Almost to say it does it once its warm maybe.

Hopefully someone can chime in with some ideas, I have tried to list as much detail as possible!

Cheers in advance guys.

Edited by tempo86

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Hi guys,

My 2010 450R has developed a hesitation or a miss whilst riding.

I was about 3/4 way through a session when the problem began, at first it felt like I tagged the rev limiter, but when I got back on the throttle it was there again. Its not affected by throttle %, just has a 'miss' in it which can be described as a jerky feel as it cuts in and out.

I have gone through and checked as much as I can, I have replaced the spark plug. The fuel filter in the tank I did about 5 hours ago. I filter my fuel and have never had this problem. The bike has around 65 hours on it. Unsure if its still the original top end.

The bike starts fine and idles fine. I took it out to test it after I changed the plug and it was fine for about 1minute, then it had the same problem. Almost to say it does it once its warm maybe.

Hopefully someone can chime in with some ideas, I have tried to list as much detail as possible!

Cheers in advance guys.

Maybe a bad connection somewhere? Faulty fuel pump? Try riding on asphalt (no shaking), if it does not do it then maybe there´s a loose connection of broken wire. Try lending a fuel pump.

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Im always on asphalt as its a supermoto. I did think fuel pump but I haven't pulled that out yet. no real way to check it I can only check the connections I suppose.

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Im going to order a new fuel pump. I have read there is a revised pump, is this basically a '13 spec pump? are they all interchangeable between the 09-13? or do I need the revised '10 version?

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All the pumps are the same, its the plastic housing and filtering arrangement that were changed. You can run the old pumps just fine, but the filter is more prone to contaminant clogging than the newer filter configuration. Hopefully it is your filter that's clogged, but sometimes the electronic pump, itself, gets harmed, but that is very rare. The pump can take on quite a bit of contaminants and work just fine for a very long time, the injector doesn't like contaminants.

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hmm ok, I was under the impression it was the pump it self people had been having fail. I have replaced the filter on it about 5 hours ago so its not that.. I removed the pump and connected it to a battery and it operates fine, but I was thinking it could be a pressure or flow problem with the pump.

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When was the last time the valve clearance was checked ?

Unsure mate, I purchased the bike and have done around 10 hours work on it.

I am thinking the reasoning that it runs fine for the first 30 seconds or is its already got the sitting fuel in the line to use, then the pump cant keep up possibly?. Either way ive ordered the updated fuel pump they released, will report back how I go with it.

Edited by tempo86

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Well I guess on the plus side I have the new updated pump in my bike... but I still have the problem

It didn't really do it only when warm today, started doing it straight away. Bike starts easy still, does this rule out valves or not? sorry im new to 4 strokes. Thinking ill just take it somewhere instead of spending money on everything I think it could be.

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If the bike starts easy when cold, it's not the valves. The valve clearances get larger when the bike warms up, not smaller (tighter).

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Wrong - valve clearance reduces when engine warms up, when it gets to where it won't start cold, its really bad. As the valve warms up, the valve stem gets longer reducing clearance.

I am sorry to tell you this, but it is you that is wrong. I don't have the energy to fully explain why as I went riding today... I will say that the rest of the head is aluminum and expands more than the valve material given the same change in temperature, so the clearances grow, they don't get tighter.

Edited by Eddie8v
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I am sorry to tell you this, but it is you that is wrong. I don't have the energy to fully explain why as I went riding today... I will say that the rest of the head is aluminum and expands more than the valve material given the same change in temperature, so the clearances grow, they don't get tighter.

Yeh, you preset a clearance because the clearance will increase with temp and load  :banghead:

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Yeh, you preset a clearance because the clearance will increase with temp and load :banghead:

You're setting a "minimum clearance" that you're comfortable will remain as the motor wears so you can always have some valve clearance. The clearance increases with temperature. Do you think the manual-specified .005-.006" intake valve clearance when cold is good knowing that it will get smaller as the engine warms up? Aaah, it doesn't get smaller, it gets larger. Valve is captured in aluminum, valve seat is your datum: for same temp increase, aluminum head increase more than the valve stem, not to mention the cam tower. Very simple math.

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Valve sits on an angular seat - the diametrical clearance increases faster than the linear increase times the sin of the seat angle (normally 45 deg or .707) still greater than the linear expansion of the stem (simple math). The hot valve clearance is less than the cold valve clearance. If it increased as the engine warmed up all those rattling noises would get louder not quieter. But hay- don't check your valve clearance - its probably the fuel pump - wait he changed that.

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Valve sits on an angular seat - the diametrical clearance increases faster than the linear increase times the sin of the seat angle (normally 45 deg or .707) still greater than the linear expansion of the stem (simple math). The hot valve clearance is less than the cold valve clearance. If it increased as the engine warmed up all those rattling noises would get louder not quieter. But hay- don't check your valve clearance - its probably the fuel pump - wait he changed that.

Ok, so how much greater would the thermal expansion coefficient of aluminum have to be greater than the steel's (exhaust valves) or titanium's (intakes) for the clearance to grow vs shorten?

Edited by Eddie8v

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You have to look at the variation in the linear expansion in the system, the valve transfers heat from the combustion process to the seat to be cooled by the rest of the head, the valve and the seat are at a higher temp than most of the head, and the expansion also raises the rocker arms. Ideally there would be zero clearance when the engine is at its maximum temp so the lifter (thus valve) would follow the cam profile. Then you also have to look at the variation in materials, the seat is not aluminum - it is a material with much greater thermal stability, on the CRF I believe it is an iron alloy - if it were aluminum it wouldn't last a single race.

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