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normally my bike runs fine, but when the engine temp really gets up there, i find that the engine stutters a bit and is a bit weaker when pulling away from lights and stop signs. this only happens when there's a lot of lights and traffic and i find myself stopping at red lights so long that the thermostat goes up and the fan starts kicking in a lot, and the engine temp is high. is this normal? the bike is a 2000 honda cbr 600 f4.
 

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I don't know. Just going on my experience with cars here. Most engines though, you will feel less throttle response and power with higher coolant temps. That's just the way it is. That's why guys like to run 160 or 180 degree thermostats instead of the stock 220 or so. Colder is better...just too cold is hard on your motor.

Have you had any mods or rejetting done? Maybe you're running just a TAD bit lean, and when the engine heats up, thus spreading the heat to your intake assembly etc, you get less dense air in which leans your mixture just enough to make you stutter or something.. ?

I wonder if there's an adjustable fan temperature setup out there...I'd love to know. :confused:
 

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less dense air would choke your engine, not lean it out.

I think it might be electrical. check the stator output and make sure your battery is full of water and fully charged. see if you headlight bightness changes when you rev the engine, your battery might be on it's way out. check the coil outputs at high temp, I've heard heat can affect them. make sure your clutch is adjusted correctly.
 

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Oops... You're definitely right there. Sorry about that, I was a little drunk making that reply. :alky Ok, a LOTTA DRUNK.... :alky :alky :alky

Heat can affect coils...but, at least on my bike, the coils are mounted to the frame itself and there's a good amount of space between it and the motor. There's no way enough heat could transfer the coil to affect it...I would think the heat it generates on its own would be more than anything it could radiantly absorb from like 6 inches away and through heat transferred to the frame... But then I haven't done temperature testing on this, so I'm not sure. The coils have their own heat sinks, don't they? That should do a sufficient job of radiating away any extra heat.....

Heat affects ignition modules more than it does coils really. And I'm not sure that bikes even have ignition control modules......I wouldn't bet on it though. I would be surprised if they did. Maybe on the newer FI bikes.

Maybe your idle mixture is a little rich and the higher temp is causing that stuttering. But as far as making less power at higher coolant temps....that's generally normal. A lot of factors come into play as far as at what temperatures an engine will make power...newer computer-controlled engines like to run hotter for greater efficiency and better functioning of emissions control systems...so they're set up to run good hot. But older cars, and more than likely nearly all bikes, will like to be run on the cooler side.

Just tossing out ideas here!
 

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Discussion Starter #6
jim schmidt said:
That's how it works. Cooler denser air has a higher oxygen content. That feeling you get on a cool morning -- that your bike is perfect -- isn't your imagination.
haha yea, that feeling is great, but what i'm worried about is the hiccup or two i get off the line when the bike is almost on fire at a red light :p
 

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I'm betting your idle is a little rich. Did the problem develop by any chance after you added any aftermarket parts or after you had it rejetted or tuned, either by yourself or at a shop?

Mine is having off-idle bogging/stuttering issues right now with the exhaust and drop in...and I'm having to take it back to have them attempt to tune the carbs again. This time I'm paying extra for a dyno tune, so they do it RIGHT and accurately this time.
 

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~~

The F4 coils are down right on top of the spark plugs, so they are really effected by engine temp. I had one go bad on me and it caused the same problems that you are having. Try running the bike until the fan kicks on. Then use a spray bottle and shoot the exhaust header right where they come out of the engine. See if one of them is colder then the others. Mine was real obviouse about it. They are about ~$50 new. You can try ebay though. All F4, F4i, 929, and 954 use the same coil. Good luck
 
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