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Bike runs like crap when it gets warm

23702 Views 14 Replies 7 Participants Last post by  Fazerman007, 
Z
I have a CBR600 F2, and it idles fine until its ridden and warms up. Then it feels like the bike isnt getting fuel, or missing, or something like that when accellerating, and when I come to a stop it wants to die on me unless I keep revving it to keep the RPMs up. Any ideas?
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Deznuts05
find your idle screw and get familer with it.

once warm turn clockwise to lower the idle speed

turn counter clockwise to increase the idle speed

if you have your manual refer to that but otherwise I believe 1k-1.5k is the proper setting for most sportbikes.

I believe what the problem is when your motor gets to temp its running too lean. which will give the affect that you've stated.

When you warm up your bike do you use the choke or not?
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Z
I generally dont use choke cause it revs it so high... Ill use it to start, then shut it off pretty quickly
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Deznuts05
I'd say reset your idle speed.

from a cold start your bike should use the choke until 135 and yes it annoying/loud but you are on a race bike that's how they sound :/

get the bike up in temp however you can/want and then reset the idle to 1k-1.5k

remember clockwise increase idle speed. counter clockwise decreese.
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Z
the idle was a little high, around the 2000 mark... dropped it back down but havnt had a chance to ride yet to see if it happens again. Would a high idle actually cause a lean condition though?
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Gimpdiggity
Deznuts05 said:
find your idle screw and get familer with it.

once warm turn clockwise to lower the idle speed

turn counter clockwise to increase the idle speed

if you have your manual refer to that but otherwise I believe 1k-1.5k is the proper setting for most sportbikes.

I believe what the problem is when your motor gets to temp its running too lean. which will give the affect that you've stated.

When you warm up your bike do you use the choke or not?
Click to expand...

First off, when a bike warms up it tends to run more rich than it does when it's cold. The warmer air being pulled into the intake is made up of molecules that are farther apart...hence the engine is getting less air with the same amount of fuel...which means the engine is getting a richer mixture than when the bike is cold.

Second off, adjusting the idle speed doesn't change the air/fuel mixture. It only adjusts what the engine is revving at. If the engine is running too rich, which it more than likely is, then adjusting the idle is just going to make the bike idle at a higher rate with that same rich mixture.



To the original poster...first check your air filter. Make sure it's nice and clean. A dirty air filter will cause less air to reach the engine, causing a rich condition. Add that to the bike warming up which is also causing a rich condition and you could have a bike that's running a bit too rich because of a dirty/clogged up air filter.

If that doesn't fix it...then...when was the last time you cleaned your carbs?? And I mean a good cleaning...not just dumping some carb clean shit into your gas tank or spraying some carb clean into your carbs. I mean taking them off, taking them apart, and actually cleaning them really well.

More than likely a new air fliter and a good carb cleaning will fix this issue right up. If it still doesn't, then it's possible that the bike needs to have it's fuel mixture screws adjusted. This is something that's totally different than your idle adjustment screw. I'm not exactly sure where they'd be on your specific carbs, but they are GENERALLY located on the bottom of the carb on the ENGINE side of the bike. They are covered by little plastic caps that need to be drilled out and pulled out in order to get at them. These screws are what change your air/fuel mixture at idle to about 1/4 throttle. They are set from the factory, and I DOUBT that they would be the issue...but if the carb cleaning and the filter don't handle the situation then you may need to adjust them.
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Z
Air filter is good to go, just checked it the other day. I feel like if it was a carb issue, it would happen all the time. This is only when it gets warm.... when its cold it pulls like a raped ape, no issues at all. I would think a carb problem would occur all the time, no?
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Deznuts05
to gimp thanks for point that out +1

simply put get the bike to a shop have the following done:

1. Carb rebuild
2. Sync
3. pay the man
4. ride home happy
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Gimpdiggity
zimdogg said:
Air filter is good to go, just checked it the other day. I feel like if it was a carb issue, it would happen all the time. This is only when it gets warm.... when its cold it pulls like a raped ape, no issues at all. I would think a carb problem would occur all the time, no?
Click to expand...
No, not at all.

A carb problem can manifest itself in different spots of the RPM range and at different times depending on how warmed up the bike is.

If a bike starts fine and starts running bad when it warms up that means it's a bit too rich. If it starts hard and runs fine when it's warm it's too lean.

Trust me, I've been monkeying with the carbs on my bike for a few months now, and just when I think I've got it dialed in it gets colder outside and then I'm running too lean again.

Also, the way a carb works is dependent on throttle position to determine how much gas it's letting into the engine...so you COULD have a bike that's running too rich at idle but runs fine when it's revved up a bit (which is what I gather you're saying is going on).

It's definitely something up with your carbs if your filter is clean. Take them apart and clean them up. Then sync them. You should be good to go.
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B
change the sparjk plugs before you bring it to the shop see if that works. had a very similar problem on my fuel injected bike it would run great cold run like shit when warm
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YAM93
Mine runs fine all winter and then starts to stumble between 5 and 6k as summer comes on.

I can't be 100% positive but I believe it's running a bit lean at that particular RPM range and needs to have the clips (on the needle jets) moved 1 or 2 positions towards richer. Cleaning the carbs on your bike probably wouldn't hurt either. I had a new jet kit installed last winter, carbs cleaned, new fork springs, and all fluids changed and everything was running top notch. Obviously they adjusted it to run perfectly in 32 degree weather. Now it's 80 - 100 degrees and running too lean. I need to take it apart pretty soon. If I'm wrong I'll let you know.

It's possible you need a new jet kit, if it's the original one ... (what happened to mine a couple years ago) the needles / emulsion tubes get worn out after a while. I assume this bike is over 10 years old so, that could very well be the problem. If you've got the money just have them install a new jet kit and clean and inspect the carburetors while they are in there. Make sure they "SYNC" the carbs also, if they don't the whole thing will run out of balance and you'll have a crappy running bike again.
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Z
I was actually just going to bump this...

Some advice I got on another board was to change the cdi first, cause its cheap and not labor intensive at all. So I spent 30 bucks on this thing from ebay, came tonight, put it on and all is well at this point. :)

Thanks for everyones advice and help!
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Gimpdiggity
YAM93 said:
Obviously they adjusted it to run perfectly in 32 degree weather. Now it's 80 - 100 degrees and running too lean. I need to take it apart pretty soon. If I'm wrong I'll let you know.
Click to expand...
Bikes don't run more lean as it gets warmer outside. They run more rich.

If you're going to tear your bike apart to mess with it's settings, make sure you're adjusting the right way.

If it was jetted in 32 degree weather, that means that now your bike is running richer than it was then.

Cold air is more dense than warm air, so that means that as air gets colder more oxygen is entering into the intake system. As it gets warmer less air is making it into the engine.

So if you're going to mess with it, make sure you're messing with it correctly...because right now you're looking at it completely backwards. I highly suggest you do quite a bit of reading on jetting and such before you go about trying to do it...because having something as basic as this backwards is NOT a good way to start going at something like jetting a bike.
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mrmdik23
Gimpdiggity said:
First off, when a bike warms up it tends to run more rich than it does when it's cold. The warmer air being pulled into the intake is made up of molecules that are farther apart...hence the engine is getting less air with the same amount of fuel...which means the engine is getting a richer mixture than when the bike is cold. Second off, adjusting the idle speed doesn't change the air/fuel mixture. It only adjusts what the engine is revving at. If the engine is running too rich, which it more than likely is, then adjusting the idle is just going to make the bike idle at a higher rate with that same rich mixture. To the original poster...first check your air filter. Make sure it's nice and clean. A dirty air filter will cause less air to reach the engine, causing a rich condition. Add that to the bike warming up which is also causing a rich condition and you could have a bike that's running a bit too rich because of a dirty/clogged up air filter. If that doesn't fix it...then...when was the last time you cleaned your carbs?? And I mean a good cleaning...not just dumping some carb clean shit into your gas tank or spraying some carb clean into your carbs. I mean taking them off, taking them apart, and actually cleaning them really well. More than likely a new air fliter and a good carb cleaning will fix this issue right up. If it still doesn't, then it's possible that the bike needs to have it's fuel mixture screws adjusted. This is something that's totally different than your idle adjustment screw. I'm not exactly sure where they'd be on your specific carbs, but they are GENERALLY located on the bottom of the carb on the ENGINE side of the bike. They are covered by little plastic caps that need to be drilled out and pulled out in order to get at them. These screws are what change your air/fuel mixture at idle to about 1/4 throttle. They are set from the factory, and I DOUBT that they would be the issue...but if the carb cleaning and the filter don't handle the situation then you may need to adjust them.
Click to expand...
This actually is the issue. Had the exact same problem, just need to get all 4 carbs adjusted at the fuel/air mixture screw like you said. And sounds like it’s running a little lean. And after I took my air box out and switched too k&n filters and put stage 3 jets in. Had the same problem, got my carbs balanced been mint ever since
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Fazerman007
Good to hear you got it fixed :)
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