header turnig red all of a sudden????
Senior Member
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Joined: Mar 2010
Posts: 740
From: South Puget Sound, WA
That's dumb. Gasoline FI cars and trucks don't need to be warmed up. They don't stumble and buck.
If you think you optimized your jetting but then have to let the bike warm up for a minute before you can ride then you don't know how to jet a carb. Start over.
A properly tuned KLX250 with air injection will create a glowing head pipe if let run with the choke on for too long. The extra fuel that is being dumped into the engine is being sent into the headpipe where the air injection allows it to burn creating immense heat. I would also not be too alarmed to see a faint glow after a hard run in the dark. This is not a cast iron exhaust manifold, but a very thin SS pipe with fire inside.
I suspect that removal of the smog stuff will reduce the glowing in all conditions.
If you think you optimized your jetting but then have to let the bike warm up for a minute before you can ride then you don't know how to jet a carb. Start over.
A properly tuned KLX250 with air injection will create a glowing head pipe if let run with the choke on for too long. The extra fuel that is being dumped into the engine is being sent into the headpipe where the air injection allows it to burn creating immense heat. I would also not be too alarmed to see a faint glow after a hard run in the dark. This is not a cast iron exhaust manifold, but a very thin SS pipe with fire inside.
I suspect that removal of the smog stuff will reduce the glowing in all conditions.
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Joined: Jul 2010
Posts: 1,414
From: Missouri
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If you think you optimized your jetting but then have to let the bike warm up for a minute before you can ride then you don't know how to jet a carb. Start over..
I highly doubt that 45-60 seconds of idle time is going to hurt anything. Most people spend more time than that idling at a stop light.
If you can ride away with no choke immediately after starting a cold engine sounds like your pilot circuit is wicked rich.
I think theres some mis-understanding of how people are performing intial startup on my part.
Last edited by wildcard; Aug 15, 2012 at 01:15 AM.
Senior Member
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Joined: Mar 2011
Posts: 695
The simple fact is that a cold engine means cold gas, which vaporizes less quickly than warm fuel, and therefore burns less thoroughly, resulting in the classic symptoms of rough *idle and hesitancy to start. The antidote for this is to create more vapor by dumping more fuel into the cylinders when cold. Both carbureted and fuel injected systems have mechanisms to achieve this enrichment temporarily while the engine warms. *The unvaporized excess fuel in a cold engine enters the header where it then burns and voila, red glowing header pipe with the choke on!
There is no such thing as a fuel mixture whereby the same fuel/air ratio will be optimum for both hot AND cold running conditions. *A cold engine will ALWAYS run rough when being fed a lean mixture suitable for a hot engine. Therefore I don't think it's right that anyone should be concerned that their carb isn't jetted correctly simply because the engine runs rough when cold with the choke off.
As for the question of warming an engine by idling it vs riding it, it's been shown that riding is a more efficient means of getting the engine up to operating temp. Other than that I'd suggest it's up to rider preference to do whatever makes them feel better.
There is no such thing as a fuel mixture whereby the same fuel/air ratio will be optimum for both hot AND cold running conditions. *A cold engine will ALWAYS run rough when being fed a lean mixture suitable for a hot engine. Therefore I don't think it's right that anyone should be concerned that their carb isn't jetted correctly simply because the engine runs rough when cold with the choke off.
As for the question of warming an engine by idling it vs riding it, it's been shown that riding is a more efficient means of getting the engine up to operating temp. Other than that I'd suggest it's up to rider preference to do whatever makes them feel better.
Senior Member
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Joined: Mar 2010
Posts: 148
From: Duvall, WA
The simple fact is that a cold engine means cold gas, which vaporizes less quickly than warm fuel, and therefore burns less thoroughly, resulting in the classic symptoms of rough *idle and hesitancy to start. The antidote for this is to create more vapor by dumping more fuel into the cylinders when cold. Both carbureted and fuel injected systems have mechanisms to achieve this enrichment temporarily while the engine warms. *The unvaporized excess fuel in a cold engine enters the header where it then burns and voila, red glowing header pipe with the choke on!
There is no such thing as a fuel mixture whereby the same fuel/air ratio will be optimum for both hot AND cold running conditions. *A cold engine will ALWAYS run rough when being fed a lean mixture suitable for a hot engine. Therefore I don't think it's right that anyone should be concerned that their carb isn't jetted correctly simply because the engine runs rough when cold with the choke off.
As for the question of warming an engine by idling it vs riding it, it's been shown that riding is a more efficient means of getting the engine up to operating temp. Other than that I'd suggest it's up to rider preference to do whatever makes them feel better.
There is no such thing as a fuel mixture whereby the same fuel/air ratio will be optimum for both hot AND cold running conditions. *A cold engine will ALWAYS run rough when being fed a lean mixture suitable for a hot engine. Therefore I don't think it's right that anyone should be concerned that their carb isn't jetted correctly simply because the engine runs rough when cold with the choke off.
As for the question of warming an engine by idling it vs riding it, it's been shown that riding is a more efficient means of getting the engine up to operating temp. Other than that I'd suggest it's up to rider preference to do whatever makes them feel better.
I wonder how many of you "I don't need the choke" guys have a heated garage or live in warmer climes...
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Joined: Jan 2012
Posts: 1,405
From: Sacramento, CA
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That's me! Even during our Norcal winters it's never "that cold" in the garage. If anything I have to pull the choke until running then I can push it in and let it warm up at idle for a few minutes. I've tried riding after a minute of warming up and feel the bike lurching. So I prefer to give it a few minutes to warm up first.
Senior Member
1st Gear Member
Joined: Mar 2010
Posts: 740
From: South Puget Sound, WA
The simple fact is that a cold engine means cold gas, which vaporizes less quickly than warm fuel, and therefore burns less thoroughly, resulting in the classic symptoms of rough *idle and hesitancy to start. The antidote for this is to create more vapor by dumping more fuel into the cylinders when cold. Both carbureted and fuel injected systems have mechanisms to achieve this enrichment temporarily while the engine warms. *The unvaporized excess fuel in a cold engine enters the header where it then burns and voila, red glowing header pipe with the choke on!
There is no such thing as a fuel mixture whereby the same fuel/air ratio will be optimum for both hot AND cold running conditions. *A cold engine will ALWAYS run rough when being fed a lean mixture suitable for a hot engine. Therefore I don't think it's right that anyone should be concerned that their carb isn't jetted correctly simply because the engine runs rough when cold with the choke off.
As for the question of warming an engine by idling it vs riding it, it's been shown that riding is a more efficient means of getting the engine up to operating temp. Other than that I'd suggest it's up to rider preference to do whatever makes them feel better.
There is no such thing as a fuel mixture whereby the same fuel/air ratio will be optimum for both hot AND cold running conditions. *A cold engine will ALWAYS run rough when being fed a lean mixture suitable for a hot engine. Therefore I don't think it's right that anyone should be concerned that their carb isn't jetted correctly simply because the engine runs rough when cold with the choke off.
As for the question of warming an engine by idling it vs riding it, it's been shown that riding is a more efficient means of getting the engine up to operating temp. Other than that I'd suggest it's up to rider preference to do whatever makes them feel better.
I need a choke to start the bike and then for maybe 5 seconds. After that it should idle without stalling and the choke off. At that point I can't, and shouldn't, whick the throttle open without stalling until a bit more heat is in the engine but I can certainly ride off within 30 seconds of cold start.
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Joined: Apr 2011
Posts: 249
From: Ellensburg,WA
not mei mean the summers here her 100+ but i can start it pretty much the same if not better in -40 but i have the pumper and a way modded motor i geive it 2 pulls on the throttle then hit the button and its off to the racesand i just orderd a crf250r carb for putting hot start on the bike to make it easyer in the summer and after a stal in the slow stuff
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Joined: Apr 2006
Posts: 910
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not mei mean the summers here her 100+ but i can start it pretty much the same if not better in -40 but i have the pumper and a way modded motor i geive it 2 pulls on the throttle then hit the button and its off to the racesand i just orderd a crf250r carb for putting hot start on the bike to make it easyer in the summer and after a stal in the slow stuff
Senior Member
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Joined: Mar 2010
Posts: 740
From: South Puget Sound, WA
I timed it today. 53 degrees F ambient, stored outside overnight. Choke on and start, run 5 seconds full choke, then choke off, idle 5 seconds and take off for my commute.
With the loud FMF exhaust, I can't be sitting at work or anywhere else in a parking lot trying to rev or nurse a poorly jetted engine up to a temperature at which it will run right.
A minute is a long long time to sit there at idle waiting for things to run properly.
With the loud FMF exhaust, I can't be sitting at work or anywhere else in a parking lot trying to rev or nurse a poorly jetted engine up to a temperature at which it will run right.
A minute is a long long time to sit there at idle waiting for things to run properly.
Thread Starter
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Junior Member
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Joined: Apr 2012
Posts: 21
That's dumb. Gasoline FI cars and trucks don't need to be warmed up. They don't stumble and buck.
If you think you optimized your jetting but then have to let the bike warm up for a minute before you can ride then you don't know how to jet a carb. Start over.
A properly tuned KLX250 with air injection will create a glowing head pipe if let run with the choke on for too long. The extra fuel that is being dumped into the engine is being sent into the headpipe where the air injection allows it to burn creating immense heat. I would also not be too alarmed to see a faint glow after a hard run in the dark. This is not a cast iron exhaust manifold, but a very thin SS pipe with fire inside.
I suspect that removal of the smog stuff will reduce the glowing in all conditions.
If you think you optimized your jetting but then have to let the bike warm up for a minute before you can ride then you don't know how to jet a carb. Start over.
A properly tuned KLX250 with air injection will create a glowing head pipe if let run with the choke on for too long. The extra fuel that is being dumped into the engine is being sent into the headpipe where the air injection allows it to burn creating immense heat. I would also not be too alarmed to see a faint glow after a hard run in the dark. This is not a cast iron exhaust manifold, but a very thin SS pipe with fire inside.
I suspect that removal of the smog stuff will reduce the glowing in all conditions.
i just cant figure out what went wrong, the bike was running fine. i let it sit for 3 weeks and now its a fkng dog!
