Cold starting CBF250

**sleeqe2000** · 6th June 2008, 20:28

Had my CBF250 for 3 days now - enjoying the bike but having a few problems when cold starting .

I guess I want to know from anyone with a CBF how long they keep the choke open before they close it back to minimum. I'm finding that I'm stalling the bike alot when I first take it out and its probably mainly down to my in-experience with the clutch/gears. I do get alot better once the bike has warmed up.

So do I keep the choke open for say 5 mins then gradually close it off. Or do I keep it open in terms of km's covered and then close it off. Complete newb here so any advice would be appreciated.

cheers

Lee

**klyong82** · 6th June 2008, 23:01

You could start the engine with the choke on then wear your gears. By the time you are finished the bike should be good enough to run without the choke. Turn the choke off and ride away. Go easy on the throttle by not riding anymore than 6000rpm. Never ride away with the choke on....you are just flooding it....

**xwhatsit** · 7th June 2008, 00:36

Originally Posted by sleeqe2000

So do I keep the choke open for say 5 mins then gradually close it off. Or do I keep it open in terms of km's covered and then close it off. Complete newb here so any advice would be appreciated.

cheers

Lee

Sounds like what you're doing, is starting it (using choke as necessary when cold), then getting on it straight away and riding it. It's not considered very good form to ride the bike with the choke on, and you should be warming it up before riding it (especially on a 250 where you have to give it beans to make it go anywhere).

So, as klyong said, start the bike, and leave it idling and warming up while you put your gear on. As soon as the bike will idle without choke, take the choke off. If it won't idle without choke yet, then it's not warm enough to ride yet. Definitely don't ride the bike when it's cold

I see guys on scooters all the time, jump on, hit the starter, push it off the stand and wind the throttle open all the way. Might explain why even the four-strokes pour clouds of oily smoke out the exhaust!

**sleeqe2000** · 7th June 2008, 06:57

thanks for the advice. Completely didn't know you shouldn't ride the bike with the choke open. No wonder I am having so many problems when getting on the bike to begin with.

**CB ARGH** · 7th June 2008, 08:33

Originally Posted by sleeqe2000

thanks for the advice. Completely didn't know you shouldn't ride the bike with the choke open. No wonder I am having so many problems when getting on the bike to begin with.

My mate used to ride his old farm bike with the choke on full all of the time, and wondered why there was shit performance.

Generally you start the bike on full choke, then give it just enough revvs to stop the bike from vibrating heaps (so it goes from an old man's shaking leg to a steady rev, NOT TOO MUCH - REVVING AT A COLD TEMP IS BAD!), after about ten seconds put it onto half. Then after perhaps a min or two throw it onto fully open.

Only start riding once it's uncomfortable to put your hand directly on the top of the engine right by the sparkie. This will also improve the bike's life, I have been told, as it gives the thing time to warm up. Then you can revv the shit out of it as you wish.

That's how I did it on my dirt bike, I'm sure that it's pretty generic.

EDIT: WTF? Riding it with full choke? That's not good! (to above posts).

**Trouser** · 9th June 2008, 21:42

Originally Posted by sleeqe2000

thanks for the advice. Completely didn't know you shouldn't ride the bike with the choke open. No wonder I am having so many problems when getting on the bike to begin with.

Knowing the bike and the cold idling problems they have, may I suggest removing the airbox snorkels? Made a large difference on mine.

I would normally leave it on fast idle (4000rpm) for around a minute as I got earplugs, helmet and gloves on. Then I would still have to ride about 1-2 km before closing the choke(enrichener) to prevent it snatching.

After removing the snorkels I can thumb the starter and it will idle at around 1100rpm when cold without choke. On the frosty mornings though it still needs a little choke to prevent stalling.

My bike has around 3500ks and the hot idle is set at 1500rpm

**Freshh2o** · 17th June 2008, 08:10

My CBF is barely 5 months old, and ever since I bought it I had a wee problem in windy conditions, with the engine faltering as if it was not getting enough air. The service manager suggested a tweak on the carbs, but warned me that economy would suffer. Then last week in the big storm, it almost stalled in a gust of wind. I mean the engine almost cut out. I decided that with the wind from a certain direction, negative pressure was being created at the intake.and the engine was not getting the air it needed. To test my theory, I removed the snorkels, and sure enough the problem went away. Not only that, but the bike was much more responsive to the throttle. But it was noisier, like a Harley wannabe. Looking at the configuration under the seat, I saw that the intakes are very close to the curved wheel arch, and I suspected that if air blows hard through the vents then a venturi effect may create negative pressure across the intakes of the snorkels. So I cut holes in the bottom of each, and put them back. Result: No more hesitation in the wind, and a better performing bike.

Cheers

Alan

**francesco3** · 5th February 2009, 06:33

Hi Alan, could I ask you for a photo or two of the customization you did to the intake? I wonder what does it lok like. Thanks.

**vifferman** · 5th February 2009, 12:29

Man, there's some misinformation here - surprisingly some from people who should know better!

Firstly, how much choke your bike needs is specific to your bike, how cold the weather is, etc etc. After a while, you will get a feel for this, and should be able to distinguish between the bike needing more or less choke.
Secondly, never give a bike heaps of throttle when it's cold - this will more'n likely cause it to complain, whether it's carbed or fuel-injected.

As for the warming up thing - there is much evidence that the best way to warm up a vehicle (apart from perhaps race vehicles with very fine tolerances) is minimal warming up at idle, and to warm it up on the road. The reason for this is twofold: firstly, it ensures the revs are rising and falling, which helps oil circulation, and secondly it ensures the oil circulates around ALL the engine parts, including the gearbox. [Note: if you watch race machines being warmed up, they DON'T leave them idling, but rev them gently, alowing the revs to rise and fall, and gradually increasing the revs]
Think about it: if you're warming it up, stationary, with the bike on the sidestand and canted slightly over, not only are few of the whirly things in the engine turning, but there are parts of the engine that are not subjected to even oil coverage. In the head, f'rinstance, the oil could well be all at one end of the camshaft. Also, at idle revs, the oil pump pressure is lower.

After researching this thoroughly, I came up with this. What I do is walk out to the gargre with all my gear bar gloves and helmet on, start the bike (on its centrestand), feed the fish, put my helmet and gloves on, and ride off. (At work, there are no fish to feed, so I skip that bit). When the temperature is up to 65C, the thermostat is open, and the automatic choke is closed, so the bike is fully warmed up. Before that point, I keep the revs below about 4-5k rpm.

When I last had a carbed bike, I used to start it on full choke when cold, sitting on it so it was upright (no centrestand), then as soon as the engine note started to change, whip the choke in again. I could tell when the thermostat opened because the needle started to move up the gauge. It was a matter of feel how much throttle to give it.
Previous carbed bikes were a little different - two were watercooled and had handlebar-mounted chokes, which I used to gradually adjust while riding the first km or so. (The engine will pretty quickly let you know if it needs more or less choke).

On aircooled bikes, they generally heat up faster (no water jacket), so once it's running evenly without choke (which is hardly any time at all), you can gradually increase revs. Sometimes it's a matter of warming them up until they didn't need choke, before moving off, because the choke was in an awkward position. On the VTR, the choke wasn't really easy to reach while riding.

I've read SO many times owners saying proudly how they babied their engines and always let them idle on the stand till they were warmed up, before riding off. PLEASE don't do this: ride off as soon as you can, and adjust choke/throttle/revs/speed to what the bike needs. Learn to be responsive to what the engine's telling you.

**vifferman** · 5th February 2009, 12:35

Originally Posted by Freshh2o

Looking at the configuration under the seat, I saw that the intakes are very close to the curved wheel arch, and I suspected that if air blows hard through the vents then a venturi effect may create negative pressure across the intakes of the snorkels. So I cut holes in the bottom of each, and put them back. Result: No more hesitation in the wind, and a better performing bike.

Interesting.
I suspected I had a similar situation on my VF500, whose snorkel was behind the steering head, facing backwards. So, I reasoned that in strong headwinds, the intake may have been fighting negative pressure. Turning it around did a couple of things: made it sound louder, and also meant that it was no longer sucking relatively still air from above the engine. One day I rode over the Kaimai ranges in winter, and the bike was running very badly. I worked out it was carburetor icing: the dampish cold air was depositing ice on the carb intakes. Turned the snorkel back around and the problem never recurred.

**xwhatsit** · 5th February 2009, 12:53

Originally Posted by vifferman

As for the warming up thing - there is much evidence that the best way to warm up a vehicle (apart from perhaps race vehicles with very fine tolerances) is minimal warming up at idle, and to warm it up on the road.

Firstly, CBF250s have centre-stands. I'm sure their owners are sensible enough to use them.

Secondly, warming up while riding the bike may or may not be better than warming it up at idle for a couple of minutes (still yet to see any proper evidence either way), but warming up while riding carries the risk of the rider thrashing the poor little 250 single while still cold, which is surely no good for it. It may be easy to idle away on a big 800 four without pulling any revs or barely cracking the throttle, but it's quite a different story on a small gutless single, especially with a new rider. Maybe the oil does circulate slower at lower revs due to the oil pump producing less pressure, but the whirly bits are whirling around much slower because no tit is grabbing handfuls of throttle, so it's much of a muchness. Much safer to do it on the centre stand.

Lastly, it's all in your head about going faster with the snorkle off. Just the extra noise and less smooth power delivery (there's a flatspot in mid-range now) making you think so.

**rphenix** · 5th February 2009, 13:15

Originally Posted by sleeqe2000

thanks for the advice. Completely didn't know you shouldn't ride the bike with the choke open. No wonder I am having so many problems when getting on the bike to begin with.

Well I've mainly ridden Trail/Farm bikes and only had a few road bikes however its never done any harm that I know riding off without waiting for the machine to warm up

but then maybe I'm just lucky?

If its a cold morning I put the choke on full, give a good twist of throttle and hit the start switch once its started I then back the choke right off till just above that "shuddering" feel you get when the engine is going to stall. Drive down the driveway. You may find you need to adjust the choke up or down after coming to a stop at intersections etc.. but within a few minutes you can quickly take the choke completely off. Easy way to tell if the choke should come off is to pull the clutch in, let the engine idle, if its idling high then you need to reduce the choke and you can do that while coasting.

I do agree with everyone about taking it easy on the bike till its warmed up.

**Rodney007** · 5th February 2009, 13:33

clean your carb if you having issues, and make sure its a choke not a fast idle

**vifferman** · 5th February 2009, 14:05

Originally Posted by xwhatsit

... warming up while riding carries the risk of the rider thrashing the poor little 250 single while still cold, which is surely no good for it.

Yeah, there is that. One would hope (wouldn't one?) that the thrashing could wait until the poor victim had thoroughly warmed up, but... human nature and all that...

The 'warming up' thing comes up regularly on every bike forum, and it was posited that 'excessive' warming up on the sidestand was one of the possible contributing causes of CCT failure on VTR1000s.
I've gone with the "warm it while riding" camp, as it appealed from a logical point of view, especially after reading several mechanic's points of view.

Originally Posted by xwhatsit

Lastly, it's all in your head about going faster with the snorkle off. Just the extra noise and less smooth power delivery (there's a flatspot in mid-range now) making you think so.

Agreed.

I think you could say that about most popular mods for alleged Free! and Easy! power: snorkel removal, noisier mufflers, removal of PAIR valves, etc.

With the VFR, the ONLY mod that has made a difference was disabling the O2 sensors and fitting a Power Commander. Some of the maps I tried did just what you said: gave the illusion of power via a new flatspot.
Disabling the PAIR valves can't have helped, as it lowered the idle speed heaps and introduced a little lag at some revs; removing the snorkel did nothing except made the noise worse AND introduced some hesitation; disabling the flapper valve in the airbox made it noisier and slightly slower below 5k rpm.

The O2 sensor thing was different: it removed a factory-installed ultra-lean condition, and potentially dangerous hesitation when the EFI switched from 'closed loop' mode to 'mapped mode'.

On other bikes that I've owned, NOTHING gave easy performance increases (to a well-tuned and maintained bike). The most interesting was the Firestorm - on the forums, the only (significant) power increases came from expensive cam, head and piston mods, and even those were only single-digit improvements for 4-digit expenditure.

oops....

[/rant]