Revs creep up

**KezzaCFC** · 15th June 2016, 15:46

Hey,

So when I start riding the bike idles at around 1,500rpm (normal) then after about an hr or so of riding it creeps up to 2,500-3,000rpm?
Any idea's of what might be the cause of this?
Bike is an '08 CBF 250

Cheers

**The End** · 15th June 2016, 16:05

Are you leaving the choke on?

Otherwise:

Bike is cold = low revs

Bike gets warm = revs higher

**KezzaCFC** · 15th June 2016, 16:07

Originally Posted by The End

Are you leaving the choke on?

Otherwise:

Bike is cold = low revs

Bike gets warm = revs higher

Nah, turn it off when its warm enough.
Understood, however 3k is high don't you think when the recommended idle revs is 1400rpm +/- 100rpm?

**The End** · 15th June 2016, 16:09

Originally Posted by KezzaCFC

Nah, turn it off when its warm enough.
Understood, however 3k is high don't you think when the recommended idle revs is 1200rpm +/- 100rpm?

Yes you are correct, 3,000RPM at idle is high.

If the idle is set at 3,000RPM to stop it from stalling when cold then this could be causing it.

Otherwise, carbs could be in need of some attention.

**KezzaCFC** · 15th June 2016, 16:14

Originally Posted by The End

Yes you are correct, 3,000RPM at idle is high.

If the idle is set at 3,000RPM to stop it from stalling when cold then this could be causing it.

Otherwise, carbs could be in need of some attention.

Cheers, will continue to tinker with the idle screw. Failing that, I'll look into the carbs.
Vacuum line seems to pop up when doing a bit of research.
Would valve clearance have an impact?

**BASS-TREBLE** · 15th June 2016, 16:54

Definitely set your idle screw when engine is warm and the choke is off.
Work backwards from there, the choke should be able to raise the cold idle to a high enough level.

When starting cold, how 'much' do you need to put the choke on? Fully engaged or say 50%?

**jellywrestler** · 15th June 2016, 16:59

Originally Posted by The End

Are you leaving the choke on?

Otherwise:

Bike is cold = low revs

Bike gets warm = revs higher

is the choke actually going off? just cause you operate the lever doesn't mean the cables not seized or partly seized

**KezzaCFC** · 15th June 2016, 17:00

Originally Posted by BASS-TREBLE

Definitely set your idle screw when engine is warm and the choke is off.
Work backwards from there, the choke should be able to raise the cold idle to a high enough level.

When starting cold, how 'much' do you need to put the choke on? Fully engaged or say 50%?

Okay, thanks for that. Will give it go once I notice the rev's going up again. I
I usually have the choke fully in which puts the revs up to around 3k, then piss around putting on my gear and that, then disengage and ride away.

**KezzaCFC** · 15th June 2016, 17:02

Originally Posted by jellywrestler

is the choke actually going off? just cause you operate the lever doesn't mean the cables not seized or partly seized

That did run through my head, however once the choke is disengaged the rev's drop to around 1500. I'd imagine if the cables seized then rev's would stick at 'choke level' rather than dropping down