Topic: Idle speed changes

[beemerbum]

After startup and warm up, My K2 750 idles at 1100 rpm. After I ride a while, the idle creeps up to 2000+ rpm. Any thoughts on why this may be happening?

[dave500]

i always set and tune any engine when its fully hot and been ridden/driven,how it behaves when cold so be it,its funny to watch people try and start say a weed wacker expecting it to start on idle,anyone whos ever only had fuel injected cars and what not hasnt a clue for the feel of choke and holding a fast idle by hand.

[Kenzo1979]

After startup and warm up, My K2 750 idles at 1100 rpm. After I ride a while, the idle creeps up to 2000+ rpm. Any thoughts on why this may be happening?

Yeah, what you’re describing is completely normal.  As long as it eventually steadies and doesn’t constantly fluctuate, you’re good.  My usual procedure is to cold start the bike up with the choke on and give it a little throttle.  As the engine warms and the RPMs rise, I slowly roll the choke off, then I increase my idle screw and get on the road. First couple minutes of riding, the idle will increase even more. As soon as I hit my first couple lights or stop signs,  I reach down and back the idle speed screw off and even out the idle.  When the bike is fully hot, it will stay at the set idle.  I only do it that way because the idle speed screw is so easy to  on these bikes. My buddy had a GS550E and the idle speed screw was not so easy to get at, especially if you were on the bike.

[pjandrew99]

After startup and warm up, My K2 750 idles at 1100 rpm. After I ride a while, the idle creeps up to 2000+ rpm. Any thoughts on why this may be happening?

Yeah, what you’re describing is completely normal.  As long as it eventually steadies and doesn’t constantly fluctuate, you’re good.  My usual procedure is to cold start the bike up with the choke on and give it a little throttle.  As the engine warms and the RPMs rise, I slowly roll the choke off, then I increase my idle screw and get on the road. First couple minutes of riding, the idle will increase even more. As soon as I hit my first couple lights or stop signs,  I reach down and back the idle speed screw off and even out the idle.  When the bike is fully hot, it will stay at the set idle.  I only do it that way because the idle speed screw is so easy to  on these bikes. My buddy had a GS550E and the idle speed screw was not so easy to get at, especially if you were on the bike.

+1
I thought I had a vacuum leak or carb issues. Cleaned and adjusted carbs a few times. Rebuilt the carbs and changed boots, clamps etc etc.
Nothing corrected the warm/high idle issue.
I finally succumbed to the problem and just turn the idle down when it gets warm.  Not sure how to actually correct the issue if it is correctable. Would be interested to hear if someone corrected it.  However as mentioned, no big deal to turn the idle down on these bikes.

[Kenzo1979]

+1
I thought I had a vacuum leak or carb issues. Cleaned and adjusted carbs a few times. Rebuilt the carbs and changed boots, clamps etc etc.
Nothing corrected the warm/high idle issue.
I finally succumbed to the problem and just turn the idle down when it gets warm.  Not sure how to actually correct the issue if it is correctable. Would be interested to hear if someone corrected it.  However as mentioned, no big deal to turn the idle down on these bikes.

Nothing to correct.  If it makes you feel better, keep your idle screw set and just let the bike get up to full temp, not just warmed up, before you ride and you won’t have to adjust into the ride.  It’s just the difference between idle at warm and idle at hot. 

[ekpent]

My early K 750's have a fast idle built in,its called my right wrist. Very primitive choke system on the round top carbs.

[BomberMann650]

My early K 750's have a fast idle built in,its called my right wrist. Very primitive choke system on the round top carbs.

Not to mention the accelerator pump found on top of the seat

[TwoTired]

Cold engines don't atomize fuel well.  So it needs extra as they are more inefficient than hot ones.  If you tune for cold operation, it won't run well at hot operation, most likely too rich and foul spark plugs.
Modern automotive vehicles have an electronic computer and numerous sensors to determine the proper fuel ratios for the engine to run well.  Back in the 70's the computer and sensors for Honda's was located 2-3 feet above the seat.

Cheers,

[BenelliSEI]

+1 to everyone. Both my regular rides (K1 and K3) do the same. That’s why they have such a big, knurled knob on the idle screw. I turn it up a bit when cold, and wind it down throughout my ride.

[PeWe]

1200 rpm idle when fully warmed up works fine.

Easier to ride with not that abrupt braking at throttle off, easier take offs, less rattle  and working idle when not fully warm.

Some carbs choke has an increased idle function.

My Mikuni TMR has on-off choke. Idle begins at ~2000 rpm, soon at 3000rpm. Probably a quick warm-up for race bikes.

I think VM29 Smoothbore also have increased idle  with choke.