Topic: Engine Pulls Hard up to 5.5k RPM Then Not So Much

[MRieck]

About idle rpm.
I prefer 1200-1300rpm, adjusted when hot after at least 30min ride.  Stock as well as modified engine.
Much easier to ride. Take offs and less abrupt throttle off.
Higher compression is trickier for smooth take off at too low rpm.

Easier to keep it idling when cold too.

I can set idle on my K6 970ccc + 125-75 cam to 1000rpm. It will be a pig at take offs due to the compression and too responsive flat slide carbs.

Oil flow a good reason for higher idle.
Check when engine is really hot a very warm day. Risk that oil warning lamp will flicker if idle is low.

I agree with you Per.

[Oddjob]

Not advocating a 600rpm idle, just saying it's an indication of a well set up engine IF it can idle at that speed without undue noise.

As for oil pressure, not a great deal of difference between 1000 and 1200rpm in PSI, if Honda were concerned about oil pressure they'd have either fitted a higher rated pump or upped the idle speed but the 500 has a recommended tickover as stated in the WM of 1000. Same went for most of the engines of that era and still today it's around 1000rpm. Must be a reason for that.

Whilst I can see the sense in a higher tickover for a highly modified engine, to me it doesn't sound right at 12-1300, sounds way to fast. Never really had a problem with takeoff, you should be able to slip the clutch under an engine ticking over even at 1000rpm and still achieve a smooth takeoff. Admittedly an engine with much higher compression would be a problem doing that. 

[Finnigan]

Just tried to see what was possible since this is fresh in my mind, retarding the timing to just before knock gets me in the 6-700 range

[MRieck]

 The CR-29 or 31's can screw up idle as they produce a poor signal at idle. At a stop light RPM's will drop....and drop.......and drop until they stop. It sucked so bad I fitted a remote adjuster modified from a first year ZX-10. Had it attached to clip on the left side air box mounting tab (airbox obviously removed). It was very easy to get to sitting there.
The RS carbs don't share that fault....neither do FCR's which will idle all day at 1,100 or 1,200.

[willbird]

The CR-29 or 31's can screw up idle as they produce a poor signal at idle. At a stop light RPM's will drop....and drop.......and drop until they stop. It sucked so bad I fitted a remote adjuster modified from a first year ZX-10. Had it attached to clip on the left side air box mounting tab (airbox obviously removed). It was very easy to get to sitting there.
The RS carbs don't share that fault....neither do FCR's which will idle all day at 1,100 or 1,200.

And here I was thinking that a rack of CR29 would be just the thing to have to make a CB750K run really nice :-(

[MRieck]

The CR-29 or 31's can screw up idle as they produce a poor signal at idle. At a stop light RPM's will drop....and drop.......and drop until they stop. It sucked so bad I fitted a remote adjuster modified from a first year ZX-10. Had it attached to clip on the left side air box mounting tab (airbox obviously removed). It was very easy to get to sitting there.
The RS carbs don't share that fault....neither do FCR's which will idle all day at 1,100 or 1,200.

And here I was thinking that a rack of CR29 would be just the thing to have to make a CB750K run really nice :-(

Don't get me started on the cold start circuit.

[willbird]

The CR-29 or 31's can screw up idle as they produce a poor signal at idle. At a stop light RPM's will drop....and drop.......and drop until they stop. It sucked so bad I fitted a remote adjuster modified from a first year ZX-10. Had it attached to clip on the left side air box mounting tab (airbox obviously removed). It was very easy to get to sitting there.
The RS carbs don't share that fault....neither do FCR's which will idle all day at 1,100 or 1,200.

And here I was thinking that a rack of CR29 would be just the thing to have to make a CB750K run really nice :-(

Don't get me started on the cold start circuit.

A family friend rented space from my dad in a building and ran a Harley Davidson centered motorcycle repair shop. Some of those bikes ran a carburator that did not have a choke they had some kind of "enrichener" ?? yea nobody could start those bikes LOL.

[Old Scrambler]

I have a Triumph that needs to be 'tickled' on a cold start.

[HondaMan]

The CR-29 or 31's can screw up idle as they produce a poor signal at idle. At a stop light RPM's will drop....and drop.......and drop until they stop. It sucked so bad I fitted a remote adjuster modified from a first year ZX-10. Had it attached to clip on the left side air box mounting tab (airbox obviously removed). It was very easy to get to sitting there.
The RS carbs don't share that fault....neither do FCR's which will idle all day at 1,100 or 1,200.

And here I was thinking that a rack of CR29 would be just the thing to have to make a CB750K run really nice :-(

They do!
...somewhere above 4000 RPM...

[PeWe]

The CR-29 or 31's can screw up idle as they produce a poor signal at idle. At a stop light RPM's will drop....and drop.......and drop until they stop. It sucked so bad I fitted a remote adjuster modified from a first year ZX-10. Had it attached to clip on the left side air box mounting tab (airbox obviously removed). It was very easy to get to sitting there.
The RS carbs don't share that fault....neither do FCR's which will idle all day at 1,100 or 1,200.

The Mikuni TMR32 has a stable idle too.
Adjusting it is irritating. Need a thin screwdriver and slim hand to adjust it just behind  the cable bracket between 2-3.

I rode the bike last year with stable 1000rpm idle until I adjusted it up for easier take offs and less aggressive throttle offs in slow speed.
- Flat slides have more distinct throttle off in general?

I have got a scary moment when I decided to pass 5-6 cars driving close on a curvy road.
I had to accelerate  to pass them all in time. But 160-170kmh was not that good there. (Signs showing max 70-80 kmh)

Bumps made me to reduce throttle too much with a low frequency rear wobble as the result, forced me to give more.
Meeting cars on that narrow road  turning to the right limited the time.
After I passed the last car, a sharp turn in front of it followed by a left turn to not land outside the road.
Direct after, a sharp turn to the right and uphill followed by going down so I had to be careful to not get my front wheel to lift when giving the throttle out of the corner.
 Extra much to handle eventual scary feelings...

Reduce throttle is dangerous!!

[Tracksnblades1]

The CR-29 or 31's can screw up idle as they produce a poor signal at idle. At a stop light RPM's will drop....and drop.......and drop until they stop. It sucked so bad I fitted a remote adjuster modified from a first year ZX-10. Had it attached to clip on the left side air box mounting tab (airbox obviously removed). It was very easy to get to sitting there.
The RS carbs don't share that fault....neither do FCR's which will idle all day at 1,100 or 1,200.

The Mikuni TMR32 has a stable idle too.
Adjusting it is irritating. Need a thin screwdriver and slim hand to adjust it just behind  the cable bracket between 2-3.

I rode the bike last year with stable 1000rpm idle until I adjusted it up for easier take offs and less aggressive throttle offs in slow speed.
- Flat slides have more distinct throttle off in general?

I have got a scary moment when I decided to pass 5-6 cars driving close on a curvy road.
I had to accelerate  to pass them all in time. But 160-170kmh was not that good there. (Signs showing max 70-80 kmh)

Bumps made me to reduce throttle too much with a low frequency rear wobble as the result, forced me to give more.
Meeting cars on that narrow road  turning to the right limited the time.
After I passed the last car, a sharp turn in front of it followed by a left turn to not land outside the road.
Direct after, a sharp turn to the right and uphill followed by going down so I had to be careful to not get my front wheel to lift when giving the throttle out of the corner.
 Extra much to handle eventual scary feelings...

Reduce throttle is dangerous!!

What Pipe(s) on the right hand curve..?

Old RC sidewinders were deadly over here on fast tight right handers…Foot pegs would drag before the Yoshimuras. They were tucked up high and tight but you lost your center stand..😡

[Finnigan]

I took the bike on a 100+ all day lazy commute past beaches and cafes, stopping for burgers and beer with friends and riding 2-up for about 40 miles of the journey.

The bike did amazing, far better and more reliable than I thought was possible with these old bikes.

I'm starting to get picky on minor issues now that I think are OK but could be better.  I'm focused now on my jetting, the bike RPM stumbles a little from a stop until it gets to about 2k and I'm wondering if this is normal for these motors or should I try leaning out the jets again.

If so, start with the idle jet or raise the needle or live with it as is?

[Old Scrambler]

If slow-jets are 40s..........go up one size and then if needed, adjust the needles.

If slow-jets are more than 40.......try a half-step smaller on the mains. I like to get rid of the transition burble before messing with the needles.