Ninja EX500 carbs on an XS650?

[Jan_P]

The only horror story with carburetors I am afraid of --- Is getting to lean
Since I know of one motorcyclist trying to get one XS650 to run properly and eventually got a hole in the Piston
Here ... No stock Exhaust ---No stock Intake --No Stock Ignition -- No gasoline as machine was designed for
And on top of that No stock carburetor designed for a smaller 8 valve engine revving close to 10 000 rpm
The motorcyclist I know took far lesser risks was experienced working on a stock carburetor
and still got an overheating

So please check the spark plugs not getting to lean

 

[Adamc]

Thanks arctic! Well the downside is that it's never done haha. Sometimes feels like it's leaning towards an obsession. Good idea about plugging these holes! It always seems to be oily around there anyway.

One downside of my pipes is it's hard to reach the left carb. Like switching a jet I always need to take the pipes of. Still like the looks but not always practical...

Yeah just like me. I love my pipes but have to drop them to do an oil change!

 

[Bjorn]

Nice bike Adam!

 

[arcticXS]

Just fitted the narrower clamps from my K&N's and sanded the flanges, seems to hold better.

Bjørn, I still think that a velocity stack/ filter adapter is a better solution. This because any dimensjon changes will cause turbulence that may upset the carburation. Or at least a "filler ring" with the same OD and ID as the carbs, to take up the void space in the filter neck.

 

[Bjorn]

If I make a velocity stack out of metal, I always wonder about how to fix it to the carb. I guess you would need another hose-like adapter. Did you run stacks? And if so how did you attach them?

 

[Signal]

Mikuni velocity stacks are thin walled and are secured using a hose clip What I have done a couple of times to give more clamping area for foam pod filters is make a flange extender that is a shrink fit over the carb body but longer to match the flange on the filter. The same should work for velocity stacks.
With regard to filtering, on an 850 triple project I have velocity stacks and Ram Air filter socks to use.

 

[arcticXS]

If I make a velocity stack out of metal, I always wonder about how to fix it to the carb. I guess you would need another hose-like adapter. Did you run stacks? And if so how did you attach them?

If made out of aluminium, and fairly thin wall thickness (i.e. 1 mm or so), 4 or 6 slits is enough to make a hose clamp work. Mikuni velocity stacks have 4 slits, but are very thin. They are like these at the carb end: https://www.caferacerwebshop.com/en/35mm-velocity-stacks-aluminium.html
(By the way, the other end of those in the link are very poorly designed)
With thicker wall, a light shrink fit or maybe grub screws can also work. If you use some kind of plastic material, like POM, a hose clamp should work for thicker wall as well.

 

[Adamc]

Nice bike Adam!

Thank you.

 

[Bjorn]

Did some tests with a 1 size bigger pilot jet, went from 38 to 40. After warming up I settled on 3 turns on the mix screws. Giving me the highest idle and the fastest return to idle when I blip the throttle.

The idle seems relatively stable at around 1200. The dip in rpm when driving away from a complete standstill where not really noticeable after everything warmed up.

Did some high speed runs to test the main size, no issues so I'll stick with it for now at 138. However I did notice that after these high speed runs, coming to a standstill, the idle would be lower! Around 900-1000. Letting the bike idle for a minute brought it back to 1200. No idea why it does this? Floats are set to 0,5mm above the gasket surface. Maybe increase it a bit?

I gonna make something for the idle adjust to be reached more easily this winter. With my pipes it's hard to make a small adjustment

 

[gggGary]

high speed runs, coming to a standstill, the idle would be lower

might try a heat shield between pipe and carb.....
loosen valves a bit?

 

[Bjorn]

You think this would affect the carbs?

Sometimes It would be so much easier to go back to original style exhaust, identical left to right, low and out of the way of the carbs and you leg haha. Just the looks though....

 

[gggGary]

Cheap and easy to try as an experiment.................

 

[Bjorn]

Wanted to try it a few weeks ago, borrowed a set of stock pipes. However I revised the passenger footpegs years ago, they don't quite bolt up anymore...

I'll see if I can fab up temporary heat shield.

Regarding carbs in general: my other bike is FI and always runs perfect. What should I expect from these older bikes with (semi modern) carbs anyway? Can you even have one setting, all year round, idling always stable at 1200. Or does one need to adjust the idle adjuster every now and then? Just trying to manage my expectations here so I don't chase my tail.

 

[gggGary]

With your skills a spring wound flex cable to the idle adjust screw with easy access... just say'n.
Even my FI 1200GS BM'r is a bit variable on idle speed......

 

[arcticXS]

With your skills a spring wound flex cable to the idle adjust screw with easy access... just say'n.

Keihin FCR's for carburetted Ducatis have just that. A "remote" idle adjuster, and it works great. It may even fit those Kawasaki Keihin CV carbs without mods.

 

[arcticXS]

Not a tuning tip, rather an observation;
I just noticed how much more streamlined the intake bell of the Kawasaki carbs are, compared to the OEM carbs. Surely they must flow better at full throttle !

 

[gggGary]

a bit of idle chatter; We tend to think of flow as this smooth process but with the intake valve rapidly opening and closing it's more like a jack hammer of jerky air movement.
My is this is root cause of slide flutter. I noticed on later carbs, Yamaha used a long velocity stack that keeps the vacuum port at the top of the bell further separated from the hurly-burly "vibratory" air flow near the venturi.


Always mean to do a velocity stack that leaves the vacuum port separated on an XS650. (someday)

 

[Jan_P]

Wanted to try it a few weeks ago, borrowed a set of stock pipes. However I revised the passenger footpegs years ago, they don't quite bolt up anymore...

I'll see if I can fab up temporary heat shield.

Regarding carbs in general: my other bike is FI and always runs perfect. What should I expect from these older bikes with (semi modern) carbs anyway? Can you even have one setting, all year round, idling always stable at 1200. Or does one need to adjust the idle adjuster every now and then? Just trying to manage my expectations here so I don't chase my tail.

If FI is fuel injection that is an entirely different setup with other possibilities
On a Fireblade I have there is a vax plug that regulates idle
and electronically controlled ignition with a lot of sensors that affects ...it has variable intake and exhaust lengths
above 8000 rpm it opens

I don't believe it is possible to get a even spot on idle on an XS 650 i have never had it
It depends on outdoor temperature and engine temperature. and so on
Yesterday I was out opening up 5 -6000 rpm down shifting while overtaking
140 Km / h a short while
outdoors ca 10 -13 Celsius
At home put it on the central stand to listen after mechanical rattle Idle close to 2000 rpm
At other times it is 1300 - 1500 at upstart
Dont stall which has happened that also over the years ..
The carburetor is serviced 2 years ago in a rebuild
With 2 step up pilot and one Main don't remember needle position.
That is probably a bit to much but it starts and above all No vibrations at all NOTHING
at cruising speeds.

I admit I am no Carburetor guru or so but this is a setup that works for me and the little extra fuel .Makes me sleep better not running lean.

Judging by your video in # 964 that is as good as it gets in my view there is a " Rough " sound very slight like pinging but it is difficult to asses on this video Can be something else ... Bearing play a loose washer
I don't think it can get much better at idle I would focus on how it behaves on the road throttle response ( It appears good on the video not perfect but good ) and
Foremost keep an eye not running lean .. I have had a worse idling for 35 years than that ..
Many years with a worn advance unit not being able to let go of the throttle at all.

 

[Bjorn]

a bit of idle chatter; We tend to think of flow as this smooth process but with the intake valve rapidly opening and closing it's more like a jack hammer of jerky air movement.
My is this is root cause of slide flutter. I noticed on later carbs, Yamaha used a long velocity stack that keeps the vacuum port at the top of the bell further separated from the hurly-burly "vibratory" air flow near the venturi.
View attachment 199331
View attachment 199335
Always mean to do a velocity stack that leaves the vacuum port separated on an XS650. (someday)

So you would need to run a airbox in order to filter both air streams I guess?

Regarding the air stream and fuel atomisation, this a a really interesting video about that. With super slowmotion to see the pulsing air stream, very interesting to watch! And carb related I guess haha.

 

[Bjorn]

If FI is fuel injection that is an entirely different setup with other possibilities
On a Fireblade I have there is a vax plug that regulates idle
and electronically controlled ignition with a lot of sensors that affects ...it has variable intake and exhaust lengths
above 8000 rpm it opens

I don't believe it is possible to get a even spot on idle on an XS 650 i have never had it
It depends on outdoor temperature and engine temperature. and so on
Yesterday I was out opening up 5 -6000 rpm down shifting while overtaking
140 Km / h a short while
outdoors ca 10 -13 Celsius
At home put it on the central stand to listen after mechanical rattle Idle close to 2000 rpm
At other times it is 1300 - 1500 at upstart
Dont stall which has happened that also over the years ..
The carburetor is serviced 2 years ago in a rebuild
With 2 step up pilot and one Main don't remember needle position.
That is probably a bit to much but it starts and above all No vibrations at all NOTHING
at cruising speeds.

I admit I am no Carburetor guru or so but this is a setup that works for me and the little extra fuel .Makes me sleep better not running lean.

Judging by your video in # 964 that is as good as it gets in my view there is a " Rough " sound very slight like pinging but it is difficult to asses on this video Can be something else ... Bearing play a loose washer
I don't think it can get much better at idle I would focus on how it behaves on the road throttle response ( It appears good on the video not perfect but good ) and
Foremost keep an eye not running lean .. I have had a worse idling for 35 years than that ..
Many years with a worn advance unit not being able to let go of the throttle at all.

Good to hear your thoughts about the stability of an carburettor idle. I think the video doesn't do the sound any justice. I like to be on the save (rich) side too. My general plan is to dial in the carbs as best as possible with the riding season coming to and end. I want to revise my exhaust system this winter to make it quieter and have it dyno'ed next year. Nice to be in the ballpark to safe some expensive time on the Dyno.