a developing saga

[650Skull]

I've stripped my carbs today so can confirm it is as far as I'm aware set to US specs going by the carb guide on here. The one thing I have noticed is that the mixture screw was a lot more than the book starter point of 3/4s of a turn out, more like 2 1/2 on the choke carb which might explain the popping?

Not my thread. This is Crasedkiwi's thread. Although he might get some helpful information from your posts you have hijacked someone else's thread.........Didn't you start a build thread of your own??

 

[Dom]

Not my thread. This is Crasedkiwi's thread. Although he might get some helpful information from your posts you have hijacked someone else's thread.........Didn't you start a build thread of your own??

See post #15

 

[650Skull]

I stand corrected.............its JP' fault.....lol

 

[Crashedkiwi]

Hi All - This is a global thanks to all of you for your insights - really helpful. So the "saga" of the carbs is ended for now with a bike that starts and runs, well purrs actually. I ended up stripping the carbs and mounts and ensuring that there was no air leaks anywhere, anyhow. I replaced the primary jests with ones sized 49 sourced from MikesXS carb kits, reassembled, checked the cam chain tension, set the valve clearances and checked the timing. Oh and replaced the throttle cables that looked like they'd been used by the prior owner when they practiced macrame.
It starts literally at a touch of the button and idles away at around 900/1000rpm. RIde wise the change to the 49 primaries has it pulling off the line liek that proverbial schoolboy. Learnings? Patience and do it right (or as close as my abilities take me) once. Really appreciated all your help. Thanks. Now off to build the cafe racer out of the second one.....

 

[jpdevol]

Hi All - This is a global thanks to all of you for your insights - really helpful. So the "saga" of the carbs is ended for now with a bike that starts and runs, well purrs actually. I ended up stripping the carbs and mounts and ensuring that there was no air leaks anywhere, anyhow. I replaced the primary jests with ones sized 49 sourced from MikesXS carb kits, reassembled, checked the cam chain tension, set the valve clearances and checked the timing. Oh and replaced the throttle cables that looked like they'd been used by the prior owner when they practiced macrame.
It starts literally at a touch of the button and idles away at around 900/1000rpm. RIde wise the change to the 49 primaries has it pulling off the line liek that proverbial schoolboy. Learnings? Patience and do it right (or as close as my abilities take me) once. Really appreciated all your help. Thanks. Now off to build the cafe racer out of the second one.....

Congrats on the progress!
Sorry for prior hijack (and this one).....
So, as mentioned, it's unknown what a Mike's (Keyster, et al) #49 pilot jet is size wise. Mikuni never made a #49 pilot jet. Did you perhaps happen to note what pilot screw, needle and needle jet are present?

 

[Crashedkiwi]

Congrats on the progress!
Sorry for prior hijack (and this one).....
So, as mentioned, it's unknown what a Mike's (Keyster, et al) #49 pilot jet is size wise. Mikuni never made a #49 pilot jet. Did you perhaps happen to note what pilot screw, needle and needle jet are present?
View attachment 229875

Hey - no problem for the Hijack at all. I appreciate being able to add to my knowledge base on these bikes and the dark art of these carbies.

With regard to the pilot screw, needle & needle jet as fitted now are, they are the standard ones for these carbies; the needle jet is also set to the standard height. I did not change the existing main jet set to components from the MIkesXS supplied kit. I ignored the Main & Needle recommendations as I'd no issue with the bike once on the main jet & changing one variable at a time makes sense to meT. he kit is indeed a Keyster per the iattached mages. I based my primary jet selection on the attached chart using the jet specified in the column headed "RR". So indeed, Mikuni may never have made a 49 jet, but these guys (Keyster, also Japanese) did. I didn't measure the actual dia. of the 49 jet, which out of pure curiosity, I now wish I had done so - then I could correlate to the Mikuni chart you've kindly provided. However, whatever the size is in actuality and where it correlates, it has the benefit of working. I think as mentioned above, it's just a dark art & not for the fient hearted or the impatient!

 

[jpdevol]

Of course ya shouldn't argue with success

I have an agenda: my curiosity on your '75 carbs caused by the possible differences in set-up of US and Non-US during that and '76-'77 models. I see a lot of issues arise in tuning on bikes that may be originally Non-US and then get replacement parts that are intended for US models.

 

[Crashedkiwi]

Of course ya shouldn't argue with success

I have an agenda: my curiosity on your '75 carbs caused by the possible differences in set-up of US and Non-US during that and '76-'77 models. I see a lot of issues arise in tuning on bikes that may be originally Non-US and then get replacement parts that are intended for US models.

Apologies - I should've mentioned althogh I'm located here in NZ, I brought the bike in from the US. It looks like it had quite a bit of work done frame stripped and powdercoated, I found new Bronze bushings in the swingarm ( so the needle roller kit I brought sits on the shelf...) looks to be rewired and the engine clean with new oil in so suspect a tear down at least and rebuild at best. Took me a year plus to get here due to shipping etc. so it had been sitting on a wharf in LA for some time. On initial starting (still on points) ran like an arthritic dog hence the carb strip and clean excercise. When that did not work, I removed the points & condensers, looked carefully at them ( they were new) & threw them on the highest shelf in the workshop and fitted the XScharge kit. A new bike emerged - but still had the rubbish idle and lag off the mark. Carbstrip clean etc. for third time as per post and volia, I've a fairly mint XS that I love riding. An XS was my first big Japper at 19 - many years later I have one, well two actually again and I still get the same buzz from riding her. I think my Duke has attachment issues!

 

[650Skull]

Congrats on the progress!
Sorry for prior hijack (and this one).....
So, as mentioned, it's unknown what a Mike's (Keyster, et al) #49 pilot jet is size wise. Mikuni never made a #49 pilot jet. Did you perhaps happen to note what pilot screw, needle and needle jet are present?
View attachment 229875

Hijack i when someone else take over asking ongoing questions relating to their problem/s...............Don't think it was you JP.

On the difference between, US and the rest of the world, carbs. To my knowledge it only made a difference with the BS 34's. The needle/needle jet where the other jetting range was still as a choice the same as the US models. Needle Jet extra emulsion tube holes and different taper of the needle seemed to make the main a 1/2 size smaller than US Carbs. Adjustable needle was the big difference.

 

[jpdevol]

On the difference between, US and the rest of the world, carbs.

Ongoing research - up through '74, I've found no difference. After that OEM carb p/n's and some internals began to be different depending on export market. '78-79 things appeared to get uniform again.

I've noticed that '75-'77 bikes report more tuning issues here, particularly when the OP is located outside US (Canada, UK). Who knows the history of the carb internals? Have aftermarket kits been introduced at some point (US Spec?), have needles, jets or fuel screws become mismatched?

In this thread, OP from NZ, bike from US - but I'm asking what's in there to get the info. as I'm curious.

 

[freddy3]

But still missing on start up and sluggish off the mark. Stripped carbies again, changed to larger primary jet (49) and double double checked cleanliness of carbies. Remounted and I'm extremely confident that there are no air leaks from flanges or rubber mounts (these are new also).
Damn thing starts - not quite as well as first fitment of elec. ignition and misses and is difficult to move off idle from cold. Once warm, runs like a train; noticably better for changing the primary jets. Still does not like to start or idle, will idle away around 1000 & just stop. I'm now running out of ideas to fix this so appreciate any suggestions. Its the only flaw in an otherwise really enjoyable ride so your help appreciated.

Have you checked timing?
Are you getting good, clean spark at the plugs?
Have you checked the valve adjustment?
Are the air/fuel screws properly set?
Have you equalized the two throttle cables?