NONclow
Confirmed Laquer Breather
Just a thought.... how about removing the throttle levers from the carbs and winding the throttle return spring (around the shaft seal) one more revolution tighter? It might hold them closed better.
I was hoping to get some advice from someone that knows what they are talking about
you don't use a manometer to correct idle or correct backfiring.
Your description of the idle change after pressing on the throttle shaft and observing your videos leads me to believe that you may have worn throttle shaft bores in the throttle body, an issue I've not seen discussed here in excruciating detail yet.
Just a thought.... how about removing the throttle levers from the carbs and winding the throttle return spring (around the shaft seal) one more revolution tighter? It might hold them closed better.
You have received a lot of good advise Out of sync carbs will cause both of them issues. I have fixed a bunch of peoples "bench synced" bikes with a simple set of mercury stix. Good luck with your bike maybe you just need a little more RTV goop around the boots
Peanut, no offense meant, but when 5twins and I wrote the XS-650 Garage Carb Guide, he did a very nice job in the chapter on tuning for modifications, and you won't get more information by asking him to write it all again just for you. And for cryin' out loud don't smear gumpucky on your carb spigots (they aren't stubs unless somebody decided to "build" them with a Sawzall).
an excellent write up twomany albeit a little wordy
What I have discovered however is some huge gaps around the butterfly vanes where they seat on the venturi surface .
At this point 30+ years ago I would probably have launched into a detailed explanation of Bernouilli's Theorum lol .Theres a name to strike terror into the heart of an Engineering student
I have never seen such ill fitting vanes so I am not sure whether they are as originally fitted ? or if someone has stripped them and rebuilt them without properly aligning them or switched them between venturis perhaps ? either way the carbs are going to need to be completely stripped and refurbished now over the winter.
I might even consult a local precision Engineer about the possibility of rebushing the throttle shaft buses and replacing the shafts.
I certainly need to do something about a stripped thread on one of the bowl fixings ...yes the only blind one of the four !
I have done a significant amount of reading around the net on the BS38 carbs and when I've refurbed mine I intend to draw up a full troubleshooting flowchart but whether I get around to it remains to be seen.
thanks for your advice and encouragement .. its much appreciated. I know I come across as a grumpy old git sometimes but in my defence I would say that it is because I am a grumpy old git !
I like your thinking
I think I realised the problem straight away. the butterflys were not synced properly . The RH idle adjustment screw was set slightly too high preventing the LH butterfly from returning fully . It took only a moment to correct .
chris I appreciate your imput and suggestions thank you but I will probably not be rushing out and buying a set of manometers just yet.
In my experience It is neither necessary or essential to use manometers to set the carbs in sync for initial tuning.
You'd have to be pretty ham-fisted ,or blind ,to set your butterflys that far out of sync for it to effect your idle circuit that much.
There's a strong correlation between grumpy and pain. My chemotherapy nurses knew to avoid me if I wasn't cracking jokes.
Is your back acting up?
I would belatedly like to thank all those members that offered advice even if I didn't accept It it was appreciated .
It is interesting to note how unhelpful skulls 'contributions' were even back then in 2013....nothing changed there then