XS650 Brat Build Ep 8: How to clean BS38 carbs

Disassembly, cleaning and reassembly of Mikuni BS38 Constant Velocity Carburetors

[@guypigache2105]

Nice video. Took your time, not too much fast forward and no music. Cool

[@gconor101]

Thanks chief, I feel a little more confident about giving it a go now.

[@ericdrake3084]

Really helpful material you post. Thank you for your time and knowledge. Greatly appreciated

[@NeoPreload]

You forgot the choke plungers while they were apart also you didn't clean and visually check the jets. Lastly the lower brace bar was missing. Otherwise a good quick and easy video.

[@benyarwood7335]

Hi Brodie I could really use your help hombré! I just purchased my first 1st xs650, it's a great bike, however it's been fitted with pod filters and a high flow exhaust by the previous owner, the bike idles fine and runs when at slow to mid rpms but when I get on the gas it starts bogging out. I bought an original airbox and it ran even worse so I'm not sure what to do, I asked the original builder and he said the carbs were standard. Ive never jetted a carb but I'd really appreciate some advice! Cheers mate

[@johncooper7242]

Another excellent presentation but you'll need to be much more meticulous in your cleaning and setting up proceedures with these BS38s if you want to get those carbs running well. Looks like those carbs are bitsa made up of parts from several different BS38 model years. They are 1978-1979 model BS38 bodies but they are fitted with a 1976-1977 slide and jet needle assembly.? A stock 78-79 BS38 should have 502 needles and a Z2 atomiser a 125 main jet and 27.5 pilot jet and the jet needle should have a 'top hat' needle retainer plate . The slide , plastic wheel type needle retainer and jet needle fitted to your carbs are from a BS38 76-77 model but they do transfer and work fine in the later 76-77 carb body . The atomiser and jet needles are marked and should be matched as a pair. I found it essential to clean the choke piston assembly and replace the choke body gaskets or there is a potential for un-metered air leaks around the choke body to carb body joints which can cause a lean idle mixture and rising idle speed

[@2wheelworkshop]

Thanks for the info. The whole bike is a bitsa so none of this surprises me. They do run quite well though.

[@johncooper7242]

@@2wheelworkshop the 76-79 BS38 carbs are a great performance carb but they take a huge amount of work and meticulous cleaning and setting up to get the best out of them. I put my 79 special in the garage for over a year after I bought it and nearly gave up because I couldn't get the carbs to run right. Electronic advance and ignition is a great investment If you haven't already fitted a system. Lots out there but I always recommend Boyer Bransden who were the first to design and supply an electronic ignition system. As soon as the weather improves I'll do a 0-100kph standing start to see how my bike compares to yours . Your videos are superb quality and I have learnt a lot from you about presentation techniques .

[@2wheelworkshop]

Thanks mate. I'm running vm34s on it atm and am very impressed with them. They are destined for another bike but I am considering getting another set and making the change permanent. I have plans for more upgrades such as ignition and charging but I have other projects that should take precedence and I have been very slack lately.

[@2wheelworkshop]

I am very interested to see how your bike compares in the 0-100kph. I feel that the gearing on mine let's it down in the acceleration department.

[@johncooper7242]

@@2wheelworkshop yes i think you're right on the money about the gearing. My 79 is a Special ll and has the 16" rear wheel which does improve acceleration over the 18" but it probably effects the top end quite a bit. i'd always trade outright speed for acceleration though as most of the roads I ride are twisty country backroads .... I will need to check the sprockets and gear ratios as I've forgotten .

[@greyy357]

Hey dude thanks for this video. I just bought my first bike, 77 xs650d (I'm pretty confident it uses bs38's). It was super cheap and came with a bunch of issues including a very leaky carb and it likes to idle at 2500 sometimes. I don't have any wrenching experience but I'm excited to work on it. Any advice would be appreciated

[@greyy357]

@@2wheelworkshop sorry I forgot to reply, but thank you! Yeah I just looked at the cost in australia and damn, that's crazy! I will say that I definitely hear a kind of "tssh" sound when I move the kick starter. I know little about engines and stuff so I thought it was normal. I'm waiting for the rebuild kits to arrive and I'll try that out, then I'll tackle the air issue.

[@nicolasgrim6253]

for a dunce like me is there a way to clean them without disassembling the whole thing, like pouring gas through it or something? i think my float is stuck - first time running for year after turning off gas poured out the air filters

[@2wheelworkshop]

Sorry, mate. You could give the float bowls a tap with a screwdriver handle to try and free up the floats, but even if that works, it will keep happening. By the time you have finished stuffing around with shortcuts that won't work, you will wish you pulled them apart and cleaned them properly at the start.

[@ttmmaacc]

10:52 So... turns out if you put the needle upside down fuel rains from the overflow hose

[@2wheelworkshop]

🤣 yep. Suck to find out that far in, then have to pull the carbs back off.

[@GpunktHartman]

Now i see why your originals Carbs so "lazy" : your spring is very far to long ...

[@2wheelworkshop]

Too much tension you think?

[@GpunktHartman]

@@2wheelworkshop Off course: ... she looks like double so long as she shut ... Compare the length to the carbspring from the miagyguy at 2:30 kzbin.info/www/bejne/oIaQnKmbi8monKs

[@letscheckitout1985]

These are not bs38s by the way

[@2wheelworkshop]

I'm not an expert but the manual says they are, the throat measures 38mm and they are the same as every other set of bs38 carbs I have lying around off pre 1979 xs650s. I'm happy to be proven wrong though.