BST38SS maintenance

[Upshotknothole]

Changing out the emulsion tubes on my carbs, was bogging in mid range and already lowered the needles as far as they’ll go. Been procrastinating for a while because I hate pulling the carbs or doing anything under the tank on this bike. 

One of the previous owners fit an aftermarket petcock with a single outlet, that also needs to all get fixed. 
 

Dynojet really didn’t want to sell me replacement emulsion tubes. Multiple emails and a long phone call finally get me a set of new ones. 
 

 

And something I’ve noticed with these carbs over the years. I think most sets have at least one broken connector for the powerjet on the float bowl. I run dual pods so can’t use them, but they seemed to be a lot of trouble for the level of fine tuning they gave when dyno tuning the bike. 
 

 

It’s gonna be raining the next couple of days here, so should have it all back together with some of that rats nest under the tank cleaned up by Thursday. Then I’ll take it out and test it. I don’t think there’s a single shop with a dyno within an hour of here that’ll touch carbs now. Well, maybe one Harley shop, but would prefer not to go there. 

[DAZ]

Definitely a dying art .... 

[Upshotknothole]

So I've been working on the bike this afternoon. Went to swap out the single outlet aftermarket petcock that was installed when I bought it for an old spare stock one I had. And of course the stock one just pisses out fuel everywhere. Tried pulling it apart and cleaning it up, but I think it's just been sitting for far too long. Gonna try one of those K&L rebuild kits for right now. Always heard mixed results with them, but I don't feel like installing a pingel or paying for an OEM petcock.

 

[Upshotknothole]

Never had a problem with this petcock in regards to flowing enough fuel for the stock carbs, but it is next to impossible to change from “on” to “res” while riding. The lever is just too short to be useable with gloves on, and it’s a different fit to stock ones. 
 

[Upshotknothole]

Stopped wasting my time with the petcock for now. Carbs have the new emulsion tubes in them, needles on the 2nd notch from the top, AFR 2.5 turns out, and it won’t do anything other than idle. 

I’d tried running the fuel lines under the filters this time, thought that might be the issue, and rerouted them vertical again, same thing. If the bike sits, it starts and idles fine, but try and rev it and it dies like it’s out of gas as soon as you hit 4K. 
When I pulled the carbs off originally, the mixture screws were anywhere from 3.5 to 4.5 turns out, I tried adjusting them back to 4 turns out and same thing, just runs richer now before it dies. Gonna let it sit over night while I think about what to try next. I guess I should pull the carbs again and double check the float heights. Just feels like it’s barely getting enough fuel to idle and anything more than that and it dies, and needs to sit for a few minutes before it’ll start again. All new fuel line, but who knows, maybe some dirt got knocked loose and clogged stuff up. 

 

[Upshotknothole]

Maybe I’ll go get fresh gas in the morning as well, not sure how old the stuff in the bike or the stuff in my gas can are right now. 

[Dezza]

How does it behave with a small auxilliary fuel tank instead of the proper tank? If it's the same you can eliminate tank/tap issues. I helped my mate when he had a 750w and lost the will to live when I saw that mess under the tank so I feel your pain .

[Upshotknothole]

4 hours ago, Dezza said:

How does it behave with a small auxilliary fuel tank instead of the proper tank? If it's the same you can eliminate tank/tap issues. I helped my mate when he had a 750w and lost the will to live when I saw that mess under the tank so I feel your pain .

I started with an auxiliary tank, switched to the actual tank to make sure that wasn't the problem, and then switched back to using the auxiliary tank ever since. I really prefer working on naked GSXRs without all the excess crap under the tank, and Ws are a nightmare.

Thought about it some more and it feels like it's dying as soon as it comes on to the needle, might swap the old emulsion tubes back in and see what it does.

[Upshotknothole]

Fired it up a couple times this morning here. Air fuel screws are still way too far out, but it starts right up with no choke, still won’t rev above 4K without bogging and dying. Let it sit for a bit and fired it up with full throttle and it rev’d all the way up, then immediately acted like it ran out of gas and died, so still thinking a fueling issue. 

[Upshotknothole]

Swapping out emulsion tubes has turned into almost a full tuneup now. Floats were all off, and I was lazy and didn’t bench test the float valves before putting the carbs back on. Flooded and fouled the plugs. Finally pulled them tonight and they’re shot. 
 

New plugs are on order, gonna pull the carbs off again tomorrow and double check the floats and bench test the valves this time. It’s gonna be really nice here by the end of the week, need to get this back on the road. 

[2scars]

Try raising the needles up one position when they go back in.  DO you have new needles as well or just the tubes?  Sounds like to me the needles are the culprit.

 

Good luck!

[2scars]

Changing needle height is easy since you don't have to pull the carbs to adjust them.

[Upshotknothole]

Needles are Ti, I'd lowered them previously because the emulsion tubes were warn, put them back to the recommended setting with the new emulsion tubes. I need to pull them and check the float heights again, part of why I haven't touched them in over a week. Ordered a set of replacement O rings for the cages that hold the floats in place, and been dealing with home repairs and decided I needed to swap the forks and front brakes . Might try working on them again today otherwise it'll be next week.