M
mokosai
Guest
Hello all, and thanks in advance. First some background, then the question.
The bike:
1980 GS250T with stock everything (that's BS30SS carbs) except that I've attached the mufflers from a Harley Sportster since the originals rusted out to nothing.
The symptom(s):
Bike starts near-instantly (faster than any of my newer FI bikes) and idles well. *Any* amount of throttle while the bike is warming up (first 5 minutes?) stalls it.
As it warms up, it starts to be possible to turn the throttle a little, and the bike will rev a little before hitting a "rev wall". Increasing throttle to try to get it to rev higher than this "rev wall" stalls the engine. When the engine is fully warmed, the "rev wall" is probably around 6000RPM, and you can no longer stall the bike with the throttle, but it still runs poorly WOT. It seems to make no power above 5000RPM or so.
Also interesting to note: if the bike is warmed and idling, pulling out the choke/enricher will cause the bike to rev, including well past this "rev wall". It will rev to ~4000RPM even cold with the choke held out (and no throttle applied).
What I've done:
I took off the carbs, dipped them, set float height (one side was 2mm too high), and checked that each carb passage was clean. I confirmed that all of the jets and the needle are stock sizes (main jets were sized one size down: stock is 105, 102.5 was installed), and that the needle has no non-stock spacers installed. I used the o-ring kit to replace all o-rings during re-assembly of the carbs.
I've also replaced the intake boots between the carbs and engine as well as those o-rings.
I intend to install one-size-larger-than-stock main jets (107.5) to work better with the freer flowing exhaust.
Ok, wow, that was long-winded. Now the question: is there anything else I should check or change while the carbs are apart and off the bike? Or, should I re-assemble and hope that the problem had to do with clogging somewhere?
Thanks for reading!
The bike:
1980 GS250T with stock everything (that's BS30SS carbs) except that I've attached the mufflers from a Harley Sportster since the originals rusted out to nothing.
The symptom(s):
Bike starts near-instantly (faster than any of my newer FI bikes) and idles well. *Any* amount of throttle while the bike is warming up (first 5 minutes?) stalls it.
As it warms up, it starts to be possible to turn the throttle a little, and the bike will rev a little before hitting a "rev wall". Increasing throttle to try to get it to rev higher than this "rev wall" stalls the engine. When the engine is fully warmed, the "rev wall" is probably around 6000RPM, and you can no longer stall the bike with the throttle, but it still runs poorly WOT. It seems to make no power above 5000RPM or so.
Also interesting to note: if the bike is warmed and idling, pulling out the choke/enricher will cause the bike to rev, including well past this "rev wall". It will rev to ~4000RPM even cold with the choke held out (and no throttle applied).
What I've done:
I took off the carbs, dipped them, set float height (one side was 2mm too high), and checked that each carb passage was clean. I confirmed that all of the jets and the needle are stock sizes (main jets were sized one size down: stock is 105, 102.5 was installed), and that the needle has no non-stock spacers installed. I used the o-ring kit to replace all o-rings during re-assembly of the carbs.
I've also replaced the intake boots between the carbs and engine as well as those o-rings.
I intend to install one-size-larger-than-stock main jets (107.5) to work better with the freer flowing exhaust.
Ok, wow, that was long-winded. Now the question: is there anything else I should check or change while the carbs are apart and off the bike? Or, should I re-assemble and hope that the problem had to do with clogging somewhere?
Thanks for reading!
I'm taking tomorrow off (b-day, turning 30... groan) and my "present" to myself is to work on my carbs all day. I'll let you know if it fixes it, although i'm probably doing it the wrong way as I'm adjusting valves, rebuilding carbs, replacing intake boot o-rings, among other things so I won't know exactly which one it was if the problem goes away, after working on all of them...
