smokinjoefission
XS650 Member
At Wit's End with Carbs [looks more and more like it's electrical now]
Ok, first off, this is a longish post, 'cause I want to make sure I give all the information I can.
I've got a 1981 XS650 Special II bone-stock from California, and I have never been able to get this bike running right (bought in 2008, rode a couple times, stuck in storage until 2 months ago). The ODO says just under 13,000 miles, and the condition of the bike seems to agree. The bike always seemed to start off ok, then would start to backfire, I'd have to keep the throttle cranked so it wouldn't stall and then it would eventually die. That problem turned out to be a dead rotor not charging the battery. Now, for the life of me, I can't get the bike to do much more than an idle. I can coax it up to about 40mph, but if I give it much more than part throttle, it breaks up, starts stuttering (no backfire) and loses power. This is what I've done:
- carbs are BS34s, synced with a manometer
- adjusted the idle set screws from 1 1/2 turn out to 3 turns over various tests
- compression test: left cylinder has 152lbs pressure, right 150lbs
- new battery and cables
- replaced the old tube-style fusebox with blade fuses (the old headlight fuse was too hot to touch when the bike ran)
- adjusted valves to recommended in manual (0.002 IIRC)
- new NGK BPR7ES plugs (was BP7ES but they're no longer available in my area). Oh yeah: I tested for spark, both cylinders by grounding a plug to the engine. Seems to be healthy.
- new rotor and brushes (confirmed old rotor was only ~1ohm and wouldn't push out more than 11.9v, new rotor is ~4ohm, battery gets 13.0+ at 2000rpm and up)
- dismantled the carbs and soaked overnight in real carb cleaner. All seals are in there, and in good condition
- set the float levels on the bench using the clear tube method. Fuel level is within a couple mm of the flanges.
- engine oil change (I know, nothing to do with the carbs, but still)
- tried running with and without filters in the air box (stock filters, no pods). Very little difference.
- the bike runs a little bit better after it warms up a while, but still no power and breaks up if I open the throttle more than a third.
- before I rejetted the carbs, both spark plugs were whitish/grey, indicating a lean condition.
- the carb sliders are in good shape with no rips or tears and drop slowly when I push them up and hold pressure with my thumb over the port.
Right, now that you know a bit of the background, what I've done recently is purchase the dyno jet kit from XS650 direct. I put in the 'Canadian' needles at the recommended #3 position and replaced the main jet from the stock 132.5 to the next one up, 135, replaced the pilot jets. It ran even worse; couldn't even get the bike going much past idle. This seemed to me that too much fuel was getting in through the primary jets, so I moved the needle clip to the next lean position; no difference.
Tonight I went back to the stock needles, left the new 135 main jets in and gave that a try. It was marginally better, but still horrible.
I've gone up, down, inside and out of Dick Russell's and 5twins' carb guide looking for answers. I've read forum after forum but don't get much more than 'Oh, those carbs are lean right from the factory, you should re-jet them'.
So, other than buying a new pair of performance carbs, which I'd rather not do due to budget constraints and wanting to keep the bike stock, can anyone tell me where I can go from here?
Thanks in advance.
Ok, first off, this is a longish post, 'cause I want to make sure I give all the information I can.
I've got a 1981 XS650 Special II bone-stock from California, and I have never been able to get this bike running right (bought in 2008, rode a couple times, stuck in storage until 2 months ago). The ODO says just under 13,000 miles, and the condition of the bike seems to agree. The bike always seemed to start off ok, then would start to backfire, I'd have to keep the throttle cranked so it wouldn't stall and then it would eventually die. That problem turned out to be a dead rotor not charging the battery. Now, for the life of me, I can't get the bike to do much more than an idle. I can coax it up to about 40mph, but if I give it much more than part throttle, it breaks up, starts stuttering (no backfire) and loses power. This is what I've done:
- carbs are BS34s, synced with a manometer
- adjusted the idle set screws from 1 1/2 turn out to 3 turns over various tests
- compression test: left cylinder has 152lbs pressure, right 150lbs
- new battery and cables
- replaced the old tube-style fusebox with blade fuses (the old headlight fuse was too hot to touch when the bike ran)
- adjusted valves to recommended in manual (0.002 IIRC)
- new NGK BPR7ES plugs (was BP7ES but they're no longer available in my area). Oh yeah: I tested for spark, both cylinders by grounding a plug to the engine. Seems to be healthy.
- new rotor and brushes (confirmed old rotor was only ~1ohm and wouldn't push out more than 11.9v, new rotor is ~4ohm, battery gets 13.0+ at 2000rpm and up)
- dismantled the carbs and soaked overnight in real carb cleaner. All seals are in there, and in good condition
- set the float levels on the bench using the clear tube method. Fuel level is within a couple mm of the flanges.
- engine oil change (I know, nothing to do with the carbs, but still)
- tried running with and without filters in the air box (stock filters, no pods). Very little difference.
- the bike runs a little bit better after it warms up a while, but still no power and breaks up if I open the throttle more than a third.
- before I rejetted the carbs, both spark plugs were whitish/grey, indicating a lean condition.
- the carb sliders are in good shape with no rips or tears and drop slowly when I push them up and hold pressure with my thumb over the port.
Right, now that you know a bit of the background, what I've done recently is purchase the dyno jet kit from XS650 direct. I put in the 'Canadian' needles at the recommended #3 position and replaced the main jet from the stock 132.5 to the next one up, 135, replaced the pilot jets. It ran even worse; couldn't even get the bike going much past idle. This seemed to me that too much fuel was getting in through the primary jets, so I moved the needle clip to the next lean position; no difference.
Tonight I went back to the stock needles, left the new 135 main jets in and gave that a try. It was marginally better, but still horrible.
I've gone up, down, inside and out of Dick Russell's and 5twins' carb guide looking for answers. I've read forum after forum but don't get much more than 'Oh, those carbs are lean right from the factory, you should re-jet them'.
So, other than buying a new pair of performance carbs, which I'd rather not do due to budget constraints and wanting to keep the bike stock, can anyone tell me where I can go from here?
Thanks in advance.
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