78E Carb Slide Springs (Mikuni BS34)

[Diskman01]

I * think* I found a solution to my bike running too rich at low speeds. I think at some time, someone installed the wrong carb rebuild and used later carb slide springs. The floats are plastic on mine which is incorrect, AND someone set the needles on the diaphragms to the second from the top setting (lean). So, I am assuming that they also changed the springs to the shorter later model ones by accident.

Does ANYONE know the length of the original 78 XS1100 Slide springs? I will have the carbs off tonight for some adjusting and I will check the slide springs.

It's almost too lean at top end according to my plugs, but the low end is waaay too rich. I think the sliders/mains are opening up too soon due to the shorter springs.

Any input?? I purchased some new 2003 carbs and have a build thread starting.. But, I am leaving for a long trip late Thursday and I don't have time to mess with the new carbs. If I can just adjust the originals a little bit better, I will be ok for now.

[mikubuilder]

if you think your springs are too short, which I doubt, you can stretch them a bit, but position of your needles would be more critical (higher set= richer, lower=leaner...that is, how it sits in emulsion tube...)

plastic floats are fine in early carbs, as long as you set them to proper height(23mm)

running rich at idle could be few factors, like your pilot jets(original 42.5 Mikuni), mixture screw set, enrichment circuit etc.

[Diskman01]

if you think your springs are too short, which I doubt, you can stretch them a bit, but position of your needles would be more critical (higher set= richer, lower=leaner...that is, how it sits in emulsion tube...)

plastic floats are fine in early carbs, as long as you set them to proper height(23mm)

running rich at idle could be few factors, like your pilot jets(original 42.5 Mikuni), mixture screw set, enrichment circuit etc.

That's what stumps me. I'm almost too lean at high speed but the plug rings/electrode blacken very quickly at slow speeds < 30mph. If I lean out my idle screws even 1/8 turn I start popping badly (to lean) on decel. Running the correct jets for low and high speed. The main needles are in the stock position and have been for a few years. I will fiddle with the floats to at least fatten up the top end. Don't want to burn it up on the interstate.

I just don't trust previous owners or the shops they bring old bikes to.

[motoman]

That's what stumps me. I'm almost too lean at high speed but the plug rings/electrode blacken very quickly at slow speeds < 30mph. If I lean out my idle screws even 1/8 turn I start popping badly (to lean) on decel. Running the correct jets for low and high speed. The main needles are in the stock position and have been for a few years. I will fiddle with the floats to at least fatten up the top end. Don't want to burn it up on the interstate.

I just don't trust previous owners or the shops they bring old bikes to.

Possibly a bit lean even though plugs show rich at low rpm cruisin'. I know, sounds kinda backwards and can leave you scratchin' your head. Just for grins, check your input voltages at the coils while running at an idle, and at that 2-3000rpm range(just guessin' the 30mph rpm depending on what gear its run in). Interested to know your findings as I've been arguing with my Venturer on and off for a few years having the same issue. Finially last fall, not checking what I've suggested as of yet, got peod at it, cleaned and polished it, parked it in corner of garage and put bike cover over it so I wouldn't get grumpy having to look at it, and been ridin' the STeed ever since. IMO, don't believe early or later carbs are a factor. Primary or secondary ignition I believe is the source of this issue, just haven't totally sourced out where the missing all important smoke at lower rpm floated off to.

[Diskman01]

Possibly a bit lean even though plugs show rich at low rpm cruisin'. I know, sounds kinda backwards and can leave you scratchin' your head. Just for grins, check your input voltages at the coils while running at an idle, and at that 2-3000rpm range(just guessin' the 30mph rpm depending on what gear its run in). Interested to know your findings as I've been arguing with my Venturer on and off for a few years having the same issue. Finially last fall, not checking what I've suggested as of yet, got peod at it, cleaned and polished it, parked it in corner of garage and put bike cover over it so I wouldn't get grumpy having to look at it, and been ridin' the STeed ever since. IMO, don't believe early or later carbs are a factor. Primary or secondary ignition I believe is the source of this issue, just haven't totally sourced out where the missing all important smoke at lower rpm floated off to.

Hmmmm.. Interesting. It *could* be voltage related. I did upgrade my coils this past winter with some Honda VF coils. It's been behaving badly at low RPM for years. New coils didn't fix that. It does seem a bit low on voltage at anything under 3K RPM tho. I still need to adjust my high mix for now. Heat index is 102 F here today AT NOON and MUGGY as hell. Another fine evening drenched in sweat in the garage. ugh




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[trbig]

Us southern boys are laughing at your 88 degree whining. lol..

[Diskman01]

Us southern boys are laughing at your 88 degree whining. lol..

Heat index hit 105 today. I know.. I know.. When I was in Texas, it would get down to 88 and 100% humidity at 4AM.

[bikerphil]

I am assuming that they also changed the springs to the shorter later model ones...I think at some time, someone installed the wrong carb rebuild and used later carb slide springs

I don't see how the diaphragm slide springs could be interchanged, the late carbs use a much fatter diameter spring width than the early models.

[motoman]

Hmmmm.. Interesting. It *could* be voltage related. I did upgrade my coils this past winter with some Honda VF coils. It's been behaving badly at low RPM for years. New coils didn't fix that. It does seem a bit low on voltage at anything under 3K RPM tho. I still need to adjust my high mix for now. Heat index is 102 F here today AT NOON and MUGGY as hell. Another fine evening drenched in sweat in the garage. ugh




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Any adjustments would be a moot point if coil voltages are down. Key on, check OUT voltages at ignition switch, for grins...