I have a 81 xs650 that I am having some issues with. On my left cylinder the exhaust sounds great, has a nice pop,pop sound. On the right cylinder it sounds very blubbery. Left cylinder heats up more than right also. The right is definently firing but it just seems like something isn't right there. Compression on both cylinders is 145, coil tests at 22,5k on both sides. Plugs are new and look good. Carbs have been takin down many times latly while I have been working on jetting, all jets are new and carbs are clean. Diaframe looks good. Exhaust valves have been adjusted but I haven't done intake yet because my feeler gauge doesnt go small enough, gonna get a new set this week. So anyone have a ideas what may be going on here? Thanks for any help
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Normally the right side is your warm side. What does a throtle chop show you? I'm betting your right side is rich and the left lean.
opps double post
Haven't done a actually throttle chop, just checking the plugs after a good ride. I have changed them several times so they are freash to read. I now that's not the best way but they both look the same, jetting seems to be good. I will try a full chop and see what it shows
PhatTony
I love twins
+1 on the carb sync, My triumph had that problem all the time until I built a manometer to get it dead on.
PhatTony
I love twins
I'm not familiar with 81 carbs but I don't believe that you can adjust the idle independently. They have to be synced and then you can adjusted the idle as a pair. There is no left and right idle adjustment. If I'm wrong someone else please chime in.
sync screw only turns one butterfly relative to the other one; left side idle speed adjust screw turns both the same amount
Exactly so turning the sync screw will bring up the idle on the right cylinder. Like I said bring the idle up or down on the cylinder did not make a difference and I'm sure there off a bit now I will properly sync them and go from there. I think it's a valve problem but not sure what to look for. I'm a long time 2 stroke guy, still learning about thumpers.
Ok where to start. My initial post was part of my problem, The main problem which I thought was assioated with it is that at 3/4 to full throttle the bike blubbers and misses really bad, I understand that to be to rich. Let me in as few words as possible start at the begninning.
Bike is a 81 xs650, running drag pipes from greatscott and pod filters. I bought the jet kit with the needle from mikes. Right away I installed the larger pilot with the 140 main and the needle with the clip in the middle,fuel screw 3 turns out. Ran fine up to 3/4 throttle then falls off. Put the stock needles in and it was 90% good but still blubber at wot. Tonight I sync'd the carb,still no good. Went to a 135 main, got a little worse. Put the mikes needle back in, clip 1 down from top, really bad. Blubbers from 1/2 throttle on up. Moved the clip the other way, 1 from bottom and it got a hair better. Put the 140 main in and again a hair better but still not as good as it was with the stock needle and 140 main. I am lost where to go next. Went from lean to rich to lean to rich and none seem to get it right there. Please all u xs guru's give m e some ideas. Thanks.
Bike is a 81 xs650, running drag pipes from greatscott and pod filters. I bought the jet kit with the needle from mikes. Right away I installed the larger pilot with the 140 main and the needle with the clip in the middle,fuel screw 3 turns out. Ran fine up to 3/4 throttle then falls off. Put the stock needles in and it was 90% good but still blubber at wot. Tonight I sync'd the carb,still no good. Went to a 135 main, got a little worse. Put the mikes needle back in, clip 1 down from top, really bad. Blubbers from 1/2 throttle on up. Moved the clip the other way, 1 from bottom and it got a hair better. Put the 140 main in and again a hair better but still not as good as it was with the stock needle and 140 main. I am lost where to go next. Went from lean to rich to lean to rich and none seem to get it right there. Please all u xs guru's give m e some ideas. Thanks.
- dont forget to synchronise too
- check float level
- this is the relationship between the main carb variables
- i look for the optimal main jet first, at wide open throttle on level ground the engine shouldnt bog or splutter-jets too big...should be crisp-increase jet size until it bogs then go back one
- then the pilot air screw and idle speed screw dance to get the lowest revs at the best fuel/air mix...pilot air screw should be between half and 2 full turns out...under half increase the pilot jet, over 2 decrease it...then go through the dance again
- if youre game you could play with the throttle slide cut-away
- needle and needle jet...if the needle is adjustable in its taper and clip, setting the clip in the lowest slot is richest, in the upper slot is the leanest...adjust to richen until the engine bogs then go back one
- check float level
- this is the relationship between the main carb variables
- i look for the optimal main jet first, at wide open throttle on level ground the engine shouldnt bog or splutter-jets too big...should be crisp-increase jet size until it bogs then go back one
- then the pilot air screw and idle speed screw dance to get the lowest revs at the best fuel/air mix...pilot air screw should be between half and 2 full turns out...under half increase the pilot jet, over 2 decrease it...then go through the dance again
- if youre game you could play with the throttle slide cut-away
- needle and needle jet...if the needle is adjustable in its taper and clip, setting the clip in the lowest slot is richest, in the upper slot is the leanest...adjust to richen until the engine bogs then go back one
kmb81xs650sh
kmb81xs650sh
Make sure your alternator brushes are good. I've got an 81 and if they get to low and the battery starts discharging my bike does the same thing. Check the brushes and make sure battery is fully charged.
What kind of pod filters are you running? Cheap ones can cause problems like this. Try a test run without the filters. Also, are the pipes 1 3/4"? That may be too large and need AR inserts at the head.
They are just cheap eBay pods, I will try it without them and see. I just pulled mikes needels out to put the stock ones back in when I noticed mikes are much larger. Measured them up and they are 6mm longer than the stock ones, is that right?? Maybe he sent the wrong ones.
What MikesXS needles do you have? The Canadian ones or those ones in the custom kit that comes with jets? I'm pretty sure the Canadian ones are the same as the originals except they have adjustment slots. I've never seen the ones in that kit however 6mm is a huge difference when it comes to needle length. When you move the clip on an adjustable needle, it changes the height by 1mm so that would be like moving the clip 6 steps. That can't be right. A longer needle is leaner. That would make this new needle leaner than the already too lean stocker it's replacing.
When you compare needle lengths, you should be comparing what's called the working length. This is from the clip slots down to the tip. Don't measure the overall length as this can be deceiving. The portion of needle above the clip slots is not important and sometimes varies on 2 of the same numbered needles. If you're comparing two 5 slot needles, you can measure from the top slot down to the tip. If you're comparing a 5 slot needle to the original one slot item, it would be best to measure the 5 slot one from the center slot.
When you compare needle lengths, you should be comparing what's called the working length. This is from the clip slots down to the tip. Don't measure the overall length as this can be deceiving. The portion of needle above the clip slots is not important and sometimes varies on 2 of the same numbered needles. If you're comparing two 5 slot needles, you can measure from the top slot down to the tip. If you're comparing a 5 slot needle to the original one slot item, it would be best to measure the 5 slot one from the center slot.
This is the kit i bought. I did measure the overall length so i will measure it again the way you said. I wish I could just figure out if I am rich or lean. The plugs look good. Thanks alot for the help you guys have givin. This place is so helpful.
Heiden Dyno Tune Needle & Jet Kit
Dyno Tune Needle & Jet Kit for Mikuni BS34 CV carbs as used on North American
model 1980-84 XS650's.
Kit smoothes out the powerband and removes the midrange hesitation and leanness
resulting in a smooth acceleration from idle thru redline.
Kit Contains: 2 slide needles with clips
2 pilot jets
4 main jets (2 sizes)
1 Drill bit to modify slide
Instructions for tuning with various Exhaust & Carb/Intake setups
Part #48-0667 $44.00 USD KitADD TO CART
Heiden Dyno Tune Needle & Jet Kit
Dyno Tune Needle & Jet Kit for Mikuni BS34 CV carbs as used on North American
model 1980-84 XS650's.
Kit smoothes out the powerband and removes the midrange hesitation and leanness
resulting in a smooth acceleration from idle thru redline.
Kit Contains: 2 slide needles with clips
2 pilot jets
4 main jets (2 sizes)
1 Drill bit to modify slide
Instructions for tuning with various Exhaust & Carb/Intake setups
Part #48-0667 $44.00 USD KitADD TO CART
Yes, I've never seen those needles but it does seem odd that they would be so much longer. Measure as I told you and maybe you'll find the difference is really less. Also compare how fat the needles are along their tapers. A skinny needle will be richer even if it is longer.
I think the major cause of your problems is probably those cheap pods. Many have a large inner rubber lip or stop to keep them from sliding on the carbs too far. Well, it stops them alright but also blocks the air feed holes around the outside of the intake bell in the process. This causes rich running even with the right jets. The effect isn't too bad at idle and through the lower midrange but when you hit the upper midrange and the main starts kicking in, the bike breaks up and stumbles or blubbers.
I recommend you get some good air filters, UNIs or real K&Ns. The MikesXS performance pods supposedly don't block the air passages but reports are starting to filter in that the rubber flanges are giving out. Maybe the same rubber his crap intake manifolds were made from?
I think the major cause of your problems is probably those cheap pods. Many have a large inner rubber lip or stop to keep them from sliding on the carbs too far. Well, it stops them alright but also blocks the air feed holes around the outside of the intake bell in the process. This causes rich running even with the right jets. The effect isn't too bad at idle and through the lower midrange but when you hit the upper midrange and the main starts kicking in, the bike breaks up and stumbles or blubbers.
I recommend you get some good air filters, UNIs or real K&Ns. The MikesXS performance pods supposedly don't block the air passages but reports are starting to filter in that the rubber flanges are giving out. Maybe the same rubber his crap intake manifolds were made from?
