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If you were doing full throttle at the higher rpm's, then it sounds like your mains should be 135-140 based on the guy running VM32's on a bigger cc twin, and your hunch that it was lean. Lean produces more of a zingy sound, where rich can produce more of a deep muffled throaty sound. Lean is BAD BAD BAD at high speeds at full throttle, be careful. The AFR gauges are awesome for very quick assesment of jetting for that reason and a multitude of others.
If your main jet going from 185 to 130 changed the way your bike idled, then you are running quite lean on the pilot jets (idle jets) I'd venture to say. Bump that up one or two sizes.
I was really suspecting that with this setup, you'd have the hardest trouble tuning the low mid to mid throttle area with the needle jet and jet needle combinations. If you can get it set up to give you a good AFR reading just by adjusting the needle height, you are quite lucky.
You really need to approach it this way:
#1 main jet in the suspected vicinity of size based on similar bikes and your quick test runs
#2 needle probably in middle or higher positions (if 5 nothches to adjust, I'd try #4 for starters)
#3 adjust valve shimming and bench synch carbs, then adjust idle jet size
#4 tune idle perfectly (a Gunson Colortune for $40 used on ebay is AWESOME for this) and vacuum synch carbs
#5 find a remote location (desolate uphill straight road is best) and roll on to full throttle 5000-10000rpm pulls, swapping main jet sizes until 6500/7000rpm+ feels and sounds the best
#5.5 take some extra spark plugs and socket, do plug chops when you get the mains close. do advanced search for "plug chops" under my username Chuck78 to get detailed info - most of the info I posted above in your thread.
#6 now with main jet sizing set, do 5000-8000rpm pulls at a little above and then a little below half throttle, while tweaking the needle height to get it to feel best, and do plug chops to confirm mixture at that range. If you have a lot of trouble at all needle positions, I'd stop here and weld an o2 bung on your exhaust and get an AFR setup, or go visit your friend with a Dyno, as he may likely have an AFR exhaust probe for his Dyno tuning, and he could tell you with that real quick if your mid throttle positions at mid to high rpm's are far too lean or too rich.
If you have trouble tuning the 1/8 to 1/4 throttle range after that, you may need to look into upsizing or downsizing the needle jets slightly, and then re-adjust the needle height (down if larger needle jet, up higher - lower clip position - if smaller needle jet.
I believe this to be the best possible method to attack tuning this setup. Again, I HIGHLY recommend the AEM, Innovate, or similar wideband o2 AFR setups for their incredible ease of getting exact results immediately, as opposed to spending a ton of time with trial and error on jet sizing etc - especially for your setup running non stock carbs that are not tuned at all for this size engine. With a stock carb, you know that your needle jet and needle and other settings will be remotely close, but with XS650 prepped VM34's. you may be far off in tuning specs, and the AFR readings would really help get you going the right direction immediately. I think I paid $140-170 US dollars for mine. Very well worth it. The Gunson Colortune glass spark plug was an awesome tuning tool for the idle as well. With only 2 cylinders to tune, the AFR setup and careful attention to engine rpm;s while tuning as well as careful plug reading,a nd you might be able to tune the idle just as easily with the AFR gauge. On a 4 cylinder with the AFR gauge, tuning the idle is just too complicated with a single o2 sensor in the collector vs individual sniffer in each head pipe. The Gunson is really awesome though, I still recommend it. yellowish flame, too rich. blue with occasional flickers of yellow, slightly rich and slightly fouling. blue flame, perfect. blue-ish white, too lean. Very easy to read.
Excited to hear your progress.
If your main jet going from 185 to 130 changed the way your bike idled, then you are running quite lean on the pilot jets (idle jets) I'd venture to say. Bump that up one or two sizes.
I was really suspecting that with this setup, you'd have the hardest trouble tuning the low mid to mid throttle area with the needle jet and jet needle combinations. If you can get it set up to give you a good AFR reading just by adjusting the needle height, you are quite lucky.
You really need to approach it this way:
#1 main jet in the suspected vicinity of size based on similar bikes and your quick test runs
#2 needle probably in middle or higher positions (if 5 nothches to adjust, I'd try #4 for starters)
#3 adjust valve shimming and bench synch carbs, then adjust idle jet size
#4 tune idle perfectly (a Gunson Colortune for $40 used on ebay is AWESOME for this) and vacuum synch carbs
#5 find a remote location (desolate uphill straight road is best) and roll on to full throttle 5000-10000rpm pulls, swapping main jet sizes until 6500/7000rpm+ feels and sounds the best
#5.5 take some extra spark plugs and socket, do plug chops when you get the mains close. do advanced search for "plug chops" under my username Chuck78 to get detailed info - most of the info I posted above in your thread.
#6 now with main jet sizing set, do 5000-8000rpm pulls at a little above and then a little below half throttle, while tweaking the needle height to get it to feel best, and do plug chops to confirm mixture at that range. If you have a lot of trouble at all needle positions, I'd stop here and weld an o2 bung on your exhaust and get an AFR setup, or go visit your friend with a Dyno, as he may likely have an AFR exhaust probe for his Dyno tuning, and he could tell you with that real quick if your mid throttle positions at mid to high rpm's are far too lean or too rich.
If you have trouble tuning the 1/8 to 1/4 throttle range after that, you may need to look into upsizing or downsizing the needle jets slightly, and then re-adjust the needle height (down if larger needle jet, up higher - lower clip position - if smaller needle jet.
I believe this to be the best possible method to attack tuning this setup. Again, I HIGHLY recommend the AEM, Innovate, or similar wideband o2 AFR setups for their incredible ease of getting exact results immediately, as opposed to spending a ton of time with trial and error on jet sizing etc - especially for your setup running non stock carbs that are not tuned at all for this size engine. With a stock carb, you know that your needle jet and needle and other settings will be remotely close, but with XS650 prepped VM34's. you may be far off in tuning specs, and the AFR readings would really help get you going the right direction immediately. I think I paid $140-170 US dollars for mine. Very well worth it. The Gunson Colortune glass spark plug was an awesome tuning tool for the idle as well. With only 2 cylinders to tune, the AFR setup and careful attention to engine rpm;s while tuning as well as careful plug reading,a nd you might be able to tune the idle just as easily with the AFR gauge. On a 4 cylinder with the AFR gauge, tuning the idle is just too complicated with a single o2 sensor in the collector vs individual sniffer in each head pipe. The Gunson is really awesome though, I still recommend it. yellowish flame, too rich. blue with occasional flickers of yellow, slightly rich and slightly fouling. blue flame, perfect. blue-ish white, too lean. Very easy to read.
Excited to hear your progress.
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