81 Carb idle mix adj.

[motoman]

I have my garbs off my 81 Venturer and re-set my float levels as I believe my gauge slipped out of adjustment when previously setting floats last fall. They were all at 20-21mm. Re-set them at 23.8-24mm being at a 4800ft elev. Before puting carb bank back on I noticed the idle mix screws were out 3 1/2 turns from seated. It responds quickly without hesitation off idle so I have left them at that setting like they were. Somewhere here I remember reading the 80-81 carbs idle circuit play a partgoing into main circuit above idle. Correct me if have misread something. The carbs have 105 mains, stock 42.5 pilots and stock 185 air jets. It also is running stock airbox with foam Uni-filter, and no holes drilled in airbox(wanna leave it original). My question is: would that be a fairly standard adjustment(3 1/2 turns out) on this stock set-up(cept for air filter) for these later carbs at this elevation? Like I said, it runs good from idle all the way up to and past redline, cept for it acting a little rich at the lower rpm(3000 down to and including idle), which initially cause me to pull carbs and check float levels, as plugs were showing some black around thread base and on electrode. At this time it has been at a 35-37mpg@ 4500-5200 cruising rpm range on a long ride. If someone has any alternative ideas or adjustments that may improve the smoothness before re-installing carb bank, chime in and let me know............Thanks!

[81xsproject]

Well for starters, I thought the stock jetting on the 81 mains was 110 w/ 42.5 pilots. That uni with a stock box should breath better but at that altitude I am not sure if you should rejet or not. As far as the 3.5 turns on the idle goes, that is what I run with a 4-1 and pods, real close to sea level. If it feel good and the plugs look good stick to it

[Ken Talbot]

Motoman, those pilot screws sound to me like they may be a bit on the rich side. Try fine tuning them as follows:

- warm up the engine and sync the carbs with a mercury tool or vacuum gauges
- adjust the idle down to approx 700 or 800 rpm
- adjust one pilot screw out slowly while listening very carefully to the engine sound and watching the tach needle
- listen for the engine speed to pick up a bit then fall off
- if it doesn't pick up, adjust the screw slowly in, again listening for any increase in idle speed
- when you her the increase, adjust past it a half turn or so, then come back to it again until you've got the sweet spot
- adjust the idle speed back down to your low starting point
- then work another screw, again looking for its sweet spot
- each time you get a screw adjusted, drop the idle back down
- once you've got all four screws set, resync the carbs
- take one more pass through the pilot screw adjustment for each carb, still working at 700 to 800 rpm
verify that the sync still looks good
- adjust the idle back to 1100 or so depending on your personal preference
- go for a ride!

This procedure is basically what you're doing when you use a colortune sparkplug, only it is a lot faster. You are adjusting the pilot screws to achieve the optimum fuel/air ratio at the bottom end, which is why you will hear the engine speed up a bit and sound smoother at that low rpm.

[motoman]

Hey there Ken! Thanks for that procedure, have save it for getting those carbs dialed in to a nat's #*ss. Have a nice vacuum gauge, so guess it's time to build the sync. tuner using the PVC, etc. Put carb assembly back on after resetting floats to the 23.8-24mm and spraying carb cleaner in all orfices to make sure all was clear. Left all jetting and idle mixture as it was. Rode it some ten miles, immediately shutting off and pulled all plugs since I still had lowers off fairing. All had a dark brown greyish color around thread base and no more black on electrode. It was also very smooth at all rpm's and no more ocassional stumble or stutter at 3000rpm in all gears. From 1500-2000rpm in fifth, twisted it WOT and was extremly smooth accelerating. In third from a 3000rpm it went to redline 'pegging' speedo with no leaning out. Right now it is as smooth as it was(however good my memory is) as it was when I rode it off showroom floor back in the day. I'll get the vacuum syncer built and use your procedure to get pefection. I believe the main jet size that's in it is perfect for this altitude as that altitude increases most any direction I go from here at 4800ft, clear up to 11,500ft. With that, don't think at this point I have to worry being too lean in the mains. A big thanks to you, Ken and all others here for the great input!