High Elevation Tillotson Adjustment

Classic short-frame models

High Elevation Tillotson Adjustment

Postby jOe » Sun Dec 07, 2014 11:30 am

Hi Everybody---'69 XLCH,standard bore,stock cams,new valves. Tillotson HD. Fixed main jet.
I live at 6500ft. elevation and within 25 miles from home, I can be anywhere between 4500 and 9000ft elevation. Does anyone have any suggestions about carb tuning for these conditions? I think it's dialed in pretty well right now, runs well, plugs read ok. Back in the day I had a Tillotson with an adjustable main jet, but I don't know if that's something that I should be concerned with.
A joker in the deck is that we snowbird it during the winter at a place that is actually below sea level. If I take it down there............

Just interested if anyone has any thoughts on the matter.
Thanks
jOe
 
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Re: High Elevation Tillotson Adjustment

Postby DaveC » Sun Dec 07, 2014 12:13 pm

Joe,

The Tillotson carb is a diaphragm carb which like the later Harley CV carb is altitude compensating, leaning itself out as air density decreases. Once properly adjusted it will compensate for air density variations by nature of its metering function (the diaphragm). That assembly meters fuel by using a combination of manifold vacuum and ambient pressure. Years ago I would go from sea level to over 9,000 with no over rich condition, while my riding partners with Bendix carbs would be belching black smoke. One point is that the gasoline today is lighter in specific gravity than that of 40 years ago, so a larger main jet is required.

Dave
DaveC
 
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Re: High Elevation Tillotson Adjustment

Postby jOe » Sun Dec 07, 2014 8:43 pm

Thanks Dave....I really haven't had a chance to do a comprehensive road test .... snow,rain,ice etc. Starting seems to be accomplished most easily with a few squirts and half choke. Not really bad. (temps in the low 30s now).
I'll know more when things clear up weatherwise and otherwise.
jOe
 
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