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Old 08-03-2010, 07:44 PM
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Rzeppa Rzeppa is offline
Cruise Moab Chairman
Join Date: Aug 2005
Location: Kittredge CO, USA
Posts: 6,722

Originally Posted by MDH33 View Post
Regarding the vapor lock issue; I'm not sure. I ran those hills no problem two weeks ago (and last year), but this time I vapor locked. I usually run high octane, but that day I ran 85... Only difference I can think of. I feel like my carb and 2F are running great and haven't had any issues lately.
The higher the octane, the lower the vapor pressure and less likelihood of pre-ignition or vapor lock. I didn't want to hurt people's brains with the long explanation, but I already did. Suffice to say that gasoline formulation is a mixture of different hydrocarbons, generally C4 through C12. The fewer carbons atoms, the lighter and more volatile it is, and more susceptible to vapor lock.

This might be a teaching opportunity: If you are planning a run to high elevations in the summer, it might help to fill up with "premium" to avoid vapor lock.

Obviously the sample size is very small (4 rigs out of 20 had issues, including one with FI), but it might be an interesting experiment if we had all carb'd rigs fill up with premium next year, or our next high elevation run, and see if we have as many vapor lock issues or not.
Jeff Zepp
Kittredge CO USA
1971 & 1976 FJ40s, 1978 FJ45, 1987 FJ60
Rising Sun 4WD Club, TLCA #4063
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