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Old 08-03-2010, 04:02 PM
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Rzeppa Rzeppa is offline
Cruise Moab Chairman
Join Date: Aug 2005
Location: Kittredge CO, USA
Posts: 6,717

Originally Posted by Air Randy View Post
Could be. On the other hand it was a relatively cool day, especially on top of the passes it was down right cold. We were all pretty much using the same type of fuel, why then did many of the mechnically pumped, carbbed vehicles never skip a beat?

Several of the "vapor lock" issues I saw appeared to actually be engines loading up from being too rich. That could be due to a carb needing rebuilt, floats too high, sea level jets at high elevation, ignition timing not set for high elevation, etc. All of those things are amplified at elevation and we were running between 11,000 and 12,600 most of the day.
There was no question that Bob (blue topless rig with repeated idling problems) had fuel starvation. He had an odd, but effective way of fixing it. He would put his glove over the air horn as if it were a choke while his buddy cranked the engine over. When it would catch, he would take it off, it would start to stall, he'd put it back on, repeat until it would run without the glove. He claimed the vacuum of choking the air horn would "pull" the fuel into the carb. I would speculate that he used that method instead of the regular choke because with the regular choke, the vacuum breaker opens the butterfly as soon as the engine catches, which in his case would have made it stall.

I think he had some kind of carb issue. The carb looked like it had been recently rebuilt, and the pump was nearly-new kyosan-denki from a parts store. It is unknown whether the pump may have been faulty, or the fellow had some kind of other fault (filter?). Except the thing ran fine when he didn't have to idle on an incline for very long. I kind of kept him close to me in case I needed to strap him up the hill. In fact I offered a strap several times but he didn't want it.

I thought it was interesting that the guy with Multi-port injection on his V8 was also having fuel delivery issues, but that may have been a faulty pump. My understanding is that multi-port requires higher pressure than TBI.

In any case, the items Randy mentions at the end of his post are frequently contributors to problems, and are certainly exacerbated at high elevations. Again, the definition of boiling is the temperature at which the liquid's vapor pressure equals the ambient pressure. Thus, as you gain elevation, the temperature at which the liquid boils becomes lower and lower. And to make it worse, on an incline you lower the ambient pressure in the plumbing between the tank and the pump because it has to "suck uphill", so the boiling point of the fuel is lower on an incline than on the level.
Jeff Zepp
Kittredge CO USA
1971 & 1976 FJ40s, 1978 FJ45, 1987 FJ60
Rising Sun 4WD Club, TLCA #4063
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