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Further WUR issues, altitude or both?

Started by raueda1, 13 September 2022, 02:56 PM


Per an earlier thread I'm now 1000 miles into my high speed, high temperature, high altitude blow-out-the-carbon road trip.  High altitude = +7000 ft.  It's going fine though not totally without issues:

Cold (parked overnight) starts instantly, though initially idle is very low and bumpy.  Doesn't stall though and speeds up to spec and smooths out in about 3 minutes.  I assume that the WUR is doing something but maybe altitude, enrichment setting or mixture isn't right for 7000 ft.  Or would it make a difference?

Warm start is perfect as long as it's within 30 minutes or so of shutting down.  Presumably that confirms that pressure accumulator is OK?  However, if the car partially cools down, say an hour or 2, it's an issue.  Car fires instantly but then stalls.  It will start after cranking maybe 5-10 seconds (an eternity) and seems to be aided by some very light throttle.  This is way past the time that fuel system should be pressurized.  So what might be going on?

I'm a bit reluctant to start fiddling with it.  All was perfect when I left.  Maybe it will be again when I'm back down to 4000 ft?  Oh yeah, no more soot on cold start, so that's nice. Comments appreciated and welcome.  Thanks and cheers,

[sidebar:  I drove by some vintage sports car rally at a local hotel, about 50 cars.  Most were early 70's 911's, lots of 356's and numerous 50's-60's Jags.  The Jag guys seemed to be having a rejet-the-carbs party.  They said that they all barely ran at the altitude without rejetting.  Obviously they had done it many times.  Fun stuff.\
Now:  1976 6.9 Euro, 2015 GL550
Before that:  1966 230S, 1964 220SE coupe, 1977 Carrera 3.0


Just throwing out some guesses: vapor lock?  loose fuel line letting air in? Moisture in distributor cap?

Anyway - happy motoring!
'68 250S
'77 6.9 Euro
'91 300SE,
'98 SL500
'14 CLS550,