Altitude & black smoke

[richard5933]

Arrived in Santa Fe today. Took 4-1/2 days driving to get here from Wisconsin taking it pretty easy. No real problems, and only a small amount of downshifting to climb the steeper sections of road. Temp only rose a few degrees each time and came back as soon as I downshifted.

However, I noticed a distinct increase in black smoke as I got to the higher altitudes. We were at 7,300 feet at one point. Home is only 640 feet.

I'm guessing that the black smoke is just unburned fuel due to the lower oxygen concentrations from the higher altitude.

Correct?

In all other ways, other than slightly lower power, the bus ran great all the way up (knock on wood.)

[luvrbus]

Arrived in Santa Fe today. Took 4-1/2 days driving to get here from Wisconsin taking it pretty easy. No real problems, and only a small amount of downshifting to climb the steeper sections of road. Temp only rose a few degrees each time and came back as soon as I downshifted.

However, I noticed a distinct increase in black smoke as I got to the higher altitudes. We were at 7,300 feet at one point. Home is only 640 feet.

I'm guessing that the black smoke is just unburned fuel due to the lower oxygen concentrations from the higher altitude.

Correct?

In all other ways, other than slightly lower power, the bus ran great all the way up (knock on wood.)

Yep old N/A stroke engines don't like thin air they lose about 3 to 5% of of the HP rating at every 1000ft above sea level

[dtcerrato]

So 150 HP pushed us & the toad through the Eisenhower Tunnel! Geeze she's a good ole' girl. Too bad there weren't amy mosquitoes...

[luvrbus]

So 150 HP pushed us & the toad through the Eisenhower Tunnel! Geeze she's a good ole' girl. Too bad there weren't amy mosquitoes...

Yep all the rating on the 2 strokes are at sea level and 70 degrees lol that is why they have a 1st gear

[HB of CJ]

Way back in 1970 the custom 671-TI 4104 GMC bus belonging to the Yosemite Park and Curry Company ran North up from the valley floor (4000 ft) over Tioga Pass, (nearly 10,000 ft).

The A/C pony motor seemed to run OK at high elevation.  The head mechanic guy told me seriously not to stop along the way up the hill.  The Detroit just did not have the starting torque up high.

Very short clutch life would result if any stops were made.  The starting gear, (first) was not low enough.  Did have to double clutch down shift a couple of times to first gear.  Slow RVs ahead.

But no smoke.  Ran OK but was very slow.  A crisp Jake Brake coming down both sides from Lee Vining.  Carried two O2 masks and an oxygen bottle for the very old or frail.  Long long ago.

[dtcerrato]

Cool! Your description really painted the picture... Was that a turbo engine? We've been that route in our 04, NA real slow, real dependable we love it. Thanks for sharing your experience. Chazmon used to be on these forums, he recently sold his 4104 and it was a Yosemite bus!

[freds]

I have a turbo in my rig and I went over numerous 6000 foot summits on my way to the BCI rally and yes I saw a lots of black.

However I didn't get my tune up until on my way back, would be interesting to do that route again.