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Elevation and Bogging issues
Posted: Sun May 10, 2009 10:17 pm
by Joe
The snow level was 4000 feet Thursday night. Sawmill Ridge got 5 inches of new snow overnight. We took Friday off from work and parked at 2400 feet elevation near the Pyramid Creek SnoPark.
The Polaris snowmobiles did not like the warm temperature (40 F) and high elevation. Both of them developed a bad bog when trying to start moving from a stopped condition. It only appeared above 4000 feet.
Both Polaris sleds ran normally again on the way down the hill once we dropped below 4000 feet. Plug readings and EGT were normal both above and below 4000 feet.
What could make the sleds run so badly in such a short change of elevation?
Posted: Mon May 18, 2009 1:09 am
by Joe
The Polaris manual indicates a clutch weight change as elevation changes.
I don't recall seeing this before.
Sea level to 3000 feet calls for a 60 gram weight.
3000 to 6000 feet calls for a 58 gram weight.
6000 to 9000 feet calls for a 56 gram weight.
9000 to 12000 feet calls for a 54 gram weight.
My Yamaha Viking 540 and Venture 480 manuals have a chart that recommends changing rivets in the weights.
Is it in the VMAX manual, but I missed it?
Posted: Mon May 18, 2009 8:07 am
by Vmax540
Joe, this is from the Articles section in 1986 specifications.
VMX 540 K High Altitude Specifications
Standard Settings High Altitude
Idle 1500 rpm Standard
Clutch Engagement 4000 � 200 rpm 4200 � 200 rpm
Shift Speed 8200 � 200 rpm Standard
Main Jet # 290 See Setting Chart
Slow / Pilot Jet # 40 Above 6000 ft: # 45
Pilot Screw 1/2 Turn Out Above 6000 ft: 1.0 turn
Jet Needle Clip Position # 3 # 3 or As Needed for Response
Gear Reduction 18-33 See Sprocket Chart
Primary Spring Pink Org- Sil (8U9-17643-10-00)
Primary Spring Shim As Needed for 4000 rpm Engage As Needed for 4200 rpm Engage
Secondary Spring Preload 40� (C-2) for 8200 rpm Shift 70� (C-3) or As Need for 8200 rpm shift
Posted: Mon May 18, 2009 8:11 pm
by Joe
So if I read this correctly...
Yamaha changes spring preload (shims on the primary and reindexing the secondary)
and
Polaris changes primary weights.
to allow the engine to rev up to the same operating RPM at higher altitude.
I think it would be cool to develop a way of adjusting the clutch characteristics like a fuel curve on an EFI box.
Any ideas on how to do that?