High Altitude GS1000

[Bob Koenig]

Hello,

I have a 1979 GS1000 with VM28 Carbs on stock jetting with an aftermarket Delkevic Megaphone that runs well here in Ohio ~400 feet above sea level.

I will be trailering the bike to Colorado and riding around Rocky Mountain National Park for a week. The town I will be staying in is about 8000 ft and one of the roads through the park reaches a max of 14000 feet.

I have taken other bikes with CV carbs on this ride and not had any rideability issues.

Does anyone have any suggestions as to whether I will in fact need to re-jet and if so what might get me in the ballpark?

thank you

[salty_monk]

I've ridden mine at high altitude without changing jetting. Not quite 14,000 though (but I'm jetted for Sea level). You'll notice the smell & be down on power but I didn't really notice that my CV 1000G or 750E was any different really...
My guess is you could probably just tweak the screws for better idle and get away with anything else or drop a slightly smaller main jet in as well if you really wanted to.

[Nessism]

The GS1000 used VM26 carbs. Do you have the stock carbs, or carbs off a different bike?

[zed1015]

The GS1000 used VM26 carbs. Do you have the stock carbs, or carbs off a different bike?

The 79 GS1000-S model ( aka Cooley rep of which only 500 were imported to USA) did have VM28's and as with all other GS VM's they have both air and fuel screws present..
The Australian GS1000S had VM30's .
1979 Suzuki GS1000S Wes Cooley Replica | Bike-urious

[KEITH KRAUSE]

As Nessism said, a ‘79 GS1000 uses VM26. Kawasaki’s used VM28’s. Either way, if you’re happy with the way your bike runs in Ohio, the higher altitude in Colorado won’t require jet changes. Not for running around for a week. You won’t be at 3/4 to full throttle position when riding in a National park, so you don’t need to change mains. Lowering the jet needles 1/2 of a position would probably be perfect compensation but I wouldn’t bother, not for one week. You’ll be a bit rich at 1/5 to 3/4 throttle, but again, you’ll mostly be at approximately 1/4 throttle position or less and not running the engine hard. At 1/4 throttle position there’s an overlap effect from the pilot circuit, and you’ll be adjusting the pilot circuit as I suggest as you read on. The needle position will be ok as is. What’s easy to do and will improve the jetting for better drivability is to adjust the pilot fuel screws and side air screws. I still wouldn’t get all rocket-science about it. I’d use a mirror and adjust the pilot fuel screws underneath 1/4 turn leaner(in). Then adjust the side air screws using the highest rpm method. The side air screws will be adjusted out a little more to compensate for the thinner air/higher altitude. You KNOW that without the leaner screw adjustments the bike WILL run richer at those higher altitudes. Higher altitude=lower air density=less air=richer air to fuel ratio. I don’t have hands-on experience with altitudes that high. Your bike may run a bit sluggish due to running richer. A 1/2 leaner jet needle position would probably be correct as I said earlier, but I’d try the screw adjustments. Just depends on you. Do you have jetting spacers used for making 1/2 position changes? I think a full position change on the needles would be too much compensation.

[Nessism]

The 79 GS1000-S model ( aka Cooley rep of which only 500 were imported to USA) did have VM28's and as with all other GS VM's they have both air and fuel screws present..
The Australian GS1000S had VM30's .
1979 Suzuki GS1000S Wes Cooley Replica | Bike-urious

All US market GS1000's used VM26's. No fancy 28's or 30's for the USA.

[bwringer]

I'd also perhaps make sure my air filter, whatever it is, is fresh and flowing freely, and maybe tuck in a spare set of plugs.

[alke46]

The last time I spent a week in the Colorado Rocky mountains with my 79 GS 1000, the only adjustment necessary was to open the side air screws 1/2 turn each. Bike ran just fine with more air being used. YMMV. Let us know what you did and how it worked for you.