High Altitude / Low Performance

I just moved myself and my ’86 VF500F from Syracuse, NY to Denver, CO. With the change in altitude has come inevitable performance changes. I have a couple of related questions:

-What particular mods would improve my extreme high-altitude (>10,000 ft.) performance, in terms of re-jetting and whatnot?

-Would this then compromise my performance at Denver’s ~5,000 ft. altitude, or would those same mods work for Denver’s elevation too?

-In Denver, with my present sea-level engine tuning, the bike seems to run very smoothly with little or no loss of power, but it does run very hot (runs hot up in the mountains too, even when very cool outside). The fan is running pretty much non-stop unless at highway speeds. I assume this is owing to both altitude and humidity changes. What can I do to remedy this?

Thanks in advance.

 

At that altitude you would want to take more air in since there is less at your current altitude. Jetting would be determined by a dyno or plug chop at the RPM's you are tuning for. I am sure there are some people on here from higher altitudes that could help you out to dial in a decent jetting.

 

Right. So I'm guessing that both an air screw adjustment and a needle adjustment are in order. From what I've read, the proper jet would be the one most appropriate for the highest altitude, or perhaps somewhere in between since there will be days I'll climb or descend 5,000 ft., which is kind of huge. I'd love it if someone out there has a needle size in mind that might fit this bill, and some ideas on air screw adjustments.

Thanks much, Dukiedook.

 

Vintage bikes do pose a problem here. Without a computer making constant adjustments to fuel/air mixture you'll have to decide what altitude the majority of your riding will take place and have it jetted accordingly. It seems like a lot of the guys I talk to with carbs usually shoot for an ideal fuel/air to be set somewhere in the 7000ft range. I'm not too familiar with your bikes mechanics (or any for that matter) but any way that you can think of to get more oxygen into it is usefull. There is a great tuner here in town that can probably help you out. I'm not sure how great their knowlege would be on an older bike but it would be worth your time to contact them. Faster Motorsports off of I-25 and 8th ave. I've included a link for you, hopefully they can tell you exactly what it is that can/should be done. Let any of us know if you're ever up for a ride in the west/rocky mountain regional section of this forum under the "Colorado riders out there" thread.

Faster Motorsports

 

tinkerswithstuff might have an idea on a jetting combo that might work well for you, I think he has had a 500 in Denver. I think the only thing you can adjust on these needles is shimming with washers to get more fuel flow, not what you want here.

I would think at that altitude you would be running a little rich which would run your engine a little cooler, weird.

And these vintage of carbs do not have air screws, they are just fuel mixture screws, you would be only adjusting your fuel mixture at idle with this screw.

 

Good shops have realtime A/F readouts, so find one.

First set idle mixture right with the screws. (Engine at full operating temp.)

Next do whatever main jet changes are necessary to achieve good A/F at top speed, about 12.5 to 13 is a good range with today's fuel.

Then dial in midrange with needle adjustment.

As dudie says, your set up is too rich, so you need to lean it some, but not too much.

Power loss is a physical fact at reduced air density, not much you can do.

 

Okay, I think I'll try contacting tinkerswithstuff about additional details. Thanks for the advice, folks!

 

I'll be riding one of my VF1000R's to first Thursday in October. PM me if you are instered in riding.