Altitude changing bike performance

[Jacob2]

Hello all,

I recently brought my all stock 1979 CB 750k from Illinois witch is at 700 foot elevation to out Colorado, 7200feet where I reside now.

Obviously the bike is going to run rich but how rich? What I’m wondering is am I going to be forced to rejet it? (we all know how much of a pain in the ass it is to take the carbs off)

Has anybody else had this experience and can share some insight?

Thanks

 

[Old_Crow]

When I bought my bike in Albuquerque I got all the service records back to 2015. At some point the carbs were rebuilt and "high altitude" jets were installed. I have no info on the sizes of those jets.
I do know that the bike ran fine all winter at around 800-1500 feet of elevation. We'll see here in another couple of weeks how it does at 7200' where I'll be for the whole summer and fall. I'm not so sure the CV carbs are as sensitive to elevation as the round top carbs.

 

[Jacob2]

Yeah please share when you do take it for a ride.

I purchased some iridium spark plugs to throw in because I know they don’t foul as easy(worked on my old two stroke dirtbike ). Its my back up if I do run into a lot of fouling issues with the coppers.

 

[HoosierHonda750]

Jacob2 I was wonder the very same thing for my 81’ cb750c. I just had the carbs rebuilt in Indy and moving back west again to Boulder, CO area where the roads are great riding, but will be living at 6k feet. How did that affect things? Hate to leave a good bike sitting for a year or two when I can ride it

 

[Jacob2]

Ha, I was in the same boat.

So as of today I have about about 120miles on her. No fouled plugs yet, she does run rich as hell. Exhaust stinks, backfires a little bit at high speed throttle let off, and of corse, less power. But its not to bad really, I have the jets for it, but thats a rainy day project.

At about 200miles Ill pull the plugs and check it out.

I would say send her for a ride, just be like me and bring ALOT of tools in a backpack and spare plugs.

I live up the hill in Evergreen, shoot me a message on here (or however this site works) if ya ever need a guy to ride with.

Goodluck

 

[Old_Crow]

I live up the hill in Evergreen, shoot me a message on here (or however this site works) if ya ever need a guy to ride with.

Goodluck

Totally OT here, but when I was a young kid back in '57-'58 we lived outside Evergreen in a subdivision called Hidden Valley. I remember my dad towing us on our sleds behind his Jeep in the winter.

To get back on topic, I took the bike out for a ride and it runs great at altitudes up to about 8500'. When I got close to 9700' it didn't want to idle, but got it back down to 7200' and it runs fine.

 

[Jacob2]

Sounds like we need to have a CB 750 ride with all you guys living so close to Denver, haha.

But that’s awesome man, I’m on the opposite end of the spectrum. 23 years old but really just appreciate the old shit.

It’s amazing how resilient these bikes are, I think I’m gonna run my bike up to 10,000ft here later in the summer just to see what happens. Obviously I’ll have the lady on speed dial with the truck to pick me up if I break down lol.