Up Hill Battle & Wheelies

[Cormanus]

Papa Weeley, that's right, but the OP reported almost no power. He reported nearly stalling if he wasn't in 1st or 2nd. I find that interesting. I've ridden up lots of hills, even some pretty steep ones and I've never found the CB short of power. In really steep twisters I'd be in 1st or 2nd, but I can't recall a long, straight hill of any gradient that I haven't been able to accelerate up in top.

[The A-man]

I'm riding the foothills east of Nashville NC. Rarely do I drop into 2nd gear. Usually it's 3rd, doing maybe 40mph and 3000 to 4000 rpm from what I can recall. Lots of twisty hilly back roads. It's a 6 speed, and I've been amazed by how much low end torque it has, even down to 2000 rpm. Most of my riding is 1200 to 2500 feet of elevation. I can't imagine needing to
Bush the revs up to 5000 rpm to get it to accelerate. Hope this data point helps.
Correction, it's Ashville.

[Papa Weeley_imp]

Papa Weeley, that's right, but the OP reported almost no power. He reported nearly stalling if he wasn't in 1st or 2nd. I find that interesting. I've ridden up lots of hills, even some pretty steep ones and I've never found the CB short of power. In really steep twisters I'd be in 1st or 2nd, but I can't recall a long, straight hill of any gradient that I haven't been able to accelerate up in top.

Me either, but I'm wondering if it has more to do with the gradient of his particular hill. I've tried that in my '93 Miata (stick) in the local mountains, and had the exact same experience. Many times I've had to pull down into 2nd to keep from what nearly feels like stalling on a couple of the steeper sections. I'm betting it has more to with using higher gears and a STEEP hill, than any true loss of power. At least, that's what I'm hoping for the guy, rather than some massive engine problem!

[Cormanus]

I suspect you're right PW.

[LongRanger_imp]

I've never had my CB below 5,000 feet! It's been as high as 12,095 feet. There are no performance issues at altitude that I can discern.

If you've never had your CB below 5,000 feet how would you know?

Very true, I don't know how the bike responds at sea level, but I imagine the change in elevation that I experience (+7,000') is similar to what you experience (+5,000'). We're just starting from a different place.

[the Ferret]

I'm not at sea level (if someone in FLA rides to the shore are they then at sea level? lol) but close at 820 ft and have ridden to 7000 feet and not experienced any issues.

[Pterodactyl_imp]

Ferret, you are correct. No issues will be apparent at the altitudes most bikes operate, even up to the 12000ft mark. EFI (depending on its complexity) will compensate somewhat for altitude by leaning the mixture and, perhaps, adjusting timing. This optimises the fuel burn. Normally aspirated carbs, as fitted to, say, an old CB750, will not compensate for altitude. If your bike is fitted with normally aspirated carbs and you spent all your time at altitude (Rocky Mountains or wherever) you could change jet sizes to suit. This would mean a more optimum fuel burn. This is what EFI does for you.

However if you happened to have a dynamometer in your back pocket, and you used it to check HP at intervals during your climb to altitude, it would soon become apparent that as you climbed higher HP decreases. More so on the carburettor bike than the EFI bike. But still both bikes will lose power. However unless you are doing timed runs on a drag track it is unlikely to be noticeable. This HP loss occurs because for every induction stroke the same volume of gas contains less oxygen. Strapping on your portable oxygen mask and continuing the climb on that twisty new road to the peak of Mt Everest would mean that at some stage during the climb you would notice a HP decrease, and perhaps the engine might even give up the ghost completely. I say perhaps 'cause I don't know when this would happen, but it surely would.

Cheers
For my US brethren when I said "gas" above I did not mean petrol (or flatulence) but simply "air".

[Elipten_imp]

I was taught that for every increase of 1,000ft in elevation a normally aspirated engine decreases 3% in horsepower


2014 CB1100 DLX
2013 CB1100 Std
1990 BMW K75 RT

[Pterodactyl_imp]

I was taught that for every increase of 1,000ft in elevation a normally aspirated engine decreases 3% in horsepower


2014 CB1100 DLX
2013 CB1100 Std
1990 BMW K75 RT

That's a good approximation. If Ridem took his re-flashed bike to a dyno at 5000ft he would be pulling about 6-10% less power. About, and I say about because that 3% figure is more applicable to carbureted engines, what us ordinary mortals get at S/L.

Cheers

[4 Paws_imp]

Routinely ride in the mountains on steep to stupidly steep grades but generally the roads are so tight 3rd or 2nd are the only gears I'd consider. Rode the same hills on my former bike, a BMW R1200GS, and used the same gears on the same hills. Granted the GS seemed to develop its grunt lower and sooner but I still had to downshift to keep from stalling.
There is one unpaved hill I could do in 2nd on the BMW that my Ural required 1st, truck uses 4wd - haven't tried the CB.
On the big wide open sweeping up hills with no traffic I do need to keep the revs up - that's a 4cyl vs twin cylinder issue. Different powerbands, big twins can be fun but a big single rocks in the hills.
Elevations in my mtns 2 - 3.7k normally, a few higher but you have to look for them.