81 gs550 highway speed?

[81gs550l]

i ride my 77 GS550 on the interstate all the time. i can't get the speedo needle over 95, but i also don't think it's very accurate or that i should be riding that fast anyway, so i don't really mind. my tach is also of questionable accuracy. replaced the cable this past spring after it broke, but it doesn't seem to be any more accurate now than it was before it broke. it's always bouncing +/- 1k, regardless of how steady the throttle is.

Your speedo in mph? Mine only goes 85mph

[tkent02]

Your speedo in mph? Mine only goes 85mph

That sounds like you're just opening the throttle in sixth.

[Plinius10]

Again, lugging a 550 is no good. Wind it out. The real power starts at about 8,000 or so, and continues as far as you want to go.

Does this also go for a 650? I just started riding and am used to a diesel van so I usually ride around the 3 to 4k revs. I'm I smothering the bike? Oh dear.

[tkent02]

The 650 is not as bad as the 550, it does make some torque down low, due to a different cam. You actually can ride it around slowly if you want, the mid range goes pretty good. Still if you want to accelerate, anything under about 6,000 or 7,000 is not using it's full potential, and it will also make good power well past the 9,000 red line. It's just that it's not a complete dog below that range like the 550s are.

I put the 650 cam in my 550/675 project mostly because it's too hard to wind the 550 out everywhere you go. It's nice to have some mid range grunt, but I am missing that extreme 9,000+RPM hit that the 550 cam provides. I think something halfway in between might be nice.

[Plinius10]

Okay that's good to know, and as for milage? Is it noticeable riding high revs with less load per ref so to speak as to less revs but more load per ref? Logic tells me more revs equals more fuel in so it's more efficient to shift back a gear. The question is for regular riding not for a fast overtake scene
sorry for hijacking the thread

[tkent02]

No, they are most efficient cruising in the range where the cam is beginning to work. Lugging them around wastes fuel.

I have another bike with a real time fuel consumption readout, at a given cruising speed the fuel used doesn't change in any gear that gives between 4,000 and about 8,000. Below 4,ooo it uses more fuel, below three it chugs it down. Above 8,000 it uses a tiny bit more fuel, not much. This is a modern 800cc FI twin, the old carbureted bikes are probably using more fuel with more throttle opening than with higher RPM, but I have no way to check accurately.

Fuel use is directly related to speed, to speed through the air (Headwind sucks a lot more gas than tailwind) and slope, with speed being by far the biggest influence. Slope makes some difference too, but you generally make most of that up going down the other side.
On an old school carbureted bike, the RPM that gives you the power you need with the least amount of throttle is close to the most efficient RPM.

On a 550 at highway speeds that's probably 6,000 to 7,000 RPM, on a 650 probably about 5,000 to 6,000. Lugging it around with the throttle open to get it to go is no good.
Having to downshift three times to get it to accelerate if you need to is no good either.

[Plinius10]

Thanks for the elaborate reply! I can't wait to get experimenting on my bike! One more trip when the rain isn't pour get down and I can refuel the bike for the first time I'm very curious. And I'll pay attention to where my rev needle is during riding around. Thanks again!

[81gs550l]

That sounds like you're just opening the throttle in sixth.

I'd love to see just how exactly you ride an 80's 550 do you live in Massachusetts?

[tkent02]

I ride it about like I ride any other bike, except with the 550 you have to wind it out to get anywhere.
And no I don't live anywhere near Massachusetts. Too many Patriots fans.

[cb1ocker]

Your speedo in mph? Mine only goes 85mph

yep, 95mph. before i replaced the previous owners super loud slash cut, no baffle exhaust i could only get it to 70, and it was hard to do. stock exhaust made a huge difference.

[tkent02]

And winding it out properly will make a bigger difference.

[Falcon Taco]

No, they are most efficient cruising in the range where the cam is beginning to work. Lugging them around wastes fuel.

Just curious, what do you mean by "when the cam is beginning to work?"

[tkent02]

Just curious, what do you mean by "when the cam is beginning to work?"

Certain RPM the engine starts to breathe well, feels happy, makes quite a bit of power, seems to gt great throttle response, just seems to work well. A tractor makes most of it's torque just off idle, a car maybe by a few thousand RPM, a big motorcycle maybe somewhat higher, but the little 550 takes a lot of RPM to work well. Mostly because to it's very unusual cam timing, designed to make the most power it possibly can at very high RPM, it doesn't work very well at all at a low RPM, which would be a normal RPM for most four stroke bikes. In comparison to just about any four stroke bike that's not a pure racer, the 550s need to really scream to work efficiently.

[ddaniels]

There's is just no information out there on how these old gems should be cared for.

Sure there is.....right here on this forum.

[TxGSrider]

Just curious, what do you mean by "when the cam is beginning to work?"

Most gasoline engines have between a 1500 and 2500 rpm spread that they make the most power (between peak torque and peak hp)- that's where the cams begin to work - the engine's "power band". The power usually rises pretty quickly just before peak torque, and usually drops off pretty quickly after peak hp, but shifting a little after the peak HP (about 500-1000rpms) usually results in quicker acceleration as the RPMS drop after you shift and puts you back into the engine's "powerband".