Speed problem

[LonewalkerX]

Ok, after all my searching I've read quite a few people post that shifting early in the RPM range, say 5k-6k RPM, will get them to maybe ~70mph by 6th gear and that the bike won't accelerate past that. But if you run through the gears, that is, ~8k-redlining, they could achieve a speed of 100+mph. I just can't comprehend why this is so. Shouldn't you be able to accelerate to the bike's top speed just at a slower rate depending on when you shift? I'll have to wait till this weekend to test this out though because I haven't been able to get my bike past 70mph since I always shifted early to save gas. Whether it works or not I'll be sure to let y'all know. For now, can anyone explain why this may be so?

Here I quote tkent02:
"Have you tried winding it out?
Fourth gear until it tops out, fifth to the red line, then wide open in sixth.

550s need high RPM to make much power, especially if someone changed to taller sprockets.
Quite often sixth won't go as fast as fifth, just don't have the power to pull 6th.


On a 550 the power starts to increase at about 7,000 RPM, anything less it won't have much.

When I had tall sprockets on my 550, it would only go about 75 - 80 if you just open the throttle in 6th.

If I ran through the gears redlining each it would go about 110 - 115 mph in 5th.
Sometimes shifting to sixth it would go faster, but usually it would drop back a little.

Just didn't have enough to pull the taller gears."

So why won't the bike accelerate to 100+mph unless you really ride it hard?

[Bevo]

The short answer is its a 550, we need more information to help you.

What year is it, what model, what mods, whats the mileage, how much do you weigh?
All of these come into play and will affect your top speed.

Track down the post of how fast your GS is and you will see they are not the same as a modern sport bike...not even close!

[Steve]

Regardless of engine size, it's going to take a certain amount of power to accelerate a bike at a given speed. Smaller bikes, like the 550, tend to concentrate their power more to to upper end of their range. I don't know specific numbers, so I will just make some up. Let's say that horsepower peaks at 9000 rpm and torque peaks at 8000 rpm. Riding at 60 mph in top gear might have you at 5000 rpm. (am I even close?) At 5000 rpm, the engine just can't make enough power to accelerate you, although it can maintain that speed. A simple downshift to fifth gear would put you up to 6500 or 7000 rpm, where the engine makes enough power to get you going faster.

.

[Guest]

I would think that a properly geared and healthy running 550 would attain it's normal top end speed regardless of whether you red lined it through the gears or just accelerated from a lower point. However, if you geared it higher the inertia that would you have by redlining it through the gears would be lost and it may not be able to overcome that.

It didn't seem to matter on a 450 I had, the only difference was in how quickly it got there.

[tkent02]

Regardless of engine size, it's going to take a certain amount of power to accelerate a bike at a given speed. Smaller bikes, like the 550, tend to concentrate their power more to to upper end of their range. I don't know specific numbers, so I will just make some up. Let's say that horsepower peaks at 9000 rpm and torque peaks at 8000 rpm. Riding at 60 mph in top gear might have you at 5000 rpm. (am I even close?) At 5000 rpm, the engine just can't make enough power to accelerate you, although it can maintain that speed. A simple downshift to fifth gear would put you up to 6500 or 7000 rpm, where the engine makes enough power to get you going faster.

.

All true, the 550 has little power below 5,000 - 6,000 or so.
Tiny little pistons, very short stroke, they just don't do much at low to medium RPM.

Enough to cruise at 60 or so, although cruising at 60 would be easier on the engine and more efficient at higher RPM. Not to mention if something happened in traffic where you had to accelerate to stay safe. Downshifting three times and then nailing the throttle takes too long. At the lower RPM there will not be enough power to accelerate much, if any. When you add taller sprockets, it can't do much at all.

I would think that a properly geared and healthy running 550 would attain it's normal top end speed regardless of whether you red lined it through the gears or just accelerated from a lower point. However, if you geared it higher the inertia that would you have by redlining it through the gears would be lost and it may not be able to overcome that.

It didn't seem to matter on a 450 I had, the only difference was in how quickly it got there.

True with a properly geared 550.

Taller gears are no longer proper for this tiny engine.

[LonewalkerX]

Well, finally got to testing it (didn't make it past 70mph) and have now revealed some problems. I want to say around mid throttle the bike starts to bog; but if I open the throttle all the way, it takes a few seconds to get past the 5k-6k RPM bog range and will rev higher. It'll reach about 8.5k RPM in 1st-2nd gear. About 7k RPM in 3rd and 4th gear (now at 70mph). In 5th or 6th it stays around 65-70mph and at around 6k RPM. I can let off the throttle a little from wide open and it won't affect the riding much; but close to 3/4 throttle opening (maybe closer to 7/8) it'll lose power again. Any help?

[gearhead13]

Have you done all the maintenance on the bike? cleaned the carbs with new o-rings? Checked voltage at the coils? Adjusted the valve lash and checked compression?

[Bevo]

Sounds like its bogging when it hits the main jet, time to clean those carbs..also check your air filter and make sure your plugs, wires and ignition is all in good shape.