[Briarwk]

So the other day I did my first oil change on my bike and I over filled it just a bit, after riding for about twenty miles I noticed that my speed in 6th gear when crusing around at at 6000rpm seemed about 5 mph slower. After looking at it for the rest of the ride I am certain that I lost some type of power. I just recently lower the oil back down between the two oil marks. I was just wondering if the oil being filled a bit above the limit could cause such a dramatic drop in speed. I know like 5 mph doesnt sound like much but for a bike that doesnt wanna go above 90mph, 5 is very noticeable and quite substantial.

 

[Unkle Krusty]

What was the top speed after you drained some oil out?

UK

 

[Briarwk]

It's not necessarily top speed, but before the change I would cruise at 60mph at 6000 rpm roughly and now it's like 6500rpm. This trend seems to carry for just about any speed aswell. Like the moment I got on the bike and into sixth gear I noticed something wasnt adding up

 

[Briarwk]

And draining the excess out has had no improvement in performance

 

[cmonSTART]

Well, if everything (including your clutch) is working properly your engine, transmission, and rear wheel are all mechanically linked together while in gear, so if your bike does 60mph at 6000 rpms it should ALWAYS show 6000 rpms at 60. If it's not, your clutch is slipping.

Two questions: What oil did you use?

Do you have a clutch cable and have you adjusted it recently?

 

[Briarwk]

I haven't messed with the clutch cable since I bought the bike and the used Honda's GN4 10w40 oil

 

[cc rider]

should be 10w-30 (especially if you're in warmer area)

 

[Briarwk]

The exactly oil is 08c35-a141l01, andi live in north western Pennsylvania so a decent amount of my ride time is 60 and below. Could the oil being that little bit thicker really shave off that much performance though. And going back to the previous comment, it still should always go 60mph at 6000rpm in 6th gear.

 

[cmonSTART]

Ya, I'm sure the viscosity isn't the issue, and as long as you're running an oil which works with a wet clutch that's not the issue. Try a cable adjustment and see where you're at.

 

[Briarwk]

Will do, cable wouldn't be my first guess because of the sudden change but at this point it's worth a shot.

 

[cmonSTART]

Understood, I agree. But, it's one of the easy/free things to check and worth crossing off the list.

 

[Briarwk]

Confirmed the clutch is not slipping due to a the cable being too tight

 

[Briarwk]

Took it out for a ride, still 5 mph off from 6000rpm, cant tell if it gets worse the higher I go as I dont remember what the crusing rpm was at 70 or 80. Figured this was worth it, the following two photos are after a ten mile ride, up to 9000rpm and then in neutral revving it up to 8000rpm twice. Bike was warmed up. But had some air bubbles it seemed in the oil. The bike is still under warranty but I dont know if they will do anything as the bike still runs smoothly, but I dont know what else could be effecting it. Also I double confirmed the oil was hondas motorcycle oil.

 

[Unkle Krusty]

Well Cmon beat me.
If the bike did 60 at 6000, and now it does 6500 at 60, then either the tach is off, or something is slipping in the drive chain. Are you sure you have the numbers correct?
My old XS400 does 60 at 6000.

UK

 

[Briarwk]

Yeah I am certain of the curse speed and rpm. And I have checked everything in the drive train and it all checks out.

 

[cmonSTART]

If it's under warranty still I would visit your local Honda dealer and have one of their techs check it out.