what should the RPMs be on my 1980 Honda GL1100 @ 70MPH?

when I am going 70 mph my rpms are about 4.5 is this correct or what may be wrong and how do I fix it?

2500 rpm

Without digging through my reference material for gear ratios and stuff, that does sound about right.Things that will change that is a lower profile rear tire, a larger rear tire, a larger or smaller front tire, speedometer error (although your 85 mph speedo was by law required to be more accurate than previous ones) and tachometer error.

Just for comparison 2006 Kawasaki 900 Vulcan cruiser turns 3500 at 60 MPH. Hope this helps.

I had a ninja 250 and that sucker would be at 7000 or 8000 rpms going 60 lol!Now I have a zx10 and the rpms are around where yours are.I like lower rpms at the higher freeway speeds rather than higher rpms as its less strain on the motor.You can adjust the rpms easily by changing the sprockets, either your front sprocket or rear sprocket or both sprockets.Some guys like to do wheelies and so they'll change the sprocket to get the rpm's up higher in the lower gears. Some also like to be fast off-the-line but a sacrifice is higher rpms on the freeway at speeds of 70 or higher.It's a personal choice and if someone lives in a very small city with traffic lights all over then I reckon they'd like higher rpms and they can get a sprocket to do it accordingly.If however you live where you take the freeways a lot or there are long roads that go on and on for miles with no stopping then an rpm reading of 4.5 is perfect.I have noticed the smaller the motor the higher the rpms. A 250 motor tends to rev higher than a 600 cc motor and of course a 1000 or 1100 cc motor will rev lower at higher speeds.This is good news if someone owns a higher cc bike (I know I'll probably get hell from the guys with 600-700 cc bikes but here goes) as it has been proven factually that over all higher cc bikes last longer when it comes to their motor.

4500 rpm is pretty normal for cruising speed with an in-line 4.

79 yamaha 1100 special is at 5,000 revs at 70. your number sounds about right. it gets annoying on longer trips running that high though.