Topic: My bike runs great

[mycb750k6]

It idles perfect, accelerates hard, shifts well and seems to have lots of power until I get to around 90mph. Then I have considerable trouble getting it to 100. 1971 CB750 completely stock down to that last bolt completely tuned and dialed in.
What's up? Clutch, advance, compression? How fast do you folks go, seriously? What won't mine go fast?

[Queeg]

try driving south on I5 instead of north up all those hills. 
  is it a wall while accelerating. or does sit slowly climb and tapers to 90 and then even slower to 100?
air box or pods?  just sounds like your running out of fuel at the top end.
how much you weigh?

[vern401]

Wow that is odd to me. If this was a 500cc bike I would say it is normal. I remember alot of friends that had the 750's back in the day hit 110 with no problem and then maxed out at about 115-120. My CX500 had no chance against these bikes. Whay color are your plugs? I know stock filter since you said stock right down to the bolt. What is your compression running?

[mycb750k6]

Slowly climbs and tapers to 90 and then even slower to 100 - yeah that's it.  Honestly I haven't ducked in and waited to see where it would peak. Just gave up around 95 but this is supposed to be a 120 mph bike. Maybe it's just old, modern gas, I weigh too much (185)

Running out of gas is intriguing. Routing the carb top breather hoses into the air box is supposed to raise float level at high speed. I'll try that.  Bike is totally stock except the K&H filter.

[zzpete]

Are we talking the Polynesian Blue bike? HM300 exhaust? My old green 1971 HM300, stock air box, 18 x 48 gearing got to 115 pretty quick and would go to 120 and I'm 215lbs. I could redline in every gear. Low floats? Do you have 120 main jets?

[CB750Ken8]

When you're trying to get top speed are you up in 5th gear? I know with mine when it was running and i could ride it was hard to get to 90+ in 5th but the last time i rode it I was able to get to 90 in 3rd gear no problem, started getting into town so I couldn't shift up into 4th and 5th to see how high she'd go.

[Spanner 1]

Try pulling the clutch at about 60 and just let the bike roll and idle.... should be real quiet .... any chain probs would be heard and any 'extra' slowing ( chain or front brake drag ) should be easily ' felt '......
BTW... what rpm are you showing @ 90mph?.... my stock K1 (18F x 48R sprockets ) shows right at 6K rpm @ 90mph.

[mycb750k6]

I'll try a few things today. I was trying to creep it up from 70 in 5th. Perhaps I'll downshift to pick up some HP first.

[CB750Ken8]

Yep sounds about right and I think it would have taken some time to get to 90 and you might have ran out of road before you got to 100, in 5th without getting to 90 in 3rd gear, which with stock parts I think would put you in the...7500RPM range.

[Johnie]

You said it all in the heading, "my bike runs great." I would hate to see you push it up to high and damage something. Guess that is the conservative in me thinking about a vintage bike. Let us know when you max it out. And be careful...scarey things can happen at those speeds that make it tough to turn back.

[mycb750k6]

OK, OK. You talked some sense into me. ( I'll try 90 in third instead  )

[zzpete]

OK, OK. You talked some sense into me. ( I'll try 90 in third instead  )

WIND IT OUT!!!