Top speed and milage CB750

[jwag]

I just found your forum and thought I would ask a question. I have a 79 cb750k. I have had it for about 10 years but I doubt if I have put 4000 miles on it since I've owned it. The top speed on it is about 80 mph which has always seemed slow to me but I have never had plans on needing to take it any faster so that is no big deal. My gas milage averages about 31 mpg. I would appreciate knowing how fast these things can go with stock engines and what kind of milage you guys get. Am I even in the ball park? I have a vetter fairing which adds quite a bit of resistance so that probably hurts some. My bike sounds good but I am wondering...

[Re-run]

Well my 78K would do over 100 with a vetter on it. I can also get over 40 mpg. So it sounds like you have a tuning issue. What color are your plugs? Are you running a stock honda filter? How about your exhaust?

[jwag]

The filter is an aftermarket foam. Exaust is 2 into 1 on each side and there seems to be no obstructions. I will check the plugs. It has been awhile since I pulled them.

[jwag]

Pulled the plugs. I am running on 3 cylinders. plug was as clean as it was when it was put in. Put a different plug in and there was no difference. I do not have a compression tester but that will be the nest step. I tried to plug the hole with a finger to get an idea of compression and I was unable to keep air from coming out no matter how hard I tried to plug it. That is a good sign but not a complete sign about compression. I am thinking it is probably a bad carb. Maybe a plugged jet. Any thoughts?

[Re-run]

So on 3 of the 4 cylinders, the plugs where white? Not sure how you would get bad mileage from that. A white plug means very lean running. You should have a light dusting to a light tan on each plug.
Is the filter in the airbox or is it a set of pods? Sounds like airbox but I thought I should ask.
Also, what rpm are you running at when the bike tops out?

[jwag]

3 of the plugs looked very nice .None of them were white. They had hardly any residue. One plug was wet. Looked like it had not been firing.  Air filter is in the airbox.

I took it out today to see what it would do. It hits 80mph right about 7000 rpm. It then starts sputtering like it is starving for fuel. I can hit 8000 rpm in 1st 2nd  3rd etc  but not in high gear. I guess that might be because you do not have to open up the throttle all the way in the lower gears. I will pull the fuel screen and look at it and check the fuel hose and make sure that it is not kinked and cutting down the flow.

[Kiwibiker]

Well, my 80 750c exlusive has a four unto one, and gets about 200ks a tank, and can top out at over 160 ks.Im sitting on 4500rpm at 100 kph.

[Dw07u]

I have a 1980 K, I have a four into four exhaust aftermarket system, other than that everything stock, and I get about 170km/h at about 7000rpm (without accelerating and shifting to redline), as far as riding fast(150km/h) for sustained periods, it does great! Took it on a breakfast run yesterday :D

Only thing is tho it starts to wobble(or snake as some have called it) at around 160km/h, is this normal? have checked the balancing and it was fine, what can cause this?