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What's your best MPG???

Tate

CB750 Member
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I have a 1975 CB750F Super Sport... I get 22MPG on highway and 18 in town. What is the best MPG that you get or the best you've heard of for my make and model...how was that good gas milage achieved? I am well aware that with a older bike that I won't be getting 100MPG but I should be getting better milage than what I'm getting...right? Thanks for the info.
 
Hey Tate, yes that is very low. Good gas mileage is achieved with a bike in good condition that's properly tuned up and jetted. What's the history and condition of the bike?
 
My 72 k got 34 mpg and was running rich my 79 dohc 750f gets 45 mpg consitantly. I think the 72 should get around 40 running proper.
 
I never got better than 35 with my 72 motor. My dad gets from 35 to 40 with his original 74. I have never checked with my 836 motor I just ride.
I would check all the tune up parts, do all adjustments(timing, dwell, carb sync, timing chain adjust, valve adjust) And do a compression test to see how healthy the motor is.
 
Hey Travis thanks for your reply. I thought that my bike was in great shape but from the replies maybe not. I have had the dyna starter and the dyna coils installed by professionals...I am having second thoughts about these "pros" since I have found subpar work. One of them said that it is common for a lower mileage. I see below that dirtdigger has made some suggestions... in addition when I got it I replaced the chain and sprockets and I asked for a lower gear ratio since I was an inexperienced rider and live in Seattle with steep hills and weigh 250lbs. I don't know the ratio I got off hand.
The bikes history is that it is pretty much all original,except for the above things, and was bought from a guy who loved his bikes and took really good care of them. He told me that he spent $1100 on the carbs alone...seems like alot for that.
Again thanks for your reply and I look forward to hearing more opinions on here. I've gotten some good feedback,FYI, since you're on the forum staff! ;-)
 
A lower gear ratio will cause engine rpms to be higher at a given speed compared to stock and will cause worse fuel mileage but only a couple of mpg. Does it run rough? Smoke black? I like the dyna ignition and run it on my stuff, if it was installed correct and timing set correct it should get the same if not better mpg because it does put out a better spark. Are they stock carbs?
 
dirtdigger
I believe the carbs are stock. I am wondering about a compression test...the #2 cylinder has gave me a few problems on firing as hot as the others but I think that the dyna coil wasn't making a good contact in there with the spark plug wires which I remedied and it ran so much better! I've asked all the mechanics if they they thought that the compression needed checking and they all say no.
Thanks for a quick response to my reply to travis's post
 
I couldn't agree more with dirtdigger's suggestions of checking the compression and timing, adjusting the cam chain, checking valve clearances, and syncing the carbs. They are all the first things you should do. I was going to suggest the same after hearing the condition and history. You might also want to check or replace the air filters. Even though the previous owner put a lot of money into the carbs, they might need attention again with the crappy ethanol gas we have these days. Maybe whoever worked on the carbs rejetted them really rich. New plugs and an oil change wouldn't hurt anything either depending on how long ago they were done. How long have you owned the bike? Your weight and gear ratio are both going to affect your MPG, but not to the point where you're only getting 22MPG on the highway if everything else is in order. You can count the number of teeth on your front and rear sprockets and we'll be able to figure out how much lower your MPG will be from that alone.
 
Something sounds way off, compression, timing, floats sticking. With my wife on my stock cb750 we got around 50mpg. Just me crusing the highway to work the best I got was 70mpg. But that took a bunch of tuning to get that.
 
Tate......I am wondering if there is something diff with the F models. I had a new in 1976 750F and it got only 28 to 30 mpg from day one. I just purchesd a 1975 750F WITH 15K. Went thru it and with stock jets and settings it gets 28 to 3o mpg also. I sure would like to get alittle better mpg. What are you other F models getting, and with what settings? thanks
Bucky
 
So many things affect mpg. Gearing is a big factor, tire pressures, engine tune, speed, how far you twist with your wrist, fuel quality. But then again I dont ride bike to get good gas mileage:D
 
Well here I am again...checked the gas mileage again today and averaged 14 mostly in town. This is messed up! I will be changing sparkplugs, oil filter, air filter and oil. This bring me to another question...how DO you check your oil level? Such an easy thing but I've been told: check it cold, run it 5 minutes/shut off and wait 1-2 minutes/check and finally run 5 minutes and check while running. I would not suggest that last one. I wish the mechanics on this site lived in Seattle...I'm just sayin'
Feel free to comment on any of my problems...
 
Run engine for couple minutes at 1000 to 1500 rpm, shut off engine and check level right away. This is factory Honda manual method. Dont check while its running because it will read low.

How does your bike run? With that bad of mileage it should run like crap and be blowing all kinds of black smoke. Does the oil smell very gassy? Does the choke come open all the way?

Something is really wrong.
 
Actually when I ran it 3 minutes at 2k and checked it while it was running it ran all over...
It is running bad right now. #1 and #2 cylinders are running only warm at best. I'm thinking that the dyna coil is not making a good connection. I had this problem a few months ago and rebuild the spark plug wires and reconnected to coils...might need to use that gel that helps make a better connection. How reliable a those dynacoils for longevity? It seems like most of my latest problems started when I installed that. Always has had about the same gas mileage though...
 
The return side of the oil could be spraying all over with the cap off at that rpm.

The dyna coils do have a reputation for going bad. But I run them and dont have a problem. Are you running points with these coils or the dyna setup? Cylinders 1 and 2 are on seperate coils so if they are not firing right then you have an issue with each coil. 1 and 4 are paired and 2 and 3 are paired.
 
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