Author Topic: CB750 mpg  (Read 1577 times)

Offline MrDavo

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CB750 mpg
« on: April 27, 2017, 06:30:07 PM »
I can't find the recent previous thread on this (or maybe, as happens on here, it was a diversion on a thread about something else entirely) but, for the record, after careful measurement I am pleased to find I am doing 37mpg, I guestimated it to be far worse after nearly running out of petrol the other week.

I'm sure there will be gentle riders who get more, and Earnest Thrasher who will get much less, but my K1 is bog standard inside, most moving parts subject to wear have only a few hundred miles on them, and the carbs were synched professionally, so a pretty good yardstick.

Unfortunately I am too stupid to work out how to set up a poll (if you can with this forum software) to see what you all get. I always treat published road test figures with contempt (don't want to upset the advertisers etc), and anyway most figures on the 'net are in US gallons which are different.
« Last Edit: April 27, 2017, 07:03:32 PM by MrDavo »
1969 Honda CL450 'Scrambler'
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2005 Harley XL1200R Sportster
1985 Porsche 911 3.2 Carrera Sport
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Offline Skoti

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Re: CB750 mpg
« Reply #1 on: April 29, 2017, 08:13:08 PM »
Have you ever renewed the carb needle jets?  :o
Motorcycling is Life, anything B4 or after is just waiting...


1976 Honda CB750F1

Offline MrDavo

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Re: CB750 mpg
« Reply #2 on: April 29, 2017, 10:18:50 PM »
Yes. It was a pig to start when I got it so I changed everything. In the end it all came down to needing a carb synch.
1969 Honda CL450 'Scrambler'
1974 Kawasaki Z1A
2005 Harley XL1200R Sportster
1985 Porsche 911 3.2 Carrera Sport
1978 VW Bay Window camper van

Offline Skoti

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Re: CB750 mpg
« Reply #3 on: April 30, 2017, 08:40:51 AM »
I only ask because my F1 also had poor fuel consumption of around 35mpg when I first bought it.

After a service and tune up including carb synch the fuel consumption problem was still the same.

Met a bloke on a F1 at the Moto Piston rally in Santander and he told me to renew the needle jets with genuine Honda items. He said they would need renewed about every 12,000 to 15,000 miles to maintain decent fuel economy.

He was correct, on a recent 3,000 mile round trip to Ireland I averaged 52mpg. :)

 
Motorcycling is Life, anything B4 or after is just waiting...


1976 Honda CB750F1

Offline steff750

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Re: CB750 mpg
« Reply #4 on: April 30, 2017, 09:18:37 PM »
Quote
on a recent 3,000 mile round trip to Ireland I averaged 52mpg.
im sure ive said this before ? yes that is what i got from ,my k0s i usually stick to speed limit these days,only my combination does worse i think i get about 45 mpg from that and its got a f2 engine so it does rev a lot harder when pulling the sidecar

Offline Spitfire

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Re: CB750 mpg
« Reply #5 on: May 02, 2017, 05:50:13 PM »
Touring around Wales with a friend at legal speed limits I got 48 mpg from my F1, the carbs have not seen any new parts since I bought the bike new in 76.

Cheers

Dennis
1976 CB750F

1977 CB750F2 In bits

1964 BSA A65R In bits

Offline MrDavo

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Re: CB750 mpg
« Reply #6 on: August 07, 2017, 11:19:51 AM »
As an update to this thread, I changed the coils and HT leads, which had got hard with age and 'hollowed out' at the plug cap ends.

What a difference! - the flat spot at low revs, with occasional temporary lapses onto three cylinders, and the hard starting from cold went away, and mpg is now around 41mpg, which I can happily live with.
1969 Honda CL450 'Scrambler'
1974 Kawasaki Z1A
2005 Harley XL1200R Sportster
1985 Porsche 911 3.2 Carrera Sport
1978 VW Bay Window camper van

Offline sprinta

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Re: CB750 mpg
« Reply #7 on: August 07, 2017, 07:20:50 PM »
As an update to this thread, I changed the coils and HT leads, which had got hard with age and 'hollowed out' at the plug cap ends.

What a difference! - the flat spot at low revs, with occasional temporary lapses onto three cylinders, and the hard starting from cold went away, and mpg is now around 41mpg, which I can happily live with.

What did you change the coils with, new original pack or a pattern set?

Offline Moorey

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Re: CB750 mpg
« Reply #8 on: August 07, 2017, 08:11:13 PM »
I only ask because my F1 also had poor fuel consumption of around 35mpg when I first bought it.

After a service and tune up including carb synch the fuel consumption problem was still the same.

Met a bloke on a F1 at the Moto Piston rally in Santander and he told me to renew the needle jets with genuine Honda items. He said they would need renewed about every 12,000 to 15,000 miles to maintain decent fuel economy.

He was correct, on a recent 3,000 mile round trip to Ireland I averaged 52mpg. :)

 

Is that just the jets or needle and jets.?
Last tank of fuel on my F1 worked out at 40.2mpg but more often than not 37-39 but I am not exactly gentle with it.

Offline MrDavo

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Re: CB750 mpg
« Reply #9 on: August 07, 2017, 09:48:50 PM »
What did you change the coils with, new original pack or a pattern set?

Original Honda, from DS. £ horribly expensive, but worth it if they last another 45 years.
1969 Honda CL450 'Scrambler'
1974 Kawasaki Z1A
2005 Harley XL1200R Sportster
1985 Porsche 911 3.2 Carrera Sport
1978 VW Bay Window camper van

Offline Moorey

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Re: CB750 mpg
« Reply #10 on: August 08, 2017, 03:16:55 PM »
The witch piss we call petrol these days could have something to do with not getting as far on a gallon as back in the 60s 70s.

Offline Moorey

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Re: CB750 mpg
« Reply #11 on: August 13, 2017, 10:31:39 PM »
I had a steady ride out today up to Hawes through the Dales and back. Round trip 162 miles 46.8mpg. That's the best i've ever had on a run. Shows what you can get if you ride like an old man.  ;) Might have to do it more often.! On second thoughts  Nah.

Offline Skoti

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Re: CB750 mpg
« Reply #12 on: August 18, 2017, 08:21:24 PM »
I only ask because my F1 also had poor fuel consumption of around 35mpg when I first bought it.

After a service and tune up including carb synch the fuel consumption problem was still the same.

Met a bloke on a F1 at the Moto Piston rally in Santander and he told me to renew the needle jets with genuine Honda items. He said they would need renewed about every 12,000 to 15,000 miles to maintain decent fuel economy.

He was correct, on a recent 3,000 mile round trip to Ireland I averaged 52mpg. :)

 

Is that just the jets or needle and jets.?
Last tank of fuel on my F1 worked out at 40.2mpg but more often than not 37-39 but I am not exactly gentle with it.

That's the slide needle and needle jet (supplied as a set from Honda, part number 16012 392 004)
Motorcycling is Life, anything B4 or after is just waiting...


1976 Honda CB750F1

 

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