Author Topic: Fuel mileage questions (Read 2366 times)

JerrodR · « **on:** November 26, 2020, 02:12:53 PM »

Hey what's up guys, last Spring I bought a 74 750/4 for dirt cheap. Over the Summer I replaced one of the Rocker Tower's and installed a Camshaft from a 78 Hondamatic. It runs great now, and it's actually my Daily at the moment. Which led me to calculate how many miles I'm getting out of a full tank. Its getting 127.6 Mile's out of a 5 Gallon tank. Doesn't seem very good, but I've been told CB-750's aren't the best to begin with. Is this about average, or are you guys getting better?

robvangulik · « **Reply #1 on:** November 26, 2020, 02:25:04 PM »

That is 25.5 mpg, is that at constant top speed?

JerrodR · « **Reply #2 on:** November 26, 2020, 02:29:24 PM »

Yeah, that's what I got too. And I live in Rural Ohio, spend the majority of the time in 5th gear at 3700 RPM which is 55 MPH.

JerrodR · « **Reply #3 on:** November 26, 2020, 02:31:13 PM »

I mean, I do play around a bit. I think Motorcycle's should be fun. But most of the time it's just average Commuting like I would do in a car.

robvangulik · « **Reply #4 on:** November 26, 2020, 02:33:38 PM »

I never got worse than 35 to 40mpg at average speeds of 90 miles per hour with any of the four 750's I have had over the years.

bryanj · « **Reply #5 on:** November 26, 2020, 02:59:35 PM »

Matic cam is different grind for gearbox that might make a difference, dont know for certain as matic never came to UK

ekpent · « **Reply #6 on:** November 26, 2020, 05:01:05 PM »

Mid 40's up to 50 or so are what I can get from 750's riding around my country haunts.

Kevin D · « **Reply #7 on:** November 26, 2020, 05:39:43 PM »

Quote from: ekpent on November 26, 2020, 05:01:05 PM

Mid 40's up to 50 or so are what I can get from 750's riding around my country haunts.

+1
48mpg +/-
K1
18/48 sprockets
90000 mi
Shell VPower

seanbarney41 · « **Reply #8 on:** November 26, 2020, 06:21:59 PM »

Ok...but where did you get a 5 gallon tank?

goodtryer · « **Reply #9 on:** November 26, 2020, 06:42:15 PM »

Been getting 25-ish on mine. Got it running a couple of months ago and have put over 1000 miles on it. Stock engine as far as I know except Dyna ignition and a Kerker 4-into-1 exhaust.

HondaMan · « **Reply #10 on:** November 26, 2020, 06:50:27 PM »

Quote from: goodtryer on November 26, 2020, 06:42:15 PM

Been getting 25-ish on mine. Got it running a couple of months ago and have put over 1000 miles on it. Stock engine as far as I know except Dyna ignition and a Kerker 4-into-1 exhaust.

In this case, maybe try using resistor-type sparkplugs to try to extend the spark duration a little bit. The Dyna S makes for very short spark. I'd suggest the ND XR24ES-U or maybe the NGK DR8ES-L plugs.

HondaMan · « **Reply #11 on:** November 26, 2020, 06:54:23 PM »

The Hondamatic cam has very short intake dwell. It opens about 15 degrees ATC on the intake stroke. So, maybe try using resistor-type sparkplugs with extended tips (DPR8EA9 NGK or XR24ES-U in ND) and turn the carb's air screws inward a little bit, to like 7/8 turn or 15/16 turn instead of 1 full turn out from the inward stop. Also make sure your plug caps are good: they should measure close to 5,000 ohms if they are the SD05F and XD05F types.

goodtryer · « **Reply #12 on:** November 26, 2020, 06:59:11 PM »

This place is a literal gold mine!

Thanks, Mark!

Bodi · « **Reply #13 on:** November 27, 2020, 05:09:58 AM »

"average speeds of 90 miles per hour"

What race track do you commute on?

JerrodR · « **Reply #14 on:** November 27, 2020, 07:13:49 PM »

The Tank was on it, it is off a 78 750/4. I say 5, Because after I Cleaned it out. It held right at 5 Gallons when I filled it. This Bike is a true Hodgepodge of CB-750's, but that's partly why I love it so much. And yes, I was told the Hondamatic Cam had a different Duration. And that the Hondamatic's had Low Compression Piston's. And the Camshaft will make a little more Tourqe with the Standard 750 Piston's. I also Replaced the 18" Lester that was on the Rear, with a 16" Lester. While I'm fixing up the 18". Don't know if that would effect GM. But it did effect Acceleration. This little Bike Scoots from a dig for what it is. I outran a Harley 104 Heads up to about 90. Then, yeah he came around me lol.

HondaMan · « **Reply #15 on:** November 27, 2020, 07:45:25 PM »

The 'Matic's pistons aren't different, but that magic cam was what reduced the effective compression ratio. Also the 'Matic heads are a study in choked intakes: you can add almost 20% more flow to them by making the ports look like a K1 or K2 and then switching them to the K1 cam. Honda was more than 'conservative' for the tranny on the 'Matic, but they do last a long time for their effort!

Don R · « **Reply #16 on:** November 27, 2020, 10:42:52 PM »

Did you ride until it was empty? If it just hit reserve there was still a gallon or so still in it. If that is true it got 32mpg. I always refill and see how many gallons were actually used, then I reset the odometer after my phone does the math.

HondaMan · « **Reply #17 on:** November 28, 2020, 02:13:23 PM »

Yeah, and my 4.8 gallon tank goes on Reserve at 1.3 gallons, so I can only measure it for 3.5 gallons (maybe). It runs happier on Reserve, too.

tlbranth · « **Reply #18 on:** November 28, 2020, 05:28:34 PM »

When I first resurrected my 75 k0 after it sat unused for about 25 years, I was getting about 17mpg. After a lot of tweaks and fiddling it's now getting 45-50mpg. Runs great but doesn't idle too well. What I found was: there's no magic bullet. Mine took a lot of adjusting of carbs mostly. I chucked the old coils and replaced them with Dynatek. New Dyna plug wires and NGK caps too. Hondaman ignition keeps the points pristine. One big faux pas was using an Emgo air filter. It let air through like a sheet of plastic.

PeWe · « **Reply #19 on:** November 30, 2020, 10:21:17 AM »

40mpg has been a very common fuel consumption on my bike, CB750 K6.
Riding very slow, like 40-50mph, 10% less fuel.

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Author Topic: Fuel mileage questions (Read 2366 times)