Topic: Re: New Member with a question/Re: AHHHHH DAMMIT, I NEED HELP!

[fuwad84]

Hi everyone, after lurking on the forum for a bit  I decided to join up. About a month ago I bought a 77 with about 7000 miles on it and the original rear tire in hopes of replacing my scooter as an ideal college commuter and occasional 400 mile touring bike (to visit my Mom up north). Didn't pay much, but since buying it I've had to replace the stator(not easy), the front and rear brakes, the tires (which is fine cuz they were old) and the swapped out the stock sprocket for a 38 tooth in the next few days I'm going to replace the front fork seals and possibly swap out the entire stock ignition system for a pamco system(not cheap but I'm hoping its worth it). So far I love the bike, I love how stable it is, even at high speeds, I love the way it looks - be it parked or me on it, but I do have one major hang up and its kinda a big issue with me. See even though the bike is old, in pretty good shape and considered a classic in some circles my primary use for it is as a year-round commuter, what attracted me to it was the clutch-less transmission, however after going through a few tank fulls of gas it seems like the bike is averaging about 22-25 MPG no matter how soft or hard I ride it, even if I go 2-up most of the way, strange I know! Along with installing the new ignition system, I'm going to try the best I can to sync up the carbs and adjust the valves. I'm hoping this helps. My question is, for you stock 750A's out there is what kinda gas mileage are you getting on these badboys. I realize that these machines were built in an era before the oil crisis and EPA regulations for bikes so I'm not expecting this thing to be any match to my 150cc scooter gas-miser wise, but for a motorcycle, even one with a slushbox, is 40MPG really that unreasonable? Thanks all.

[05c50]

I can get about 35 mpg on my 77 'matic pretty much all the time, but I don't think you'll be able to get much more than that. Checking with other 'matic owners, that's about it.

.............Paul

[77 CB750A]

30 shouldn't be a problem.

[fuwad84]

I can get about 35 mpg on my 77 'matic pretty much all the time, but I don't think you'll be able to get much more than that. Checking with other 'matic owners, that's about it.

.............Paul

got any recommendations?

[Sam Green Racing]

Not sure how I can say it without sounding rude but I think your problem might be the rear fender rubbing on the rear tyre.

Sam.

[madmtnmotors]

Did you log any miles with the original 41 tooth rear sprocket for a mpg comparison? Also, the front caliper on these old bikes tends to want to start sticking so make sure your front brake isn't dragging.

[raymond10078]

Have you tried second gear?   

[raymond10078]

Ok, something helpful - from another recent post:

On the entire trip, I got 38 MPG, with speeds ranging from 100 km/h (60 mph) to 160 km/h (100 mph) Average speed was about 130 km/h

I maxed out the fuel mileage on one stretch at about 60 mph at 50 mpg!

[fuwad84]

The front brake does drag a little bit so I will look into that. I'm pretty sure the fender does clear the tire, but most of the riding I do is with just me on it anyway. Thanks for the pointers guys.

[madmtnmotors]

Try changing the oil too. The transmission likely uses the same oil that also circulates through the engine (I know the standard trans do) hence the 1500 mile change interval. If the oil is tired it may affect transmission performance.

[fuwad84]

Try changing the oil too. The transmission likely uses the same oil that also circulates through the engine (I know the standard trans do) hence the 1500 mile change interval. If the oil is tired it may affect transmission performance.

I already changed the oil to a 20W-50 synthetic, although it is a bit thicker than what is recommended, given that its an old motor and it gets real hot during the summer I don't think this is too bad of an idea.

[Sam Green Racing]

7000 miles is nothing for these old motors, try useing the recomended oil or even lighter.
I was joking about the fender rubbing the tyre but even one up, you look a very big guy from your picture this won't help the fuel consumption.
Check all settings (normal service settings) plus tyre pressures (per yours and passengers weights) chain tension, and brakes for binding.

Sam.

[madmtnmotors]

Lighten up on the oil, synthetics work well so stick with the synthetic if you like. 20W-50 is too heavy, and like Sam said "7,000 miles is not old", it is hardly broken in. Mine is pushing 60,000 miles and lives on 10W-40, even through our six months of summer here in Florida.

[05c50]

I can get about 35 mpg on my 77 'matic pretty much all the time, but I don't think you'll be able to get much more than that. Checking with other 'matic owners, that's about it.

.............Paul

got any recommendations?

Check to make sure the brakes aren't dragging and the wheels turn freely, tune it to perfection, replace the air filter, and don't crank on the throttle everytime you pull out from a stop.

............Paul

[Dave Wyatt]

I average 30 with my 270 pounds on the seat.  More (as high as 45) on long hauls with no stop and go, less with traffic. 

I lose 2 mpg with Marathon fuel, so I always try to use other name brands, or an off brand that I know that works well. 

I would ditch the 38 tooth sprocket and go back to the 41 to get the bike moving easier.  What you tried to gain on the top end by slowing the engine down was lost on the bottom end by making it work harder taking off. 

[tomsweb1]

When I first got the bike I had a huge problem with fuel consumption. I could get maximum 66 miles out of a tank. That's 13 mpg. It was awful! I rebuilt the carbs with all new rubber, replaced the spark plugs and caps, and balanced the carbs. I'm the one who got 50 mpg.

[fuwad84]

When I first got the bike I had a huge problem with fuel consumption. I could get maximum 66 miles out of a tank. That's 13 mpg. It was awful! I rebuilt the carbs with all new rubber, replaced the spark plugs and caps, and balanced the carbs. I'm the one who got 50 mpg.

Thanks Tom and everyone else, I'm replacing the ignition system now...and I'll probably have a cheap local shop look at the carbs as it seems fixing and calibrating them may be a little out of my league. Hey you guys know ANYWHERE I can get replacement intake boots, if I have to pull the carbs I might as well replace em?

[tomsweb1]

There is a guy on the Yahoo groups Hondamatic group that actually makes new ones... I'll see if I can find a link...
 Here is the repacking kits:
http://cgi.ebay.ca/Honda-nos-CB750A-CB-750-Hondamatic-carb-gasket-kit-/300576755959?pt=Motorcycles_Parts_Accessories&hash=item45fbc550f7#ht_500wt_1156

[05c50]

There is a guy on the Yahoo groups Hondamatic group that actually makes new ones... I'll see if I can find a link...

I'm that guy. At present, I don't have any of the insulators available and I'm not sure when they will be available. I'm looking for a new rubber compound that is more resistant to ethanol now being added to the gasoline. Be careful removing the carbs. The insulators are hard to find........at least for now,

...........Paul

[Danno]

bud the problem I see is that you pulled the teeth too far down on the rear sprocket put a 48 tooth back on and you will get at least 32 mpg and as the other member said you can get higher on the highway anyway i would not go below 42 teeth with one rider and i would still use 48 if you are riding 2 up if you want to lower the ratio try a 18 tooth front sprocket that will give you the ratio you want without changing the rear or the chain

[fuwad84]

bud the problem I see is that you pulled the teeth too far down on the rear sprocket put a 48 tooth back on and you will get at least 32 mpg and as the other member said you can get higher on the highway anyway i would not go below 42 teeth with one rider and i would still use 48 if you are riding 2 up if you want to lower the ratio try a 18 tooth front sprocket that will give you the ratio you want without changing the rear or the chain

The stock sprocket I replaced was a 42 tooth which is what came stock on the 77, I don't think that going down to a 38 is THAT much of a change is it?

[Sam Green Racing]

Try a 52 rear, that should make life easier for the poor thing.

Picture in post reply 1631.  http://forums.sohc4.net/index.php?topic=61876.1625

Sam.

[Danno]

my 77 A came with a 48 and the book for mine shows 48 in a 530 chain the big chains had fewer teeth but a 38 in a big chain is too big a drop for it these bikes
they do well with the 530 chain and a 17 front 48 rear also if you want to keep it use castrol regular oil in 10/40 the 50 weight will kill the torque converter although sam may know better for racing situations  and you are talking about a fluid dynamic clutch (torque converter) one way to make sure it slips too much is by using the synthetic oil it is too slippery

my 76 came with a 41 in the big chain in my experience with honda going down in teeth will never give you better mpg but going up a few has especially if you ride 2 up

[fuwad84]

Hey guys thanks for your help. So far I've replaced the oil with 15W-40 Rotella, swapped out the ignition for a pamco electronic deal along with replacing the coils, wires, plugs, and had the carbs synced and adjusted. Performs much better, but MPG... a consistent 26.75 miles per gallon. Still really #$%*ty and I'm just about out of ideas here. As much as I REALLY like the bike and how well it suits me, I don't know if I can justify commuting in something that gets worse in-city mileage than my car. The sprocket was the first thing I replaced and I went from getting 83 miles a tank to 97, than after doing all the other stuff I'm up to 107 miles a tank...but I think I've run out of things to do.

[raymond10078]

What air filter are you running?  I'm asking because some filters are being sold and OEM that are very, very restrictive.  I run a K&N with no problems.

Poor mileage can be caused by a number of things, some are:

• wrong sprocket sizes - running the motor outside of designed speeds
• chain too tight
• air filter too restrictive
• rider too agressive
• timing off
• ignition advancer not working
• low compression
• valves incorrectly adjusted
• exhaust blockages
• brakes dragging

I know some of this is a repeat - but it doesn't hurt repeating.  Other chime in with their ideas . . . .