1981 Honda CM400 build log

[Daox]

Haha, that would be more helpful if it had a tach. Its a CM400E (E for economy). Thus the drums too.

[Frank Lee]

You might want to calculate it then!

[renault_megane_dci]

Sprocket change should be the highest ranking mod.
Makes for a relaxed cruise too.

I found it very hard to improve my mileage with a bike.
I blame too short a gearing since one can ride in top gear from 30 mph ...

[user removed]

The primaries are probably dirty and the main emulsion tuibes. The hole in the primary jet is so small you have to file the tip of a needle to get in in the hole. Put it in some tarn-X then mechanically clean that hole. Get something that will fit in the emulsion tube holes and mechanically clean them then tarn-x. WD 40 and a blast of compressed air.

Not sure if it has accelerator pumps or not. I think the 450 Rebel did and the 250. You might need to check the floats. Use a clear hose and plug it into the drain and open the drain to see the fuel level in the hose with the top above the float chamber. Make sure both are the same.

I left old gas in the GS500 too long and when I last tried to start it one of the carbs flooded. Haven't messed with it since I pulled the tank, valves need adjusting and it really needs to be stripped cleaned and repainted, frame, swing arm and rear wheel. I think I was pushing 65 MPG in warm weather, 1989 first year of the GS twin air cooled.

Honda twins is a great forum but I sold my 71 CB 350. I prefer CDI ignitions.

regards
Mech

[jkv357]

I personally would run a 5W-30 synthetic cycle oil (not standard auto oil) in it if I was looking for mileage, even though most likely 10W-40 is the recommendation. You will get plenty of protection for a 30-grade synthetic, even though it's not as "heavy" as a 40-grade. You will be chugging along at low RPM and load, and will not be putting any amount of stress on the engine. 5W-30 synthetic will flow easier, especially before you hit operating temp. If you do short rides it will help more.

As far as the fuel goes, I would run ethanol-free in a cycle engine of that age. You can get all sorts of carb problems from running ethanol if it's not designed for it. Cenex stations in WI usually have ethanol-free 87 octane.

I would sync the carbs and adjust the idle mixture to get the highest RPM, which is slightly lean for max power and the best acceleration but should be fine for you. I might check into a 1-range hotter plug also. The stock heat range is a compromise, and you will not be operating near peak power levels for an extended amount of time so you should be fine there also.

I would add Techron Concentrate anyway. I feel it's better than Seafoam. The carbs may still need manual cleaning of the pilot jets and all of the tiny orifices.

Gearing up/taller may help, as would some lower handle bars.

[Daox]

What kind of tire pressures are you guys running in your motorcycle tires?

[jkv357]

Originally Posted by Daox

What kind of tire pressures are you guys running in your motorcycle tires?

I run stock recommended pressures, but I'm not commuting and looking for MPG.

Run maybe 5 psi over the recommendation, but not a bunch more. There should be a "maximum pressure" for the tire listed somewhere.

[user removed]

I run 35 PSI in my bikes.

10W40 synthetic oil.

Never had a problem with 10% ethanol, even in my (sold) 1971 CB350 with factory carb jet sizes.

My GZ250 came with Metzler tires from the factory and they hold air better at 10 years age than brand new chinese tyres and tubes, many times better.

In winter I just run the bike occasionally and drain the gas and pour it in my car about once every 6 weeks, but there are riding opportunities here year round.

I have began to alter between regular and midrange fuel when it gets hot here, seems to pull better and low speed slight spark knock is eliminated.

regards
Mech

[mechman600]

I run stock tire pressure. I know I could increase it a little, but I am too scared of the possible ill-handling effects.
It might be hard to find aftermarket sprockets for your old bike, but you never know. Cafe racer websites might be a source. As already stated, gearing is the first step. Sounds like you are all over it already.
I find that coasting is nearly impossible on a bike compared to a car. Annoyingly so, and there's not much you can do about it.

[mechman600]

I run stock tire pressure. I know I could increase it a little, but I am too scared of the possible ill-handling effects.
It might be hard to find aftermarket sprockets for your old bike, but you never know. Cafe racer websites might be a source. As already stated, gearing is the first step. Sounds like you are all over it already.
I find that coasting is nearly impossible on a bike compared to a car. Annoyingly so, and there's not much you can do about it.