1981 Honda CM400 build log

[jkv357]

Even though your speeds aren't consistently very high, I think you still would benefit from better aero.

There's a lot of air hitting your chest and helmet because to the upright riding position. Lower handlebars and/or a small fairing to divert the air around you would help.

A non-o-ring chain may help also. If you put it up on the center-stand and spin the rear wheel you would get some idea of the amount of drag you are getting with the current set-up. If it's anything but pretty decent you would most likely see improvements with a new non-o-ring chain.

I would also go to a 30-grade synthetic cycle oil, or at least Rotella T6 5W-40, which is on the low end of the 40-grade and is superior to conventional oil in every way, especially in an air-cooled engine like the CM.

As far as technique, I would try to get your accelerating done in a shorter time and into top gear (or the appropriate cruising gear) asap. When the cruising speeds are low, top gear may even be too high and might cause you to open the throttle more that necessary. Moderate RPMs and small throttle openings are better than low RPMs and larger openings.

You may want to go through the carbs also. There may be improvements from getting your idle mixture optimized by adjusting the idle mixture screws.

Ethanol-free gas will improve mileage, and is generally better for an older engine and fuel system, but will cost more per mile.

[MetroMPG]

. Not a very impressive 39.6 mpg. This is typical of the first tank of the year though.

Technique?

Or because you're idling it while getting it ready for the season?

[Daox]

I think its mostly from sitting. I drain the carbs in fall, but the first tank of the season is never that great on fuel economy. It raises after that.

[jkv357]

Originally Posted by Daox

I think its mostly from sitting. I drain the carbs in fall, but the first tank of the season is never that great on fuel economy. It raises after that.

Depending on when you filled-up, you may be running winter-blend gas - which is going to lower mileage.

I still think your mileage should be better though. My SV650n will run 50+ MPG (on 87 octane ethanol-free) all day long - in-town or on the hwy without any consideration to mileage.

Cenex stations in this area of WI have ethanol-free 87, and I run it in all the bikes and small engines.

[MetroMPG]

I drain the carbs in fall

Well, when you throw away 1/10th of your fuel capacity, no wonder the first tank is poor.

[Daox]

I'm sure the carbs could have a good look over. They probably could use a good cleaning too. Its never really run great, it has to be warmed up to have good throttle response.

As for the oil, I'm a bit leery of going to a synthetic. The clutch and trans share the motor oil which is specced to be a 40W. I've heard going to synthetic can cause the clutch to slip a bit.

[Michael Moore]

Originally Posted by Daox

Its never really run great, it has to be warmed up to have good throttle response.

That is common on older carb'ed bikes, they were set up quite lean near idle for emissions.

[jkv357]

Originally Posted by Daox

I'm sure the carbs could have a good look over. They probably could use a good cleaning too. Its never really run great, it has to be warmed up to have good throttle response.

As for the oil, I'm a bit leery of going to a synthetic. The clutch and trans share the motor oil which is specced to be a 40W. I've heard going to synthetic can cause the clutch to slip a bit.

Running the correct synthetic oil, like Rotella (a diesel oil) or a cycle-specific oil, is not going to cause clutch slipping. A synthetic isn't any more "slippery" than conventional oil, it just has a closed molecular structure that makes it stronger and flow better. It also will not breakdown with excessive heat like a conventional oil.

The oils you need to stay away from are current auto oils. In lower grades (20, 30) they have Friction Modifiers (Moly) that can build-up on clutch plates and cause slipping. Even though auto oils in the 40-grade range (10w-40 mostly) don't have Modifiers, they also don't have the amounts of additives (Zinc and Phosphorus aka ZDDP) you want for a cycle engine. ZDDP protects the cams and rockers from galling in certain conditions before there is adequate oil flow - you want it for an engine that doesn't have roller rockers.

You shouldn't have any issues with Rotella T6 5W-40 if your clutch is currently working properly. It's going to give you better mileage and protect the engine better - and it's not expensive. I run it in many of my cycles, even my older ones, without a problem.

[Daox]

The bike got its first ecomod yesterday! Good for essentially no MPG boost, I put in a fancy dancy LED headlight bulb. I noticed my lowbeams were shot on my first trip of the year, so I figured I'd throw in a LED to get a few more lumens which is always welcome on bike.

Fitting it was a bit fun since its pretty tight in the headlight housing.

Old H4 bulb.





New LED H4 bulb.








In order to get enough room, I had to put the electrical connector out the back of the housing.





So, I decided to wrap it up and tape it as best I could to avoid water getting in the connection.





Overall, it'll work good. The high beam doesn't work the greatest, but the low beam works quite well.

[Stubby79]

Good stuff. Most of the bulbs on my bikes are now LEDs, particularly the headlight. Have one ready to go on my ebike/scooter...running out of things to put them in!