HELP 1981 Honda CM400

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offroader · #1 Unread post by **offroader** » Sat May 06, 2006 4:19 pm

I have an 81 honda CM400 it has been sitting for a few years and i just decided to get it back out. I put in new plugs fresh fuel and battery. I run it for a few miles but it still runs pretty rough even with a quality fuel treatment. Im not sure what the plug gap is supposed to be so maybe that is the problem? Or it may be something else. If anyone can give me some tips i would be greatly appreciated. Also can anyone tell me what kind of gas mileage should i be getting with this bike?

BuzZz · #2 Unread post by **BuzZz** » Sat May 06, 2006 4:59 pm

The old girl probably needs a good carb cleaning to get all the old gas varnish out of the small jets and circuits. Often, just a chemical treatment won't get that crud out, and you have to go inside each carb and carefully clean everything manually.

camthepyro · Sat May 06, 2006 8:18 pm

Yep, like Buzz said, the carbs need to be manually cleaned if the bike has been sitting for a while. Everywhere fuel has been sitting should be thoroughly cleaned to keep from junking up the system. Get a shop manual for that bike (I use Clymer's) and follow the instuctions on how to disassemble the carbs. Take them apart and clean every part you find with any kind of junk or residue on it. Or you can take it into a mechanic, and it shouldn't cost more the $80 to clean them, and thats a high estimate.

JCS · #4 Unread post by **JCS** » Sun May 07, 2006 12:39 am

I went through the same thing with a 81 CM400 that had been sitting for 5 years.

Your carbs definitely need cleaning. I never could get the main jets to clean up so I just replaced them. Only 2 and they are cheap and not hard to change.

If it has been sitting for quite a while plan on putting new tires on it ASAP. The old ones are probably hard as rocks (no grip).

Change the oil and filter.

Check seals for leaks. Mine had a leaky seal at the top of the forks for the air adjustment.

Check your chain and sprockets for wear and make sure the chain is lubed well.

Check for wear on the brake pads.

Change the plugs.

Make sure the clutch and throttle cables are in good shape and adjusted correctly.

I was getting around 50-55 mpg in mixed/commuting use. My wife usually got better mileage than I did but I tended to crank on it a little more, too.

I have since sold the bike but I still have a shop manual if you are interested.

These bikes are very easy and fun to ride. If you need to things quickly you need to rev them a little but will move along just fine in low to mid-range, too. Easily capable of keeping up on the highway.