am i miss fireing ?

Question

i think my bike may be miss fireing... it vibrates a lot more than i think it normally would... though i just got it a few days ago... its a 1980 honda cm400e... but one side near your leg gets real wark, and the other side you can touch... i also taped my shoe, with a wet bottom to the one header, and it hissed (normal) but on the other side nothing happened... i didnt have enough balls to grab each header... but the one on the right gets hot and the one on the left doesnt... i havent gotten a chance to check the plug yet... but im told they were just replaced... what else could it b other than plugs ?

its a dual carb... split behind the filter in the airbox... and another quick question... i think the idle is too low... when i let go of the throttel, it dies... shouldnt it idle and not die... im new to bikes... thx for all the help...
im gonna check the plugs tomorow, and try to get new 1s just in case... depending on how much they r

Answer 1

This is a 2 cylinder bike with a single carb and a manifold between the head and the carbs. It may be a simple matter of a fouled plug. It doesn't matter if the plugs are new. There's a number of things that can foul a plug quickly. Including riding with the choke on or an overflowing carb, a head gasket or bad rings that leak oil into the cylinder. Since it's the left side that's not firing (the side that leans down from center when the bike is on the side-stand) It would make sense for it to be a leaking carb. Pull the plug on the left cylinder. If the electrode is black and/or wet then this is likely to be the case. Dark brown is different and is a sign of an oil leak. The good thing is that it can easily be remedied by remembering to turn the fuel valve to the "off" position every time you park the bike.
You might also want to check compression of the cylinder if the plug appears to be ok and you have verified that there is spark. A crude but good-enough test is to take both plugs out put your thumb completely over the spark plug hole with very firm pressure and hit the start button (is this bike electric start?). The compression should pop your finger off pretty smartly. If you can hold your thumb on while the motor is turning then you definitely have low compression and it's going to require either valves done or new piston and rings or possibly a re-bore..

Sorry I'm wrong about the one carb. I was thinking of the CM200 twinstar and not the 400. I guess I had twinstar on the brain since I have two of them in for repair at the shop now. Everything else I said is valid though including the left carb overflowing when the motor is off.
Also if it is a fouled plug thats wet, before you put in a new plug crank the motor several times with the spark plug hole open to clear out the cylinder and prevent you from fouling a brand new plug right away.
The idle is too low now because the left cylinder is not firing. Once you get the bike running on both cylinders the idle will pick up, possibly too high if the previus owner tried to compensate the bad cylinder with the idle adjustment. 1,200 RPM is a good idle speed.
Lastly turn the fuel valve off and pull the fuel line off carefullyfrom the fuel valve. There's always a little residual fuel in the bottom of the valve that will leak out, but after a few seconds the flow of gas should stop completely. If it doesn't, even if it's just a slow drip, then you really need to get it fixed. Probably with a new valve as I doubt rebuild kits are available for this. Ebay is always a good source.

Forget about the lastly bit. It's sunday and I'm off work and it's raining in san antone. This carb set has air cut-offs which, if they have bad diaphrams, will be another source of running badly. These carbs also have an accelerator pump, meaning that if you twist the throttle on and off repeatedly and rapidly especially when the motor's cold you could foul a plug by putting too much extra fuel down the throat of the carb. Definitely try everything else before this though because getting at the air cut-offs and accelerator pump will require a lot of work. Too much for me to want to go into detail about here.

Answer 2

You have a cold cylinder, one that is not firing. Now whether it is fuel or spark related is the question. Just because someone has replaced the spark plug does not mean that the plug is good. I have purchased new plugs that were no good several times. The easiest way to check for spark is to remove the plug and with the plug wire on place it on its side so you have a good ground. Then crank the engine and watch the electrode for spark. If you have none, then it is either the plug or if the bike has dual coils then the coil could be the problem. If you do have spark then the problem is fuel and you probably have trash in that particular carburetor.

Answer 3

-Check for spark on the cold cylinder. Remove both spark plug caps. Install a plug in the cold cyl's cap and lay the threads on the engine. Turn on key and push starter button. Check with a known working plug. Then install the good plug in the cold cyl.
-Your bike has a single coil. If no spark on one side, unscrew that spark plug cap, and screw the other cap on that side. If still no spark, cut 1/4" off the end of that wire and screw the cap back on (it might not be making a good connection).
-If still no spark, have the coil checked.
-The carb on the cold cyl could have clogged jets. Remove carbs and clean the jets. Hold them up to the light. You should be able to see through them.

Sorry Ron. The 1980 cm450e has two carbs.