1973 Honda CL450 Losing Power and Dying

Hi,
I've got a restored 1973 Honda CL450 (K5) that I bought as my first bike last summer. It's got 16k miles and it's been running great up until now.
Several months ago I was riding home late one night when at around 45mph in 4th gear I began to lose about half my power. I downshifted and tried to make it back home but after about .5 miles the engine completely shut down.
I got it hauled back home. Last week I thought I'd replace the plugs and add fresh fuel because several people were saying it was probably "the fuel or the fire" So I decided to take it out for another run. After about 20 min into riding the same thing happened again only this time the bike was only at half power for 10 seconds before the engine died.

Is something overheating?

A friend mentioned piston rings and compression but compression seems fine. The kick start is tight and I get a nice bit of air from the spark plug openings.

Someone else mentioned the ignition coil? I haven't tested it yet.

Don't know if this is related or helpful but also several months ago I started noticing smoke or vapor coming out of the breather tube on the back side of the engine.. It happens after the engine has been running for 10 min or so. Just thought I'd mention that in case it's related.

I'm no repair expert but would love to try and fix it myself if someone is fairly confident as to what might be the problem and it doesn't seem too difficult.

I look forward to hearing your thoughts!

Thanks
Brent

To start with, it should not be too difficult to fix yourself..

Secondly, many times have we thought the compression "seems ok" when in fact it was not. My advice there is that if there is any doubt, check them both with a guage to be sure they are within correct measurements.

When you seem to loose power, does it still seem like you are running on both cylinders?

Problems like this are usually, like you had said, fuel or fire.

Let me ask, when was the last time the carbs have been cleaned? If has been a while, that would be the first thing that I did, along with the rest of the tune up procedure - i.e. timing, points, cam chain tensioner,etc. All fairly easy, but essential in the troubleshooting procedure. When cleaning the carbs, be sure that the needles to not have grooves in them (where they go into the jet), and that the floats are in good condition and they are the right height.

Once you get all of that done (to be quite honest, even with minimal mechanical ability should take only a couple of hours), you should have better response. If not, then it is time to start looking at other things, like coil, etc.

How do the spark plugs look? Are they gapped correctly?

Do you have a manual? If not, GET one these things are worth 10 times their weight in gold.

Mike

Mike,
Thanks for the advice!
To answer you questions, when the bike looses power, I think it does run on 1 cylinder for a brief moment and then 10 or so seconds later dies on the remaining one.

I've owned the bike for a year and I've never had the carbs cleaned. Not for sure when the previous owner did that either. Maybe I'll check into that next.....

Also the spark plugs are brand new and I replaced them with exactly what was already in the bike.

And yes I do have the clymer manual if that's what you're referring to.

Thanks for your help!
Brent

To me it sounds like it is in the fuel system. Dirty carbs, fuel filter, dirt in the petcock, etc. Just to give you an example, ever heard of someone sticking a condom in a gas tank of a car. It will float around in there until it gets pulled to the sending unit then the car will die, once the car is dead, it floats back away, the car will start back up, run for a little bit, than when it gets sucked back over to the the sending unit it will die again. Maybe that isnt a great example but this is what dirt can do in a fuel system. I would empty the tank off and flush it with some new gas, run the new gas into a glass from the petcock to make sure its flushed and flowing good, then check the gas you emptied from the tank and the glass of new gas (you flushed with) for dirt and/or water. Replace the fuel filter (or clean the filter screen in the petcock if its not supposed to have a inline fuel filter) (If its supposed to have one and doesnt, get one). Then after that pull the carb bowls and check the gas in them for dirt, grime, or water. Then pull the carbs and carefully take them apart, inspect the needle jets for grooves at the seat, and clean with proper carb cleaner. Put it back together, (unless the needle jets were bad and the carbs need rebuilt) put some fresh gas in it and see what happens. I bet it will fix it, if not, you know you have ignition problems. Its not like youll be wasting time or money taking the fuel system all down and cleaning. Its something that should be done periodically regardless.

Well guys......
I had a mechanic clean and flush the tank/fuel filter and clean the carbs.
I also bought new coils and replaced the original ones which were shot and still no luck? The bike is still randomly dying and I can't figure it out??? It does have a lot more pep though!
The mechanic said the compression and points looked good too? I also threw in a new battery and the plugs are still very new....
Anyone else have any ideas as to what the problem might be?? It's been 4 months without riding and it's killing me. :) Thanks for all the great advice so far!

I am sorry for your bad luck. I also am experiencing problems with my CL450. I can only get one plug to fire & would like to replace the coil. Could you tell me where you sourced the coils? I recently purchased aftermarket universal coils, but cannot figure out how to connect them as they only have one connection point for small wire & the existing have two wires. Any help would be greatly appreciated.

Wire connections. Clean 'em. I'm leaning towards electrical problem because of the intermittent nature. As things heat up they expand. Electrical components can act up when heated.
Check your plug wires and boots. A great product is DeOxit. A small can is expensive but this stuff REALLY cleans electrical connections. Don't try to save and get something at the auto store,it ain't the same.
BTW how's the charging system?

Plug wires would be next on my list as well. As temperature increases so does resistance, so a wire that's okay cold but is on the brink may very well fail when it heats up. Rest assured though, with everything you've done so far you have to be close. Old bikes are great to work on, fuel and fire, that's all there is. One way you could check for poor spark would be to remove the plugs immediately after the bike stalls out to see if they're wet. If that's the case, you know you're losing spark.