Fuel or Fire

[sammydub]

Hello everyone,
I first would like to say how much I appreciate what a great website has been established here. It has already given me a ton of insight on how to approach my bike.  
I own a 72 honda cb750 4. I have had this bike for over 2 years.  I have always been blown away by how much power my beast has. Its all pretty much stock except for some ape hangars and saddle bags.
Yesterday, I got on my bike after a week of sitting in the garage.  The bike felt different, almost as if one of the cylinders was not firing or getting any fuel. I figured this because the bike was not accelerating as fast as usual.  Really, the bike still has alot of power, just not what it used to. After riding 30 minutes I parked the bike.  After a few hours, i went back out and started it up.  A Ton of fuel smelling white smoke came out of the pipe and cleared.  For the rest of the day, the bike ran excellent the way it used to.  Today, I got on it and it reverted back to running slower again.  I went to the Advance store and got some Seafoam and filled it up with fuel and ran it for about 20 minutes.  It is still bogging down.  I feel that one of my carbs are clogged but I'm just not sure.  Does anyone have any ideas about what is going on? (Also, the bike has new plugs and an air filter from last year.)
Thank you for any help.

[Re-run]

Well the seafoam will need some time to run through so give that time and miles.
First thing is to figure out which cylinder is not firing. Couple of fast/dirty ways to do this.
Either hold your hand behind each pipe, one at a time, as the bike idles. You should be able to tell which one is cooler. Another option is the spit test. Put some spit on your finger and touch each pipe FAST! At normal temp, the spit will sizzle. If one does not, that is your cold spot.
I would guess that the carb might have sediment in it clogging the jets. Drain that bowl and see what comes out.

[sammydub]

Thanks Cornholio! Excellent advice! I will check these solutions out tomorrow.  I never thought to try these techniques.  I love this website!!!

[fpcb750er]

Another thing you might consider is checking if there is water in your gas.  White smoke is a telltale sign of something other than oil or gas in the cylinders.  Did the bike get stuck in a rainstorm or snowstorm?  Water will sink in the tank, so it will be the first thing into the engine. You can test this by attaching some fuel line to your petcock and draining some gas into a clear jar, then let it settle, you may see a very small ring of water at the bottom.  Just another thing to check, you'll have a busy weekend!

[sammydub]

I will try that technique as well and get back to youl.  Thanks for the advice.

[sammydub]

Ok, So here is the deal. I did the spit test on the pipes to figure out which cylinder was not firing. After I figured out it was the far left one, I unscrewed the bold on the bottom of the carb bowl. After clean fuel with a few particles came out, I figured that it was not a fuel problem. Anyway, i took the bowl completely off and discovered that the bottom jet screw was out of the bottom of the jet.  After replacing it, it ran better but not perfect. Next, I took off the plug wire and put a nail in it to see if it had spark...it did. So I removed the plug and discovered that the one year old plug was black and disgusting.  After cleaning it and lightly sanding, I replaced it and fired the bike up...Wallah! Bingo! Booyah! I figure that the plug fouled due to the fuel problem stemming from the jet.  The bike runs faster and better than ever!  I couldn't have done it without you guys! Thanks alot and I look forward to using this forum for as long as I am around.

[mikey440]

the float on that number 1 carb could have stuck and flooded that cylinder and gave you all the smoke,
 if it happens again try tapping on that float bowl with a handle of a screwdriver to knock the float loose,
 sounds like that 1 plug was fouled due to flooding of that 1 carb, hope this helps in future, mikey440

[sammydub]

Thanks for the info!