73 cb750 four / engine help

[Tonup76]

Alright I'm a newbie but I need a little assistance.  Hope someone can help.  

I've got a 73 CB750/Four, it's a nice little cafe racer.  The other day I was riding and about 15 min into the ride I started losing power, the bike was slowing and it felt like it was losing compression.  I made it to where I needed to go and when I pulled into the lot it just stalled.  I waited a half hour and it started right back up as if nothing was wrong.  15 minutes into the ride it did it again.  It took me a bit longer to get it home, I kept stopping and letting it sit and then starting it, a few times it would only start it the choke was open.  Now when I start it I'm getting a "pop" or backfire sound from one of the exhaust pipes.  I havent taken it anywhere since.  Any suggestions or help would be appreciated.  So far here's what I'm thinking, tell me if I'm wrong.

-Just bought the bike and maybe it needs newer gas or even some dry gas?
-clean the carbs?
-needs new points and a coil?  
-fuel line is getting clogged?

Thanks for reading this and hopefully thanks for the help.

TON UP.  

[Tonup76]

Anyone?  

[pena750f]

Try the easiest route first. Pull the plugs and inspect. They will provide great insight into your fuel system. It helps to have a shop manual to help with this. Next I would drop the bowls from the carbs and look there. You will see if the fuel is dirty, floats need adjusting and you can remove and inspect your jets. It sounds like you have an idea in the dirty fuel. This will clog your jets restricting flow under throttle. You are likely safe from anything electronic as it starts right up after settling.
I have just gone through the same thing with my 75 750f and I had to derust the tank and clean the jets. Again your plugs will tell you if your running rich or lean.

[Tonup76]

Thanks!  I actually drained the tank and put new gas in it and it seems to be running like a top.  I just took it out for an hour and no problems whatsoever.  Thanks so much for the advice, I think I'm going to clean the carbs anyway, I just ordered velocity air filters and figure it wouldn't hurt to clean the carbs b4 putting those babys on.  

Thanks again.  

[kiwi727]

Greetings all,
Ths problem returns in winter (most likely). To me it sounds like carb venturi icing. Were you riding in foggy, misty or rainy conditions at the time. Does not have to be in outside air temp at or below zero to occur. Most likely on humid days. Even occurs in the tropics.

It happens when moist air enters the carb throat in one or more carbs. The temperature drop is as a result of evaporation of the fuel (can be 20 or so degrees). Has everyone stumped who encounters it - so hard to diagnose. Classic symptoms are gradual loss of power over afew minutes, rough running like the choke has been left on and in worst cases engine stops completely. So you scratch your head a few minutes and kick the tires, then proceed to light the fires and the problem has magically gone. That is because during the intermission the heat from the engine melted the ice. A few miles down the road same problem.

On a low humidity day not a problem and other apparent cures may give false impression of "the cure was found. Next humid day the problem comes back.

There is only one cure for this and that is to stop and let the ice melt.

This is a very common cause of power failure in aircraft piston engine. Has killed a lot of aviators over the last 100 years. Carb heat applied by pilots to clear problem before it gets out of hand.

Yes I have had this happen to me in aircraft, on motorcycles and in cars. Some cars have a winter and summer air filter intake setting. Winter setting puts intake close to hot exhaust.

I may be wrong but if nothing else works 100%,then suspect carb icing.

Kiwi727

[corona_del_leon]

I recently had the same problems, pops, loss of power,...  Overhauling the carbs helped tremendously and afterwards the bike was running like, well, like a super sport.  Unfortunately this did not last because i had not noticed the rust in the gas tank (this is my first project bike).  I removed the rust, recoated the inside of the gas tank, and then cleaned the carbs once more.  Wow!  again, like new!  But this didn't last.  I got caught in a rain storm a month ago and my air intake pods seemed to have absorbed a lot of moister.  This caused the bike to die a few times while riding it, and it eventually forced me to park it over night where it last stopped.  The weather has since cleared but the bike now pops, has trouble idling, and has less power.  What should I do?  Could water still be in the carbs?  Can the moister from weeks back still effect the engine?  Further, I don't have a garage, but I do cover my bike.  Should i also add another moister prtective cover to the pods.  last,  what can i do if i want to ride but the day has high humidity?   Any tips are much appreciated.   thanks