my son has a cb900 1980 it started popping on 2cly both on same side looking for any imput as to what is caosing this ha also lost power help

I'm no mechanic but Rex might be on to something - I'd definately start there -

its a 4cly with 4 carbs

its popping out the exhust on the 2 left cly has 4 carbs with seperate air cleaners 4 each

Did this start suddenly? Got two coils, If yes ck. the one for left side. Cam timing? I have not worked on a Honda in yrs., but it don't really sound like carbs, if it started all at once.

yes it has 2 coils but 1 is for 1&3 the other is for 2&4 and the popping is comming from the 2 left clys

So far you have checked
All intake and exhaust gaskets, water in the gas, and All related bolts and fasteners for tightness so it's not sucking air, swapped coils from side to side to see if one is bad, checked spark plugs to see if they fouled or carboned up, air cleaner and plenum for obstructions or restrictions......all the basics, all good.

You may need a shop manual to go farther, look under "Popping or Backfiring", whatever it is doing, the manual will tell you to check everything above and then some, check the power values of all the ignition componants with a digital volt meter, check valve adjustment and do a compression test to see if you have a valve train problem, worn cam chain could have jumped a tooth and knocked the timing off.

The process of elimination.

may sound silly but give the carbs on left side a few hard taps with the plastic end of a screwdriver as you rev the bike..carb floats tend to stick in them old hondas...otherwise sounds like plugs have a bad connection

4 carbs? 4 air cleaners? Good goobly woobly. You'll be busier than a cat coverin up shit trackin that down. lol

Just because its happening on two of the cylinders, doesn't mean its just one problem. I find that when you have more then one of the same part, they can quite often wear or go bad right around the same time.

Without actually hearing it I can only guess, but I always find the best way to go through the process of elimination is do the easy stuff first.

Remove all the spark plugs, if one is bad, change them all. If they look ok put them back in different cylinders. See if the problems moves.

Check the plug wires. I am not real familiar with the bike, but if you can swap them do so. Both ends of course!

To be honest I really think its a air/fuel mixture problem, but like I said, the stuff above is easy, so why not...just in case. The mixture problem could be anything from leaky gaskets to dirty or mistuned carbs. Depending on the mileage, may be a good time to pull all the carbs, give em a good cleaning, check all gaskets and seals, and re-install.

Sorry I can't be anymore help, just hard to say without actually hearing it. If you can find a small shop with an honest mechanic, he might be able to point you in the right direction if you let him hear it.

had a 72 900 chech to see if the air hose going from the two carbs on the left side fell off or has a hole in it ..just remember these carbs are tune with float gauges and they have to be about the same ... did your son just change anything on that side of the bike recently????

no have not changed anything but all the plugs

think we sovled the problem I finally got back in town (truck driver) took alook told him to change plugs and wires 2months agoi come to find out he only did plugs no wires put new ones on runs fine thanks for all help Cricket

Check the wires for the left cylinders...I have one of these bikes, rode it for years. If the boots are loose and will spin on the wire (they should be fairly tight), trim about 1/8th of an inch off the wires, then "screw" the boots back in place. This'll give you a better electrical connection, and should help with the popping...I learned this one through alot of trial and error on my ol' 900Custom!