Backfires on deceleration and also is getting black above shift side carb.

it sounds like its starving for fuel, when it runs lean you will get backfires and if its running rough then it may be starving for fuel at idle. Try adjusting you mixture screw and see it the engine will smoot out. Your carb my be dirty and not allowing enough fuel through it.

overfuelling ,check needle valve in carbs

The most common reason for backfiring is lack of back pressure from changing the exhaust. To compensate for the flat spot you get you put in a jet kit. This leaves the possibility of more unburned gas getting into the exhaust. Honda uses Kei Hin carbs with a fuel shut off diaphragm to help limit this condition (backfiring) by turning off the fuel to the carbs during deceleration. Even stock exhaust can pop or backfire. Typically it is caused by air getting into the exhaust either past the copper o-ring gaskets in the head or leaking muffler connections from the head pipes to the mufflers. Try replacing all the exhaust gaskets and you should minimize this condition.

is it a straight thru exhaust, or is it just a head pipe with nothing attached? If it's just a head pipe, you need to get some sort of muffler on it or you'll burn your valves out from a lean condition. The backfire is due to the vaccum fed carbs that yamaha runs. They work wonderfully, but under heavy deceleration, the vaccum still feeds the bowl, and it builds up excess fuel, which eventually burns off as a backfire. If it were fuel injected, you could have the fuel map adjusted to lean it out under deceleration.

Your idle mixture is too lean. You can adjust this by locating the mixture screw on the carb(carbs) and turning it counter-clockwise an 1/8th turn at a time. This will not affect running above 1/4 throttle, but will richen your idle circuit and the lean popping on deceleration. If you have misses above 1/4 throttle when accelerating, tou likely have trash in your jets and the carb will need to be removed and thoroughly cleaned.




*Help me out. Rate me!

Two things can cause popping or backfiring on deceleration. The most common is air leaking into the exhaust through the exhaust pipe copper o-ring gaskets. This typically happens when the exhaust is replaced without removing the old ones (doubled up) or simply reusing the old gaskets and they don't seal. The other thing that can cause popping is bad air cut diaphragms on the carburetors. If they are old and sticky or have holes in them they don't properly shut off the gas on deceleration causing the backfire.

hi mate on the carb you will find 2 screw 1 is for the idle and the over is for mixture the idle one will be the furthest out screw it in 1/4of a turns will the engine is running this will take the idle up on the engine and the backfiring is fuel in the exhaust not being burnt so on the over screw on the carb screw that in 1/4 of turns this will decrease the amount of fuel going into the engine if it still backfires screw it in 1/4 of turns again and see what difference it makes good luck

check for leaks around the exhaust headers,mine did what yours is doing,i replaced the copper exhaust seals in the head(exhaust ports),air is getting into your exhaust system and it mixes with the unburnt fuel and ignites causing the backfire,i replaced copper seals(about $2nz each) and problem went away

try pulling the choke out a little and see if that doesn't help.  If it does that is a sign that you are running too lean and need the jets in the carb increased or just the air mixture screw adjusted.  If the coke test doesn't help, please tell me more about how and when it acts up. Like after the motor is warmed up does the backfiring quit?

Buy a new car!