Backfire

[Steve in Sunny Fla]

Bubba.....Where's Bubba...?...

   Bubba was camping / fishing at the beach with the family for a couple days 

  Actually, I expect the problem lies in the carb work; maybe there's a vacuum leak, maybe the pilot screws are turned to far in... I've personally not seen problem come from the blockoff plates or the sprocket unless  incorrectly installed.My 36's don't have air cut valves on them and I get backfiring on high rpm hard throttle closes. If the decel valves are ripped the bike will get horrible mileage and show rich plugs. The more normal burbling on decel can usually be controlled by opening the pilot screws abit more. steve

[snarf]

Lets deal with this fellow's USA bike, as I doubt he's riding  GTR.....
1- GTR had restrictive carb tops that the spring projection moulded in did not allow as much slide opening as US models.
2-many Euro models actually had coolant pasages in the carbs to prevent freezeups.
3-euro models were jetted much leaner
4- I don't believe ALL years were delivered without the air injection
5-I DO believe they were all assembled WITH the air-cut valves on body 1&4
6-Euro bikes were all delivered producing reduced H.P. from the american counterparts.

with that said, we do not know at this time HOW he negated the air injection, and he MAY have a leak, which WOULD cause this problem. Leaky carb boots do not generally create this scenario as that leak is on the inlet side, and intake and exh valves working correctly negate this from occuring. Backfiring (not burble) occurs when a rich exhaust mixture is exposed to oxygen midway or futher from there before the end of the exhaust unless there is an exhaust valve hanging open or timing issue exist. A leaky exhaust pipe gasket is NOT generally a cause, as the pipe is pressurized at this point, and usually does not "suck in air".
The air cut valves still can be dumping excessive raw gas enrichening the mixture as they were intended, and this can cause the problem as they function only on decelleration mode of the carburation cycle.
We still do not know if the exhaust is stock, or the aftermarket has a non-conducive volume (sized accordingly for the actual flow).

I'm still awaiting Bubba's thought here.... :popcorn:

MOB I don't want to debate you, rather I am unclear as to what you are saying. The reed valves are pressurized also. The way I understand it; when they open under decel ngative air pressure sucks fresh air from the airbox. I don't understand how raw gas could be entering the exhaust from here.  So unless he has gas in his airbox I don't see that happening. If he does have gas in his airbox I would be willing to bet that's his problem.You know a heck of a lot more about these bikes than I do, that's why I am asking for further explanation. If an overly rich combination of fuel and air are in the exhaust wouldn't it have to be coming from before the exhaust?
I do have one off topic question. My 86 has reed valves, my keys are stamped GTR. Was that just a first gen thing?

[MAN OF BLUES]

My comment about raw fuel was directed towards the aircut valves on carb 1 & 4, not the reed valves...totally different animal. The aircut valves enrich a lean condition during decel.

My 86 keys were marked GTR also, and it was a Cali bike, I don't know if they all were marked like that. My 88 ones were marked Kawasaki.

to add to what steve related to, I'm also running 36mm Ninja carbs (without aircut valves) on COGZilla, with the reeds still in place, and a set of SuperTrapp Ninja mufflers (zero restriction, and loud), and that bike is just radically loud and obnoxious on decel, you can hear it coming for miles.....doesn't backfire, but it pops and growls a lot.

[snarf]

MOB, my bad; I misinterpreted 'aircut valves'.  Yes very different animal. I was sorta surprised that you made those statements, now that we are on the same page; your comments make sense.

[Steve in Sunny Fla]

yeah, "Aircut Valve" is, to me, a poorly chosen name. The valves don't cut air as far as i can determine; they actually blend more air into the pilot circuit. The diaphram is pulled by high vacuum to allow more air to the pilot circuitry. steve

[MAN OF BLUES]

yeah, "Aircut Valve" is, to me, a poorly chosen name. The valves don't cut air as far as i can determine; they actually blend more air into the pilot circuit. The diaphram is pulled by high vacuum to allow more air to the pilot circuitry. steve

agreed, but the result of its "actuation" is adding fuel above that which is normally supplied with throttle shut down and slide dropped.