1980KZ1000 factory electronic ignition. No adjust?

When I checked the timing with a timing light, at 1000 rpm it is around 1/8" off the T mark but there is no adjustment. Should I slot the backing plate and get it right? It does advance to the F mark-I don't remember how close it was on the F. I'm having the backfiring (mostly when cold) issue at 10% or so throttle. Idle is good-most of the time-and ~2200 and up it really runs well. New carb boots. new 120/117.5 jets. The idle also hangs. I checked the valves last night. 3 intakes are a little less than .002"=(0.0508mm). 1 intake is .006" Exhausts are all .005-.007". I am going to run some Seafoam and torque the cams and recheck the valves before ordering shims. I also am going to look for intake leaks by putting some low pressure air (10-20 lbs?) thru the vacuum sync plugs with the carb boots blocked and check with soapy water. I checked for vac leaks with (unlit) propane but didn't find anything. Maybe bubbles will work better. If nothing shows up I'll mount the carbs, plug them and test again. The backfiring and hanging idle sux.........Going to check the slow passages on the carbs also. Fuel level is ~1/16 below carb body. Any help greatly appreciated. I did all 6 carbs on my CBX, and it runs great. I've gotta work this thru.

rekit wrote: When I checked the timing with a timing light, at 1000 rpm it is around 1/8" off the T mark but there is no adjustment. Should I slot the backing plate and get it right? It does advance to the F mark-I don't remember how close it was on the F. I'm having the backfiring (mostly when cold) issue at 10% or so throttle....

The F mark should be used incident to ignition timing, and not the T mark.

At idle rpm, the F mark should align with the permanent mark on the engine.

A timing light is useful to assure proper function of the advancer, by watching the F mark move back and forth as rpm is varied by blipping the throttle.

As to the backfiring, is it through the carbs or exhaust?

Good Fortune!

Thanks, I had "mis-remembered" F- not T. At least the advancer is working. The backfiring is thru the carbs, mostly 3 and 4 (on the right side). Checking my drawing the valve clearance is I-1 is .002-.003" I-2 is .006" I-3 is.002-.003" I-4 is .002" On the exhaust it is .004, .005, .005, .006
I know this is tight on the intake side. Could that be it? Or is the big money guess on the carbs. Oh, compression is 150, 145, 130, 120. VM28SS carbs

Presupposing correct cam timing and correct ignition timing, backfiring through a carb may be through an intake valve that isn't completely closing (for whatever reason).

When backfiring, the combustion within the cylinder is getting past the supposed seal of the supposedly closed intake valve, and exiting through the intake port and carb.

Given intake valve clearance within specs and correct cam timing, possible reasons for backfiring through the carb could be a burnt valve, or a bent valve, or a damaged valve seat, or any condition that might prevent the intake valve from fully sealing when it's supposed to seal.

A leak-down test could be helpful to indicate the extent of intake valve leakage.

Good Fortune!