Topic: Backfire after installing CDI in 77CB750K

[jensorooni]

I recently installed a Dynatek CDI in my 1977 Honda CB750K after suffering issues with failing condensors.  The bike actually works great, more power, smoother, great pick up.  I installed using static timing and think that I am pretty much spot on.

The issues is that it now backfires under heavy deceleration.  Does this mean that the timing is still a little retarded?

Bike is stock with 8K, only changes CDI and K & N air filter. 

[Don R]

 A decel pop is often a sign it's going a bit lean. Early Goldwings have an air valve in the carb rack that cures the decel popping, a stock 77 carb was probably jetted lean when new.

[newday777]

I recently installed a Dynatek CDI in my 1977 Honda CB750K after suffering issues with failing condensors.  The bike actually works great, more power, smoother, great pick up.  I installed using static timing and think that I am pretty much spot on.

The issues is that it now backfires under heavy deceleration.  Does this mean that the timing is still a little retarded?

Bike is stock with 8K, only changes CDI and K & N air filter.

Backfires through the carbs or is it popping in the exhaust?
How much/loud is the backfiring?

[TwoTired]

The 77s had PD style lean burn idle carbs as stock using pure gas.  (Ethanol added will make it leaner)  On deceleration there may not be enough fuel to burn so it gets pushed unburned into the exhaust, until there is enough to ignite on successive exhaust cycles during a wasted spark event. (Popping exhaust)

You can try turning your IMS screws outward to enrich the idle.  Or, raise the float bowl fuel Level to enrich the entire operating range of the carbs.

[bryanj]

I would guess it aint cdi as that is new coils, BIG black box etc.
I would bet its just transistorized electronic triggers for the coils

[HondaMan]

I would guess it aint cdi as that is new coils, BIG black box etc.
I would bet its just transistorized electronic triggers for the coils

+1, unless it is designed like the pseudo-CDI of the CB650 bikes. Regular CDI would draw like 8 amps of power, and the bike would make it about 12 minutes before the [fully-charged at start] battery died.

For the backfiring, you can also try this: use premium gas and an ounce or two of oil in the gas tank. If it (or if TwoTired's method) works, maybe raise the float bowl levels in the carbs a little bit, like 1.0-1.5mm. Reason: if the OEM float valves were recently replaced they will make for lower float bowl fuel levels, on average. The new ones have much stronger springs, causing the lower level.