Backfiring

Just wondering. Well stupid question mabey.
When idling cold just after start up there are some
Backfiring from exhaust. Not much but annoying.
When warmed nothing.
The bike is KZ1000A2 ´78 stock.
:huh:

air leak would be my first thought. When things get hot they expand, which could explain the only happening when cold

Could be plenty of causes, from a leaky exhaust valve to a bad spark plug. I would start with a full tune-up; points/condencer check, new spark plugs, coil and HT lead check, spark plug caps check, timing check, valve clearance check, compression check and carb clean and synch. But before all that you can check for leaks by spraying starter fluid around the inlets and see if revs climb.

Thanks for the info. Looks like I have plenty to do for the next days..
I will take a better look at it. Same problem on my friends Z1.

Thanks again,

faffi wrote: Could be plenty of causes, from a leaky exhaust valve to a bad spark plug. I would start with a full tune-up; points/condencer check, new spark plugs, coil and HT lead check, spark plug caps check, timing check, valve clearance check, compression check and carb clean and synch. But before all that you can check for leaks by spraying starter fluid around the inlets and see if revs climb.

Good to be occupied :laugh:

The reason for the popping is incomplete burning. As mentioned, there are lots of issues that can cause this, and a full tune-up is the easiest way to eliminate the most common causes.

A leak in the exhaust system can make it easier for unburned fuel to ignite, and since the exhaust becomes hot with time such a leak can seal itself. Or the hotter engine can be the help as it will burn much cleaner when it's nice and warm than when cold.

That’s true but if you have many bikes and all need
some maintains then sometimes it too much...
I’m the one of the blokes who is always chasing for near
as perfection and therefore wasting maybe to much time in
the garage at the winter time. (Single..!!)
But the riding season.., its one big smile instead…

Hawk1 wrote: Just wondering. Well stupid question mabey.
When idling cold just after start up there are some
Backfiring from exhaust. Not much but annoying.
When warmed nothing.
The bike is KZ1000A2 ´78 stock.
:huh:

You possibly have an air leak. Does the bike pop through the exhaust when you let off the gas when riding ? If yes then you have a exhaust system seal leak somewhere. You also might have your air screws set a bit too lean. Try richening the screws 1/2 turn. Last resort (I did this on my GS1100) was to bump the pilot jets one size richer. This made a huge positive difference in my GS's cold start idle and warmup behavior. It also rid my bike of a frustrating slight stumble "off idle"

Only pop through the exhaust when idling and only when cold.
Small pops and nothing when warmed up.

How cold is it where you are? Could it be that the choke cannot supply enough fuel for winter running? Bikes were jetted lean in the late 70s and early 80s.

Hawk1 wrote: Only pop through the exhaust when idling and only when cold.
Small pops and nothing when warmed up.

Try richening the air screws 1/2 turn, that should make an improvement.