Popping from exhaust, just on idle, runs great,

77 B1 KZ650. Bike has run perfect for 2 years after a carb rebuild. A couple of weeks ago I noticed 2 changes in my bike after a particularly long ride. The first thing was that my bike seemed to warm up faster, meaning that it used to start on full choke instantly and then take a few minutes to warm up before I could shut the choke off... Now I start the bike and after about 15 seconds of choke it starts to bog down to the point that I need to turn off the choke right away. Idles a little rough since it hasn't warmed up yet but seems to warm up faster then before and runs great.

The popping from the exhaust started happening shortly after this. Very faint at first, to the point where I thought I was imagining it, then over the course of two weeks became louder and louder. Pop comes from the right exhaust (which flows from exhaust 1+4, not stock pipes, came from a different model KZ650)

I'm pretty militant about regular maintenance, so I check plugs, points, valve clearance, oil change very regularly.

Valve clearance was all well within spec in the spring with the exception of #1 intake being at the bottom of the spec. Plugs look good, points are good.

Regardless I'll be:

Checking for vacuum leaks on the carb boots
checking points again
valve clearance (I'm not really sure valve clearance would play a roll in the popping?)
Cleaning carbs again (If I have to)

I would appreciate any advice from the old pros around here if they have any hunches on what might be happening.

If not already done, would address the following areas:

Fresh air filter, clean and unobstructed (gloves, shop rag, etc. stored under seat);

Clear tube test to assure fuel levels within spec;

Watch timing advancer under a timing light to assure rapid movement back and forth as rpm is varied by blipping the throttle (lube the pivot points);

Assure choke plungers are fully closing down.

Good Fortune!

If running pods, would assure there's no obstruction at the pilot circuit air intake.

Good Fortune!

Thanks for the tips Patton, It's has the stock air box which I decided to keep because of all the advice on this forum. Brand new Air filter and no obstructions.

I will check the timing advancer with a timing light once I get my FSM back from a friend, but could you explain where I need to oil? Where are the pivot points?

Patton wrote: If not already done, would address the following areas:

Fresh air filter, clean and unobstructed (gloves, shop rag, etc. stored under seat);

Clear tube test to assure fuel levels within spec;

Watch timing advancer under a timing light to assure rapid movement back and forth as rpm is varied by blipping the throttle (lube the pivot points);

Assure choke plungers are fully closing down.

Good Fortune!

Advancer weight arm pivot points should be accessible for lube through the timing inspection window.

If the advancer moves quickly back and forth while viewing the timing marks with a timing light and changing rpm by blipping the throttle, may rule out the possibility of a sticking advancer as the cause of the performance issue.

If the advancer is sticking in one position, it should be lubed, and probably both cleaned and lubed.

From the reported history, would most likely suspect that the bike began running richer for whatever reason.

Good Fortune!

Everything is cleaned and lubed now and I still get the popping from the right exhaust which is coming from cylinder 1+4. I pulled the number 4 plug and it's nice and tan, but #1 plug is very very dark.. Running very rich, which might be the cause? I put a new plug in and it still pops and darkens quickly. I checked all my float heights and they are bang on from when I set them after I rebuilt the carbs a couple of years back.

So I guess the next course of actions would be:

1. check for a strong blue spark?
2. check points (I ordered new points and condensers as the old ones where getting pitted, I cleaned and filed and set the old ones so they work but they are so inexpensive I'd rather replace them with new
3. Replace coils and wires.

I had purchased a new set up EMGO coils for a previous KZ650 and took them off after a summer as they seemed to run very poor in comparison to the old coils (stalls, hard to start etc) Can someone recommend a better coil set? I don't mind spending some money if they are worth it for performance. I love my old KZ.

#1/4 spark plugs are in the same secondary loop from the coil, whereby number 4 plug being nice and tan would indicate adequate high intensity voltage, and suggest some other reason for the dark #1 plug.

Given decent spark quality on #1, the dark plug would result from weak compression and/or an over-rich fuel mixture.

Ruling out weak compression leaves over-rich fuel mixture. Unless it's oil fouling due to a damaged oil ring.

If the clear-tube test shows fuel level within specs, the excessive richness might result from such things as a loose pilot jet (or the earlier mentioned possibility of a choke plunger issue), or perhaps an obstructed air passage in the pilot circuit, or a damaged needle on the pilot adjuster screw.

Good Fortune!

Thanks for all the help Patton. First thing I'm going to check next is compression. I haven't checked it in a while. I don't think the plugs are oil fouled. If they were oil fouled from bad rings, would I be seeing smoke out of my pipes? There is zero smoke coming out of them and the exhaust has no hint of oil.

I'll report back once I eliminate a few more things.

Patton wrote: #1/4 spark plugs are in the same secondary loop from the coil, whereby number 4 plug being nice and tan would indicate adequate high intensity voltage, and suggest some other reason for the dark #1 plug.

Given decent spark quality on #1, the dark plug would result from weak compression and/or an over-rich fuel mixture.

Ruling out weak compression leaves over-rich fuel mixture. Unless it's oil fouling due to a damaged oil ring.

If the clear-tube test shows fuel level within specs, the excessive richness might result from such things as a loose pilot jet (or the earlier mentioned possibility of a choke plunger issue), or perhaps an obstructed air passage in the pilot circuit, or a damaged needle on the pilot adjuster screw.

Good Fortune!

possibly try switching plug wire with 1 from a working cyl, to rule out the wire itself.
also , it wouldn’t hurt to check that all exhaust bolts r tight. if they r ok, i might take the exhaust off. then examine the seals. u would be looking for signs of exhaust leakage, such as a dark soot path . the gasket should show no sign of soot escaping . exhaust leaks can cause exhaust popping sounds.

While you're waiting for your manual to come back, here's an electronic copy:

www.scribd.com/doc/48655900/Kawasaki-KZ-...B1-77-Service-Manual

What spark plugs are you using? The ones recommended in the original manual (including the electronic one above) are 1 heat range too cold. Later manuals corrected this error. Correct plugs are NGK B7ES or ND W22ES-U.

If possible, swap spark plug connections at the spark plugs between 1 & 4. If the problem stays with cylinder 1 the coil, wires, and cap are ok. If the problem moves to #4 you have isolated the problem. Ed

Using the B7ES, which are getting hard to find around these parts. I'll try changing out the cables, but they are pretty brittle and old. I would really like to change out for coils that I can replace the cables on but keep the points as well, regardless of whether they are the problem or not, it's really only a matter of time before they start giving me grief.. Can someone recommend any models or brand?

650ed wrote: While you're waiting for your manual to come back, here's an electronic copy:

www.scribd.com/doc/48655900/Kawasaki-KZ-...B1-77-Service-Manual

What spark plugs are you using? The ones recommended in the original manual (including the electronic one above) are 1 heat range too cold. Later manuals corrected this error. Correct plugs are NGK B7ES or ND W22ES-U.

If possible, swap spark plug connections at the spark plugs between 1 & 4. If the problem stays with cylinder 1 the coil, wires, and cap are ok. If the problem moves to #4 you have isolated the problem. Ed

Am thinking that Kaws with points ignitions came with 4Ω coils (Ω = ohm), but am unaware of a source for good 4Ω coils with replaceable plug wires.

Would consider these 4Ω coils from Z1E:
www.z1enterprises.com/ItemDetails.aspx?i...cap&item=IM01143-55S
www.z1enterprises.com/ItemDetails.aspx?i...aps&item=IM01143-55L

Good Fortune!