Exhaust Popping

I've read a number of threads on this subject but can't get rid of the exhaust popping on my 81 KZ1100A1, both on deceleration and some at constant throttle. The valves are new, the air suction system is gone and I've sealed off the holes in each side of the valve cover, exhaust gaskets are new (fiber-filled copper ones from Z1). Air cleaner is stock paper filter although I've tried a foam filter with no effect. I have 19" aftermarket mufflers that I've put various baffles in with no effect. Carbs have recently been cleaned and rebuilt, and I went up two sizes in jets (120 to 125 mains and 37 to 40 pilots) on the theory that it was running lean with the short mufflers. The plugs look better now - they were white before but now brownish gray, but it didn't affect the popping. I finally tried it last night with the stock mufflers (still with the larger jets) and it still pops, both on deceleration and a little at idle. Carb holders are new and intake boots are all in good shape and not dried out. Vacuum caps and hoses on carbs are new.

The bike runs well - very strong and idles well, no flat spots, and will pull to redline. The only problem I know of is that the compression is low across the board - all four cylinders are between 105 and 115 pounds, and it uses about a quart of oil every 400 miles.

Any ideas about what to look at next to get rid of the popping?

white lugs are not good - too lean.
Beige/brown plugs are ideal.
Dark / black is too rich.

Could try enriching carb pilot circuit, say 1/4 to 1/2 turn. Good Luck!

KYKZ1100 wrote:

The only problem I know of is that the compression is low across the board - all four cylinders are between 105 and 115 pounds, and it uses about a quart of oil every 400 miles.

Any ideas about what to look at next to get rid of the popping?

First, I would check valve clearances.

If those are the true (warm) compression readings with adequate valve clearance, the engine needs work.

Patton, I'll try that.

Bountyhunter - The valves are new (~1,000 miles on them) and all were within specs after they were replaced, but if I can't figure anything else out, I'll check them again.

I checked the compression several times after the valves were redone, both cold without the carbs installed and warm, and the reading were pretty consistent. The highest I saw was cold and one cylinder was 120, the others between 105 and 112 or so. When I put oil in the cylinders, the pressure went up to 145-150 or so on all cylinders.

I bought three NOS 2nd oversize OEM pistons on eBay a month or so ago. If I can find a fourth I'll use those, otherwise I'll look at Wiseco, and I plan to have it bored and put in new pistons and rings this fall. I don't really need more performance and don't really want higher compression so I'd just soon stick with stock.

KYKZ1100 wrote:

Patton, I'll try that.

Bountyhunter - The valves are new (~1,000 miles on them) and all were within specs after they were replaced, but if I can't figure anything else out, I'll check them again.

I checked the compression several times after the valves were redone, both cold without the carbs installed and warm, and the reading were pretty consistent. The highest I saw was cold and one cylinder was 120, the others between 105 and 112 or so. When I put oil in the cylinders, the pressure went up to 145-150 or so on all cylinders.

So the ring to wall seal isn't holding well.

KYKZ1100 wrote:

I bought three NOS 2nd oversize OEM pistons on eBay a month or so ago. If I can find a fourth I'll use those, otherwise I'll look at Wiseco, and I plan to have it bored and put in new pistons and rings this fall. I don't really need more performance and don't really want higher compression so I'd just soon stick with stock.

Smart move, those bikes make plenty of power stock.

My 82 A2 did that until I replaced the rings. Nice and quiet now. I just used stock rings from Z1, after inspecting the pistons to make sure they were ok and did a glaze break honing on the cylinders. I could not afford to bore and go oversize pistons at this time. This bike had 39000 miles on it and the engine had never been apart until I did the valves at 37000 miles. One of them was leaking....should have done the rings too but I had hoped the valve job would cure the ills...chris3

Thanks chris. I don't understand the mechanism by which poor compression causes backfiring but I know the rings have to be done anyway. I'm going to try Patton's idea of adjusting the pilot circuit (haven't had 2 minutes this week to try it), but if that's not the problem I'll just put up with it until I can have the pistons and rings done this fall.