Compression increase? Pinging, detonation..

Hey guys, recently my 81 started getting harder to kick, as if the compression has randomly increased for some reason. Also it is pinging a little at about 1/8 throttle under load. My plugs appear to be getting too hot and I started getting a little popping on deceleration. It also has been taking 3 or 4 kicks to cold start it instead of the usual 1 or 2 kicks. Looking at the top of the Pistons through plug holes I can see some light gray grainy/pitted looking crusty debris on the Pistons.

I made no changes before this started happening.

Current setup:

Uni pods
Stock pipes with emgo shorty mufflers.
New exhaust manifold gaskets
BS34 carbs
New carb boots and gaskets.
Pilot jet - 45
Main Jet - 145 (I just changed this from 140 yesterday in an effort to richen the hot/lean mixture)
Fresh new spark plug wires, ngk 5k resistor caps and bp7es plugs.
Factory tci ignition setup.
Adjusted cam chain, set valves .003 intake/.006 exhaust.
Balanced carbs and mixture screws are @ 4 1/4 turns out (up from the normal 3 1/2 I have been running)

I am going to try out the cooler bp8es plugs after work today in an effort to cool it down inside the cylinders. I realize this is just masking whatever is really wrong.

I have been running bp7es plugs and 140 main jet for a couple years now and my plug color has been really nice.

I am about to take the top off and start lurking around to see if I can find anything obvious. It is currently running really good, almost too good. I'm worried.

I need help. Any ideas on what else I can check to get to the bottom of this? I can provide any further info and/or pictures that may be needed.

Thanks.

1st 2 pics are left side, the last 2 are right side.

Carbon buildup on the pistons and in the combustion chambers can eventually raise compression and induce pinging. Have you ever had it apart and if not, how many miles are on it? I would think it would take 20 to 30K miles (or more) before carbon buildup might get excessive. But that's on a good running and properly jetted motor. Run it rich and you could build up carbon quicker.

You might consider retarding your timing a couple of degrees. That will help ward off the pinging. Unfortunately, it won't do anything for excess carbon buildup. It would have to come apart to clean that out.

Thanks for the reply 5twins. So here is what I did since reading your response today.

Checked my timing @1200 rpms. It was already firing on the right leg of the horseshoe just as in your "tci timing tweak" guide here: http://www.xs650.com/threads/tci-timing-tweak.55209/

I enlongated the top hole and set it back a couple more degrees anyhow. I ran it up the freeway, through the country at medium speeds and then back home through town around 25mph. Ran great, still slight pinging at just the right rpm. Checked the plugs and they are a solid brown color. All of it. The grounding strap and the porclean. I have attached pics. This was with my already used bp7es plugs.

I picked up some bp8es plugs and installed them. Ran around town for about 20 minutes, 25-40 mph. Checked the plugs, they look to be coloring up very nicely, not a whole lot of color yet, but some and it appears to be good. Less pinging and almost no popping on deceleration. The bike does have slightly less pull now, not much though. I am considering advancing the timing a tad almost back to where it was set from factory and then checking these cooler plugs again after some miles with that setup. What do you think about that?

To answer your questions:

I have had the top end off a couple of years ago when I first got the bike and inspected the cam, rockers, chain etc... All appeared to be in good working order.

The odometer reads just under 12k miles. I have not been using it but I'd say I've put at least 5k on it. probably more. I doubt it is over 20k.

The carbon buildup makes sense, I have been running it just slightly rich up until now. To be clear there is not a ton of build up, just a small patch near the center of each piston and it is not black. It looks burnt, light gray. Probably 1/16" thick.

Here are pics of the hotter plugs after retarding the timing. I imagine the pictures might tell a different story had I used fresh plugs. Added a pic of my bike just for fun.

Boy, those plugs really are brown, lol. You don't see that much with today's gas. Your 1st set of plug pics is more the norm with the gas today. Maybe you should do an actual compression check, see if the numbers reflect what you feel is higher compression than before. Sure, tinker with timing settings. This is a strange one for sure and I'm really not sure what the issue might be. For the leaner running, maybe you've developed some air leaks in the carbs?

How old is the oil?

I would die for plugs that colour on my Triumph. I have no complaints about it’s performance, ticks over like a watch, pulls like a train, doesn’t pink, in fact it’s nigh on perfect, but the plugs are really white, like yours in the first picture.
My XS is much the same only it doesn’t pull as good, but it is quite a bit heavier, when I check the plugs after a run at mid throttle the plugs look really weak.
You have to do a constant speed for a while at a set throttle to get an accurate reading from your plugs for a specific jetting area. Low speed jetting may be rich, mid throttle, and full throttle may be quite different.
I agree, running the timing a little shy of full advance will make for a nicer engine, I would try a quarter turn richer on the air screws also.

Haha! Yeah I laughed a bit when I saw those brown plugs too. I will definitely run a compression test. Taking the family camping in a couple days so won't be able to run that until Sunday or Monday. I'll update here when I do.

The oil has about 650 miles on it (we went on a couple day ride last weekend), I changed it last week. It has been changed once a month since winter this year.

I will mess with the mixture a little more too.

Thanks for the help so far fellas, much appreciated. Will post updates soon.

Those plugs may prove a bit too rich. They may turn even darker, maybe even black, after some more miles. You actually don't want any color at the top of the porcelain, only around the bottom. The top should stay clean and white, like in your 1st set of plug pics. That 145 main may be a bit much.

I was wanting to put on 142.5's but only had 145's on hand. Maybe I'll go back to the 140's now that the timing is changed and the plugs are cooler.

Might pay to take the sump filter off and have a look at your crank to see if it's spread, that feels like an increases in compression as the crank only rubs in places when it spreads

This is a picture of a plug from my TX750. This I think is about as good as it gets.
I looked at the plugs after the first real ride, long story but it hadn’t run for years when I got it, cleaned out the carbs and the exhaust collector that was full of grease, why grease,I can’t answer.
Anyhow after a bit of running and love, turned out OK.

After the weekend when we're back from camping, I'll put the 140's back in. I will pull the sump filter and check the crank. Solid ideas guys, I hit a mental wall after awhile and need input from others.