Take a look at these plugs...never seen this before

[JP50515]

Hey guys so here's my situation. Did a recent rebuild on the top end, had the cylinder head blasted, port and polish. Got a feeling they didn't clean it nearly as well as they claim they did and my cleaning obviously didn't do it either because there is media on top of my pistons....

Anyway this is what my plugs currently look like.

Pics are of same plug but they both look like this...I have no idea what to make of these.

Any ideas?

 

[Tomterrific]

Detonation scouring the insulating laminar layer from the top of the piston. The extreme heat of combustion melts the surface and the detonation shock wave blasts off the molton aluminum as small globules. Tough to tell without a magnifying glass. There could also be grey ash from burning oil. Oil in the fuel mixture will lower octane.

Use premium fuel at the pump.
Check timing at full advance.

 

[JP50515]

I run 91 nonoxy only. What's the solution?

 

[weekendrider]

Check your advance, is it running past the full advance mark?
If so it needs to be corrected soon if those two little shiney bits/balls in the plug(1st pic) are an indication of what Tom said.

 

[JP50515]

How do you adjust that? I have a pamco. Is it simply hitting it with the timing light while hitting the throttle and watching the mark and adjusting the pamco to bring it back?

 

[weekendrider]

Did you put on a new ATU with the pamco then yes.

 

[pamcopete]

How do you adjust that? I have a pamco. Is it simply hitting it with the timing light while hitting the throttle and watching the mark and adjusting the pamco to bring it back?

Yes, but also make sure that your advance rod is not binding as it could be stuck in the full advance position.

 

[JP50515]

yea new atu and springs. Advance rod is fine. The bike runs and idles fine

 

[weekendrider]

Then the pivot ends of the bob weights should be within tolerance.
Worn they will let it advance too much.

 

[5twins]

On your '77, full advance is indicated by a slash mark on the far left. It is not labeled with a letter or anything .....

Rev the bike to 3 - 3.5K and make sure the timing isn't going past that slash mark AT ALL. On many of these, the timing image will bounce around a little. Make sure even the "bounce" isn't going past the slash mark. For your idle timing, there is a range of 4 or 5 degrees that is acceptable. As long as the idle timing is somewhere between the 2 slash marks, you're good and in spec. It doesn't need to be centered between the slashes (right on the "F") .....

 

[JP50515]

Sweet I'll check it out. Thanks

 

[wherearewe]

Not trying to thread hijack but since we are talking about advance timing, Is the only way to reduce the 'range' of timing peening the bob weights? On mine, at idle i have to position on the right hand range of the Fire 'F' so that on throttle it comes hard up to the advance line, maybe bouncing a touch past on occasion. This would be the maximum allowable 'range' in timing correct? I dont want to move my idle timing further past really, so I tried peening the bob weight tabs a bit using a caliper. However then the advance mechanism became a bit sticky and it wouldn't snap back smartly. I lightly filed them until smooth again and the snap returned. To be honest it didnt make a huge difference, a little. Do i need to try and peen a tad more?

 

[GreasyC]

More than one way to skin a cat. Personally I wouldn't do anything to them that involves force or stressing them. I've had too many oh shit moments doing that and I just about throw the hammer through the shop wall when I do. I don't need that kind of stress.

You can add a dab of solder or epoxy to the stop and they will hit it and stop advancing sooner (less total advance). You can file the blob to just the right thickness to get the advance you need. It can be removed, put back, whatever, without stressing anything.

 

[grizld1]

wherearewe, where you are going to be is stranded by the side of the road, and rather soon. The tabs on the ATU will--not might, will--fail, usually within a couple of hundred miles, if they are tapped, bent, or otherwise tampered with. You've started small fractures in the metal, and vibration will do the rest. It pays to read the manual; in most cases you can believe what's written there, and this is one of those cases.

 

[wherearewe]

Thats a bugger. I took the advice of a couple of threads on here! If i have to replace the assembly, would you go Mikes unit (which i assume is not oem) or genuine yamaha? Cost difference is erm, quite large. Or i could buy a used unit but it could be no better...

 

[grizld1]

Hold on mo, I might have misunderstood you, wherearewe. If you widened the tips of the bob weights by peening them to better fill the slots in the timing disk, that's fine; but if you tapped in the tabs on the ATU rotor to close the advance interval, that's going to be trouble--usually sooner rather than later.

 

[5twins]

There might be a little misinterpretation going on here. This is the part you want to peen, the little ends of the weights that fit into the slotted disc .....

If that's what you were hammering on, you should be fine. What Griz is referring to is the stops for the weights on the backing plate, the little tabs they fling out against. Don't be bending those.

 

[wherearewe]

Ah no i only peened bob weight tabs as per 5 twins pic above. Never bent in the backing plate tabs. Like i said though it didnt make much difference as it became a bit 'sticky'. Ill give it another shot. Just out of interest, anyone have any thoughts on Mikes assemby vs oem?