Signs of Detonation/Pre-ignition?

Hey folks, I've had my 82 XJ550 Seca on the road for about 2 weeks now and I've put around 500km on it so far. It's running pretty darn good I'd say but, upon taking the plugs out I noticed that there are some small black specks on it which if I'm correct is typically signs of the fuel pre igniting. I'm sort of puzzled though, because I hear no pinging and it goes like stink right up to redline. Could these black specs just be pieces of carbon breaking up? The bike has been sitting for 20 years.

I've ran a few tanks of high octane fuel through the engine and it appears to respond positively but it may just be a placebo.

let me know what you think.

 

Are you using the correct plug?

 

I'm using NGK D8EA plugs which I believe are correct.

 

I can't comment on the plug read, but here is a very good article on detonation and pre-ignition.

http://www.clubwrx.net/forums/tunin...26-engine-basics-detonation-pre-ignition.html

 

It does look like pre-detonation, and your plugs are in the correct heat range.
Some questions:
Are your valve clearances in spec?
Have you confirmed that the valve timing is correct?
The plug color looks decent aside from the flecks, but how did you set the idle mixture, and did you thoroughly clean the carbs (church of clean)?
Are there any signs of the engine having been opened up?

I will assume that the head was not off, and that it was never decked and it has standard pistons (which may be a bad assumption given people do things without marking the engine so other people know). This leaves me to think that there may be enough carbon buildup on the piston tops to be the cause. I would get some additional vacuum line, enough fittings to make a manifold to join them into one inlet line, and hook it up to the intake vacuum ports. Start the engine and get it warm. Stick the vacuum line into a can of Seafoam so it slowly sucks in the naphtha until the engine stalls. Let it sit overnight. Start the engine the next day and run it until the smoke clears (return the vacuum setup back to normal), then ride the snot out of it for a few miles (get above 5K RMP in fourth, then shift down and open the throttle hard like you were going to pass. Coast back down, and repeat a few times). If you can manage looking in your mirrors you might see a cloud of blackish crud spewing out of the exhaust; that's the carbon being blown out.

Put new plugs in and go for another short ride. Check the condition of the new plugs.

 

Valve's were adjusted as soon as I took ownership of the bike.
I did not check if valve timing was correct, if the cam chain were to have jumped a tooth would it still run well?
I've gone one size up on the pilot jets due to the muffler change, pilot jet screw was set by warming the bike up and screwing the screws into until idle dropped, out until idle dropped, then set the screw somewhere in between.
I've yet to sync the carbs, awaiting on my gauges to come in the mail.
Carbs have been gone through extensively.

I bought the bike off of the original owner and he said that it was never opened up. I did a compression test before the bike was on the rode and I got 125psi cold on all 4 cylinders.

I'll definitely give the seafoam a go, I put some in the gas on the first run but I believe it was to diluted to have any affect on the carbon buildup in the combustion chamber.

I've never ridden another 550 before, so I'm not sure if this is correct engine behaviour. However, once the rpms crest 6000rpms and the engine comes on cam it becomes noticeably "angrier" for lack of a better term. The tone of the engine changes slightly and pulls very hard, this is the first inline 4 I've owned so I'm not sure if this is normal.

 

Yep, that's how they do that


If the cam timing was off slightly it would still run well. It's not a huge concern to me now that you've explained how you set the idle mixture, though it won't hurt to check. At this point I'm going to stick with the hypothesis that there is carbon buildup.

 

i did that seafoam through the vacuum ports once and had such a explosion in the pipes i almost dirtied my pants, how about just squirt it in the spakplug hole?
looks lean to me, there's very little carbon on that plug and just barely see a heat range line on the tang, is the air filter seated right ?

 

The plug is a little lean, but the dark flecks aren't coming from being just a little lean. If there were flecks of aluminum, then that would be from being lean (very lean).
The point of sucking the Seafoam in via the vacuum ports is to induce a thermal shock that will help to loosen any carbon deposits. The same effect can be had by using ATF instead of the Seafoam.