Spark Plug Reading - What's your read?

[rustybronco]

Steve, thanks for taking a peek. Reading the porcelain I noticed that plugs 1 & 2 are showing tan where 3 & 4 are very clean. Could that be from carbs that aren't synched (which mine aren't yet)?

at least # 3 shows tan, can't see #4 clearly.

[Steve]

Haven't really done much at full throttle yet.

This is the base from which all other settings are derived. :shock: The main jet also feeds the needle jet. Together they control just about everything but idle mixture. If you start tweaking at the idle end, then work your way up, if you have to change the mains, you have to start over. Start with WOT tests to get the main jet right.

I've got a stock airbox, but I suspect that I've had an air leak at the intake boots. In addition, I've got two pilot screws that are stuck and stripped out and I was running the other two about 1.5 turns out.

Just out of curiosity (so I can compare with the picture), which ones are stuck and which ones are 1.5 out?

I'm thinking that I need to do the following:

1) Get the two stuck pilot screws unstuck and set all screws to 3 turns out.
2) Ensure that I've got an air tight system from the air box to the cylinders.
3) Sync the carbs.
4) Tweak #1 as needed based on future reads.

Not bad.
1) Get the two stuck pilot screws unstuck (replace them, if necessary) and set all screws to 2 turns out.
1a) Bench sync the carbs.
2) While you have the carbs off the bike, check the intake tubes and their o-rings.
....If you haven't changed them, chances are they haven't been done.
3) Install carbs and use gauges to sync them.
4) Shouldn't have to tweak much if you started at 2 turns.


.

[GS750]

Yep, lot's of idling and then I pulled the plugs. Still have some carb tuning to do. Now I have a good read to work from. Thanks!

I was taught that you need to use the kill switch at W.O.T (wide open throtttle) to be able to correctly diagnose the fuel mixture from the plugs.

For nearly all engines I have worked on, at idle will run either rich or lean.

Thats why "emission" controlled carbs had the mixture screw capped off...... You can still change jets, but you cant f*ck around with the mixture.

[MelodicMetalGod]

This is the base from which all other settings are derived. :shock: The main jet also feeds the needle jet. Together they control just about everything but idle mixture. If you start tweaking at the idle end, then work your way up, if you have to change the mains, you have to start over. Start with WOT tests to get the main jet right.

OK, so I need to do plug reads after shutting down from WOT. Had NO idea. Thanks all!

Just out of curiosity (so I can compare with the picture), which ones are stuck and which ones are 1.5 out?

Stuck pilot screws are # 2 and 4. # 1 & 3 were set to 1.5 turns out.

Not bad.
1) Get the two stuck pilot screws unstuck (replace them, if necessary) and set all screws to 2 turns out.
1a) Bench sync the carbs.
2) While you have the carbs off the bike, check the intake tubes and their o-rings.
....If you haven't changed them, chances are they haven't been done.
3) Install carbs and use gauges to sync them.
4) Shouldn't have to tweak much if you started at 2 turns.

RE:
1) I've got two sets of backup carbs waiting for me to pull replacement pilot screws! I've been recommended everything from 1.5 up to 3.74 turns out. Why do you recommend 2?
1a) Bench syncing is part of my standard carb install process.
2) Are you referring to the infamous intake boots (between carbs and engine) and their infamous o-rings? If so, I've just rec'd a new set of both. I've seen a recommendation of applying a coating of hi-temp bearing grease to the o-rings to ensure against any leaks...?
3) Gauges sync is on the list.

Thanks!

[MelodicMetalGod]

I was taught that you need to use the kill switch at W.O.T (wide open throtttle) to be able to correctly diagnose the fuel mixture from the plugs.

For nearly all engines I have worked on, at idle will run either rich or lean.

Thats why "emission" controlled carbs had the mixture screw capped off...... You can still change jets, but you cant f*ck around with the mixture.

My pilot screws were capped off, but the PO drilled 'em out, as many folks do. My understanding is that the factoring settings are generally a bit lean, especially for emissions purposes.

Thanks for your time!

[lecroy]

Sorry I did not read any of the links, so my post may be a repeat.

For starts, I really only care about WOT and idle. There is no way to shut down my engine at WOT without doing some damage.

The spark plug is a memory device and it records the maximum temperature. So, say I make a 1/4 blast down the road and then drive it another 3/4 of a mile to get back home. The data from the 1/4 mile WOT blast is still recorded in the plug and will not be effected by our slowing down and returning home.

The key is to look at the heat line. The heat line can be seen by looking at the side of the plug. The threaded part will show a dark line as the heat moves towards the top of the plug. This line is very distinct. If your using the newer NGK D8EA plugs you can bring this line near 3 threads. I try to keep it under 1 1/2 threads. Real safe.

You could look at EGT. Hotter would seem to be leaner, but there are problems with this. For example, you could be so rich that unburned fuel it being burned in the exhaust. Looking at the EGTs you may think it is lean when it is really rich. Always start with the plugs and verify with EGT.

Just something else to add to the mix....

[lecroy]

The far left plug was from an engine I damaged. Notice how much hotter this plug got. The next 4 plugs are from the next 4 passes. Notice that they start very rich and as I bring the jetting in the heat line moves up into the 1 thread area. Still a little rich, but very safe.

The top plug in the next picture was from my first 8 second pass. Notice that the line is very solid in the 1 thread. The bike will run faster as it is leaned down, until it melts.

[lecroy]

sorry, only 1 picture per post.