How do these look?

[Guest]

This is all stock jetting on a 79 GS750. VM carbs, 15 pilot jet, 102.5 main, middle clip on needle height, 23.5mm float height, stock airbox, kerker 4-1, 1 turn out on fuel screw, started at 2 out on air, and adjusted for highest idle. Finally did some plug chops. How do they look to you?

Pilot circuit: 1/8 throttle


Needle position: 1/2 throttle


Main jet:


There is still carbon buildup on the lower strap.

[Chuck78]

For the mains especially, a wide open plug chop should be on fairly new plugs that have been ran for about a half hour, and then you need to be cruising at a lower speed and go WOT through the gears quick and hit 5th gear at a lower speed and run it for 10 seconds total at WOT up a hill on a straight and deserted road, kill switch./throttle closed/clutch in all simultaneously. then take the plug(s) out, replace with a spare set, go home, put the hex of the plug in a vice, and use a hacksaw/sawzall/bandsaw to chop off the threaded portion so you can actually read the area of the plug that you need to see for wide open throttle. you can't learn much from the main jet sizing without seeing the affected area of the plug insulator

[Chuck78]

Here is what you want to see. These are from my bike, and I'm running 112.5 or 115 now, can't remember:




Here is my first attempt, the 122.5 main plug above, but I hadn't cut the threads down far enough:



See, you literally have to CHOP the plug up to see the mains and even best to do it for 1/2 or 3/4 throttle.

Your plugs look a little darker than I'd have thought for a stock airbox and jets with a wide open 4-1 with no baffle whatsoever. And all three plugs look about the same. I'd drop in at least one new plug and repeat this procedure. Get those K&N Pods and the V&H exhaust you want and then order up a selection of JetsRus.com's OEM Equivalent jets starting at maybe 122.5 and going down from there a few sizes. 117.5, 120, or 122.5 will probably be the mains you want for your bike but that all depends on your valves and seats condition, as well as the piston ring and cylinder wall condition, as well as your altitude.

[Chuck78]

By the photos you can see that the area you need to inspect for wide open throttle chops is definitely not visible without cutting the threaded portion of the plug off.

[Chuck78]

VERY USEFUL!

[tkent02]

You can easily see the bottom of the insulator if you use a loope or magnifiing glass and a strong light.

There is no need to cut anything.