Strange

[mack]

I had a bit of a surging problem. Plugs looked to be running lean. I checked the gap on my plugs with a digital caliper and appartently the chiniese don't make real accurate feeler gauges or gaping tools. So I changed my gaps to what matched my caliper and now the surging is gone but after a 125 mile ride I pulled the plugs again and 3&4 still look lean to me. Gaps are the same. I just spent a week doing the float levels individually etc. Tach is still jumpy, I,ve just put on Geezers voltage regulator and last year was when I bought the battery. All Grounds secure, and I ultra sonic'd all electrical connections. No stagger at any RPM and starts and runs real strong. Just can't get the right color on the plugs. Do I need to get a better set of gauges and re-do the valve shim spacing? Or is this an electrical problem just waiting to manefest itself and kick my feet out from under me when Im a few hundred miles from my shop?

[TopCatGr58]

Hey Mack,

You say you spent lots of time setting the float levels, but you didn't say anything about vacuum synching the carbs? I don't want to assume anything, and if you only bench synched them, then that could be a source of a surging problem/symptom. IF you have vac. synched them, then what other settings have you set the carbs at, ie. jet sizes for pilots and mains, the pilot idle SCREW setting...how many turns out from gentle seat, did you tune the pilot circuit with a color tune or the by ear method described in the tech tips? Have you checked for vacuum leaks at the carb boots, boot synch ports, throttle shaft seals on carbs, etc.?

When you cleaned(did you clean) the carbs, did you closely inspect the vac. diaphragms for pinholes, and then to the push the slide up, cover the arced vac port and verify that the slides didn't drop very quickly?

You say the plugs are LEAN looking. The unleaded gas doesn't show up as well on the plug insulators as well/easily as it used to, and it's also suggested to perform the throttle chop technique for reading the plugs, not just pulling them after running around town...that will mostly show you the pilot/idle circuit jetting.

MORE INFO PLEASE!
T.C.

[mack]

Info

Yes TC, the carbs have been vac sync'd. When I originally colour tuned the carbs my pilots where all over the place. Thats why I went back into them and wound up readjusting the float heights individually with a hose hooked up one bowl at a time. Now after color tuning my pilots are all about 2 turns out. I've been burning shell gas with the nitigen additive in it. Maybe I'll run a tank of the other through it to see if thats whats going on. The surging started after I bought a spark plug gapping tool, and thought I was doing a good thing by putting in a new set of freshly gapped plugs and resync'd. It was very subtle but I could feel it and knew it wasn't right. I'd removed the octy at the same time so I was first looking for a fuel starvation issue. Then it came to me to recheck the plugs. So although the tool said they were correct, I thought I'd just check the tool against my calipers and what was .75mm on the tool turned out to be .624mm on the caliper. I re-set them back to .75mm and the surging went away, 1&2 plugs look good but the insulaters on 3&4 still look new. I was looking for the chop method in the carb section but couldn't find it.

[mack]

Additional info

Just to mention this is the 79 sf, all stock jetting, diaphrams were good, c-clip in center / neutral position. Octy gone and no crimps in tygon lines.

[TopCatGr58]

Okay, for us folks still used to the Imperial scale, the plugs were eroneously set at ~0.25 ", had surging, reset to ~0.30" and surging gone, but 3-4 plugs looking a bit lean compared to 1-2.

With symptoms linked 3-4 points more towards fuel/carbs and tuning/setup vs. ignition.

The Throttle chop method is have at normal operating temps, then find a place...hill, where you can run a sustained ~4-5k rpm engine load for 30 seconds, then using kill switch shut off engine, clutch coast to a stop and pull the plugs and look at them on the side of the road. This gets you the plug color of the mains, not the pilot circuit.

I've never done this, and don't know how accurate or useful it really is, but I've read this from several mechs on the site. I think it might be more helpful IF a bike is running RICH on the pilots and coloring the plugs too dark when in the garage, but a bike might still exhibit lean running symptoms on the top end?

I know you've spent a lot of time with the float height adjustment, but if 1 pair of carbs have more plug color than another, same jet sizes, etc, then sounds like it might still be a subtle float height difference being the contributing factor/variable....aside from other things like compression. 1 member reported as little as a 1/2mm making a difference!? YMMV!

T.c.

[mack]

Thanx

It's very close to being right. I'll retune it then if l have to, pull the carbs one more time if the chop test doesn't look good. I've ordered a german set of feeler guages and plug gaping tools. They will be accurate. If I have the carbs off, I may as well pull the valve cover and recheck the shims with accurate gauges. All I want to do is just ride this thing. Patience, patience.

[79XS11F]

I would be inclined to think there is a fuel supply issue happening there as well. Could be as simple as the in tank filters not suppling as much fuel to 3 and 4 as to 1 and 2. Try turning the fuel petcock for 3 and 4 to prime and see what you get. If you have in-line fuel filters make sure they are good.
I really don't think that plug gap will have that much of an effect unless they are way out of range. You could also try slightly cooler plugs on 3 and 4 if need be.
Rob