'78 XS1100E, '80 carbs low rpm funk

[gtem]

All,

An update on the '78E with '80 carbs situation: I think I've almost got it. So the current setup is the gentler 5IZ7 needles with 120 mains, I went down to #40 pilots, and am finally getting a decent color on the plugs, pending more testing. The last remaining issue was cyl #4 kept getting a sooty plug. I checked and rechecked everything, tested the choke circuit for leakage, etc. The rest of the carbs had the idle mixture screws set out to 3 turns out with the #40 pilots but #4 would get sooty even with just .75 turns out. Finally I pulled the mixture screws from cylinders 3 and 4 to compare, and did some flow testing with WD40 through the idle circuits and saw that #4 was flowing more past the idle mixture screw even though it was turned in tighter! Upon disassembly of #3 and #4 idle mixture screws I found that the o-rings are all pretty compressed into a tapered conical shape (the seat that they are pressed against). Well it seems that at some point when messing around I had reversed the direction of the o-ring on #4, and somehow(?) that was causing problems. Or maybe my "flow testing" fixed something. I don't know. But I swapped the idle mixture screws on 3 and 4 and the rich condition on #4 seems to have been resolved. The bike has the cleanest idle it's ever had, I've never been able to lug it down to 2000rpm like this before. I'll be fine tuning the idle mixture screws a bit more, I think I'm a tad lean at the moment (set them to 2.5 turns out). I'm also considering repacking the RC pipe with some looser type fiberglass wrap to help it flow a bit better (hopefully without getting too loud).

[gtem]

A further update on the '78E with '80 carbs and RC 4-1 pipe (#40 pilots, #117 mains, 5IZ7 needles),:

I had started to get sooty plugs again, I had about lost my mind! Well I finally thought to take a peek, and realized the crusty old baffle had collapsed inside of the exhaust, restricting flow quite a bit. Re-welded the baffle and repacked it, I'm now back to clean plugs. The baffle in the pipe has roughly a 1-3/4 to 2" ID, perforated metal surrounded with fiberglass packing. When the bike is warmed up it will do some light juddering from a 3000rpm roll-on but then cleans up and pulls nice and hard to 90+mph Some backfiring when coasting down in gear, that seems to go away when I put choke to the halfway on position. It doesn't like to sit and warm up on choke, I almost immediately take it fully off and just bounce the throttle lightly until it holds and idle about 30 seconds-1 minute after starting the bike.

So it seems like I'm back to some low-speed/transition circuit tuning. A check with my colortune shows a nice blue at idle and it mostly maintains that when revved, there is a moment where it looks a bit orange, but it's hard to simulate accelerating against a load when just doing static revving. Below are photos of plugs #4 and #1 with the idle mixture screws turned out 3 turns with the #40 pilots.

Does the sooty base ring imply a rich idle/low speed mixture? I'm not experienced enough yet to have that dialed in feel to tell a lean stutter or backfire from a rich one. Bike doesn't smell too gassy or anything at idle, idle feels very nice and smooth. Before, the plugs would be totally sooty including the entirety of the ground strap. They're staying remarkably clean now.

[gtem]

A further update on this:

I took the '80 Special carbs back to their stock jetting and needle arrangement. I had mentioned a rough sort of warm up procedure, that ended up being one clogged up choke fuel pickup passage in the bowl of one cylinder. The #40 pilots were just too small, I went back up to 42.5, although once again, I only have .75 turns out from seated on the idle mixture screws (with new o-rings). The low end response is... good enough. The bigger issue had turned out to be some breaking up at high load (full throttle, from 4000rpm on up). I was convinced my change to 115 mains was to blame, so I swapped back to a stock (for a a 1980 Special carb) #110. Still the same issue.

At this point I realized, I may very well be dealing with an *IGNITION* issue. It feels *exactly* like when I had a broken pickup coil wire.

So I started by checking over the pickup coil wires, I had repaired one previously. No obvious issues. I traced that cloth-loomed harness all the way back to the connector behind the fuse panel, again, nothing obvious. I then started to inspect around the coils (PO had swapped them to Dyna 1.5ohm "orange" units at some point, keeping the stock ballast resistor). One thing I tested was said ballast resistor, and I got a resistance value of 3.4ohms, a good bit more than the expected 1.6. Could this be my problem? I'm going to test the coils themselves this evening and inspect the wires closely. I had recently replaced the plugs with brand new NGK BPR6ES (running non-resistor wires). I will inspect the plugs as well.

[LAB3]

Don't know how many times I've seen "carb problems" turn out to be ignition problems! Can I say it's the fault of the ballast resistor? No but one thing is for sure, if it's that far out of spec then replacement is in order.

[gtem]

"Don't know how many times I've seen "carb problems" turn out to be ignition problems! " I had that very same thought last night.

I was definitely peeling back the layers of the onion on this one, so to speak. The collapsed baffle was the cause of my idle/low speed richness, now my high load higher rpm backfires which cropped up at some point in all of this tinkering are (likely) ignition problems. This '78 has truly tested my patience! I'm just glad I have another bike to ride in the meantime.

I ordered up a supposedly good used ballast resistor on ebay, will test it of course before installing.

[LAB3]

You could always go to 3ohm coils and ditch the ballast resistor all together, it's one less thing in the chain to cause issues although I can also see wanting to continue using Dynatech coils as well.

[gtem]

You could always go to 3ohm coils and ditch the ballast resistor all together, it's one less thing in the chain to cause issues although I can also see wanting to continue using Dynatech coils as well.

I certainly had that thought, though I want to do some more testing before I commit to buying all new coils. I found a lightly used set of the same orange 1.5ohm style for reasonable money, a new set of Dynas is about $200 these days.

[DiverRay]

I do have one or two ballast resistors here.I'll check them later today, and I could send one out if you need a "known good" to check with. Just send me a pm.

[gtem]

I do have one or two ballast resistors here.I'll check them later today, and I could send one out if you need a "known good" to check with. Just send me a pm.

I appreciate the offer Ray! I've got one coming from Ebay-land, hopefully I'll be all set, but I will keep your offer in mind!

[DEEBS11]

If you are measuring that circuit and it is connected, it is possible to read about 3 ohms. You may be looking at the primary side of the coil and the problem could be in the secondary. Cracked/leaky high tension wires. Spray some water on the spark plug wires while it's running and see if there is a change.

[gtem]

Deebs I had disconnected the ballast resistor from the connectors when testing it, for what it's worth. And yes the plug wires are under suspicion as well. I can't quite tell if I'm losing one cylinder (plug wire) or two (coil/pickup wire going down). Bike doesn't act up when revved statically, only under load.