Pilot screws/jets settings on XJ?

[macnut xj]

I cleaned the carbs fully on eXJunk a few months back, but haven't done much with it since then, except work on the brakes and a few other minor things. Otherwise, it's just been sitting in the shop. I seem to remember that I set the pilot screws at about 2.5-3 turns out, and it ran fairly well, tho it did have a bit of a stumble about mid-tange. I put my temporary gas tank back on and hooked up the battery charger and got it running again recently, but I noticed that I could only get it to run with partial choke, it revved poorly and had a bad stumble at mid rpm's, but past that revved smoothly. I started backing the pilot screws out a quarter turn at a time, and it kept getting better. At this point, I have the screws backed out about 4-4.5 turns, and it will idle fairly decent with no choke, and will rev with some roughness, then smooth out after 4-5k. Is it possible that my pilot jets have gotten a bit gummed up after sitting for 4-5 months? That's the only thing that makes any sense to me, with the screws backed out that far. Could I take the pilot screws out and spray some Gumout down the openings? Anything else I can do without pulling the carbs again? I really don't want to have to resort to that, since it's such a major PITA on the XJ !

[TopCatGr58]

Hey there John,

What grade/octane of gas did you start with?? If regular 87, then after sitting for 5 months, without stabilizer, the octane can degrade about 1 point a month, so you could be running 82 octane by now?? Try draining the gas and putting in fresh, or adding some octane booster, along with some Techroline or Sea Foam!? That's my thoughts!
T.C.

[macnut xj]

It just had regular gas in it, but the tank didn't stay on the bike all this time. It's a plastic lawnmower gas tank that I use for test purposes on mowers and other equipment. It holds about two quarts, and I have run at least a tank and a half of fresh fuel thru the bike so far. Oh, it does have a fine screen on the outlet too. I do plan to get some Techron or Seafoam for the next tank of fuel, and get it out of the shop and ride around the neighborhood a bit. (I live in the country). I'll see how it goes with that, and I think I will try blasting some Gumout down thru the pilot screw holes. I figure it can't hurt anything. Anything to avoid having to pull those d*mn carbs again!

[macnut xj]

Now maybe ignition problem?

Okay, a bit of an update. I had the bike running again tonight, and just for grins I took my plug-wire pliers and started pulling wires off the plugs one at a time (at idle). I figured this might show which cylinders had carb "issues". I noticed that when I pulled the wires off cylinders 1&4, the engine would change tone and slowed slightly, but still idled. But when I pulled the wires off 2&3, the engine slowed so much it nearly died! I removed the caps from the wire ends and checked for corrosion, but didn't see anything. I even trimmed about a half inch off the ends and reassembled, but it still ran the same. I remember reading in a thread the other day that 1&4, and 2&3 are paired at the coils, so now I'm wondering if maybe I'm having a problem with the coil for 1&4, and it's not really a carb problem at all. Any thoughts? I can pull the coil off my parts bike and swap it over if needed. Or maybe it's just a coincidence that it's on 1&4 and it's still in the carbs. Any way I can verify where the problem is??

[wiredgeorge]

There are two checks you need to make on the suspect coil. First is for primary impedence and the second for secondary impedence. These checks are made using a multimeter and are documented in your shop or Clymer manual. These impedence checks will show up any shorts in the coil. A short is caused when the winding coverings internally get fried and wires touch. These shorts can cause total failure or intermittent operation which is sometimes tough to deal with. You can also have a poor electrical source going to the coil which doesn't allow it to fully fire. The power for your coils comes from a single source though and it isn't as likely this is your problem as it would also show on the other coil equally. The power for your coils goes through a lot of very old wire, connectors, your igntion switch and the kill switch. The contacts on the switches and connectors are typically not conducting electricity as well as when they were new and the power to your coils will be far less; hence you spark will not be as good. Start by checking the impedence on the coil to troubleshoot this problem. Also, idle problems can be terrible to fix if you leave a cap off a vacuum port either on the carb or on the intake rubber manifold.

[TopCatGr58]

Hey George,

Thanks for playing, but not entirely accurate! There are two different circuits, 1 for each coil, controlled by separate Pickup coils in the timing cover/advance plate area! And each PU coil sends a signal to the CDI to send to the Ign. Coils, one for 1-4 and one for 2-3, so you CAN have a poor/bad signal to one set and not the other.

However, on the XJ, both Vacuum and Centrifugal advances have been replaced with electronic boxes, so I don't believe the PU wires have to flex like they do on the XS's! Just checked the Parts Diagram, and the plate is just bolted in place, no rotation of the plate, hence no flexing of wires, so less likely to get fractured from repetitive stress syndrome!!!!

Macnut, the Red/White wires to the Ign. coils are direct hot/power leads, and with the ign. on, you should get 12volts! The green and grey wires go to the CDI. Check the resistances of the Ign. coils. And yes, you could easily swap out the loaner coils to test as well!! Aside from individual problems with the carbs, the supplies are paired 1-2 and 3-4, so it does sound more like electrical!? Good Luck.
T.C.

[macnut xj]

Update

Well, this evening I dumped some Seafoam in the temporary tank with about a quart or so of gas and ran that thru the carbs. I mixed it pretty heavy. I also swapped out the coil for 1&4. Still no change. I haven't tried shooting carb cleaner down thru the pilot screw holes, but I'll try that next. The only thing left that I can think of is to pull the carbs and go thru them again. I did notice that when I left it idling for a while this afternoon, that I smelled something getting hot. I started looking the bike over and noticed that the mufflers were turning color right near the cross-over pipe underneath. I have no idea why that was happening. I had the choke completely off. Amy ideas? I do know that when I give it throttle from idle, if I give it some choke, the engine picks right up. Otherwise it bogs badly when you open the throttle. That's what makes me think the problem is something in the pilot circuit. I'm really starting to think that it's just a coincidence that the problem is on 1&4, but I'm considering swapping the CDI box just for grins, tho I'm not expecting it to fix the problem. I'm still open for any suggestions, but it's looking like I'm going to fighting with getting those stupid carbs out and in again!

[Ken Talbot]

Go back to the pick-up coil wires and check for breaks. You'll find a detailed explanation in the tech tips.

[macnut xj]

I didn't think the XJ's had the pick-up wire problem, but I guess I can check it just in case. I've tried about everything else! I just tried swapping the ignition box over from the parts bike. The good news is that I now know that I have a good spare, but the bad news is that it didn't solve the problem. I also opened up the air box and checked to be sure a mouse hadn't decided to build a nest in there and cause trouble, but I didn't find anything. Even running it with the box open didn't help. I'll take a look at those wires next. I'll try anything to avoid having to pull those carbs again! But I really have a feeling it's going to be inevitable. The way it responds to the choke, and the discoloring of the mufflers seems to point to a lean condition at low revs. I just can't figure out why the discoloration is happening where it is. That's really got me baffled.

[ratbyk]

Discoloration in Exhaust

Discoloration in the crossover pipe sounds to me like things are too rich. A lot of unburned gas is getting past the cylinder and down into the exhaust system. There is not enough oxygen present to allow it to burn until it gets closer to the end of the exhaust system. Now, with some oxygen seeping back into the system the unburned fuel can light up. This is overheating the exhaust system and causing the discoloration in the cross over.
Does the exhaust have that "rich" smell to it?
Ken/Sooke
78E Ratbyk
82 FT500 "lilRat"

[ratbyk]

Discoloration

Further, just remembered that I have seen exhaust systems over heat if the timing is late as well. Spark occurs so late that the exhaust valve opens before complete combustion has taken place and the fuel continues to burn as it exits the exhaust system causing it to over heat/discolor. A spark advance that is stuck, either vacuum or centrifugal could also cause late ignition timing.
Ken/Sooke

[macnut xj]

Well, this afternoon I decided to pull the plugs before doing anything else. I really expected to see the inner (2&3) plugs black, while the outers wouldn't be. Surprisingly, none of the plugs show black/carbon fouled. All were still mostly white! Now I'm totally baffled..... This is really making no sense at all. With the way this thing is running, I would expect to see at least some difference in insulator color between the inner cylinders and the outers, since 2&3 seem to running much stronger than 1&4 (at least at idle). I really don't have a clue where to go next...... And to top it all off, I noticed that a couple of the plugs appeared to be slightly wet with fuel, even tho the fuel was shut off when I finished running it last night. And no, I don't have the stock tank (or octy) on it right now, and I know the inline shutoff I'm using works.

[Ken Talbot]

Please humour me, John, I'm not trying to be a wi$e@$$, but have you checked the pick-up coil wires yet? One broken/intermittent/flakey wire will affect a pair of coils, and it will be a 1-4 pair or a 2-3 pair. Two cylinders acting up together, and in this kind of grouping, is highly suspicious.

[macnut xj]

Okay, further info. Just in case I had a couple of bad plugs, I swapped 'em all out. No change. Next I opened up the XJ service manual and did the test for pick-up coil resistance. Manual says 120 ohms, plus/minus 10% @ 65 degrees. I measured about 121.5 ohms across each @ considerably more than 65 degrees here today. I'd say everything is okay there. I even pulled the side cover off the engine and did a visual inspection of the coils and wiring. everything looks like new. I even tried swapping out the pressure transducer unit, just in case. Again, no change. I think I've done pretty much everything I can to eliminate an ignition issue, so I guess it's back to a carb problem.

[Ken Talbot]

The problem with broken pick-up coil wires is that can spec out okay with a multimeter, and visually you will not see a problem, but they are still broken within the insulation. When things are sitting right, the broken ends of the wire make contact and things seem more or less okay. With the vibration of a running engine, and movement of the vacuum advance plate, the contact starts to break down and you lose two cylinders. You have to check the wires with the engine running, and you can really be quite aggressive with pulling on the wires. If the wires are not already broken, you will not break them even if you're tugging at them with a pair of needlenose pliers.