Maxim revisted

[Angie]

Hello Everyone! Just have a question I'm working on a XJ that seems to be having afew little problems, it was run in October ran fine and on all four. Now its acting very strange and the spark seems to be weak. Lots of gas, the plugs are black. Not sure if its the CDI box acting up or coils anyone have any input on this? Tanks!

Angie

[TopCatGr58]

Hey there Angie,

Well, you've got two of the best XS11 mechs up there in your neck of the woods, Ken Talbot in Revelstoke, and Ken Daniels(ratbyk) in Sooke harbour, so a PM to them may get you some "in Person" assistance in the future!?

Okay, now to the problem at hand. The Xj's pickup coils plate is stationary, so getting broken wires there is quite rare.

All of these CDI/TCI type boxes can have problems with their solder joints, and can work loose. Also, just general corrosion in the connectors can cause problems. Ignition coils can go bad.

You need to provide a bit more diagnostic info, like are ALL 4 plugs going bad, or just 1 or 2, which ones? Sooty black is running too rich, but wet is even richer!! You could have some stuck floats/needle valves in the carbs. Have you checked the air filter?

If the plugs are acting up in pairs, if 1 & 4 or 2 & 3, then it could be electrical, if 1 & 2, or 3 & 4, then it's more likely fuel related. Write back with more info, we'll try harder!

[Angie]

XJ

Hi Top Cat, Thanks for getting back to me on this little problemo. All four plugs are black, I forgot to mention that this is a xs motor out of a standard the timing has been out abit on it as I believe the CDI boxes are a different number on the xs from the xj (already tried another box). The bike is minus a airbox it has k & n's and header system so the mains have been changed. The carbs are super easy to pull but its just not seeming like carbs cuz it won't fire at all. You would think that if the carbs where getting too much gas then I would have gas overflow, this isn't happening, so I think the floats are doing their job. I have checked all the fuses and nothing happened, think its some sort of electrical problem though just what arrrgggghhh.

[DiverRay]

Angie;
I would start at the begining. pull all 4 plugs, connect the plug wires back up and look for a spark as you kick the bike over. That will test the coils/ignition. if you don't get any spark, use a VOM to check for voltage going into the coils. one at a time, put the VOM on the 1/3 or 2/4 coil wire. Not the red/white that goes to both, but the other one. connect the ground for the meter to the negitive terminal on the battery, and the positive to the coil wire. Do this WITHOUT disconnecting the coil.
With the spark plugs still out of the engine, but connected and grounded, turn the bike over and watch the meter. and analog meter will have the needle jump every time the coil tries to fire. The voltage range should be set to 10 or 20 volts, as you should see about 8 to 10 volts at the coil.
If you can, Ken or Ken can probably help you close in on the problem. Good luck, and I hope to see you riding again soon.

[John]

When you installed the XS engine, did you swap out the ignition pick up coils? If you are still using the XS P/U coils, then that will explain a lot. The XJ uses different P/U coils. The two shouldn't be compatable. It may run, but not too well. Just like a 2H7 CDI on an 81 model bike. It'll run, but...

[TopCatGr58]

Okay,
First what's the beginning serial number on the engine case, 2H7, 4RO or somewhere in between? You can then use the serial number lookup to determine what year it's from, and that will determine which TCI (they are all transistorized ignitions, but not Capacitive type). If under the timing plate, you can find centrifugal advance parts, then it needs the 2H7 box, if there isn't a cent. advance, then it needs the 4RO box.

Also, the carbs can be set too rich without overflowing the throats. Are the carbs the XJ's, or an XS11's, and if so, which style? Do they have an extra side port just above the float bowl fuel supply port, if so, then they are the 78-79 series, and those extra ports need to be vented, NOT JUST PLUGGED!!! It would be nice to see what size main jets are in there, cause with Indy filters and Headers, an increase from STOCK is recommended, about 3 sizes=7.5, so if 78-79's, from 137.5 to 145; if 80-81 carbs, from 110 to 117.5 there abouts, cause some had staggered sizes, inner larger than outer for cooling!

Ooooh, talking electrical, and which box used, got me to thinking, the XJ's coils are 3.0 ohm, the earlier boxes are rated for 1.5ohm, with addition of a ballast resistor inline on the power leads to the coils. But since the XJ doesn't have that resistor, using an earlier box should be no problem, cause the TCI will still be seeing 3 ohms for the coils, so it shouldn't damage them! or the TCI.

Keep at it! T.C.

[chevy45412001]

inner outer

didn't the inner carbs have different jets because they got less air than the outside carbs?

[skids]

Re: inner outer

Inner cylinders get less cooling air from the outside because they are confined. Don't confuse this with "carb air" (not that you did). Richer mixtures = cooler burn.

Originally posted by chevy45412001
didn't the inner carbs have different jets because they got less air than the outside carbs?

[Angie]

XJ revisited

Hey thanks guys! Really appreciate all the input in my little problem. I haven't had a chance to check out these things but hopefully this weekend I can get around to it. I'll keep you posted on anything I find, I'm thinkin' coils forsure but hey ya never know. Oh and the bike does have a xs stator, it was never changed. I bought this bike as a wreck and the engine was fried, so bought a donor xs for the engine. This might be my problem.

[skids]

TC, I have an 81H, and I swapped-out an 80 engine for it. I also kept the 81's timing pickups and its black box (4RO). I am pretty sure that it does have a centrigugal mechanism behind the timing plate that triggers its pickup coils. I don't think the coils rotate and they are larger (I think) than the older mechanical coils. It does use a vacuum hose from the No. 2 carb, but I don't really know how the vacuum operates the pick-up unit. I never really had to examine it that closely. Can anyone elaborate on the 4RO system a little on the pick-up side? Is there a pressure sensor in there or a variable resistor activated with a mechanical slide?

Originally posted by TopCatGr58
Okay,
First what's the beginning serial number on the engine case, 2H7, 4RO or somewhere in between? You can then use the serial number lookup to determine what year it's from, and that will determine which TCI (they are all transistorized ignitions, but not Capacitive type). If under the timing plate, you can find centrifugal advance parts, then it needs the 2H7 box, if there isn't a cent. advance, then it needs the 4RO box.

Keep at it! T.C.

[TopCatGr58]

Hey Skids,

I'm pretty sure that the 81's got rid of the cent. advance, that's why they had to change the TCI to the 4RO series, it incorporates the advance curve within it,(this is also what Randy found, that's why he can't replace that unit, can't program the EPROM) the vacuum module is actually a RETARDing unit, that reduces the advance when under load, but allows it to advance more when running just off idle or easy throttle. There isn't any cent. advance under the timing plate! The 78-80 series do have the cent. advance units.

Then in 82, they got rid of the rotating vacuum unit, that's why the XJ has that vacuum sensor box, and a different TCI again!
T.C.

[skids]

I'll be damned! I'll have to take another look at it...later when it is warm. There must be a rotating thing behind there to trigger the coils, but like you say, it doesn't expand the weights outward against spring load... I will take a good look.

Originally posted by TopCatGr58
Hey Skids,

I'm pretty sure that the 81's got rid of the cent. (snip) There isn't any cent. advance under the timing plate! The 78-80 series do have the cent. advance units.

T.C.

[Ken Talbot]

TC's got it right. I've got two '81s, and they've both got vacuum lines coming from carb #2 to a vacuum mechanism behind the pick-up coils. My understanding is that they do in fact retard the spark. When it warms up a bit more, I'll try to remember to have a real close look at their operation with the cover off to verify just what does happen as the vacuum changes.

[TopCatGr58]

Well, Ken and Skids,

I'm kinda cheating, I got that tech info about the retarding advance from that nice Cycle Guide Road test article /CD that Randy was selling, it was quite informative in explaining about how Yamaha used the vacuum module to control/retard the advance from something like 50 degrees BTC when very little load is on the engine down to the 30 something degrees desired under heavy load/throttle!

[Ken Talbot]

Aw, now you're just being modest!