Possible Weak Spark

1981 XJ 550 Maxim. Has new battery, new spark plugs, newer CDI unit that was tested good, new start/kill switch. Bike wont fire but does turn over really strong. There is a spark but the spark seems very weak. In the dark the spark is very faint and hard to see. I dont have a manual yet just wondering if anyone has any suggestions on what would cause a weak spark. I have a good voltmeter to do testing with.While trying to start the bike is one the side stand, clutch pulled in and in neutral. Any help would be great!

 

Internal combustion engine 101.

Fuel
Air
compression
and spark

If you have these, in all the right time, you will get combustion.

So, I am guessing you need to look at your plugs and see if they are wet with fuel.

Also, you need to make sure you are firing on the right cylinder.

A weak spark can be a weak coil, bad plug wires, bad spark plug caps, or those little resistors in the plug caps.

If the coils are original, they are probably done in. Even if they "ohm" out OK, 2.5ohms on the primary, and 11k ohms on the secondary, without the plug caps, they may still not give you enough voltage to consistently jump the plug gap every time.

The magnetic pickups should ohm out at around 690ohms.

A weak coil may give you ignition, but it won't give you performance.

Good luck and report back.

 

I will replace the coils, are there any aftermarket coils that would be worth spending the money on?

 

Before you start throwing parts at it, How long has it been sitting?

Are you getting fuel to the carbs? The Petcock or fuel valve on the tank is vacuum operated and if it's stuck from sitting it may not let fuel flow in the ON or RES position. If this is the case you need to put the fuel valve on PRI so the carbs will fill up. Don't continue to run it like this, fix it or you'll have more problems...
If it's been sitting a long time(years), have you pulled the carbs off and cleaned them ?

 

Man RPGOERLICH, you are as eaten up with Yamahas as I am!

Are you in the XS11 group. xs11.com?

I have a few friends in Katy that I ride with. They are all XS11 nuts too!

 

Has been sitting about a year. i have taken carbs off and petcock. I am rebuilding the petcock right now and will start on carbs after. only reason why i am considering replacing coils is that the spark is really weak. my weedeater has a stronger looking spark. I will wait to replace the coils unitil the carbs and petcock are rebuilt.

 

Weak spark on these is normal, and it's TCI not CDI. CDI is a completely different system that uses a different type of coil as well.

I would try cleaning the plugs, then disconnect fuel and spray a bit of starting fluid into the air cleaner. If she catches and runs for a few of seconds, you'll know spark isn't the problem.

 

I will give that a try and let you know the results. I am used to my yamaha dirt bike that uses a cdi just got to learn the lingo.

 

SQLGuy,
I tried disconnecting and spraying starting fluid. Still does not start. I did notice that plugs 1 and 3 have faint spark but 2 and 4 have no spark. The plugs are brand new and I swapped plugs from 1 and 3 to 2 and 4 and it still does the same. So I can rule out spark plugs. Anything else I can try before replacing coils?

 

I'd say you have a plug cap problem since you have spark on 1 & 3, they should be different coils right ? If they are on the same coil you could still have one bad coil, You just have the wires on the wrong cylinders... 1&4 are one coil and 2&3 are the other.

This is where a good paper manual come in handy! With all the resistance specifications and checks on the coils & such. Chacal can hook you up with one and most anything else you may need like those plug caps or coil.

You can remove the plug caps from the coil wire by unscrewing them. Once you have them off, Ohm them out, should read around 5kohms. While you have them off the coil wires, Ohm out the coils to see if you have a bad wire maybe. They should be like 2.5ohm +/- 10% on the primary and 11kohm +/-20% on the secondary . If they are still long enough you can snip a ¼" off the end to make sure when you screw them back on you have a good connection.

You might check the clearance between the rotor and the pickup coils as well. I believe it should be .7mm. You could ohm them out as well to be sure they are good. They should be like 650ohms each +/- 20% at 68ºF.

Also when your checking spark, be sure and have all the plugs hooked up and grounded or you could damage that TCI.

Richard

 

rpg,
Thanks for the good info. I will try what you suggested and check out chacal as well. I will be back with the results once I am finished.

 

Sounds pretty weird. This ignition system needs to fire both plugs on each coil for either plug to fire.

Are you sure the caps are on the right plugs? Normally, when there's a problem with the ignition, you lose a pair of plugs, so I'm wondering whether you have both a bad ignition channel and swapped caps, like maybe 3 & 4 swapped.

 

SQLGuy, that is possible. I picked this bike up about a month ago and I havent got a manual yet. So the plug wires could be in the wrong order. What is the right order for the plug wires? I contacted chacal for a manual, so hopefully I will have one soon.

 

I believe the left coil does 1 and 4, and the right coil does 2 and 3.

The thing for sure is that 1&4 share a coil, and 2&3 do. So, if you don't find that to be the case, something's mixed up.

 

Do you happen to know the firing order?

 

1,3,4,2,

but, it's a wasted spark system. So spark fires around TDC of compression AND TDC of exhaust.

 

apologies but is it imperative that the left coils match 1&4 and the right 2&3?

 

It is required that 1&4 share a coil and 2&3 share a coil. It's possible to wire the system up either way (i.e. 1/4 coil on left or right), but I'm pretty sure the stock setup is with 1/4 on the left.

 

SQLGuy, i have one bad coil and have found that the wire harness has been spliced into and some wires are missing. So I am going to get 2 new coils and a wireharness. After I replace those items, I will post my results.
Since it is too cold to ride, I am also going to rebuild the carbs. Any suggestions on a good carb kit?

Thanks again for all the help.

 

If you need parts for anything, check with Chacal at info@xj4ever.com (no spaces) He has almost everything you will need, including a manual.

 

I have pmed and messaged him, but no response. Does he have a website?

 

No web site, but if you give him till tonight, check in the morning and you will have a message from him. Unless he has the flu and ...nah even then you'll get a message from him.

 

Hemi, I'm here!

But I just checked, I have not received a PM from you?

Might want to try again, or better yet, click the "e-mail" button below and send me a real-world e-mail with the items you need..........thanks!

 

See, no flu...

 

Thanks Chacal. You guys are very helpfull and this site reminds me of the hemi truck club site that I belong too. Thanks again for everyones help! I will keep you all posted on what happens.

 

Well after months of waiting, I finally was able to get a new wiring harness, and coils. This bike sure has taken me a long time.

My question for you guys is: where is the best place to begin when replacing the wiring harness? Should I start from the back and work forward or start at the headlight bucket and move back?

Thanks again for all of your help. I really appreciate it.
Dodgehemi7

 

Thanks for the follow up.
I usually start from the headlight bucket but it really doesn't matter just so long as you take your time and note routing. A factory manual really helps in this effort.

 

Well before I replaced the wire harness, i tried to get the bike to turn over and nothing. It used to turn over, and now it doesnt even make the click sound that it used to when you first turn the key on.
So I decided to go ahead and replace the wire harness and hope that it fix's my problems. Well after replacing the wire harness, the bike still does nothing. The click sound when you turn the key to the on position is gone. All of the lights and horn work and I made sure to clean each connection and hooked them all up right.
Any help would be great!

 

Ok, let's start from the top.
1. New battery properly charged and installed.
2. Known good TCI.
3. Known good coils.
4. Replaced wiring harness, condition unknown.
You don't mention if you checked for voltage at the pickup coils (should be measured across the orange(+) and brown wire(-)) or the ignition coils. You NEED to check these.
Second, have you ensured that you have 12 volts at the ignition switch?
How about at the TCI?
Do you see 12 volts on the upstream of the starter coil? Does the starter coil see 12 volts from the ignition switch when it is pressed?
I'm sorry to hand you a list but you need to go down the list and eliminate each step (check twice if you have to).
Biggest tool you can get is the manual. This forum comes in at a VERY close second. Put the two together and you have an unbeatable team. Now get to your homework and let us know what you find. We'll lick this one way or another...

 

Thanks Robert,
Printed your list and will get to work on it.
Will post once I know more.

Thanks

 

Heres what I got for numbers

1. Battery is good
2. TCI is good (Worked before I replaced wire harness)
3. Coils are good (Worked before I replaced wire harness)
4. Wire harness appears to be in great condition
5. Pick up coils. I dont have a brown wire. I tested orange to black, also orange to grey, and got nothing. I have a extra set of most electrical parts and the pick up coils i have laying on my bench dont have a brown wire either. Am i doing something wrong?
6. I have 11.62 volts at ignition switch
7. I have 11.62 volts at the starter coil
8. I have 11.62 volts when the ignition is pressed.

A little more history of what has gone on.
It would turn over and had spark before. On saturday morning I tried cranking it over and it would crank over with spark. Pushed the bike outside to prep for the replacement of the wire harness. Pushed the starter button and then it would not do anything. That is when I replaced wire harness. After putting the new wire harness in, I had the same problem. The bike would do nothing. I then yarded the new harness out and put the old one back in. Still nothing. So I pulled the old one out and put the new one back in and that is where I am at right now. New one in the bike.
I have 2 sets of coils, extra set of each relay, a set of pickup coils and 3 starter coils.

 

Any help on what to do from here would be great. Tomorrow I will replace the orignal fuse box with a aftermarket mini blade style. So if that helps me any. Will post results.

Thanks again for all the help, I wont give up yet.