1982 XS400 - Running on one cylinder ... still.

[KoryGable]

Hey everyone ... I'm on the verge of getting my bike running like it should, but I need some help. See below ..

Problem: The bike will start and idle on the right cylinder. I can occasionally get the left cylinder to fire, but I have to give it quite a bit of throttle to get it going. Once I do, the exhaust is very smoky (white smoke). After a few minutes, the smoke goes away and it will run a bit smoother.

Here is what I've done thus far.

- Cleaned the carbs (3 times). I haven't done a full soak, but everything looks good visually.
- Cleaned the petcock.
- Checked the coils.
- Visually inspected the CDI box (joints look good, but I have no way of testing this from what I gather)

Other things to note:
- When cleaning the carbs, I noticed a few holes in the diaphragms. I patched them with gasket sealer and noticed an improvement. Eventually, I plan to replace these.
- Before this issue, the bike was dying whenever I gave it throttle. Not sure if that has anything to do with whats going on now.

Any suggestions would be GREATLY appreciated!

Kory

 

[Scorpio1963]

Check your plugs I had the same problem last year after I changed mine.Even being brand new one of them was bad.Also check and make sure both carb floats are working properly.

 

[mcrissjr]

Compression test the left cylinder.

 

[bcware]

Hit the passages with compressed air and change the diaphragms out. You won't have any real reliability until you do. Maybe it's fixed right now or maybe not. Maybe the patch will fail 50 miles from your house.

 

[Arclight88]

Hit the passages with compressed air and change the diaphragms out. You won't have any real reliability until you do. Maybe it's fixed right now or maybe not. Maybe the patch will fail 50 miles from your house.

Ditto on the diaphragms. Also, double check the spark action on your left side by (1) removing the plug from the head, (2) connecting it to the the plug wire as usual, (3) lay the left plug on the engine block (4) remove the right plug (5) and turn the engine over as if you are going to start it (Oh yeah, and darken the garage.) Observe the left plug as you turn over the motor. You should see a spark in the gap of the left plug. You should see a constant series of sparks. If you do not, the spark plug or iginition is faulty in some way.

 

[KoryGable]

- Compression is good - 150 on both sides.
- I THINK the plugs are good. It's been a while since I've checked them. I'm certain I'm getting spark ... not entirely sure if its strong enough or not. Any way to test that? I suppose I could switch plugs.

ALSO .. I can sometimes force the cylinder to work by slightly pulling off the plug cap. Not sure if the arcing causes a stronger spark, but it seems to work.

 

[mcrissjr]

- Compression is good - 150 on both sides.
- I THINK the plugs are good. It's been a while since I've checked them. I'm certain I'm getting spark ... not entirely sure if its strong enough or not. Any way to test that? I suppose I could switch plugs.

ALSO .. I can sometimes force the cylinder to work by slightly pulling off the plug cap. Not sure if the arcing causes a stronger spark, but it seems to work.

Put the plug in a vice and heat it till its red hot with a torch. Don't heat the porcelain end. By heating it you'll burn off the carbon and crap. It's not as good as a new plug but for testing purposes it'll get it done. Also check resistance across the wire - simple and better to be sure. Someone else can chime in on testing the coil.

All sparks are not the same. You need a good spark.

 

[KoryGable]

What do you mean by testing the resistance across the wire? What exactly should I measure there?

Also, I think the coils are good. I switched them (same part number) and everything seemed fine.

 

[16VGTIDave]

By pulling the plug wire partially off you are increasing the resistance in the ignition system which creates a hotter spark. Because the cylinder begins firing, I'm going to say your problem is either the resistor cap at the end of the wire or the sparkplug.

Do the easy thing first. Remove the plugs, taking note of which cylinder they came from. Clean them if required and when you install them, swap them to the other cylinder. If the problem follows the plugs, you have your answer. If it doesn't, then swap the resistor boots and see what happens.

 

[Arclight88]

- Compression is good - 150 on both sides.
- I THINK the plugs are good. It's been a while since I've checked them. I'm certain I'm getting spark ... not entirely sure if its strong enough or not. Any way to test that? I suppose I could switch plugs.

ALSO .. I can sometimes force the cylinder to work by slightly pulling off the plug cap. Not sure if the arcing causes a stronger spark, but it seems to work.

If you are able to cause the cylinder to fire by changing the seating of the plug cap, it tells me that there is something distinctly suspect in the plug and/or plug wire. They good news is that for about $25, or less, you can completely put in new plugs, plug caps and plug wires.

 

[Drewcifer]

resistor cap is shot.

 

[KoryGable]

I don't think its the resistor caps. I swapped them, and the problem persists. My friends think its the CDI box, but I want to make sure its not the plugs before I pursue purchasing a new CDI box on ebay.

 

[Maxim-umm]

not sure if this helps, but after exhausting all other options look into "rebuilding" the tci box instead of trying to find a new one. It will be monumentally cheaper and you learn something as well. It's not too hard as long as you take your time.
This was the site that I used for the info.

http://www.jetav8r.com/Vision/TCIRebuild/TCI_Rebuild.pdf

 

[Maxim-umm]

also, I'm assuming you're running a bike with a TCI box and not a CDI. I have a 1982 xs400j Maxim DOHC using TCI. What's your bike?

 

[KoryGable]

Swapped coils, plugs, plug caps, etc. The issue persists. Its looking like a CDI issue for sure.

 

[Drewcifer]

Ah. negligent post on my side, didn't realize you had a black box. Hate them myself. Can't be diagnosed in many cases, the test is remove/replace.

 

[16VGTIDave]

Swapped coils, plugs, plug caps, etc. The issue persists. Its looking like a CDI issue for sure.

When you say that the issue persists, is it still on the same cylinder? Or did it move to the other cylinder? Can you still get it to fire by pulling off the plug cap slightly?

 

[KoryGable]

The problem is with the left cylinder no matter what.

I did some testing on the CDI box. It looks like both of the transistors with heat sinks (Part number: ETD41-035) are bad. I ordered new transistors from DigiKey (MJE5740G) so I will swap those when they come in.

 

[16VGTIDave]

Excellent! Let us know how it turns out!

 

[Maxim-umm]

i hope this all works out for you! I ended up replacing both transistors and all capacitors to be sure. What i concluded was the capacitors were bad (pretty much, the energy in the capacitors was taking longer to "charge" on the left than the right), thus, giving me an occasional fire.