XS400 idles, cyl dies w/throttle *Fixed, TCI problem [No56k]

Hi All,

I picked up a project XS/XJ400 a month ago, and managed to finally get it to idle today. However, as soon as I give it throttle it seems like one of the cylinders stops firing, and it sounds like hell until I let off the throttle. How can I begin to troubleshoot this ? I was thinking maybe it was the coil, but if that were the case it shouldnt idle, no ? Any help would be appreciated, thanks.

Edit: More info: Carbs look internally like they just came from the factory (ie V. clean). Haven't yet checked compression. Fuel is making it to the carbs without a problem.

 

Re: XS/XJ400 idles, but wont accept throttle

it's gagging on air...choke it and rev away

 

Re: XS/XJ400 idles, but wont accept throttle

Thanks, Ill try that asap.

 

Re: XS/XJ400 idles, but wont accept throttle

Nope... didn't help. I made a video. Heres what I know,

Idles OK
Bogs down under throttle.
Bogs down under throttle with choke.

Ill be uploading a video ASAP

 

Re: XS/XJ400 idles, but wont accept throttle

video : http://vimeo.com/2139134

 

Re: XS/XJ400 idles, but wont accept throttle

Your video is locked.
If it idles then you have all three ingredients, spark, air, fuel.
When you rev it, it bogs, it's losing or have to much, not enough, of one of the above.
Put your hand over the pipe to try to determine which cylinder is cutting out.
If it bogs when you rev it I would think you've got to much air or not enough gas.
My bet's with air if your carbs are clean.
With the motor running use an unlit propane torch, open the valve and run the propane around the boots and carbs.
If the rpms go up you're sucking propane in through a crack in a boot or somewhere else.
Good luck.

 

Re: XS/XJ400 idles, but wont accept throttle

Thanks TheHound. Ill try that trick tonight. Video is now unlocked if anyone is curious.

 

Re: XS/XJ400 idles, but wont accept throttle

My bike did the exact same thing. I was going crazy trying to figure out what it was. Turned out the plug wires were not seating properly. Cleaned them out put them back on and she ran like a champ (other than the head gasket leak, but that's another problem for another time)

Try it out, you never know. Sometimes it's the little things that you overlook.

vic

 

Re: XS/XJ400 idles, but wont accept throttle

Ok... update:

Idles great, Cylinder 2 stops sparking as soon as you give it throttle, cylinder 1 still fires. Coils are fine (I checked by swapping coils / plugs).

What could it be ? pickup coil ? TCI ?

Help!

 

Re: XS/XJ400 idles, but wont accept throttle

One coil is for #1 and #4, the other is for #2 and #3. Have you checked #3 when #2 isn't firing?

I think you are are the right track, pickup or TCI. You can test the pickup coils, you can only replace the TCI.

 

Re: XS/XJ400 idles, but wont accept throttle

kd5uzz. the 400cc is a two cylinder.... I suspect the TCI, however it does seem odd to have a fine idle, and only cut out under load. Ill check the pickup... and if that fails, i guess ebay. Thanks.

 

Re: XS/XJ400 idles, but wont accept throttle

IF it's the twin then it's the XS (there is a 4 cyl XJ version as well, but not in NA)

Bizarre problem...... I can't think of a reason for it to stop sparking under throttle.... especially if it idles fine.......

Do the revs increase using the choke?

 

Re: XS/XJ400 idles, but wont accept throttle

ZaGhost,

The revs do increase with choke. but again, with choke, any sort of throttle and cylinder 2 cuts out. it is a 2 cyl, so i suppose its an XS.


Honestly im baffled by this too. I know the carbs are good... the coils are good.. the only real thing i can see being wrong is the TCI... but only because i dont really know what else it could be!

 

Re: XS/XJ400 idles, but wont accept throttle

So you're saying that when you swapped coils #1 stopped firing and #2 was fine?
This to me would indicate the coil or wire is bad.
Or you swapped coils and the issues was resolved?
If you pull #2 leaving it in the boot and grounding the plug can you see it stop sparking when you twist the throttle?
A little more info maybe we can get her going.

 

Re: XS/XJ400 idles, but wont accept throttle

The Hound:

When i swapped coil #1 and #2, there was no change. Cyl #2 still stops firing under throttle. This seems to indicate there is no problem with the coils. Likewise the primary resistance's were more or less in spec.

When I pulled the boot out, and put another plug in, grounding it outside the engine, it DID spark, however it looked to be a very weak spark. Tomorrow I will be testing to see if it sparks under compression (friend is bringing some shop tools over).

Last night I suspected the carb diaphragms, although i had previously inspected them. Swapped carb 1,2's diaphragms, but no change.

So I decided to check the wiring. After re-power the coils (Red/white wire) directly to the fuse box, and regrounding the TCI, pickup coil, I could find nothing wrong there.

So I checked the pickup coil for resistance. It read 116 and 117 ohms per lead, which is out of spec, but I don't think is able to explain why ONE cylinder fires under load, and not the other. If anything, the pickup would improve as rev's increase.

This lead me to the TCI. I opened it up, and found a few chalky connections. One of them may lead to the sporadic coil.... before I re-solder (and very possible destroy) the TCI, are there any other tests I could try ? I think I may attempt a voltage drop test, but seeing as I already re-grounded and re-powered all the components, this test might be in vain.

Summary:
Cyl #2 doesn't fire under any throttle.
Cyl#2 fires weak spark outside of cylinder
Idles fine, starts fine.
NOT coil, wiring, grounding, power, or pickup coil [unlikely anyways] problem.

Thanks again for your help! I just want to get this ol' girl running.

 

Re: XS/XJ400 idles, but wont accept throttle

Anyway the altenator could be causing a problem? Maybe try unhooking it and running from the battery?

 

Re: XS/XJ400 idles, but wont accept throttle

I'm still leaning towards a carb issue..... there is no reason for the spark to change by adding throttle....

The carbs may look clean but clogged ports are more than possible.
I'd give them a good thorough going over, be sure all ports are clear...
all the holes in the emulsion tubes etc....

Gotta get her going, these are great little bikes, been using mine as a daily commuter after revived her from a 7 year sleep. Hasn't let me down yet.

 

Re: XS/XJ400 idles, but wont accept throttle

Well... Using a circuit tester we found where the problem in the signal was. TCI to coil #2 was cutting sporadically. Going to resolder some TCI connections this week, and we'll see how that goes!

 

Re: XS/XJ400 idles, but wont accept throttle

Great it feels good when you finally get somewhere.
Even if it is not where you wanted to be.
Sorry I didn't understand your other post.
Let us know when she fire on all cylinders.

 

Re: XS/XJ400 idles, but wont accept throttle

got her running and revvin fine!
The solution was to replace all 8 or 9 caps (except the mylar ones) and both the transistors! I suspect it was a shorted cap, but i had to destroy them in the process of removing them... soI guess ill never know! Im just glad she runs! Now to find that oil leak.

 

Re: XS/XJ400 idles, but wont accept throttle

Here's some pictures. If anyone is wanting to rebuild / resolder their TCI and has any question, go ahead and ask.












Note: The color on the welds appears to be melted epoxy... both sides of the board had some extent of epoxy.

 

Re: XS400 idles, cyl dies w/throttle *Fixed, TCI problem [No

Yeh 98, I've got some questions.
Did you pay retail for the components? if so, how much & from where.
Do you work on PCBs at your day job?

 

I did pay retail from digikey.com, came to about $20 CAD for shipping + 8 caps and two transistors. There was no diagrams or notes of anyone rebuilding a 400 TCI online, so I had to make my own list of necessary caps by prying aparts the caps and trying to read them. Also, I ordered from them on sunday... was in my hands by tuesday afternoon!

No I don't work on PCB's at my day job (Im a student... Bsc), so ill take that as a compliement. I have some prior experience soldering a mod chip onto my console and a few other little oddities, but thats all. However, I did have a friend help me with the board. WE removed the caps and transistors by cuting or pulling the legs off, then heating one side of the solder while using needle pliers to pull the leg through the other. Hardest one to re-install was the transistors because they have three legs. What we did was melt one hole at a time, insert leg, then do the next one. Go back and forth between all legs until the transistor is in the holes as deep as you want.

I would recommend practicing with some junk PCB before you work on the TCI. However, As you have to desolder the pins to remove the board, you get a bit of decent desoldering practice there. Few tips:

1. Dont suck up the solder until the entire bit is molten. Youll do less damage then trying to heat it up 4x because it wasnt all melted the first time.

2. The new parts you put in are pretty hardy, dont be afraid to get them a bit hot. Its required for a good joint

3. Take your TIME! It took the two of us about 2 hours just to replace the caps and transistor

 

any1 got this picture still? I need them badly Thanks!

 

go to this link tells how to fix TCI

http://www.xjcd.org/General_Electrical


as well as a solder sucker you can use solder wick it is a copper braid or one of bulbs used to suck noses on little kids if you are in a pinch

try starting a conversation with him he may respond worth the shot

 

Thank you very much! Saved my day