Inconsistent spark cause no start?

High everyone. I'm still trying to get my XJ900 Seca to run and I've made a discovery today.

My spark is very inconsistent. Also keep in mind these are brand new 1 week old plugs.

I noticed today that in terms of tempo, #1 was 1...2...3...4....
#2 was 1-2-3-4... (about twice the speed)
#3 was the same as 2
and #4 was 1..f..5..h...3..g.bdnbtrhj (random)

I realized the coil controlling 1 and 4 might be bad and I have a spare coil; but can that completely stop it from starting altogether?

I had the bike running very very badly (but running) a few weeks ago with full choke (started at 3000rpms and would shoot sky high) and then would die once the choke was slowly taken off. I knew I had a vacuum leak and took the carbs off and bench synced them and put new gaskets on. Now it won't start at all and I've noticed my spark issue. Any thoughts would be appreciated, I'm a bike riding noob and bike mechanic noob . You guys have been very helpful so far Thanks in advance.

 

If half the cylinders are getting inconsistent spark then the bike will be very difficult to start and won't keep running. Swap that coil out for a known good one.

 

Alright cool thanks. I swapped the coil and now get a consistent spark all around! Unfortunately, still nothing. I took the carbs off again and now I'm looking at the emulsion tubes and my God, I thought I cleaned them better, they're pretty bad. Other than that, I really hope this is it. My Dad looked at the spark and said it seemed weak, and maybe he's right. But I guess I'll have to wait until after I reassemble and test again. I must say, I am very happy the tubes are so bad, I made some progress today, and now I'll make even more!

Last question though. What kind of inline fuel filter should I use? I wasn't even aware I'd be able to until I read it earlier today (83 900 Seca). Thanks again!

 

Super,

The HT caps screw onto the coil wires. Use wire cutters and lop 1/4" off the ends of the coil wires and slowly re-screw the caps on until they stop. Also check the resistors inside the caps. Idk about the 900 but two of the caps on my 650 have screw in resistors. Make sure they are shored up. Might help with the weak spark issue.

Gary

 

Thanks I'll try that!

 

Well I replaced the coil and sheared back the coil wires a little bit and completely cleaned those emulsion tubes spotless, still nothing.

The thing that sucks is I used to have the bike running (horribly) just a few weeks ago, but now I can't get anything. It doesn't even sound likes it's trying really. What would be the next step in tracking down the issue?

I would assume by the sound of barely even trying to start it's electrical, but I really don't know. I might be able to get a youtube video up if that would help.


Also I'm not sure how to check the resistors in the caps honestly.

Thanks for the help so far guys, you're helping me stick to it.

 

After trying to start are the plugs wet ? if not see if you get any action with a shot of starter fluid. Keep battery fully charged at all times, or boost from a car (not running)

 

No, they're not wet at all.

I've tried started fluid, but even that does nothing. I always have my battery on the charger whenever I try and start it, thanks for the suggestions.

 

So I guess to add to my question, I ended up spraying some ether directly into the cylinders (for all 4) They all sparked so I'm currently ruling out spark.

I tried messing with the mixture screws, originally turned out 3 turns, and then took it beyond that and still absolutely nothing. It sounds as if it is getting absolutely no gas to the engine. What could cause this? I've torn them apart at least 3 times and made sure to get every nook and cranny.

The bike came with an aftermarket exhaust so could that mean I need bigger jets? I just have serious doubts considering the bike will absolutely act as if it doesn't want to start, not even attempt it without starter fluid.

Thanks again for all your help.

 

Anyone? I'm going to attempt to check the carbs again soon and see if that's the issue (again).

 

I found out today that when I let it sit for a couple hours and try to start it, it abruptly acts like it's trying to start for a second. Then it never happens again and I have to wait a couploe more hours.

Anyboy have any thoughts? I think this is a decent clue, somehow XP

 

Any thoughts? Yes, a new battery..

 

Ya think? It's only a few months old and it's always charged. Is there a test for it?

Thanks for your response, I appreciate it.

 

Are you sure that fuel is getting into the float bowls? You may have a faulty petcock.

Have you set the petcock to prime before trying to start it? Dry float bowls won't fill very well unless the petcock is set to prime.

Does the engine turn over every time you hit the start button? I wan to rule out electrical since you said that you have good spark now.

 

I thought about that too, but I've checked the levels and they're all good. And it's not every time it starts up. Just today it didn't start when I attempted.

I have the mixture screws backed out like 5 turns because that's the only thing I've seen that makes results. I plan on backing them out more to see what happens. Thanks man.

 

5 turns is way too much. There must be something causing it to run lean that requires you to turn the screws that much. K-moe already mentioned the float levels. Double check them. Sure the petcock is working? Try starting it on PRI. Sure the fuel hose isn't kinked? Are the enrichment plungers and their ports clean?

 

Batteries can be load tested however the easiest option is to hook the bike up to a car (engine not running) and see what happens

I found out today that when I let it sit for a couple hours and try to start it, it abruptly acts like it's trying to start for a second. Then it never happens again and I have to wait a couploe more hours.

This is leaning me towards a battery dying and then partially recovering...uncommon in a new battery but certainly not unheard of

 

https://www.youtube.com/watch?v=4xjymWd ... e=youtu.be

Here's my Seca running for a little bit. I ended up blasting it with ether and it actually worked. I'm manually adjusting the choke since none of my lines are hooked up; but pretty much whenever it dies is me slowly letting off the choke.

Thanks again for all your help guys. Just need to figure out why it's so lean now

 

I originally had it set to prime, but it never helped, I recently switched it from prime to RES (low fuel) after I started to get it to run and it kinda helped it seemed.

I just realized I may not have gotten the enrichment circuit which would explain it. I'll pull them off again tonight and check it out. Thanks again!

 

I see what you're talking about. I ended up lookng over the battery screws and noticed they weren't too tight; they weren't loose by any means, but I could tighten them considerably, so that might also have been an issue. Thanks again to you too!

 

Have you checked the valves? Have you checked the carb boots for cracks? Have you checked the throttle shaft seals for leakage?

 

As I said before these bikes defy all logic. I have NEVER seen such a poorly designed motorcycle in my life. I read these posts about people that had pulled the carbs off 6 times and followed all the post and still the bike runs poorly. As I said before I don't know how these bikes passed emission in the US. I purchased 4 new spark plugs and the piece of shit still refuses to run right.

 

The supporting part vendor. From our experience since the carbs are THE most troublesome (and thus most expensive) aspect of these bikes. I just can't believe someone hasn't come up with a way to destroy the YICS on the bike. Whoever came up with this should be in jail. It doesn't work.

 

I haven't checked the valves although I do have the feeler gauge for it.

I have checked the boots and I know one of them completely broke and I actually had to glue (yes glue) them back together, which actually works great. I'm going to check the enrichment circuit tonight and maybe take some gasket sealer sludge and go over the boots or something.

I haven't checked the throttle shaft seals, where would they be located?

 

The throttle shaft seals are around the throttle plate shafts on teh side of each carb body. The best way to check them is to remove the carbs and place a drop or two of ATF on the outermost seal and let it sit (the seal has to be parallel with your workbench. If the ATF isn't there a few minutes later, you'll find it inside of the carb throat. That means the seals are shot and need replaced.

The carb boots have to be airtight or you will run very, very lean. The valves have to be in spec or the bike will be hard to start, and run poorly.

You need to get the valves in spec. Then find a set of used carb boots, even if they need a few cracks patched. It sounds like they would be better than a set that had a boot already in peices.

Once you get rid of the extra air I will bet you'll have a good runner (and can get on to the other things that need to be done before you go riding).

 

I'm definitely checking the valves tomorrow and I couldn't find what I thought looked like seals.

I ended up and cleaned the enrichment circuits and used some gasket sealer and super glue to keep the boots sealed to the best of my ability. The bike seemed as though it might have been a little better and it actually idled at like 1000 rpms for close to a minute. It wasn't stable, but it was a noticeable improvement. And naturally it died as soon as any throttle was applied. I'm going to turn the mixture screws from 5 turns out to 2 1/2 and see what happens.

 

Also I was curious if anyone could tell me what size the jets are on a stock 83 xj900 Seca with Mikuni carbs? I wanted to get the next size up but wasn't sure what to get.

 

Have you tried starting it with the fuel cap open? A blocked breather in the cap can cause similar problems.

 

I just ended up finding a leak or two in my intake boots. I went to the market page and it said $250 for 4? Not including gaskets and o-rings? Seriously?

I'm gonna have to find a way to repair mine because I can't drop over 250+ bucks into something I'm not even sure what else it needs.

Just out of curiousty I'll open the cap though. Thanks so far everyone.

 

I can tell you exactly what it needs, and so can a whole bunch of us.

What it needs is around $600 ~$800 worth of parts and a couple hundred man-hours of you spinning the wrenches.

You can easily spend more if you pay others to do the work; but if you do everything yourself that's about what it's going to cost. Honest.

The bike will need its valves adjusted, its carburetors properly serviced and "rebuilt" as needed, the brakes fully rebuilt, probably fork seals, shocks, maybe tires, eventually the clutch, etc. Any gasket you disturb will need to be replaced as well as virtually all rubber parts and a few key seals.

Spend the money, invest the time and effort, and it's worth it. Anything else will simply lead to frustration.

 

Don't worry, I've already put in quite a few hours and can most certainly spin a wrench (though I am intermediate at best).
I damn well intend to get this thing going, for sure. I just thought over $300 just for some rubber and gaskets what insane. I'll definitely figure out a way to seal my boots, once I isolate the problem I'll have no qualms about spending money.

You guys have been great to me so far, I won't let you down.

 

Given your mechanical ability, I'm suprised that you haven't managed to do that to your bike already.

 

Be happy that brand new replacements are avaliable. I recall that the list price for a new-old-stock (now NLA) carb boot from Yamaha was $97.00 before the reproductions became available a few years ago.
Also consider that once replaced, you won't be needing to touch them again for 30 years.

 

This is true.

It just sucks since I'm working on my 3000gt as well and it's like a never ending money pit. Oh well, I wouldn't be doing it myself if I didn't enjoy working on it I suppose.

 

Superseca,

In the short term, two possible repair options for the carb joints, I've been told; either sealing them with patches of bike inner tube and rubber cement; or 'painting' them with liquid rubber (tool handle dip, paint-on wire insulation, etc.)

I was shocked at the price, too... mine are weather-checked but not cracked through, so I'm going to try the paint-on rubber solution.

 

That's what I'm thinking too. Like a plastidip type paint. It would only be temporary, but that's fine. I think mine are leaking more around where the boots meet the engine though. So I've got some ebay boots and gaskets on the way, just to see if they work.