New member with old XJ needs help...

Good afternoon everyone. I’m new to the site and hope to add plenty to the discussions. I am a former BMW owner/weekend-wrench who is now tooling around with an 85 XJ-700 Maxim-X. I was out of the cycling scene for years, but could no longer stand it. I traded an old mountain bike for the XJ with a buddy of mine. Difference is, he was able to go riding the minute I gave my bike to him and I was stuck with the poster child for troubleshooting. Nevertheless, getting this bike in top-order has become a borderline obsession. By the looks of some of the posts on this forum, the XJ’s have a way of tantalizing new and old owners alike. By the way, did I mention the bike had been sitting, untouched, in a garage for the last six years? Gulp!
It’s been about a month now. New tires, battery, brakes, grease and so on. I believe in disconnecting and reconnecting all electrical connections in an effort to establish new contacts; so I did. All of the fluids have been replaced, including new filters, i.e. air and oil. I flushed the fuel lines and gave the tank two coats of Kreem. Rebuilt the fuel petcock and carbs with aftermarket rebuild kits and threw everything back together. Now, I’ll be the first to admit there’s no substitute for tuning the carbs with a ycis tool and a the vacuum gage. I’ll get to that sooner or later, but I figured bench-syncing the carbs would be a good start. To make a long story short, this is what I am currently running into…
*When I remove the vacuum plug from the intake manifold (tube between the carbs and the block) on the #4 cylinder, it increases its idle by 1K rpm. None of the other ones do this. Note-I gave some intermittent shots of engine starter in the areas where leaks are typical (increase in rpm in the event of leak), but couldn’t find any.
*The petcock is functioning properly. So then why is it that when I attempt to prime the carbs, no fuel is seen flowing through (I have a clear inline fuel filter). There are no kinks. The only thing I can think of is that the floats are doing their job, thus not allowing any flow to pass. On a side note… when I manually flush the line with fuel, I get air pockets in the inline filter that eventually fill the entire line-causing the bike to run out of gas. Does it matter that part of the line is elevated above the petcock before it reaches the carbs?
*How is it that I can get the proper primary coil resistance (2.7 +/- Ohms) but absolutely nothing when measuring the secondary (12k +/- Ohms). Any tricks here.
That’s it for now. In the interim, I have an original service manual for the XJ700XN/XNC. Feel free to shoot me an email in the event you need anything from the book, i.e. torque specs, resistances and so on.
Thanks in advance.
Jay

 

Jay,
I wont try to help on the coils. There are opthers that are awesome here in that area!
But
It sounds like you go a petcock problem. I have heard that some of those aftermarket kits dont work well without knowing some tricks that I dont know.
When my petcock went bad I just replaced it with a manual petcock.

I wouldnt think the fuel line rising above the petcock to be a problem.
I would think there might be a float setting issue. if you look to ricks carb

post I think you'll find the best way to set them

http://www.xjbikes.com/Forums/viewtopic ... =carb.html

be sure to tread this post!

I recomend setting the floats the hard way with clear tubing connected to the float bowls and setting to the recomended levels


Good Luck

 

My book says secondary resistance should be 11KΩ ± 20%. So 12KΩ is well within spec. If I'm reading this wrong and you are actually getting ∞ between the secondary leads, THEN you have a problem (open circuit) and the coil would need to be replaced.

 

The bike fires right up though. Would this be the case with coil(s) having an open circuit?

 

You may not have your range set properly on your Ohm Meter. Make sure you're set to at least 20KOhms... too low and you'll get nada.

 

Your multimeter works at low voltage - any gap will read as an open.

The coil generates very high voltages (10s of thousands of volts) which will easily jump a rather large gap.

So, you're either measuring wrong or you have some kind of gap (open).

Are you measuring the resistance with the spark plug caps on the wires? The place where the cap attaches to the wire is a prime candidate for your gap.

 

Corrosion between the cap and the wire is a famous culprit.

 

Do you have flow out of the petcock with no fuel line on it when on PRI ?
If you do you may not see it flow through the clear line if It's full.

It didn't sound like you have a problem with the coils, when running, are all 4 pipes hot ?
If so, then all cyls are firing.
If not, I'd try new plugs.
If still not, start checking resister plug wire caps and wire.

 

Hey all. Thanks for your responses. With regards to the petcock, it seems to be working well. I let the tank sit full overnight with the lever in the on position one night and the reserve position the next. On both occasions, I found not one drop of fuel in the bowl the next morning. (It's abount time!) I am convinced the elevated fuel line was the culprit, which stopped my fuel flow. I thought the downward force of the fuel would have been enough, but I was wrong. (Imagine that) I am definately getting fire from all four cylinders, so everything is running up to par. Now it's just a matter of getting the valves adjusted, to which I will be posting another thread, and getting the the pilot and vacuum screws dialed in. Thanks again.

 

Jay, I just pulled apart three sets of coils and three of the coils had discontinuity (infinitive ohms) on the secondary lines. I have milled out the attachment point on all three (intend to replace the wire) and found that the coil is fine on all three. It boils down to corrosion in the high tension (voltage) lead causing the conductivity interuption in these things. Unfortunately, the plug wires do not just unplug for replacement, you have to dig them out and solder in new ones.

 

yes,,,,,it will fire up an run until it burns back far enough it will not jump the gap or it finds a carbon track to ground,,,,,2 scenarios I know of with cars,,,,does not necessarily happen over night