Ignition question - not sure what to do next

Hey everyone.

So I've been working on the bike now for the past couple months, and she's so close to running perfect, but I think there's one last thing left. For some background here is what I've done so far:

New spark plugs properly gapped
Cleaned carbs and replaced seats and polished slides.
Fresh battery
New chain/sprocket front and rear
Tested primary and secondary side of ignition coils. Both are within spec
Tested voltage at connection points from IC Ignitor box to coils and to the "pickoff coil" (on lower left side of bike that spins)

Symptoms:
Bike will start with warmer weather no issue. Once it's colder out it tries to turn over but rarely will start. Once we had he started we began to sync the carbs. She will idle at 3k but once we bring her down to around 2.5k she falls on her face. So we took the carbs out recleaned etc thinking it was still a carb issue. Well the carbs have been off about 5 times now and I'm positive were no longer dealing with a carb issue. So initially we tested the coils. Both coils test sat with about 2.4 ohms and 21 kohms. The manual then suggested resistance checks on the orange/gray/blue wires going into the IC Ignitor box. They tested sat. Wiring has been inspected and appears sat. We have used a spark window tester to try to see spark and it rarely sparks, and is without rhythm during starting.

I'm leaning toward a bad IC Ignitor box, but before I spend $75-$100 I figured I would ask the expertise of the community.

Lastly, the bike is a 1982 XJ 550 with about 20k miles garage kept and stored. Also, inspection of the IC Ignitor box suggests that it has been opened up before, due to a partially stripped screw on the back and a nut on a bolt inside where the stud spins with the nut.

 

How about start with STEP #1?

GET THE VALVES IN SPEC.

Then pull the carbs back off and accurately wet set the float levels: http://www.xj4ever.com/setting%20fuel%20levels.pdf

Then you'll need to carefully bench-sync the carbs.

It's not a case of what to do next. You missed "what to do first."

And that's the valve clearances.

 

Don't rush it.
The plant needs the preliminaries of Valves in spec as Fitz makes sure everybody knows.

Moving along, ...
3,000 rpm is NOT Idle.
Idle is less than half that.

Once the Valves are checked and spec-ed, ... you advance to Carb Work.
They have to be thoroughly cleaned and float height adjusted.
Pilot Air Screws able to be fine-tuned.

That's your Square-one.

 

did you make certain that the cold enrichment wells in the float bowls are open?

http://xjbikes.com/Forums/viewtopic/t=8918.html

CN

 

Hey guys thank you for the replies! I should have been a bit more forthcoming with the steps we've taken thus far. In my haste I completely forgot to mention that we have followed the suggestions under most of the idle issue posts I found using search. The valves are within spec and float levels have been set. We then proceeded to bench sync the carbs and when fine tuning the carbs while on the bike and that's where we discovered our spark issue. It almost seems that at high running RPMs the bike is getting adequate spark but at lower RPMs its not working properly.

I guess my biggest concern is I haven't found Any true symptoms that would point to the IC Ignitor box going bad.

 

your issues could be caused by the atmospheric conditions (i.e. fuel to air ratio) in each individual cylinder. hence the reason I asked about the enrichment wells. if it is too lean in the cylinder, the ability of the coil to create a spark between the electrode and ground is impaired. this could also cause the insulation on the high tension side of the coil to degrade and allow the energy meant for the spark plug to find a ground outside the cylinder. if the wells are plugged, it will not only effect the cold start, but they also heave some effect on the idle mixture as well.

CN

 

They do start hard when cold. And if you run the battery down it might not have enough juice to keep things going when the alternator drops out at about 2K rpm. I usually put a 2 amp charger on when I have one idling during tuning to make sure the voltage doesn't drop too low.

You didn't mention tuning in warm weather, so I'm guessing you didn't do that. If a cylinder drops out for any reason as you idle down it will fall flat on its face. Some things I've seen cause that:

1) Way out of sync.
2) Problem with one or more idle circuits.
3) Low compression on one or more cylinders.

Since you've been through the carbs multiple times and think you have a good bench sync I'd start with a compression test.

 

CN - I can rip the carbs off and take a look to make sure, that is an awful small hole perhaps I may have overlooked it.

 

You might want to take Carl's advice and get a compression test.