Not firing on 2 & 4: I do not know what it is!

So I made it out to the bike this afternoon and found the ignition coils were hooked up properly. Left was for 1 & 4 and the right was for 2 & 3.

So the next step was to see if the problem followed if I switched 4 for 1 and 1 for 4.

The result was the same. Cylinders 1 & 3 ran just fine as evidenced by the hot pipes.

This leads me to believe that the coils are fine, but I might have a wiring issue somewhere else on the bike.

I took off the coils to get them cleaned up and noticed a lot of corrosion where they attach to the bike via bolts to the frame along with a couple of ring terminals used for grounds.

Do the coils "ground" through the frame at all?

I will get out there and check all the other wiring too while I am at it to be sure.

Recap:
Carbs are clean and getting fuel just fine
Does not run on all 4 cylinders with the aid of Instant Start
Runs on 1 & 3 regardless of position of plugs (switching 1 & 4, etc...)
Fully charged battery every time I go out to give it a go

 

it's not clear from your post whether you swapped the plugs for 1 and 4 or the plug wires from 1 and 4.

if you swapped the plug wires and nothing changed, then you've ruled out any electrical problem.

if you swapped the plugs and nothing changed, then at least you know all your plugs are good.

i'm not sure if the coils ground through the frame - an ohm meter should be able to help you answer that question. an ohm meter will also tell you if your coils are bad.

 

first thing i would do is pull one of the plugs that is not firing, plug back into the plug wire and ground to the engine while spinning the engine over. do the same for the other one. if they spark then you are not getting fuel to the cylinder, or the mixture is severely incorrect, if they don't spark then you have bad plugs, replace them, easy fix - since 1 and 3 are firing, your coils are good and you ruled out the wires/caps by swapping plug wires between 1/4, did you do the same for 2/3 with same results? (caps are worth replacing anyway if they are original/old)

another thought, what kind of shape is the engine in? could be stuck valves or something....

 

I swapped plug wires around and there was no change.

It is possible that the mixture is incorrect and causing problems.

I will do the test against the cylinder head/block my next time I am out there.

I will also look up the specs on the coils and do the ohm test. I have all that good stuff to test this and other electrical problems.

I would hate for it to be a fuel problem, but I got the rack off once, I can do it again. I set the float levels properly to be sure. But I didn't touch the mixture screws from what the previous owner used. The PO had it running once about 5 years ago, but he never told me how it ran (quality wise).

As far as the engine condition, I have no idea. Should I pull the valve cover and tap (lightly tap) each valve and turn it over and see if all of them are moving?

 

another thought, when you pull the plugs to check for spark, take a look at the plugs themselves and tell us how they look. another thing to try is swap plugs 1/4 and see if that changes things (as opposed to just swapping wires).

when you do the ohm test, do it with the caps off and check the caps themselves too (they screw on/off the wire), not sure again for your bike but most (i think) should be 5k +-10%.

a compression test will tell you if the valves are sealing.

 

i'd be praying it was bad spark plugs right about now.

 

Have you checked the fuel/float levels? Was this bike running ok previously? What is the background please?

 

I set the float levels myself right after doing the carb cleaning. I did the 17mm setting that everyone recommends for these Hitachi carbs. But I didn't check the fuel level due to seized screws in the bowls.

The history of the bike is that it was running once...about 5 years ago. Prior to that, it was registered in PA back in 1994 and I assume that is when the bike started to sit.

Currently, it runs on 1 & 3 no problem but not the other two. Oh and the plugs looked just fine. A little dark if I had to describe them. I will check the gap while I am at it too.

I need to get out there and try swapping plugs around and see if I get some luck out of that.

 

pull the plugs first. if they are wet then they are getting fuel. and the plugs aren't firing.

if the plugs are dry. chances are they are firing. and there's no fuel. to which youi can check by pulling the drain screw out of the carb for that particular cylinder.

just becuase the plugs spark on the outside of the motor don't mean they are firing on the inside of the motor. 140 lbs compression is a lot harder to fire then standing air. compression offers more resistance.

 

FYI - i've had plugs that will spark just fine when removed from the cylinder and grounded against the engine - but would not spark inside the cylinder (compression in the cylinder creates more resistance across the gap). in my case, this was due to a coil that was on it's way out - it still made spark, but had open loop (infinite) resistance from one wire to the other.

 

Are we sue that Spark Plugs which fire -- Outside -- the Engine don't fire once they are screwed -- Inside -- the Engine.

The Higher Compression in a Cylinder is make it more likely the Cylinder -- WILL -- fire.
As Compression rises the Mixture can Ignite without a Spark.

This may be a couple of problems feeding the other.
If it coughs or tries to run on Starting Fluid, ...
The problem is going to be Fuel Delivery.

 

not to hi-jack this thread - but, for clarity's sake - are we in agreement that compression in the cylinder makes it harder for the plug to actually produce a spark?

 

gasoline needs a spark to ignite. deisel fuel needs compression to ignite.

automotive basics 101.

 

i can't see compression having any negative effect on the quality of spark, if anything i would think compression of the ionized fuel (and lacking that, simply the humidity in the air) would actually make it easier for the spark to discharge...

 

Except that theoretically if a gas engine could be built with enough compression, it wouldn't need a flame to ignite.

Physics 101

 

Well none of these Bikes are Diesel.
I'm relatively sure of that.

Plugs that fire outside the engine don't get turned-off once installed.
They can be fowled, ... sure.
But, my money's on they still spark screwed-in.

 

atmospheric pressure is 14.7 lbs per square inch. compression is 140 lbs per square inch. given the fact that compression adds to the resistance factor. which is harder for the plug to fire????? outside or inside. cuz it's defenitly not the same routine.



pull the plug out and the plug WILL BE WET so you think it's not sparking. yet you ground it out and it sparks. the cylinder isn't flooding so why is the plug wet.

faulty plugs happen all too often.

 

Welp, I have some new news.

I tested the coils after cleaning them up and found the primary on each to have 2.5 ohms as prescribed. But the secondaries had 27K ohms each which I read the spec is 11K ohms.

Let me guess, this is bad.

 

is that with or without caps?

 

if it's with the caps, i'd say you are pretty good with 27 kOhms.

your caps are most likely 5k resistor caps (so 2 of them is 10k) - so your coil is actually 17kOhms (higher than spec, but not so high that i'd suspect it's the source of your problem)

 

I guess it is with the caps. I followed the proceedure from the Haynes manaual and it did not communicate removing the caps. It seemed to say that the caps should stay on during the test.

One more thing to consider...my spark plugs do not have the screw on cap installed yet the plugs seem to require them. Problematic?

 

i've ran into confusion with different manuals and coil specs - they all seem to say to test with the caps on, but the spec they give you (i think) is actually for a test with the caps removed. as i always get around 10k too high.

as for the plugs - i have to remove the screw on cap and just pop the cap on the the threaded "pin" sticking up out of the plug. you should be able to feel the cap snugly fit onto the plug. (should be able to hear a little "vvvvt" sound of the cap sliding past the threads)

at any rate - it's kinda sounding like electrical has been ruled out here - are you able to get anything on either dead cyliner with starting fluid?

can you rev the bike up? if you can keep the RPMs up to 3k or so - do the other pipes start to warm up?

you said you weren't able to check float levels cuz the screws are stuck. if there's still enough screw head left on the drain screws, KROIL, an impact driver and heat will get those drain screws out. then you can check if you're getting fuel into those bowls and you can check the levels with a tube - although, in my experience, the 17mm is pretty dead on.

 

If you have been trying to get the Bike to run without the Spark Plugs fully seated in the Plug Caps is something you should take care of right-away.

Grab the Top of the Spark Plugs with a pair of Pliers and UNSCREW the Automotive Type Connectors and discard them.

The Threaded Post atop the Spark Plug is what fits the Plug Cap.

If the Round Connector at the Top of the Spark Plug doesn't unscrew, ... don't believe anyone who tells you ... you have to bring them too a Machine Shop and have them threaded on a slow-speed lathe.

Go to the Auto Parts Store and get a 4-Pack of Plugs with removable ends.

 

So my caps...Pulled them off and the readings are: 8.2K, 7.8K, 11K & 4.7K.

Looks like I need to replace the caps. Might as well do all 4 since they are supposed to be about 5K, right?

And both secondaries measure 11K as they should.

So coils are fine. New caps would be good and go a long way for reliability anyway. Plus, they are cheap. Do they have to be right angled?

 

Thanks guys. I agree, I think electrical is ruled out. Except that I want new caps anyway. Seems to be too much resistance anyway.

Rick, the plugs I have are the NGKs listed in the manual and they are indeed threaded. I did hear the zzzzzzzt sound when putting the plug wires back on. So I think they are seating just fine.

The bike does not run any better or on more cylinders with starting fluid. That is what concerns me. Neither 2 nor 4 get hot when run with starting fluid.

If it is fuel, I will pull the rack back off and get those drain screws fixed up so I can do a proper fuel level test.

 

at least on my bike (can't say they're OEM) but the caps for 1 and 4 are different than the caps on 2 and 3. you could probly use whatever you want on 1 and 4, but 2 and 3 need to be kinda tall to get the plug wire up over the valve cover.

 

You know, I noticed my plugs are different as well. So odd. I will bring my electrical tester to the store when I go buy them. Make sure they are low resistance.

I cracked open my TCI the other day and noticed that there were a few rusty solder joints and possibly some cold solder joints. I may open it up fully and go through it with a meter and see if things are in spec. Reading up, it seems like TCIs are getting sketchier by the year. I also know about Robert in Cali somewhere who will "freshen" them for a nominal fee.

Thanks for your guy's help here. Since I know the coils are in working order, I will put them back on the bike and forget about them (knowing they work).

More detective work ahead!

 

yes new caps are a good idea. before tearing into the tci (which i believe is ruled out by the fact that both coils are firing), did swapping/new plugs make a difference? did you do a compression test? results?

 

Try 4 new spark plugs I have had the same problem with my 1983 xj 750 seca, I think that with the wasted spark ignition system the spark goes to the plug with the lowest resistant, it helped in my case.

 

I haven't tried the spark plug swapping yet. But payday is in 2 days so I will go out and get new plugs and caps. At the very least, I should have even resistance across all plugs/wires.

Thanks tibor and fnuggi!!!

 

Oh, I don't have a compression tester though I wonder why I shouldn't go out and buy one. I would just want it to work on cars and bikes...

 

my compression gauge came with several brass fittings to fit different size plug holes, something to look for when you're shopping for one...

cheers,

Trev

 

I'll hijack it. I don't see why it would be harder for the plug to fire in the cylinder than outside. The spark is created when the voltage spikes higher than the air gap can resist. When the voltage exceeds the breakdown voltage, the air ionizes and a spark forms. I think when you compress air and add fuel mist, the resistance is lower, meaning it's easier to spark.

Back on topic, you mentioned gapping your plugs, did you check this? If the gap is too small the spark might be weak.

 

i'm no rocket surgeon but that was my thought as well (hence my previous post to that effect) :wink:

 

I will just replace the caps and plugs this weekend and report back. I will make sure they are gapped properly of course.

Should I also replace the plug wires? It looks like they are just a "build it yer self" type wire. Do they attach the same way to the coil as they do to the plug?

 

i think all xj's have the wires molded into the coil so it's a little more involved to replace them. if they test good, i would leave them alone. you could maybe cut off a couple mm's off the end of the wire before you screw in the new caps. and use dielectric grease on both ends of the cap, it keeps water out of the connection and makes it easier to screw them on the wire.

 

Roger that. I read that some people felt that even having the wires touching the cylinder head might have been causing electrical interference. So I will trim them just enough to make it to the plug without any tension or touching. Plus, new caps on a fresh part of wire makes loads of sense.

 

i was never very good at physics, because i can convince myself that both A and B are plausible. anyhow, i was thinking that compression and fuel mist is "more stuff" for the spark to try and cross, so it's more resistance. but i can also see it as "more stuff" to carry the charge, so it's less resistance . . . i dunno.


marshallnoise: i respect your desire to improve your spark situation, but i don't think it's the reason your 2 cylinders aren't running. with that said - if you want to replace the spark plug wires - you'll either need to do some coil "surgery" -or- you can buy some spark plug wire splices and splice on the new wire up close to the coil.

btw - 4 new plugs are pretty cheap - i think i paid $7 or $8 for a set of 4 a few months ago.

 

True enough Skeeter. But it couldn't hurt...right?

 

there's also the old adage: "if it ain't broke, don't fix it"

 

Ha! But I am not sure if I could tell.

 

http://forums.cycleworld.com/showthread.php?t=249528

an entire discussion on spark plugs not firing under compression.

forget the fact of gasoline being in the mixture. the more air there is. the hard it is for spark to jump the plug. same effect as having a wider plug gap.

140 lbs compression is much harder for the spark to jump gap then 14 lbs of atmospheric pressure. i've seen it happen over and over. and if you read the link. i'm not the only person to witness such a phenomily. and i'm not the only person to explain spark plug 101.

 

some of us remember back in the day when cars had points and ignition systems were weak. spark plug failure was an all too common occurence.

 

Just wondered if you checked the pick ups and wires from them near the frame. I had my motor off to do the infamour starter chain guide and when I put it back in pinched the wiring. I caught it before if set the motor toatally back in, but if you had or broken wire inside the outter sheathing, a bad wire could be arcing or decreasing the power or shorting out to the frame taking power away from one pick up? just a suggestion. For all those that remember I do have a timing light from 40 yrs ago lol, doesnt help us now though.

 

I'LL ADD to ya doug. i've still got 3 dwell meters. for points. course, it hellped that grandpa passed away and i got his 74 ford. after two months though, i took the points off and put a electronic kit in the distributor.

 

Hey, Fellows:

You got Spark ... means ... you got Spark.

Let's try to keep the Theories all on one Blackboard.

The test for spark will be:
YES
-or-
NO

We are NOT going to introduce:
MAYBE, because one time I heard of ...

 

+1, each coil is confirmed firing, you swapped wires and the same cylinders fired, if you replace plugs and caps you can eliminate the ignition system entirely, unless the spark was noticeably weak or something (the spark should have an audible "snap" when outside the cylinder). i would be looking for fuel and compression right now (air is usually a given).

cheers,

Trev

 

How can you determine if its the Carbs that need work?

Run hoses from the Intake Manifold Vacuum Ports and hold their ends all together in one hand.
Have somebody turn on the Ign and Push the Start Button.

Spray Carb Cleaner into the 4 Hoses.
a) The Bike Runs
>>> The problem is Fuel Delivery. Overhaul Carbs.
b) The Bike Don't Run.
>>> Return to Square One. Do Not Pass Go and collect $200.

Square one:
>>> Compression Test.

 

Going to get a compression tester sometime this weekend. I pray I buy it, test and all is right with the world on that front. I don't want to have to go rebuilding an engine.

That being said, my Haynes manual says cylinders 1 & 4 should have caps with a resistance of 5K and 2 & 3 should have a resistance of 10K. Why the difference? Should I even bother with getting new caps with a resistor at all?

I would think that less resistance the better. I don't care about AM radio signals.

I hope I can get those screws out without having to pull the carb bowls off them so I can see how much fuel is getting in the bowls. The other thing I didn't do was bench synch and I am kicking myself for it.

 

i believe you can get resistor caps or resistor plugs, you need one or the other with a resistor, but not both. if you need different resistances (not sure why that would be?) then resistor caps are the way to go, i don't believe you can get plugs with different resistances. i found that the ngk resistor caps are still quite common, found them at most bike shops. the original non-resistor plugs however, were not as easy to find locally. i'm sure chacal will have them though.