three cyls only

[Millietant]

I'd just go with a set of new plugs Chiz, before I dug much deeper and maybe a new set of caps.

As Travis says, a valve or compression problem wouldn't be intermittent as you describe - so I'm joining the chorus of, it's electrical (including a plug)....... until you've changed the plugs and caps and it's still not running right.

[Flynt]

 

[Flynt]

OK  I have made some troubling discoveries today... I believe that cyl #1 will work sometimes and considering what I discovered I am not sure why this happens sometimes....  I checked the temp of the exhaust again and #1 was down again so I squirted some eather with zero result I confirmed what ether does when squirted into a good cyl it bogs it at first, #1 nothing happens. There was really no suction at the carb when I opened the throttle compared to other carbs.
  I removed the carb bank and checked compression on all cyls #1 was at 130 this kind of sent me for a loop as the engine should run decent with this.. Anyway with  starter pressed #1 does seem to produce noticeable less suck when I put my palm over the carb mounting rubbers.
   It would be revealing  to do a leak down presumably but I don't have one, I think the head needs to be inspected... Do any of you guy's concur or have any tip's or stuff I overlooked?
Chiz

Some out of box thinking...

I'm assuming you've adjusted the valves...  if not, do it.  Are you sure the carbs are balanced?  You could be badly off and #1 isn't letting enough air/fuel in to ignite consistently...  Maybe balance on bench or even just try opening #1 up a little?  Maybe long shot, but being at least close to balanced is mandatory for multi-carb setup and a very lean cylinder (or very rich) could do what you describe.  

Could also be a fairly big vacuum leak...  leak between #1's butterfly and the cylinder...  intake boots are one source, but even the butterfly shaft seals leaking could make the mixture go very lean.  Have you sprayed the ether around #1 while the bike's running to see what happens (do this carefully with a straw and sparingly or I can tell you what will happen)?  A vacuum leak should react to the ether, but spraying it down the carb throat might not if it is a vacuum leak.

Not sure if you've tried running at a higher idle, like 1500-2000rpm, and then see if it's still misfiring.  If it runs on all 4, I'd say the balance might be the issue.  If not, I'd search for vacuum leak.  Anything connected to #1's vacuum port off the intake boot?

Frank

[Old Rider]

Here are some things that i would check .
You have confirmed that the plug sparks.Then you need compression It was weak but not too weak ?) Next thing needed is fuel and air mixed not too much or to little.

Take a closer look at the sparkplug if it has white deposits or is very clean the mixture is too lean ,it can be so lean the mixture not igniting
If the sparkplug is wet  (it can also be black with carbon) the mixture is way to rich drowning the plug.

If the plug is white or clean it can be many things to check. Airleak at carburetor intake boots or at the butterfly mountings O-rings.Airleak from a bent or
stuck open intake valve .Airleak because of a blown headgasket  .Crack in the cylhead.The idle mixture screw can be too far in.(if it is try to set it at 3 turns out)
stuck carbfloat or set too high .Leaking petcock vacuum diaphragm sucking false air into cyl 1.Clogged pilot jet.Big tear in carburetor diaphragm so the
slide not rising or sticking carb slide

If the plug is wet from fuel (not oil smell it) idle mixture screw too far out or Choke plunger sticking  .Wrong carb float height.Leaking petcock vacuum
diaphragm sucking fuel into carb .
good luck

[chiz]

Thanks for the input to all.... I believe the head is toast, when I shine a torch into the intake ports the only one to have evidence of blow by a dark stain on the floor of the intake port is #1 cyl. Everything else considered and working well me believes this is a sick cylinder head that needs doctoring. I checked the diaphragm it's good but seemed to have a bit of gas on it compared to the others, the plug when cyl is not firing is wet the pilot screw on this carb has NEVER had an effect on the engine. I have attained a leak down but don't think it's worth the bother my gut says it's going to leak into the intake. Hope this is not true but have to face up to it.
   Chiz

[Flynt]

pilot screw on this carb has NEVER had an effect on the engine.
   Chiz

This indicates balance and or valve adjustment problems...  or even more likely a plugged jet in #1.  I'd make sure you went through valves and carbs before taking the head off.  Or maybe I'm missing some of the data pointing to head problems?

Frank

[chiz]

Points taken did a rudimentary clean on that carb bowl off spray out jets... I made an effort to attach the leak down to all cyls and all? tested 20% or less which is good according to tester in the green. But #1 if I weren't  so deaf there is a faint hiss if I plug a hose into my ear and into the carb no such hiss is apparent with the other carbs'  I think this can deemed as unacceptable?, pulling head is daunting especially with getting cam chain right on assembly and doing this on a measly gov pension with all the bits that will need to be acquired

[Pat Conlon]

Points taken did a rudimentary clean on that carb bowl off spray out jets...

There's your problem ^^^  A leaky valve is not the cause of your cold cylinder.

[chiz]

Yeah and I'm pretty much had it I need some fresh eyes on this. Just come in from a frustrating hour i cant think logically anymore. Think I will give it a break go get me some coffee  and come back and check secondary and primary on the coils but I don't know how to find out if the system before the coils is working properly.... If 3 are being fired properly should #1 also be fired properly the plug does have a spark. don't know going for cafe

[Pat Conlon]

.. If 3 are being fired properly should #1 also be fired properly the plug does have a spark. don't know going for cafe

Put in a fresh plug in #1, then Switch #4 plug lead with #1....put #1 on #4....see it it fires off the #1 cold cylinder... if #1 fires off *and* #4 goes cold, the problem is in the plug wire or plug cap.

If #1 stays cold then look at your carb. Your idle circuit or pilot circuit is plugged...no fuel is getting to #1.

[T Legg]

Number one and number four share the same coil and fire at the same time every time the rotor passes the trigger coil. So if number four is working but not number one then the problem should be the plug wire , cap ,or sparkplug.
    In the electrical files section there is a post that describes how to test the tci (ignition module) on 84 and 85 fj1100's. It shows an easy method to trigger each coil and produce a spark from either coil.

[Flynt]

Points taken did a rudimentary clean on that carb bowl off spray out jets...

There's your problem ^^^  A leaky valve is not the cause of your cold cylinder.

Here's your personal 3 step program...

1.  Remove and send carb assy to RPM for rebuild and bench balance... 
2.  Adjust your valves while the carbs are gone. 
3.  Re-install carbs when you get them back and RIDE!

Then you can look back at this rabbit hole and laugh... 

Frank

[chiz]

Went and got coffee saw the daughter had a nap and decided what is the point of doing the coil test. This is not complicated but has become quite entertaining in it's own way. They sprayed the roads with brine today, not riding weather anymore the white stuff will be here shortly...  i will keep you posted
Chiz 

[chiz]

OK   Decided to think back to the beginning bike worked OK at highway speed but crap lower down so yup is nothing is happening with that cyl irrespective of how good spark is. So I decided to hold throttle open a bit and realized it must be firing because the exhaust pipe is hot.  So the carb is off and the bottom screws were missing that holds it to the mounting bar you can imagine what that throttle valve looked like compared to the other three when the throttle was opened... totally different. Must have left those screws out or forgot to tighten them.. Was going to ultra sound the stuffings out of the thing searched everywhere for the damn thing and the vaguely had a recollection of lending it out so sent a stinger of a reminder to the culprit.. more to follow maybe I should be checking more carefully if there are no bits left over after my work. 

[Millietant]

We've all been there at some point.

Keep at it with those carbs, they're the culprit for most FJ poor running issues