#4 dead cylinder

So I did a little research and found some other people with similar issues, but none of their solutions have helped so far.
The problem started when I bottomed the bike out on a giant bump in the road. It was in a parking lot so I was going very slow. It hit my exhaust which caused an exhaust leak at the exhaust manifold. I replaced the gaskets and reinstalled the exhaust with what seemed to be no leak. I took her out for a 15 minute ride. I babied the bike for a while until I was almost home, so I let the throttle open around a corner and notice that halfway through the powerband I lost power I didn't notice pops, or bangs. I managed to get it home, let it cool off and when I started it back up, the 4th cylinder was dead.

I have great compression in all cylinders ~150 psi. Good spark, I checked the plug, switched the caps the leads and the plug to see if I could get a misfire on a different cylinder. Nothing worked. So spark is good. I recently had the carbs cleaned professionally about 100 miles ago. The float valves were replaced and I pulled #4 bowl off to check the jets which are just fine and didn't notice crud in the bowl.

Lastly, all four plugs are a little carbon fouled, indicating a rich mixture, but funny enough, the #4 plug is the leas fouled of all.

Any suggestions would be great. Im not sure where to go from here.

 

Any chance the bump could have opened up a crack in the #4 intake boot between the cylinders and carbs?
Judging from other people's experience, "carbs cleaned professionally about 100 miles ago" is a red flag. More often than not, a 'professional' cleaning doesn't take the level of care and time required. Could be that they loosened some dirt up that floated around and lodged someplace. How well do you know and trust the person who did the cleaning?

 

Is the plug on #4 wet after you shut the engine off? If you have spark, and the cylinder isn't firing, and the plug isn't wet, then you have a fueling problem.

 

as for the carb clean, it was done well. I pulled them off and checked. the bike was running beautifully before I bottomed it out. I will check the plug for wetness after work tomorrow and get back to you guys on that.

 

The float valve may be stuck, starving #4 of fuel. try tapping it with a screwdriver handle and see if it breaks loose.

 

Could be as simple as putting in a new plug. I had that exact issue this summer..... Now, start simple and work your way up-- put in a new plug first: problem was solved immediately

 

So I put the one carb bowl back on and tightened up all the air intake boots. She fired up perfectly once the bowls filled with gas. Must've been a A/F ratio issue. Either an air leak or a stuck float. Thanks for the input guys.

 

Just discovered the right hand outside cyl isn't firing on my '85 X.
Started to take out the plug to check for wetness but then stopped... that's one deep friggin hole.

it looks pretty clean but i will blow it out with some compressed air anyway... I was unable to turn the plug.
How hard should I try?

Heading to the local HW store to get some compressed air and a proper plug wrench.

 

You need a thin-wall socket, too--

 

Thanks,
I discovered a socket in the "on-board" tool kit. Removed the plug easily.
It was wet; so gas is flowing.

As I recall this started happening late last year, when it started to get damp and cold.
Today was chilly... around 1 - 2 degrees Celcius (34/35 F). Just above freezing.

Last week, when I drove it home, it was a lovely day and 10-12 degrees . All cylinders were firing beautifully; purring like a kitten.

Does that provide any tips as to where the problem lies?

Thanks

 

Swap the plug to see if the problem follows it to a new cylinder.
If it does then you have a bad plug.
If the problems stays with the #4 cylinder then unscrew the plug cap and cut the wire back about 1/8 to 1/4 inch to expose uncorroded wire.
If that dies not solve the problem then you have bad resistor in the plug cap. You can either get a new resistor from Chacal, or a whole new plug cap.


{EDIT} This started in the damp you say? Fire her up in the dark and look for a lightshow. If the sparks are getting out of the wires you'll need to replace them (they will need to be spliced as the original wires are moulded into the coils), or re-insulate them with self-amalgamating tape, or spend some cash on a new set of coils and wires.

 

Checking the plug this AM, but have been reading @ the awesome www.maxim-x.com.

http://www.maxim-x.com/sparkplugs.html#iridium says the recommended gap is 0.60mm to 0.7mm ...
But NGKs DR8EIX Iridium spark plugs are packaged with a factory set spark gap of 0.76mm (0.030") which exceeds the specification for the Maxim-X spark gap.

It also warns about prying against an Iridium electrode to set the gap as it is brittle and will break...
So how do I gap these?... Or do I just put them in and forget it? (assuming for now that this is the problem.)

 

PERSONALLY, I just put 'em in and go. I honestly have not gapped a plug since, oh lets see.......I guess around 1983

dave

 

Agreed. If you have a healthy ignition system the extra 0.06 mm won't cause any trouble.

 

Done and Done! Miso Happy.

New NGK DR8ES-L x 4, changed the oil/filter - as it was fouled with gas.
Cracked a beer (critical).
Easy start and smooth idle - and it's just above freezing today.

Lesson for the day... Don't freak out. ...Check the plugs.

But I have to say... Those are deep plug wells.
It's difficult to get the dirt out, and hard on the knuckles to pull the caps.
Compressed air was useful, but I was still afraid I left some dirt down there.

It looks like PO changed 1 & 4 at some point, but ignored 2 & 3.
All wells had sand and crap below the plug caps (which are tight)
Is there anyway to make that seal up better to protect against the elements?

 

spt22) Spark plug drain well BRUSH and BLOCK-OFF PLUGS allow you to clean out the water-drain wells in the cylinder heads on all XJ700-X and XJ750-X (water-cooled) engines. These drain passages are only accessible by removing the cylinder head decorative, ribbed side covers (which will expose the small, center well drain-hole on the side of the head). This passage hole is used to drain water and associated grit and gunk from the spark plug wells on each side of the head (i.e. the left side hole drains plugs #1 and #2; the right side hole drains wells on the #3 and #4 plugs). Clogged drain ports allow water and other junk to build up in the plug wells, with predictable results. Our extra-long WIRE-BRISTLE BRUSH is the correct size and depth to purge these passages, while the BLOCK-OFF PLUGS replace the spark plugs while the cleaning procedure is being performed (the spark plugs must be removed to allow the brush clearance to pass all the way thru the passage).

The procedure to clean these wells ---- which, by the way, is not mentioned at all in the service manual ---- is as follows:

1) remove the decorative head side cover.
2) remove the spark plug cap/boot…….leave the spark plugs in for now.
3) using compressed air, blow out any debris in the wells.
4) remove the two spark plugs on that “side” of the head you are working on.
5) install the low-profile block-off plugs into the two spark plug holes.
6) use the wire-bristle brush to clean out the drain passage completely. Any debris will be “pushed” into the plug wells (that’s why you need to install the block-off plugs!).
7) using compressed air, blow out any debris in the wells.
8) remove the low-profile block-off plugs, and re-install the spark plugs, plug cap/boot, and decorative side cover.
9) repeat steps 1-8 for the other side.
10) this procedure should be done once every few years or so.


HCP21394 Aftermarket STAINLESS STEEL WIRE-BRISTLE CLEANING BRUSH, perfect size for cleaning out the spark plug well drain passage in the cylinder head of all the built-up gunk and debris. For use on all XJ700-X and XJ750-X engines..
$

HCP21367SET2 Aftermarket spark plug hole BLOCK-OFF PLUGS, these low-profile plugs are the correct size to replace the spark plugs while cleaning out the spark plug well drain passage in the cylinder head. For use on all XJ700-X and XJ750-X engines.. Set of 2 plugs:
$

HCP21444 Aftermarket spark plug well drain passages CLEAN-OUT KIT, contains the HCP21394 brush and two of the HCP21367 plugs, everything you’ll need to perform the cleaning procedure.
$

 

Just gotta say... I need to peruse this forum and give back some knowledge.

Best forum I've ever been on!