Not firing on all cylinders...

So i replaced the spark plugs, replaced the stock coils with new dyna coils(the green ones), new wires, new caps, and still im not firing on cylinder #3, and #4 doesnt seem to be firing strong. #1 and #2 fire fine. Spark is good on all 4 cylinders. With the bike running if I pull either #1 or #2 wire the bike sputters and dies. When I pull #3 or #4 pretty much nothing happens. Header pipes on #1 and #2 are hot after running, #3 room temoerature, and #4 is kinda warm....any help is appreciated....

 

#3 dead cylinder could be a faulty petcock. Vacuum for it comes off the #3 manifold. Check and see if the petcock flows gas through the vacuum line, if so, the diapghram is shot and needs replacing. There are some quality kits out ther for not a lot of cash. When i bought my '82 Seca it ran on 3 cylinders and that is what I had to do to fix it. As a bandaid, you can plug off the vacuum ports on both the petcock and the manifold and run the bike on prime, but remember to shut off your gas after parking to avoid gas overwhelming the floats.

 

Im using an aftermarket petcock from Z1 Enterprises, I have the vacuum line from #3 plugged. Right now I have the line capped and a bottle of gas attached to get the tank out of the way....

 

Plugged up pilot jets could be another problem. Had the same thing happen to mine. Try taking it for a short spin, with some good revs. If 3 and 4 are warm, but cooler than 1 and 2, pilot jets are a definite possibility.

 

Smells like Diaphragm Piston's on the one's not hitting good are stuck and not opening like they should.

Pop the tops off the Carbs
Take-out the springs
Do a "Clunk Test"

1982 ... that's a long time for oxidation to do a shrinking-act on the Carb Body Bores.

Clunk Test:

http://xjbikes.com/Forums/viewtopic/t=1 ... +test.html

 

I had the carbs cleaned and sync'ed in Sept, but I'll try that tomorrow...

 

Have you checked#3 and #4 for being cross-wired?

Can't tell by your post if this is happening only at idle. Have you run the revs up and held them at 5K or so for a while, and then felt the pipes? If they are reasonably close in temp at that point then you likely have a carb mix/sync issue.

If they are still cold (and warm) then you should do a compression test and check the valve adjustment.

 

Yup, checked for cross-wiring....everything is ok....all 4 carbs pass the "clunk" test....I polished up the slides a little more, and cylinder #4 is a little hotter now and #3 was warmish....ran some seafoam through it...we'll see what happens tomorrow....

 

Did you examine the Diaphragms on the ones not hitting for holes or tears?

Try a shortcut:

Take off the Carb Top
Remove the Diaphragm
Bottom-out the Pilot Mixture Screw
Remove the Float Bowl Drain Plug

Shoot some Carb Cleaner into the Pilot Jet Air Passage.
Push the Red Tube well into the Pilot Air Jet and Blast some Carb Cleaner in the Pilot Air Passage.

Look for Carb Cleaner to drip-out the Drain hole.

While you have the Diaphragm Assy out ... look for holes.

 

What do sparkplugs in 3 and 4 look like? Try new sparkplugs in 3 and 4?

If the bike has been running bad chances are the sparkplugs will foul.

Sparkplug Reading Guide

 

All 4 diaphragms look good...the drain plug on #3 carb is totally stripped by the PO i guess....
All 4 sparkplugs are brand new....#1 and #2 are a nice even tan color...#3 pretty clean since its not firing....#4 black and oily...

 

Number 3

Should be WET ... since it's not firing.

So ... Just grab another Spark Plug.
Pull the Cap off 3
Plug the Spare Plug in the Cap and ...

(If you were doing the test in the Shop, here, we'd have you hold the Plug so you could see the Spark and "Ground yourself" buy putting another finger on the top of the Plug in 3 ... that way the whole neighborhood would know if 3 was firing -- : )

Ground the Plug and see if it's sparkin'

If 3's sparking ...
There's a snag in the Pilot Jet / Pilot Air

#-4 being Oily ...
Check the Spark to 4 too
If there's Spark ...

We have to start doing some troubleshootin' ... beginning with a fresh set of Sparklers and a Compression Test.

 

Ive done that and have good spark on 3 and 4, ok so #3 was moist I suppose, not wet.....guess its time to follow your guide Rick on carb disassembly

 

Not yet ...

Run the Pilot Mixture Screw all the way IN 'til it Bottom's-out
Leave it.
Pop the top off the Carb
Don't let the Shop Foreman catch you.
Get the Diaphragm out for a minute.

Shoot some Carb Cleaner in the Pilot Air Jet.
Stick the Red Tube in Pilot Air Jet as far as you can.
Get that silly grin off your face you sick-minded ...
Shoot several blasts of Carb Cleaner in the Pilot Air Jet.
Hail Mary, full of Grace ...

Put it back together and try it.
Factory Preset the 3 Hole.
2-1/2 UP, baby!
Cross your fingers!

If it works ... you still got #-4 to deal with!!!

 

ok tried what you said Rick....after a couple of times of taking it apart, sticking my red tube deep inside the pilot air jet, #3 is firing....pipe gets hot, not as hot as #1 and #2, and im getting backfiring now, which is better than nothing I assume....

 

Backfire = Lean

Give that Pilot Screw some more OUT.

Turn it OUT and "Listen" to that engine sayin': "Tune me; baby!"

Keep bringing it OUT and you'll hear the rpm's rise.
When they do ... Micro-eyelash-tweak -- keep it going OUT if the rpm's are rising.
Eventually, you reach "The Plateau" where there's NO further increase in rpm.
Keep bring it out an eyelash at a time until the engine begins to "Cough, Pop, Sputter or "Flood-out" ...
THAT's where you Tweak it back IN until you have that Maxed Idle; again.

This spot is the Richest Mixture that will fire.
It might very well be TOO RICH for acceleration.
If the Pilot Screw IS too Rich ... you only really know when you go out and open the Throttle -- Under Load.

If is too Rich ... as the Butterfly Opens and you transition from Idle to Off Idle / Main Jet Supply ... the Bike will "Cough or Hesitate" as the Fuel -- coming just a split second before enough air arrives it too rich to fire.

Microscopically tweak that condition out-of-there by turning the Screw IN a degree at a time ... until the hesitation is tweaked away.

You're very, very close to being right on-the-money!

 

ok....tonites update....#3 is firing nicely...pipe is nice and hot...pilot screw doesnt change the idle....at about 3 1/2 to 4 turns out it stops backfiring....rpms dont increase or decrease turning the screw in or out...had a couple of times the rpms just jumped up to 2k while i wasnt touching anything....
on an unrelated note....i changed my stock coils to the Dyna DC1-1, and didnt find out till tonite the tank wont go on over the new coils....are the mounts an integral part of the coils like a ground or something, or can i just mount them with zipties for example?

 

Well ... they're NICE Coils. It's convenient to have them solidly mounted on the Frame.

It ain't written in stone!

If you happened to Nut-'n-bolt-up a heavy-gauge, BLACK wire to EACH of the Coils and securely fasten the other end to the frame ... I guess they'd be Grounded ... huh?

Just be sure to be wearing a nice, new, long-sleeved, gray Sweatshirt, with your Nickname, spelled-out in block letters, across the front, when you do it.

 

Guess I'll have to figure out some other way to get the tank over the coils then...and get the bike running correctly lol

 

all 4 cylinders are firing now....no matter how far i turn out the pilot screws on #3 I still get the popping....getting there I guess....