Cylinder dropping out after a while.

I am having an intermitten problem and need some expert advice.

Engine wise, except for the exhaust my Seca is all original mechanically. The same electrically except the stator which is OEM replacement.

She ran great for two seasons then the coils both took a dump at the end of the riding weather last year. Last week I installed 2 new Dyna coils and wires from Chacal, the plugs were new end of season. Everything went well and she fired right up and ran like a champ for three days of hard riding. Then one morning about 20 minutes into the ride home from work it started missing badly at highway speed(70mph/5.5krpm). I exited the freeway and found that if I goosed the throttle it would fire but with a steady throttle it sounded like only 3 guns were firing. I was limping it home at low rpms when it caught on was running fine again.

I figured that I had a bad connection on a coil or a bad crimp on the new wires so I went through everything and re-crimped the coil ends. For the next couple days it ran great. Then yesterday on a 60 mile ride it started acting the same way. This time I was able to determine that the no.4 cylinder was not firing at all. Again after running at lower rpms for a few minutes it was OK.

I am way over due for checking valve clearance but the carbs do not seem to need any serious attention. When its running good I can hold idle at 800+/-, the throttle response is immediate and engine breaking is hard and fast.

Is there any chance that this could a valve issue? Seems to me that if it were it would not come and go like this?... Any ideas?

 

yamaman,
Thanks for the PM. I have read your thread and have not ruled out bad new parts but was hoping there was another theory out there.

Today on the return ride it acted the same way. 15 min on the highway and she started missing badly. Crank the throttle hard and it would pick up then "POP_POP_POP" when let off. I exited the freeway and kept the RPMs down around 3.5K and after a few minutes it was running fine. Kept the revs down for the rest of the ride and did not have any problems.

I can't say definitively if I am only losing one cylinder or both because when I have been able to trouble shoot it has been running ok.

 

Can you swap 1 and 4 on that coil set? See if it moves? Plugs might tell you if it's both or 4. Also sounds like it's running out of gas. Try running it on pri and also check the tank cap vent.

 

I think you two guys ought to put-in a call to DYNA's Technical Line.
What's here to lose?
Yamaman has yanked all the hair out of his head.

I know the first thing I'd do is make sure that the DYNA Coils, ... which need "Special Mounting" ... were not only Mounted nice, ... but, Grounded to the Frame, directly ... or, by means of a Ground Wire attached to the Frame.

(( I'm running a DYNA Rev-Limiter. For the Rev Limiter to work with the YAMAHA TCI, ... DYNA Technical sent me a Pair of Resistors which needed to be installed on the 12V Lines feeding the Coils. ))

 

After reading through yamaman's thread(confirmed, confirmed...) I took another look at my ignition wiring and found a couple places where the plug wires were touching the valve cover. I rerouted them so there is no way there could be any contact anywhere and ensured all connections were secure. The ride into work tonight was uneventful, nary a hiccup. We'll see what happens tomorrow on a longer ride.

 

if that be the case then you should see some kind of burn or worn marks on the wire. where the wire COULD be arcing to the engine.

rerouting might also be a sign of a weak connection at the coil. where as the connection would be stronger since the wire was moved a little.

plug wire that is.

 

Very simple.
Run the Bike in the DARK.
Tape Tin Foil over the Headlight.

L@@K at the Spark Plug Wires.
If they are sending little Lightning Bolts to anything, ...
Insulate the Wires.

Shrink Wrap or Hose Wrap the Wires.
You can get Long Shrink Wrap at "You-Do-It"
You can get Hose at a Hardware Store.

 

that's sounding like maybe you better check those valves to me
misses after a hard run and then acts fine when it cools off a bit
the electrical system does the same thing if your going fast or slow
if the plug wires are good you should be able to just grab them, if your not sure might want to use just one finger
you mean that coil you got from me wet the bed ?.......now i feel bad

 

No worries, it got me through to the end of the riding weather and they both crapped out!

I was actually thinking the opposite. That the valves would act the same hot or cold but there might be a bad spot of insulation or a flakey connection electrically that only shows up when things heat up.

Oh well, I really do need to check the valves. I'm just procrastinating and don't want to give up the day or two it will take me.

 

OK, I'm still scratin' my head on this. Here's the update.

Valve clearance checked and re shimmed. All are within spec now. Still have an intermitten problem with #4 dropping out. I swapped wires 1&4 before and just swapped coils. The problem stays with #4 cylinder. I did a compression check. While all 4 were low, they were all 4 within 2 pounds of each other right around 95. I did not use a battery charger so this might account for the low comp.

It does not happen all the time and does not seem to be limited to running hard or any required run time. Once I was just out for 5 min and kept it under 3k. While tonight I did 25 miles at 70 MPH/5k rpm and had no problems!

When #4 is not acting up, she runs like a champ. Smoothe idle, smooth acceleration off idle. Quick throttle response and plenty of pull even in the lower revs. When it start to miss, you feel the surge and ebb and if you crank it hard and let off there are some exhaust pops.

What are the chances that it might be some debri in the carb intermiitenly blocking a jet or the float valve not allowing the bowl to stay full...?

 

You swapped the wires but did you swap the plugs as well?

 

I've traded plugs back and forth from cylinder to cylinder several times. Just to be trying something, I just pulled all plugs check the gap and eyballed them for fouling. All good. Then I removed the coils and cleaned and reconnected all connections including grounds. I'm not holding my breath on this one but just had to try something.

I should probably go over everything, clean all the electrical connections and apply a new dollop of dielectric grease all around.

 

i think you better get a new compression gauge and reverify your compression readings. i can't see you hitting 70 mph at 95 pounds of compression. i can't really see the bike running all that hot at all.

most people on here are claiming 150. i've got 140 in mine.

 

My compression tester is a cheap Harbor Freight gauge. Also I don't have a good high amp battery charger, just a trickle charger so the test was just with battery power alone. At this point I really don't care if the psi reading is accurate. What is important is that all 4 cylinders had close to the same results. This eliminates the possibility that it is a valve or ring issue...(right...?)

I ran it a little hard on the ride home this morning and it started flaking out very quickly. But just a few seconds at lower revs and it was running smooth. I am really starting to think it is a fuel flow issue as opposed to an ignition problem. I am going to have to pull the carbs and I really didn't want to do that till the end of the riding weather!

 

You shouldn't put so much energy into trying to tune an Engine that has such poor compression across the board.

The thing to do is verify the values using another gauge.
If you have compression below 100 psi you're going to be fortunate to have this Engine running without it breaking-down frequently and eventually just out-right suffering a catastrophic failure.

Spending time and energy tuning is a waste of time.

Determining why you have such low compression and either rectifying the compression issue, ... or finding a HEALTHY Engine that you can swap-out and fine tune would be a better course of action than expecting to get an engine running right which completely flunks the test for the first mandatory prerequisite.

If all you got is 90 psi, ... that engine's doomed.
Might need a valve job.
Might need a ring job.
Might need both.

 

Rick,
I hear ya.
I have been wracking my brain trying to figure out how I could have all 4 cylinders be so low(and so close to each other) and still have a bike that, for the most part runs so well.

I don't remember holding the throttle open during the compression test! I will redo the test as soon as I have the time and make sure that I hold the throttle wide this time.

I am still hesitant to think this could be a valve or ring wear issue(possibly damage but not wear) as the bike only has 38k miles or so on it.

 

Having low compression -- "Across the board" -- is a Flag that the Teat or Gauge has issues.

Re-Test:
Charged Battery
Wide Open Throttles
Plugs Out
Unplug TCI

Get new readings.

IF ... still Low.
Add Tablespoon of Oil to each Plug Hole.
Conduct ... "Wet Test"
IF compression numbers increase = Rings
No change = Likely related to valves.

 

Update

I ran another compression test (correctly this time!)

cylinders 1-2-3-4: 120psi dry+/-4psi, 180psi wet +/-4psi

So, there is definitely some leakage past the rings. I'm still not sure why this would cause the intermitten problem that I have been seeing.

I guess I will be doing some work on the jugs this winter. Hopefully just honing and new rings will be enough. Does anyone make oversize rings for the XJs?

 

Yes.
There's Over-sized Rings ... First and Second Over.

I think Over-sized Pistons are beginning to become harder to find.
I'm sure Member -- " chacal " -- would be a more informed source on finding Parts.

PM him.

 

I am having the same symptoms on my XJ650. I would start it but it had to sit and idle for a few minutes until the #4 cylinder would kick in and then it would run fine. If I gave it any gas while it was idleing before the cyclinder kicked in it would just die out.
I put new plugs in, new air filter, oil and filter but it did the same thing and now it had to have the choke on partially to run right.
I removed the carbs and put a good set of intake boots on. Cleaned the jets and journals, reassembled and it ran better bbut still missing. I took it for a ride and at high rpms it did great but kept dying on me with the cyclinder or cylinders falling out. Pulled the plugs and none were wet but the brand new plug on #4 was black carbonned up. Going to pull carbs again becuse of a good thread on here showed me that I missed removing and cleaning the main jet tube that has the horizontal airways.
Could the petcock have anything to do with this?
Thanks

 

Indirectly.

The 4-Hole is at the end of the Fuel Gallery.
If the Beenie Screens are clogged 4 will "Fuel Starve" trying to keep up.

Check the Vacuum Hose for Function and Leaks.

If it hits when you have the throttles open and starts missing at the lower rpm's ... you might be too Rich.

Post a Picture of your Plug 1, 2 3, & 4
Business ends.
Good light and focus.
That will tell us a how she looks.