1982 XS650 Heritage Special - Decel popping on one cylinder

Alright on the compression test.

Valves are set correct but will check for leak down.

Starting to find myself at a loss, carbs looked fine. The right plug is lean, the right tail pipe is starting to yellow, and it decel pops so loud it’s annoying to ride.

Left side everything is good, if anything a little rich. Bike runs strong.
 
Hmmm....so possible causes of your symptom from most to least likely:

clogged pilot circuit
air leak at intake
valve leak
head gasket leak
lean float height

Other possibilities more remote
 
I’m thinking it’s got to be a carb issue in the pilot circuit.

I just sprayed starter fluid all over I mean all over the intake boots, choke slide, and carb and no change.
 
fenbrancis, Just curious if you ever got this issue fixed and what the cause was.

Mine does the same thing on the right carb. New top end, everything mentioned in this thread checked. My drive way goes downhill so I roll in first gear and it sounds like the gunfight at the OK corral.

I'm at the point of ditching this carb set and getting new ones or possibly going to a single carb setup.
 
^What he described in the first post can be caused by being very lean or the cylinders being way out of balance with each other. Also, an intermittent ignition or pickup. You mention new top end; were you sure the cam chain was right? If you're positive it's the right cylinder only then it points to a carb problem, or the carb holder being loose.

It can be really handy to have spare parts handy to try. The reason people criticize throwing parts at a confusing problem is the expense... You might be able to buy a carb or set on ebay and return it in original condition if it's not a cure.
 
A couple other right side only possibilities related to new top end; leaky valve or valve way, way out of adjustment.
 
Hi all, I have checked carbs and the are in sync. I put in new diaphragms. Every hole in the carb has been cleaned meticulously, new exhaust gaskets, valves in tolerance, timing chain good, ignition timing dead on.

I have not done a leak down test but need to. BUT, I think I know the issue, when testing for a bad cdi/tci/ignition box a few months back I did not ground the plug on the right cylinder quite a few times which I have been told is not okay for this bike. I read online a messed up ignition coil can cause this issue. So that is my bet on what the issue is. The plug side that was always grounded when testing has no issue, the side that wasn’t always grounded runs terribly. Wondering if I messed up the coil.
 
^I wouldn't say it isn't possible. To test that theory (on a TCI model) all you have to do is pull the wires off the plugs and put them on the other plug. Both plugs always fire at the same time -- when one fires on the compression stroke as usual, the other is firing uselessly but harmlessly on the exhaust stroke
 
Now that you mention TCI, I think I've read of people having trouble something like you were describing, caused by a weak pickup magnet. It could be your old TCI was too marginal with your magnet. You can fix most TCI problems by just resoldering well every solder pad on the board. You can do it through the coating and it doesn't take long. Also most have four big fragile egg-shaped diodes inline with the pickup that can be replaced with 1N4004
 
I WANT TO UPDATE ALL THE PEOPLE THAT WERE ON THIS AND GAVE ME TONS OF ADVICE AND HELP AS THE ISSUE HAS BEEN RESOLVED!

I was certain I had damaged my ignition coil when testing my gonzo ignition. I purchased a new coil and tried that with still issues. Luckily the person I bought my coil from threw in a stock ignition he was getting ride of anyway. I slipped that on and bam no issues whatsoever.

I guess I damaged my gonzo ignition at some point and that was causing problems. All in all, i checked valves, went through carbs multiple times, new plugs, new coils, new exhaust gaskets, ignition timing, all just to find out I needed a a fresh ignition module.
 
fenbrancis said:
I guess I damaged my gonzo ignition at some point and that was causing problems. All in all, i checked valves, went through carbs multiple times, new plugs, new coils, new exhaust gaskets, ignition timing, all just to find out I needed a a fresh ignition module.
Click to expand...

I had a similar experience with my XS2. Seemed like a faulty coil, so I replaced that……not it. Thought the battery was weak, so I replaced that…….not it. Rebuilt the carbs……..nope. Took me a while to figure out the Pamco electronic ignition was breaking up when it got hot. So I replaced it with a Boyer ignition……and all was right with the world again! 😉
 
Hey hey hey, it’s fat Albert.

So this fixed the issue when the bike was cold bike gets warm we are back to super rich on left cylinder, very lean on the right cylinder.

Decel pop on right cylinder, smoke out the left cylinder.

There is no way the carb is this out of sync. It runs so strong on all ranges. I have gone through these carbs 3-4 times now, I have does every square inch of the carb and intake with ether/carb cleaner while running to for a vacuum leak to no avail.

I replaced the ignition with a stock module, I have checked Valve clearances, cam chain tensioner.

I have performed a leak down test, three tests on each cylinder. Both were very similar.

Left Cylinder: max loss of 24% pressure, min loss of 13%. Average loss of 16-18%.

Right Cylinder: max loss of 20% pressure, min loss of 14%. Average loss of 15-16%.

When performing I can hear air passing through cylinder which I’m assuming is just the rings being old and worn and accounting for that loss. I cannot hear any other air loss.

I am officially at a loss other that red building the top end.
 
If cylinders have similar compression, even if it is low, rebuild will not change your symptoms IMHO. SOMETHING else is happenening with carb, iggy or exhaust.
 
fenbrancis said:
When performing I can hear air passing through cylinder which I’m assuming is just the rings being old and worn and accounting for that loss. I cannot hear any other air loss.
Click to expand...
Persistent issue despite multiple carb tweaks (including diaphrams, etc) and ignition change. Exhaust hasn't been discussed, but a remote possibility exists that a restriction could produce strange things.

It would be helpful - prior to teardown - to know where the "air passing" was occuring. I'd remove carbs, exhaust and dipstick, run leakdown again and try to determine where it shows up; intake, exhaust or crankcase.
 
jpdevol said:
Persistent issue despite multiple carb tweaks (including diaphrams, etc) and ignition change. Exhaust hasn't been discussed, but a remote possibility exists that a restriction could produce strange things.

It would be helpful - prior to teardown - to know where the "air passing" was occuring. I'd remove carbs, exhaust and dipstick, run leakdown again and try to determine where it shows up; intake, exhaust or crankcase.
Click to expand...
The passing air very much sounded internal.
 
jpdevol said:
Persistent issue despite multiple carb tweaks (including diaphrams, etc) and ignition change. Exhaust hasn't been discussed, but a remote possibility exists that a restriction could produce strange things.

It would be helpful - prior to teardown - to know where the "air passing" was occuring. I'd remove carbs, exhaust and dipstick, run leakdown again and try to determine where it shows up; intake, exhaust or crankcase.
Click to expand...
Yeah I am to the point of not thinking this is a carb issue but you never know. I found a set online for cheap ($25) so thinking of purchasing, cleaning those up and giving them, a try.
 
If the air isn't leaking past a valve, the valve sealing (lack thereof) is not the source of the "popping"
 

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