Carb issue has me stumped

Ok Guys, this one has me stumped.

Background:

Carbs cleaned/rebuilt/synced/colortuned a year ago.

At the end of last season I started to get a popping on deceleration.

Wasn't easy to get started this season, even with a new battery installed.

I did get it running, and put about 10 miles on it for the initial ride.

It still pops on decel, and doesn't like to idle. If I put a slight amount of enrichment on, and I'm talking slight, maybe moving the lever 1/8" to 1/4", it will idle just fine and run up to 4,000rpm. Still pops on decel.

above 4,000rpm it runs just like it should, like a scalded ape.

When I pulled the plugs last season they were all black and dry (not oily). I haven't checked the plugs since the 10 mile ride, but will as soon as I get my tools here. Going through a divorce so my stuff is scattered across the county lol.

When I get a pic of the plugs I'll pop it up on here.

The part that has me stumped is the running rich, but when it's ticking over it acts like it's starved for fuel. Also the sudden onset of the symptoms at the end of last season.

I can't get it to idle without enrichment to plug the colortune in to check the mix, and I really don't want to pull the carbs if I don't have to because my new house doesn't really give me a dry spot to work on it. I think if I use enrichment for idle then my colortune will be orange/yellow (which judging by the plugs it would be anyway) and there would be no way to adjust with the enrichment on.

Also, I rebuilt the starter, added a new battery, and it doesn't want to fire off. But I can bump start it just by walking and releasing the clutch.

So it could be a carb issue, an electrical (power) issue, or a combination of the two.

Advice on what to check/where to start?

Thanks in advance for the suggestions.

 

What I mean by "runs up to 4,000rpm" is that it will idle fine and i can take off slow, medium, or fast and it will accelerate the way it is supposed to. Without enrichment it is jerky/acts almost like it's missing, until i get above 4,000rpm.

 

Have you checked your intake boots for air leaks?

 

Crappy gas? I hope I don't muddy the waters too much, but that would be a good thing to rule out...

 

Here are the plugs as I pulled them today. They are no where near as dark as they were at the end of last season.



Intakes were done with the rtv/innertube treatment when I recommissioned the bike, still no leaks.

Also checked float levels on the bike before I started it this season and those are good to go.

 

wow... our problems are almost identical, i had to pop the clutch to start mine.. until i found out i can hold the start button down and slap the battery cover. BOOM starts right up. it also doesnt want to idle. so i hold the gas ever so slightly at stops. ( ive been doing this for a long time so im used to it). but it runs smooth besides that... i also have a poppin sound while down shifting.. but isnt that just back firing? maybe im just used to it.

 

Popping on decel isn't really a "backfire", which happens through the carbs.

It IS rather, unburnt fuel that passes from the cylinder (where it is supposed to ignite) to the hot exhaust (where it ignites and makes the popping sound)

As for the gas, I buy almost all my gas from the same station for all my vehicles. For over 14 years.

The bike has never seen a drop of gas from any other station. I use StaBil as soon as the temp gets down to 40*F, so I trust the gas.

Plus, this started happening in between fuel runs, and has been filled twice since the problem started (once at the end of season, but again, I use Stabil almost all the time)

 

Last time I had same symptoms I had a loose carb hat.

 

Can you not get it to idle by turning the idle stop screw in, just for the purposes of getting the colourtune in to see what's going on?

Have you checked that the idle mixture screws are still where you set them at too? I find mine are very, VERY easy to turn & although I've never had one vibrate out of position I guess it's possible & simple to check. Also might be worth checking the air filter isn't damaged & the exhaust isn't leaking anywhere.

Just thinking of the easy/free stuff to check first off, personally though I reckon if there's definitely no air leaks anywhere (including the sync port caps too) or loose parts it'd be best to pull the carbs to at least confirm the idle circuit is still clear & the sliders still clunk etc.

 

Air leak, somewhere, or maybe a split diaphragm.

 

Boy, sure sounds like a sync tube cap air leak.

My XS11 would do just that, until I replaced the sync tube air caps, that I got from Chacal @ XJ4Ever.

Now, 1/2 choke, twist the throttle twice, and hit the start button, and VROOOM, the Scorpion roars to life!

Rosie, will start with 1/8 choke and a start button tap, and she roars!

Def, look at those caps!!

 

From the forum search it sounds like it may be an exhaust leak that I haven't noticed. I think I'll replace the exhaust gaskets and see where that gets me.

I'll probably change the vac caps anyway since they're cheap enough.

I'll let you guys know how it turns out in a few days.

 

WOW here we have a XJ wizard that's having the same problems I am having. It don't want to start. As I said before these motorcycle defy all logic. You can have everything you need and the bike doesn't want to start. I am surprised that Fritz hasn't told tskaz to check the valves as they are too tight.

 

That would be because I already know that Kaz knows enough to have his valves in spec.

YOU on the other hand already know your valves are tight but are apparently afraid to do anything about it. The only thing that defies all logic is why you continue to post the same old lame rant rather than actually fix your bike. Get back to us if you ever decide to do something besides just rant about your mechanical ineptitude.

Kaz, it does sound like an "intermittent" vacuum leak; the advice to replace the vacuum caps and check your diaphragms over is sound; I'd add maybe making sure you don't have a loose resistor core in one of your plug caps.

Also, it's a new season--- pop in a NEW set of plugs.

Oh, and one more idea: flush/drain your carb bowls. Open the drain screws, let them run dry, then open the petcock and flush some fresh fuel through. (Be sure you have LOTS of shop towels deployed and do it outside because it will make a stinky mess.) It's possible that there's some crud in a float bowl obstructing the enrichment tube.

 

Yep replace those exhaust gaskets. A very likely cause of the decel popping. Take it easy on those nuts/bolts though as they are fragile. Re-torque after a period of riding.