Very slow return to idle - XJ650RJ

In the past couple of weeks my Seca has developed an idle problem. It runs well, except that it does not immediately return to idle when the throttle is closed. Typically, as I come to a stop, it idles at about 1700 rpm, and then slowly drops to its usual 1050 over about 10-15 seconds. Blipping the throttle does not cause it to drop any quicker. Once the idle drops to 1050, it stays down and I cannot get it to "stick" by throttle blips. Ride to the next light, the idle is back up.

The twist grip, cable and linkage are all well lubricated and seem to move quite freely. I tried adding Seafoam to the tank; a half tank used has made no difference.

I've had the bike since new (62K mi), always kept it garaged. I ride it most days to work, using Stabil starting early November so that when Dec-Feb make it too nasty to ride the fuel is ready.

Is this caused by a sticking piston valve in a carb? What else can I look for?

 

If you checked the cables (throttle and choke) and they are lubed, not damaged, not pinched anywhere and free moving then:

You probably need to clean your carbs if you have not done so lately.

Seafoam and any other additive may help but they will not magically clean your carbs for you no matter what the bottle says.

I occasionally have the same problem after highway use, and I know that "I" have not cleaned the carbs since purchasing it last summer.

Also sometimes tiny pin holes in the carb boots and/or air box can cause problems. Check that after/while cleaning carbs.

 

If it isn't the throttle cable haning up, you may want to synch the carbs. Mine acted the same way before I synched my carbs to make it run better and it settled right down when I closed the throttle, like it should.

 

Id shine up the throttle shafts with 1500 sand paper and shine it out with a chrome polish.

 

Id shine up the throttle shafts with 1500 sand paper and shine it out with a chrome polish.

 

Thanks for the quick responses and good ideas. I just got my sync tool back from my son last night, so I'll check that first. I'd REALLY like to avoid rebuilding the carbs.
I also found this: http://xjbikes.com/Forums/viewtopic/t=1 ... +test.html which seems to apply to my symptoms, especially: "When you are done, there should ZERO drag. Nothing preventing the diaphragm from raising the piston when vacuum is present. And, NOTHING from preventing that SPRING and NO VACUUM from allowing those slides to slam-shut for some ABSOLUTELY wonderfully controlled engine braking." One of the downsides of being slow to idle is that sometimes I seem to be slowing the engine with the brakes.

Any chance I can polish those slide bores without pulling the carbs off the engine?

 

You *can* pull the slides out with the carbs on the bike, but, it would be very hard to get down into the bore while they are mounted. You also have the problem of not getting ANY dirt into the carb, where you would need to clean then anyway. I'm not recommending it.

 

I wanted to verify that the pistons were actually sticking before I took the carbs off the engine. When I pulled the diaphragms, it became apparent that I actually had an air filter problem. Carbs 1 and 2 clunked very nicely, but 3 and 4 did stick slightly, due to a slight film of red oil and dirt on the intake side of the piston. Since this problem began a few days after I cleaned and re-oiled the K&N filter, it's clear that I over-oiled the filter AND that the filter really is not stopping all the dirt. Cleaning the pistons and bores with carb cleaner and soft cloth removed the oil and dirt, and now the engine returns to idle properly. All four pistons have red stains on the intake side that does not polish out with 600 grit silicon carbide paper. The bores are clean, shiny and naturally wear-polished on the engine side.

I'll be going back to a standard air filter now. The renewable K&N seemed like a good idea as the bike got older and parts started getting harder to find, but I can see that it is not getting the job done. Thanks to all for your ideas and help.

 

Epilogue:
This is a very old thread, but I just came across it again in a Google search. The cleaning mentioned above was not a complete fix, but apparently I never posted a follow-up.

The slow return to idle problem returned and persisted until I replaced the throttle shaft seals. That stopped the leanness caused by air leaking in past the seals.

The bike has been sold, but I'm told that it stills runs great today.

 

This right here.

After bench syncing the carbs and reinstalling them I had a hanging and sometimes runaway idle. Running Synced them and now she’s right as rain