Xj550 high idle

Hello first time posting here also new at this. Here's the problem bike starts up fine with choke on when u give it gas it take a second for the rpm's to come back down. When the bike warms up and I give it gas the rpm's will stay up around 2500. Give it gas a few times they will come back down. But then they will slowly start to creep back up. I just went through the hole gas in the crankcase deal rebuilt the petcock, new carb holders, and I've taken the carbs numerous time gone though them everything looks fine but like I said I'm new at this and am probably overlooking something. Anyone ever deal with something like this?? Any help would be much appreciated. Thanks.

 

Bring the idle adjust down? Set this when the bike is completely at operating temp.

Could be a vacuum leak

 

Sounds like a vacuum leak, have you tested for leaks? Did you replace the throttle shaft seals when you did the carb work. Out of sync carbs will also do that.

 

Thanks for the reply. I tried that. before this prob. I had the idel set at 1200. So if I lower them the bike just wants to die (when the rpm's go down). I replaced the carb holders from engine to carbs but i didn't change the plugs (caps?). They are rock hard and their the only thing i can think of as far as a vacuum leak?? since I've already replaced all hoses I can see. I'm not sure but I think something is sticking(maybe be carbs?). my first thought was vacuum. Is there a vacuum test i can do?

 

Your caps should be pliable not rock hard-that's likely your vacuum leak. You won't be able to detect it the normal way, by spraying starter/propane around the intake, but they can cause the issue just the same. Try the local auto parts store to see if they have some vacuum caps that fit or order from XJ4Ever on this site.

Did you clunk test your diaphragms? to see if they slide easily. Did you bench synch your carbs, running synch after that?

 

Did you RVT the new intakes when you put them on? Or use gaskets?

 

I was at the store already with them in my hand but they were a 1/2 shorter not sure if it made a difference so I wanted to check here first. I've heard of a clunk test but can't find any info and not sure what it is. (new at this). I've been looking into getting a carb synchronizer. So haven't done that yet.

 

I use gaskets

 

For sure the ones that chacal has from XJ4Ever are OE style, so they work great. Length doesn't really matter its the inside diameter that is critical-if they fit tightly over the vacuum tubes then they will seal them. I had a lean issue with my 550 and mine were badly cracked and going hard-it's a common issue as the heat over time hardens the caps and then they leak.

Clunk test is what you do after you have thoroughly cleaned the carb bores that the diaphragms slide in. You should read the article posted here called "church of clean."

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

Here's a short vid of a clunk test.

http://www.youtube.com/watch?v=HIIQb_HYTrc

The bench synch if done properly will get you 'in the ballpark' or good enough to run w/o searching for it's idle and the running synch with the YICS passage blocked sweetens the deal-or makes it run oh so right. If you want to save the $$ you can make your own synchronizer, search on here or on the internet it's a pretty simple deal.

 

I will get the plugs try them. Then try the clunk. I already found the carb synchronizer. I'll post again after I try all these. Thanks again for the info.

 

Did you replace or check the throttle shaft (butterfly) seals when you had the carbs out?
That was one of my issues.

Good luck.

 

-Carbs thoroughly cleaned; see: http://xjbikes.com/Forums/viewtopic/t=31061.html

-FLOAT LEVELS "wet set."

-VALVE CLEARANCES in spec.

-Bench sync.

-Then do your running vacuum sync, with the YICS blocked.

Your symptoms are those of an out-of-sync motor. All of the above are necessary to correct it.

 

Never touched the throttle shaft seals. So today I was gonna do the bench sync but they already appear to be in sync. Did the clunk everything works but in carb #3 has 4 small tears in the diaphram. How big of a problem??? I'm gonna look tonight to see about getting one. Should I get 4 of them? (since there all probably original) I think that they are kinda expensive 50-100$ since they come with the slide. Does anyone no where I can get just a diaphram or does it come as the set only. I also bought some new caps today but I cant test them since the carbs are off and want to get this diaphram problem straightened out. Thanks again for the info!

 

Tears in the diaphragm are a show-stopper. The carbs won't operate correctly without intact diaphragms.

Good used carbs are all over eBay; and cheaper than a new slide assembly. For the Mikunis on the 550s, the only thing available is the whole assembly. Check with XJ4Ever on new ones.

Here's an exploded Mikuni: http://xjbikes.com/Forums/viewtopic/t=31061.html the same link I posted above.

You may not need throttle shaft seals (yet) I would do the basic carb service and see where you're at. But it has to be done completely, everything in the "exploded view" needs to come apart.

But you're going to get nowhere fast if your valves aren't in spec.

I'd stick around and add more to this but I wanna ride and my 550 runs like new. Yours can too.

Get a manual and have at it. Valve adjustment: http://xjbikes.com/Forums/viewtopic/t=14827.html

 

Thanks for the reply. I don't no if this makes a difference in what u already said but I have had this bike for about 8 yrs and I've never had a problem. It has sat from time to time but always fired right up. I've done my oil changes and air filters and chains... My question is could this be a isolated incident (it is getting old but low miles) or are these signs that it is time to take care of the carbs. Thanks.

 

If you have had it for 8 years then I would say some of the required maintenance has beed neglected. Just because it runs does not mean it is in good running condition. Valves must be checked in accoradence with the manual, it is necessary to prevent enging dammage. Carb tuning should be done at the same time-cleaning if necessary. I do mine every winter, it gives me something to do durring cold weather.
I do believe you need to look into carb service and valve adjustment.

 

All gasoline has by-products (long chain hydrocarbons) that will always develop gums and create varnish if let to sit for very long-in some cases even a few weeks. All carbs should either be drained or filled with a gas stabilizer if they won't be used for a while. I even keep a small amount of stabilizer in all my carb engines all the time because gas is so crappy anymore that I don't want to risk it.

You won't find anyone who owns a boat with an outboard motor that isn't aware of this if they care about hitting the lake next year.

If you haven't checked your valves this past 8 years then follow Bigfitz's advice-they must be checked and will likely be dangerously tight. He knows what he's talking about and has helped me and many others getting our XJ's off the injured list. If they are out of spec then your bench synch won't fix the problem because they will throw off your synch.

I would look for some used Mikuni's BS28 to find the parts you need. Try Cheapbay.