Yamaha XS 650 Help

[vicco27]

I have a 1983 XS650 that will start fine using the enricher however the enricher does not seem to increase RPM the way it should, anyway the only way to keep the engine running until the motor is hot is to increase the idle speed by turning in the idle stop screw about 1 to 1.5 turns, eventually when you blip the throttle the motor will start to free wind on its own, when this happens you can turn the idle stop screw back out the 1 to 1.5 turns and the engine will idle fine and the bike will operate fine until you go to restart it again when it has gotten cold. The carbs were not on the bike when I got it ( they were apart in a box ) The carbs have been rebuilt, the diaphragms are all good an the intake adapters are new, I have had my Carbtune on it and all checks out fine, the mixture screws are set at 13/4 out from seat + or - a little, the air boxes are sealed, I can't think of anything else except. HELP PLEASE .

[Yammer Dan]

Vacum leak at base???

[Yammer Dan]

Spray some WD-40 or Carb Cleaner in there while it is running and see if it make it speed up. If it does it is leaking somewhere.

[mraf]

Sounds to me like your choke is plugged up. When you say free wind on its own do you mean gain rpm without turning throttle? Were the carbs boiled out?

[MiCarl]

I have an XJ650 and have had similar difficulties when the idle circuit is set too lean.

 

Here's my theory. When lean it runs better hot, so the idle creeps up and you turn the idle screw back. When the engine is cold the lean condition is aggravated so your idle speed is then too low.

 

I know on the XJ650s Yamaha changed the pitch of the pilot mixture screw in 1982. While a 1981 XJ650 came from the factory about 1 7/8 turns out the 82 and beyond were in the 3 turns range.

 

Because of the age, butterfly shaft seals often start to leak, leaning the mixture out more. A lot of the 82-83 650s need to be set to 4 turns or so to get a consistent idle.

 

I believe the XS has Mikuni carbs vs. Hitachi on the XJ. Still, I'd try something like 3 turns on the screws. Also, a colortune will help a lot.

[vicco27]

Yammer Dan! I sprayed ether around the base of the carbs early on and that is why we put new intake manifolds on, we haven't sprayed since, we will do it again. mraf! Yes the carbs were boiled out thoroughly twice, RPM will gain and hold a little higher than the throttle blips highest RPM until you can get the idle screw turned down, I rode it a couple of times when it was doing this and I could let the clutch out with it in gear an that would bring the RPMs down and they would stay down until you accelerated again. McCarl! I have tried going out past 3 turns on the idle mixture screws but it doesn't seem to make a difference, I don't remember the carb brand names but they are the ones that have the diaphragm operated slides, As I said before I have had the carbtune on the bike and it seemed to adjust out fine, although the adjustments were made with the engine hot after it had gone through this transition period. The bike only has 7.846 miles on it so I can't believe the carbs are wore out and they seem like new. The gas tank had some rust in it and the carbs were taken of to clean, the owner had a brain aneurysm and died. I bought the bike from the mother who knows the bikes history and was willing to bring me up to date on what took place to park the bike. Thanks all. I'll look again for a vacuum leak and retry the ether. If anyone thinks of anything else let me know. I'll post if I find anything.

[MiCarl]

I believe the XS has Mikunis.

 

If the idle screws aren't having any effect the butterflies are probably too far open, so you're getting fuel from the mains.

 

You've either got plugged up pilot circuits or air is getting in somewhere. Butterfly shaft seals? I know the mileage is low, but the rubber is getting pretty near 30 years old.

[mraf]

I worked on a 920 Yamahas pilot jet once. I tell you the hole in them were almost non-existent! Had to use a piece of wire so small to clean it out that I thought that it wasn't drilled out at first. There are technical bulletins on cleaning the tank and carbs on the Yamaha site. Must have been a on going problem with this model. Mccarl is right about the butterfly seals. They say to not subject them to carb cleaner for fear of damage. Plus 25yrs old bike.

Edited May 28, 2008 by mraf

[vicco27]

Gas tank was scoured out with small sheet metal screws suspended in carb cleaner, I installed new shut of valve filters and a new rock type in line fuel filter on fuel line, pilot jets were new, As soon as I can I'm going to pull everything of and start from scratch methodically checking each problem myself rather than having my son do some of it. Thanks Again. .

[eagleeye]

I can't answer your question, but I'd suggest going over to the XS650 Garage and ask there. You might have to regester.

Steve