Having trouble getting the bike to the right idle speed

The Bike: 1981 XJ550
Purchased: a couple years ago with 8,500 miles on it
Problem: Have to start the bike up with choke all the way up. After 10-15 minutes of running the bike, I turn down the choke and the bike comes back down to 1200 rpm for a second before cutting out.

When I first bought this bike, I didn't have any problems with it. Sure, I'd run the choke for 5 mins to get it warmed up, but then I'd close the choke and ride without a problem. Slowly, the amount of time that I would have to keep the choke up kept increasing until I had to run the bike with the choke partially open so that when I came to a stop light, my bike didn't stall out on me. I know this isn't good for the valves among other parts of the bike, but I just wanted to ride.

Since then I've changed the following components on my bike:
- Air filter
- Rubber inlet manifold (from air to carb)
- Rubber outlet manifold (from carb to cylinder)
- Battery
- Tires
- Throttle chain
- Sparks

I cleaned the carbs two years. I checked the fluid from the bowls this year and it came out clean as well. I have not tuned my carbs. A recent call to a local Yamaha mechanic revealed that this would cost at least $500...almost what I paid for the bike. I also don't feel like purchasing the YICS tool.

I admit, I did monkey with the idle screw located between the air filter and the carbs. Here's a link to my pictures from when I cleaned the carbs:
http://picasaweb.google.com/Alex.Szerwi ... XJ550Maxim

However, I was having the same problems before I messed with the screw as after. Also, the screw is in a very tight location, so I didn't really have that much control when it came to turning the screw and fine adjustments.

To the XJ Forum gods and gurus, I would greatly appreciate any help that you can offer. Have you seen a similar problem with bikes this age? Is it just the idle screw or is it something more complicated? Do you have any tips for idle screw adjustment?

Thanks for taking the time to read this. Take care.

Alex

 

Welcome Alex!
My first suggestion is that you need to accept that, given the age of the bike, certain things need to be done to keep it happy. If you don't feel up to the task and feel the $500 you were quoted was ridiculous, you should think about getting another bike.
Here is the good news. This site is dedicated to giving folks the help they need to accomplish this type of maintenance for themselves. I hope you are so inclined. It sounds to me that your bike is well past the point of needing a carb cleaning. It would be the first thing I think you should examine. Remember, an airfilter should be replaced every year or so based upon your environmental conditions and riding location, you should be checking it out every oil change or so. From the sounds of it, you have made a fair investment in your machine in terms of parts, why not give it the once-over to tune it up for the season (and most likely eliminate your running/choke issue). Since I'm not 550 savy, I'm only going to offer general advise and I expect some of our 550 gurus will help you with the finer points. Glad to have you aboard, hope we can help nail down your problem. Ride safe!

 

Last winter I pulled the bowls off my carbs. They were every bit as clean as yours.

When the weather got nice and I had my sync gauges in hand I went to tweak it. I found that adjusting the #1 pilot screw had no effect whatsoever - I could bottom it out or even remove it from the carb and everywhere in between no difference. Overall bike ran well so I didn't worry about it, could wait for winter.

# 3 needle valve started leaking. Not a huge surprise, had been leaking a bit before and I'd got it to stop last winter by just cleaning the seat. Pulled the carbs this morning to put needle valves in.

Since the rack is off I had a look at the pilot circuit on #1. There is a little well the pickup tube for the pilot goes into. Filled well with carb cleaner - it did not drain down into the bowl. Turns out the little passage from the float bowl to that well was plugged up. No fuel at all to the pilot jet.

I can imagine that a similar problem on more than one of the carbs might lead to the issue you are having.