Dying when Idling

So, if you read my first post, you know that this is a fixer bike. I bought it for $325 early in the winter and was able to get it running. Rebuilt carbs and bench sync'd em, rebuilt starter motor, redid gas tank (massively rusted out) and I am redoing the front brake system as we speak.

Long story short, when I'm idling the bike wants to die. After riding for a nice bit at higher velocities, the bike will idle at 2k rpm and then slowly die down until it stalls out. I'm fairly certain that it's an air/fuel ratio problem but I have no idea how to fix it. Also, I'm sure that the previous owner was messing with the mixture screws b/c the brass fittings are gone from the top.

I don't want to start fiddling around with the mixture screws because I'm not quite sure how adjusting them will effect the bike. I've looked around for guides and 'how-to' posts to adjust them but a lot of what I read is conflicting.

Another side note that may help is that it does NOT have a hanging idle when blipping the throttle. Instead, it seems to take a moment to respond to the throttle being revv'd / opened. It also kind of sputters from time to time when riding, like small pops coming out of the muffler. It doesn't really affect the ride, more like it's 'farting' haha.

The bike is a 1981 XJ Maxim 650. Any help that you may have would be greatly appreciated!!

Zach

 

I'd say you need to check your plugs, they can tell a great story.

If you can, post pics up of the ends so we can see what they look like.

They'll most likely be brand new white, or completely black the way it's running. Knowing what colour they are will help us to suggest ways for you to fix your issue.

 

Thanks for the quick reply.

The plugs are essentially brand new. I replaced them before I got the bike inspected (about a month ago).

I just pulled the plugs real quick off of Cyl 1 and 4 (easiest to get to). The plug off of Cyl 1 looks factory fresh. Bone white at the tip. The one on Cyl 4 is essentially the same, maybe a bit of beige but nowhere near what they should look like.

My phone is dead or I would post pics up.

 

Did you check your valves??? Did you properly set your floats!!! If not then you need to do this before you sync the carbs. You also have to adust the mixture screws!!! You have to color tune so that it isn't running to lean or to rich. This is a must! Since you had a lot of crap in your tank I would put 3 oz. of SeaFoam in a full tank of gas to make sure you get all the crap out of the fuel system. If you do these things then you will find that you don't have this issue anymore. There is no miracle cure. These things must be done.

 

What is a color tune?

I also did run about 4 oz of SeaFoam through the tank.

 

Okay, color tuning is when you use the mixture screws to set the proper amount of fuel to air mixture. This may be your problem! Get a color tune to check this.

 

The floats are properly set, although I have yet to check the valves.

And I'm not looking for a 'miracle cure'. This is my first bike. I purchased it as a 'living textbook', of sorts because I'm studying to be a Mech. Eng. and wanted a practical basis for application.

I want to not just ride this bike, but to have the sense of pride that comes along from doing the work myself with the added benefit of a better understanding of how machines work.

 

As far as mixture screws are concerned

In = Leaner

Out = Richer

correct?

 

that's right
2 3/4 to 3 out from lightly bottomed is a good place to start the mixture screws.
do a running sync with the tool of your choice.
you'll do the valves later but see what this gives you

 

Thank you very much!

I believe that the screws are set far too lean at about 1.5 turns (I measured them when I had the carb's off).

I'm guessing that's why the tips of the spark plugs are ultra white.. super lean.

I'm off to work, but I can't wait to get to it tomorrow to see if turning the screws out allow it to idle properly.

I'll update tomorrow with pictures. Thanks to everybody who posted!

 

What I meant by miracle cure is it isn't going to fix itself. You need to set the valves first otherwise you are going to have to do this all over again once the valves are set. There is a proceedure to follow in order to do it correctly.

 

It's not going to run for squat (or be able to be accurately vacuum sync'ed) if you have a bunch of tight valves.

Valve clearance adjustment is step 1 in this process.