Runs good then runs bad

[J ray]

81 xs650. Started it up this week after changing oil and filters, rotor brushes, new fully charged battery, new gas, clean tank, clean carbs (38's). It started after just a few kicks but was idling rough. I thought maybe the air was too restricted, having 81 air filters on the bigger carbs, so I backed out the mix screws 1 turn. This seemed to solve the problem so I test drove it and it ran real good for about a mile or two up and down highway suddenely it seemed like someone cut the gas off then the engine revved down to an idle. I was able to run the bike back home in 1st gear at idle.
I can get it started with a kick or two but it just idles rough. It dies or pops and sputters when I try to bring up the revs.
I've checked the timing, pick up coil, valve clearance, intake for leaks, cleaned connections, tested the ign coil, air filters are good. I haven't tested compression but I get alot of resistance on the kicker and no noticable increase in the kick resistance after adding a little 50w to the cylinders.
I did find that that the right cylinder plug is dry and sooty (before oiling cyl) and the rev won't change after shooting starter fluid down the throttle barrel on the right side but that the left side plug is tan and that the rev slows after starter fluid is used on the left carb.
Cyl 2 runs cooler than cyl 1.
Does any one know just wtf is going on here?

 

[xsjohn]

Sounds like the ole carb cleaning thing to me...........pilot circuits.........

xsjohn

 

[J ray]

The thing is I've cleaned them twice I] by the book.

 

[Sundie]

Just a *really* stupid question, an only because it wasn't in your list, and i've been caught by it before. And your description is exactly what it sounds like.

Petcocks on? fuel flowing freely?

 

[J ray]

Yes there's fuel getting in and the fill cap vent is clear. I know everything points to a fuel or mix problem but but i can't find where or how.

 

[Sundie]

How about float bowl level? If it's low, same deal - you can idle, but no throttle response.

 

[J ray]

Both floats set to 27mm and no leaks.

 

[xsjohn]

27mm is for BS34's......and only the 80's with the brass floats.......you said bigger carbs.....(38's).....bet 24 is right..........

xsjohn

 

[J ray]

Oops thats what i meant, 24mm . I've checked them twice.

 

[Tomterrific]

"...the right cylinder plug is dry and sooty (before oiling cyl) and the rev won't change after shooting starter fluid down the throttle barrel on the right side..."

Try a new spark plug on the right side to get her running again. You can also look for a loose jet, loose or leaking needle valve (lets gas into carb) and a leaky float with fuel in it. Something fouled the plug, either excess gas or bad ignition. I supect a carb problem.

FWIW, I used #6 heat range NGK while I sorted my XS. It came with #8 heat range but these are too cold and carbon fouled quickly. I used the proper #7 but I was not running the bike long or hard enough to keep these plugs clean so I used the hotter #6 and they worked well and stayed clean. I use 93 octane premium fuel so I didn't worry about detonation and engine damage from the hotter plugs.

Tom Graham

 

[retiredgentleman]

I believe xsjohn has zeroed in on the problem area. Have you actually removed the pilot jets and looked closely at them? A magnifying glass will help you check if they are partially plugged.

Set your mixture screws at about 2 and a half turns for a starting point. Dead cylinder method is a good way to adjust the mixture screws.

 

[J ray]

I'm telliin ya guys, all the jets are like new clean and the needle valves new from mikes... the carbs don't leak and they're clean...they HAVE to be, I did them both by the carb guide. Is it possible there's some shit caught in the pilot passages that chem dip didn't dissolve??? and pres. air didn't blast out???
I'll try a hotter plug.

 

[xsjohn]

In case you didn't.........Best to probe the 3 tiny holes in the throat with like a .010 guitar string crooked to get up in there.......and blast the pilot circuit for all dirrections...........holding your finger over the other open holes........

And just in case.......well for the BS34's anyway.....some customers were going nuts with replacement bowl gaskets.......seems there was some holes not punched out or the punched places were not opened......

xsjohn

 

[J ray]

I did the 3 tiny holes. Reused the old bowl gaskets (were good), could a leak around the needle jet seat be a problem? Wouldn't it just leak gas out the throttle bore if there was a bad seal? (no leaks). Could the ignitor be to blame?

 

[xsjohn]

Did you clean every connection on the harness including the multi connectors and kill switch and fuse box and use dielectric grease.....andthe 2 wires at the coil.....mine acted up when I first got it until I did that.......1980......xsjohn

 

[luketrash]

As an owner of several stubborn vehicles, the first thing I do is figure out if it's spark or fuel.

Hook up your bike to a timing light on each coil wire just to watch the strobe light. If it's flickering out when it's missing, you've got ignition problems. If that's not it, THEN worry about fuel. Figure out if it's rich or lean if it's fuel and go from there.

I have a ColorTune spark plug (thanks to being involved with british cars) which allows you to see the color of the combustion.. It's a temporary glass spark plug you can see though. (video example:

) The color tune will burn bright blue/white if you're lean and bright orange if you're rich. Somewhere in the middle (bunson burner blue) for correct fuel mixture.

A timing light and a ColorTune are my quickest way to sort out issues of spark and fuel...

 

[J ray]

Luketrash, My timing light does miss when I try to bring up the idle. I think theres an '82 pickup coil on this '81 because the 3 wires at the coils' connector are different than what clymer says they should be for '81 (match '82 however) The 82 pu coil is supposed have slightly higher ohms than the 81. Problem here?
Also, when I retested the pu coil and checked connections there, I had to move the gas tank a little and spilled some gas on the connector from the fuel line. I don't know if this is coincidental but I started it up afterward and it ran like it should only to run crappy and die after about 30 seconds.
JR>

 

[J ray]

Anyone else that can offer something helpful, i'd like to hear it.

 

[Ottis]

J Ray, Im definately with these guys on the fact that it is most likely the carbs. When was the last time that they were cleaned? These carbs have so many small passage ways in them that you would be surprised how little it takes to clog one of them and make the bike run like total ass. I would be happy to help you any day you have some time. A second set of eyes is sometimes all it takes to get things figured out. I have my bike in pieces here, if you want get ahold of me and we can throw these carbs on your bike and see what happens. Or I will go through the carbs with you and see what it is we have stuck in there. If you checked for leaks and the other issues then that is leading me to believe that we are spot on with our diagnosis here. Electrical parts for my bike are all laying here too if we end up thinking in a different direction. Its up to you, you know where to find me. I will be around all night tonight and most of saturday if you want to get something done this weekend.

 

[shaas]

It is a bit of a puzzle. The dry plug suggests no fuel. The lack of response when starting fluid is sprayed implies that there is no spark. Intake valve not opening?