#4 cylinder not firing

Hey guys.

I started my own thread on this so I would not hijack LincsTriker's:

This is an 83 XJ550 Maxim, barely 9K miles.

My #4 cylinder does not seem to be getting fuel. Here's what I've done so far:

Checked the plug. It seems to be OK. No fuel smell, no soot, no "lean" color.

Replaced the plug with a known good one, just in case.

Loosened the enrichment valve arm on #4, and raised it with the engine on. The idle came up!

Played with the idle mixture screw and it did absolutely nothing.

Pulled the plug boot on #4 at around 4K, no noticeable change in RPM. Pulling any other plug boot at that RPM makes a big difference.

Checked spark. Nice blue-white color, very consistent even at idle.

Checked float level. It's pretty much where it needs to be (comparing to pics from prev. posts)

Intake boots are brand new, so are the gaskets.

Carbs are freshly rebuilt by a mechanic (about 1200 miles ago).

What I don't understand: The bike appears to run good -- I have plenty of power, no stumbling. Of course this is my first big motorcycle and I have no idea what a 550 should feel like.

Please help! I know enough to know that this is not normal

 

Probably have a clogged idle jet. I would add some Seafoam to the tank and run it through one weekend. Use one can to a full tank. If you didn't add an inline fuel filter after getting the carbs cleaned then it is easier for them to get clogged again. The idle jet has a very small opening and a very small piece of trash can clog it. Set the idle mixture screw back to it's original setting if you already haven't. If you don't know the original setting the screw it all the way in gently so as not to damage it's fragile tip and back it out to 3 full turns. The ride the tank out and see if things improve.

 

Kewl... got a can of seafoam sitting here. So... the whole thing? Will it smoke a bunch?

 

Borrow the hose connecting the Intake Manifold to the Petcock.
We'll put it back-on after we do an experiment.

Pull-out the #4 Pilot Mixture Screw, spring, washer and tiny O-ring.
Make sure you got everything out and its stored safe.

Use one of your girlfriends Emery boards and "Sand-down" the end of the Petcock Vacuum line so it will fit ... nice and snug ... in the Pilot Mixture Screw hole.

First, try Blowing into the hose. Hard.
Then, you draw a vacuum on the hose.
Suck on the vacuum line like you are trying to siphon gas.

(The Pilot Jet doesn't let a huge quantity of gas leave the Fuel Bowl. But, even a little bit will taste bad. Have a place to spit and a good tasting rinse.
Lemonade works good.)

Duct tape the Carb Cleaner Red Tube into the hose so it won't "Back flush" and blast the Pilot Mixture Screw hole with a real long shot of Carb Cleaner.

Try suckin'-up some gas; again.
If you taste gas ... you'll have fuel when you set the Pilot Mix.

Don't forget to put the hose back!!!

 

I would strongly advise against using your mouth to siphon gasoline. It is carcinogenic and will adversely affect your health. Try using a vacuum canister, you can make one yourself. Simply poke two holes in the lid of a container of your choice. Insert the line that will need the vacuum applied into the top and push it down until it almost touches the bottom of the container (depth is not a fine point here, just isolation from where you apply the suction). Push the tube you will be sucking on into the lid but don't push it in very far, just enough to seal the hole and maybe a 1/2 inch more. Now, whatever you are siphoning will dribble into the container and not your mouth. Not a bad idea to have the lemonade standing by, gas fumes ain't pleasant either. Best case senario is to use a hand vacuum pump, say the Mity-Vac. Safer and a lot easier on your lungs.
Be careful out there.

 

550 has Mikuni carbs so don't bother looking for o-rings and washers. You won't find them. :wink:

 

The battery drain hose will fit into the pilot mixture screw hole on the Mikuni BS28 carbs. Blow it out with air and pour some Seafoam stright in if you want. We did this at a carb clinic to a 650 Turbo and it opened that carb up by the afternoon ride.

 

Update:

Took off bowl from #4. Removed pilot jet. Found turd in pilot jet. cleaned.

Holy crap. This has fixed 3 problems at once.

Now my idle is smooth as silk. The rattle I've been talking about in my previous posts is gone (YAY!). The little bit of chatter at idle is gone as well.

Bike runs like a top now!!!

I feel much better about riding it.

Thanks for all your help!