Help! Cylinder 1 not firing at idle

So I get my colortune plug in the mail and go to work on the my bike. Followed the xj cd instructions exactly, and all was well from 4 down to 2. Not sure why I started with 4. That was the side of the bike I was on.

Anyway, I get to one, and find there is spark but there's no flame. I shouldn't say no flame. Every once in a while there is a small combustion of fuel, but nothing like the other three.

When I cracked the throttle, combustion started but the motor ran rough. Very strange. This was the same with setting the mixture screw to any position. From almost completely closed, to almost way out say 6 or 7 turns. There was very little combustion.

So, I had my brother hold the throttle open until I had a flame, and set it the same as the others. Bike runs great and idles fine.

If I pull the plug wire on cylinder 1 at idle, no change. If I pull any others, bike starts to spudder and stall.

If I pull the plug wire on cylinder 1 with some throttle, the bike starts to spudder and stall.

Compression test was OK as it nearly blew my thumb off!

I cleaned the carbs perfectly a month ago, bench sync'd them and check teh float levels. All great.

Can anybody help?

 

You are on the "Wrong Side" of the Blue.

There is a Point where there is enough Fuel and Air to produce a Mixture with Air~Fuel Ratio that will be Bunsen Burner Blue ~~> ON THE LEAN SIDE.

YOU need to have the Bunsen Burner Blue ~~> ON the RICH Side.

Tune ... through ... the "Early Blue" ... Until that Blue starts to break down and become Orange~Yellow and (Misfire).

From there you ease-on-back to the BLUE -- ... and, You're IN!

 

Rick,

I'll try it again tonight, but I'm sure I turned that screw almost completely in, and almost completely out. Almost no change at all at idle, except for a couple of spurts. or blue, white, orange, almost all at the same time.

 

I'm wondering if something got stuck in the idle needle?

 

There's the Pilot Jet and the Passage above it.
There's the Pilot Air Jet and the Passage for it.
Where the Pilot Air and Fuel intersect to draw-up the fuel.
The Misture Screw where it gets drawn into the engine.

Something's clogged.
I've seen it be as easy as finding a stuffed closed Pilot Jet or a flipped O-ring.
Sometimes the Passage above the Pilot Fuel Jet is clogged and needs to be probed and blown-out.

 

Oh man, the last thing I want to do is take out those carbs again!

OK, I'll have to get into # 1. Do I have to go in through the top or bottom? If the bottom, will I need a new gasket?

 

Could it also be the sync? But that would mean the butterfly would have to be litterally shut, wouldn't it?

 

Possibilities???

Wrong Jets. PO's will slap-together anything to get a bike to run prior to a sale.

Wrong Pilot Mix Screw. Same deal.
Weak spark.
Low compression
Tight valve
Oil fouling mixture

Since you have 3 - OK and only that 1 not behaving ... I'd look at Spark, and then Fuel Supply to that Screw.

 

Previous Owner is ruled out. It's my best friend's father and he's a maticulous when it comes to stuff like that.

Spark seems to be the same as the others as viewed through the colortune. I pulled the spark plug and grounded it. looks like a nice solid spark, but for the heck of it, I'll swap out the plug for a new one tonight. I'll have to pull the carb if that doesn't work.

 

Not so fast.

Stop-off at a Pharmacy and get a Ear Syringe.
Shoot some Carb Cleaner right into the end and get some cleaner stored in the bubble.
Pull-out the Pilot Mixture Screw for the one not hitting.
Power Flush by douching the Pilot Passage through the Pilot AIR Jet (or removing Air Jet).

Pull Carb Drain Screw
Pull Pilot Mixture Screw.
Remove Carb Top and Diaphragm Assy.
Put tip of Syringe in Pilot AIR Jet and Close-off Pilot Mixture Hole with finger.
Squeeze Carb Cleaner into Air Passage.
Carb Cleaner should drip from Bowl Drains
Finger should feel Carb Cleaner in Pilot Hole.

Use Syringe suction and Flush-out Passage.
(The idea is like using a Plunger to unclog a toilet)
Move the Carb Cleaner in a flushing manner to dislodge any clog.

Button-up.
Test.
Cross fingers.
50 ~ 50

 

And the story continues. I went home last night and didn't have a chance to get the ear syringe thing. So, I decided to give it another try. I pulled the mixture screw out, and put it back in, 2.75 turns out from closed. I put the colortune in and I've got some flame. I then tinkered with it until i got a blue flame at idle. then, I opened the throttle to 3000 rpm and tinkered some more until i got relatively blue flame. It's funny though, it's almost a purple flame with spirts of white flashes... Kinda like it;s going ultra lean every few seconds. It also hesitates. But when I put the normal sparkplug back in, the hesitation goes away.

Anyway, it is idling better, and there is not need to give throttle to get it to start.

BUT, if I pull the plug at idle, there is no change in the motor. Is this normal?

 

How do you mean, "Pull the plug"?

Just take off the Cap?
You don't take the Plug out ... right?

 

sorry, I meant the plug wire. BUT WAIT! There's been some developments.

Last night I pulled the mixture screw from # 1 and inspected. I then put in a new sparkplug.

Next, I sync'd the carbs using your Oldschool vacuum setup. Prior to this, I just did a bench sync. I found that hey were all over the place. So, after they were all sync'd, I then colour tuned and low and behold... we have combustion!

It runs so smooth. Starts quickly, idles wonderfully.

Thanks guys, and Rick once again, thank you for your oldschool vacuum setup.

 

Worked like a charm ... didn't it?

Just think of all those tuned-up bikes if they tried it!

 

Yup. Only issue I had was the needle on the vacuum gauge still bounced around.

An easy fix was, I just folded the pipe a couple times, freezing the presure in the pipe. I tested it a few times, and got the same reading each time. So I just did that with all 4 cylinders.

I'm thinking the fuel filter I put on may have been too big to baffel the presure.