No "Big Bang" on Cylinder #3

The bowl level is constantly good, the pick up tube is clean.
Weard ah?

 

Lets narrow it down. If that plug is truely dry and shows no signs of wet gas. Go take a deep breath and lets try it again. Fire it up and if it is not running on number three. OK pull the vacuum line to the petcock and spray some carb cleaner in the vacuum port. Does it fire now??? If yes its a fuel deal in that carb. So lets see whats is doing. I would also do the unlit propane torch trick. Flood the area around that carb and carb boot and see if you can get the cylinder to fire. If it does your looking at a serious vacuum leak. An out of place / Blown intake gasket can do what your describing.

 

I was going to say #3 has the vacume on it, that could be leaking.
But if the plug is dry that doesn't make sense.

 

I second checking the coils. Maybe an easy way to check coils out would be to swich the coils. If the dead cylinder moves, you've got a bad coil. Could also pull the #3 plug and check for spark. If you don't have a nice strong blue spark, bad plug or coil.

 

I see this post has been dead a while, but I was wondering if a solution was ever found. I have an 82' xj750 that is doing the exact same thing. My carbs have been rebuilt by a guy that I trust, have been bench tested and sync'd. I have replaced the 2nd 3rd cylider coils, which was omhs tested and spark tested. The bike will not start cold. It will start with starter fluid. Once it starts up and warms up, if it is shut off it will start right back up again. I'm sure I've left something out feel free to ask any question. Any help would be greatly appreciated. thaanks

 

Did you verify the starter jets are perfectly clean? This is very common problem and rebuild does not always include a surgical cleaning. Hard cold start is almost always this problem....

Clean enrichment circuit
http://www.xjbikes.com/Forums/viewtopic/t=8918.html

 

Zane,
that thing happened on my bike as well. Everything, absolutely everything was clean but some of the cylinders didn't fire up properly. Then it turned out that the original jets were too small for my bike. I've put larger jets into the carbs and she's fine now.

It might be the case when you're running with pods, open mufflers.

 

I'll have to check the starter jets.

ZsoltK...I've got factory exhaust on it that is in near perfect condition. but I suppose it could still be restricted fuel flow of some sort. Thanks guys I'll give these things a look, and see what happens.

 

Zane,
I couldn't find the problem yet, I haven't touched her in awhile. Mine start with no problem but cyl #3 will not fire up. I will take the carbs out again once I fix a few personal issues .

 

I got cyl #3 firing. May be a common problem. It seemed the It was flooding out. The float was not shuting off the fuel. All floats were set to factory. All floats did float ( I checked them). I switch the float, needle and seat with a working carb on a working cylinder and the problem did not follow. strange huh. With the carbs off the bike I pulled the bowl for the cylinder 3 carb, hooked up the fuel line, held the float with my finger and it worked, so I set that one float 1mm lower the the rest and it fired right up. Why that one cylinder wants to be lower that the rest I do not know. By lower I mean 17mm as the rest are at 16mm I know that seems high, but since you set the upside down, when its right side up its lower. But it still will not start cold. It wouldn't start after pool league last night, I had to leave it. Going back today to try it while its warm out. If not I have to truck it. Needless to say I am not happy. Its going to be 75* here in Baltimore tomorrow.

 

I know I just Posted but I have to add, the enrichment circuit is clear Its been check twice now, and in addition to what I posted above the float levels have been check and even set a touch higher to allow for more fuel flow, as advised by my motorcycle guy.

 

Mine is doing the exact same thing on #3??? the pug is black and dry???

 

It has probably been mentioned already but most of the time the vacume for the petcock goes to #3.
If the diaphram in the petcock is leaking it can pull extra fuel into the #3 carb causing flooding issues.

 

My petcock was leaking, i replaced it with a on-off-res type.

 

When I had this problem on my Nighthawk 650 I found the cause to be my #3 wire. It had hollowed out a hole in the wire where the pin from the coil fits creating a bad connection. My plug was dry because of the other cylinders vaccum created pulling the #3 fuel into the air cleaner. The fix was trimmimg 1/2 inch off the spark plug wire going into the coil creating a good connection. Hope this helps

 

OK, i exchanged #2 and #3 wires, #2 was hot and #3 cold. so the wires are OK, I also swaped the plugs and same thing, so the plugs are OK. I pulled the carbs and tore them apart. i am cleaning them up again. They were clean, but now they are going to be REALLY REALLY clean and shiny, i am polishing all the brass, inside and out. I am going for the surgical clean this time!!! One thing i did notice is after i bench sync'd them i sync'd them on the bike. the #3 butterfly looked "more closed" than the other 3??? Maybe i had the sync wrong on the bike???

 

pull your resistor caps and check the contacts while your there they have a tendancy to corrode at both ends dont forget to put down some white grease... one other thought, i ran into a problem where i had 3 boots leaking at the motor. remove re-seal... now all good.

 

i checked those, they were all loose, #3 actually came apart, there was a very small brass "washer" and the resistor (small white tube), i put the washer in first then the resistor. is that correct? i did not clean them up, i will clean and lube!!
EVERYONE, THANK YOU FOR ALL THE HELP!!!!
WHAT AN AWESOME PLACE!!!!!

 

now what you'll find is that you will get an inconsistant burn on them ... you'll see in my signature that i replaced my wires with 7mm accel copper by chopping into the coil packs and replaced my resistor caps .. thats the only way i could get a consistant even burn on the plugs.. total cost should be under $40