running last night. won't start today

With acknowlegements to big fitz and chacal:
http://xjbikes.com/Forums/viewtopic/t=31061.html

Www.xj4ever.com

You should find all the carb id stuff you need there.

 

The pilot circuit provides fuel when your throttle is closed, such as when idling, and continues until the main comes online. It's a tiny jet, tiny air passage, and is controlled by the adjustment screws on top of your carbs. This is often a problem because the passages and jets are so small that they easily get blocked. Also the o-rings which seal the adjustment screw can wear out or be put in wrong by a PO.

The main reason I didn't think it was a float issue was you had said you completely went through the carbs, but it isn't complete until you've done the wet set and to be fully complete a vacuum synch is needed. The wet-set is verification that your float height adjustment via the tangs is accurate and has all four bowls within spec. All that being said I still think your symptoms point towards ignition issues. Sometimes you can have compounding issues like both ignition and carb, and when you fix one (say the carb) the problem can change but not completely go away. It seems like that happened to you with the misfiring changing it's pattern.

If it's only running on two cylinders you will know as it will sound like a crippled horse trying to gallop, on three it is hard to tell by the sound but you can def. tell when riding. Easiest way I know to check is to start it up and just keep feeling your pipes, at first they won't burn you but before they do you will know which ones have fire in the cylinder because they will start getting hot and your dead(s) will only get warm and you can still hold the pipe.

Having low float levels will also cause it to run lean on those pots, so you can check your plugs as well and look for lilly white insulators and dry plugs.

 

Oh crapppppp! I did the pilot jet at the bottem but not the one at the top!
Kk I'm going to pull it out to set the floats. That is what u mean by wet set right?
And I checked out the specs for pilot screw. I have an air cooled 750 but not sure which exact one it is..... So I'm guessing 2.5-3 turns out?
Also, a little lost on the vacumme sync still... Care to explain?

 

Oh and I'm an apprentice auto mechanic so I can tell when I'm running one 3 cylinders. And yea I am having a very weird problem which ha changed after cleaning carbs so either it's the floats/pilots, or it's ignition as well. Totally agree on that

But I pulled my plugs time and time again. All looks healthy. So no lean and no rich

 

Yea wet set procedure is to have the carb rack perfectly level and using a clear tube on the drain make sure the fuel (or whatever your using to check it) comes up to the level of spec right below the top line of the bowl. You can check it on the bike but most say the carbs need to be level and that's hard 'on' the bike.

2.5 is a good starting place, mine are sitting about 10minutes past 3-or 1/6 a turn past 3-my 550 has tended to be lean so that's its happy place.

Vacuum synch means you get each carb at the same level of vacuum with the engine running. A bench synch of the butterfly valves gets you most of the way there, but because there can be error in that technique and each carb is experiencing a unique cylinder vacuum-they won't be exactly the same. This means they won't be contributing equally to the fuel charge and so your cylinders won't all be pulling equally hard on their power stroke. By using a vacuum synch tool and matching all four carbs you eliminate this problem. The difference between a well bench synched motor and a well vacuum synched motor is the smoothness and beautiful rhythm that vacuum synching achieves. You can hear the difference as you bring them into line. Obviously you can ride a bike that hasn't had this done, but imagine it's like having four horses pulling a wagon and one or two aren't pulling as hard as the others-it's not efficient.

Do a Youtube search for vacuum synching carbs and look for one with an XJ- you can see the procedure being done. It's really easy with the right tool.

 

Cleaned the pilot circuit. Wasn't plugged before. Didn't make a difference.

Gonna check floats now

 

Ignition coil for 1&4.
Specs say 11k ohms which ignition coil 2&3 show.
But ignition coil 1&4 shows no connection at all.


Need a replacement.
Thanks for all the help. It was one of the last things I expected

 

Good work! Curious how this suddenly happened "overnight" though?

 

My brain clicked after a few drinks. Clicked OFF that is.
I knew it wasn't the carbs from the start, or at least it didn't fit partly because I ride it every day. But it was sparking just fine so it doesn't justify ignition issue.
But when I have rebuilt the carb, wet set the floats, and it still ran like crap, I knew I had to stop assuming, and start following some instructions and finding the specs and getting down some numbers.
While swapping the ignition coils did change the way it ran, it didn't solve or make the problem worse.

But someone posted here that I should grab a manual. And I already have a Hayes manual. So I read up on the ignition system and found some specs for the resistance for the ignition coils. Mine didn't fit at all. No need to give a crap if there's spark or not. It could still be more than just the coil. Maybe the tci or pickup. But for now the coil needs replacing for sure.

 

glad to see you got that ignition problem sorted out. you're still gonna want to get the carbs vacuum synced, a vac sync is never a bad idea just to ensure everything is working equally across the cylinders.

 

Is there a way to vaccuume sync without paying big bucks? Home made tools or smth? Once cylinder at a time?

I want to color tune as well.... What do u think of that?

Maybe someone local would have the tools?

 

Carbs should be balanced by pairs, at least. If you blance carbs 1 and 2, than you should do 2 and 3 and then 2 and 4, then check 1 with 4.
I should have a link to a very cheap way (less than 5 bucks) to balanced two carbs, I'll have a look in my files.

 

Here is a link for a VERY cheap tool for two carbs at a time

http://www.powerchutes.com/manometer.asp

YOu could also find a DIY four-carb tool if you google "cheap carb sync tool".

 

CRAP
I still need help guys.

So I got a new ignition coil. Fires up nicely now.
Cylinder 1&4 exhaust is getting hot quickly as it should.
Same with cylinder 3.
But not cylinder 2

Before I replaced the ignition coil, cylinder 3 was the one that gets hot the quickest. But 2 follows next.

Now that cylinders 1&4 are firing as it should, cylinder 2 is the problem i'm left to tackle.

I tried playing around with primary fuel adjuster screw, didn't help.

I tried swapping plugs as well as switching the coil wires of 2&3 (they fire together apparently) but it didn't help either. cylinder 2 remains the issue.

So this time it's definitely not ignition.

Gonna do a compression test right after dinner but I did one a few months back and everything was in spec......

oh right, the plug was black and moist when i pulled it out..... so i'm getting fuel....

 

a buddy of mine told me to vacuum sync the carbs first..... hopefully that solves my misfire.....

it's misfiring at idle and low throttle and WOT
firing but lacking power when part throttle

 

vacuum sync didn't help and i'm about to throw my bike off a cliff

 

Since you started a new thread based on current symptoms, let's pick this up there.

I've given you a couple of things to look at.