running last night. won't start today

I left my dvom on last time..... Arg.....

Will check voltage while cranking when i pick up a new batter for my doom


I actually do get ignition and spark while cranking. And a battery charger doesn't help. Warmer weather does help slightly.

Now here's some more clues.

I do get popping in the exhaust when i'm cranking. And I noticed that cylinder 3 exhaust pipe gets warm even tho the engine didn't manage to catch on and run. Yet the other exhaust pipes are cold. And when the bike finally catches on, it sounds like it's running on 2 or 3 of the cylinders. And cylinder 2 and 3 are definitly running and their exhaust pipes get hot fast, but not 1 and 4. 1 and 4 takes a while to warm up.

once the bike is warmed up, i get fully combustion above 3000rpm. Runs like a charm. But idles like it's on 3 cylinders most of the time. Sometimes even stalls. And if i don't rev it to 3000+ rpm before releasing the clutch, it will bog on me and try to stall.


wtf is going on......


Oh right, I replaced my valve shims. they are now all in spec. Didn't seem to help with the hard start

but I did notice, when the gas tank was off, I used a funnel to pour gas into the line which would normally be connected to the petcock. The gas is hardly moving when i'm cranking her over..... but once it's running then it goes down.

Now I know a lot of people tell me the choke system is clogged. I see the pieces moving up from the outside, and the choke is definetly enriching the bike when it is running. but is it working in all 4 cyclinders exactly the way it's supposed to be working? I got no clue! heck i don't even have a clue as to how the choke is supposed to work. My first bike, and my first set of carbs.

but what pisses me off is that i'm not banging in all my bangers... which only started happening a week ago, and started only at idle then got worse.

 

The "choke" pulls fuel from an odd passage inside the casting of - - the Float Bowl Body !! There's even a pressed-in jet and a siphon tube with a drilled port to work as an emulsion tube !

It's all about the clean ! And knowing where to clean. And "crud" could have migrated into your Pilot circuit since you got your bike running, after sitting.

 

sitting?
.....
i must have assumed that it was understood that i've managed to get it to start after the second day. Not easily, and it's putting up a fight every morning. and running like crap. But it's my only source of transport other than the unreliable, over priced, crappy bus system. So yea, the longest she'd sit for would be 2 days in a roll.


So are we really down to the carbs? because it's not running any better with the choke off when it's warmed up......


doesn't it kinda smell fishy that cylinders 2 and 3 are doing much better than 1 and 4?

 

Okay, now I'm curious. I'm following this thread to learn something. Not the battery, loose or un-connected wiring at the fuse box, starter, rotor, stator, brushes, coil packs, ht leads, plugs, valve shims, tci, rectifier, carbs, petcock, gas cap, ignition, relays, filter, oil, vacuum sync, battery ground, earth ground, timing plate and whatever else mentioned here I thought would surely find Rd's problem. I'm stumped...going to be interesting to find out what it is. Keep looking Rd, you'll find it.

Gary

Rd,

Have you tried the tsp. of oil in the hole(s) compression test to see if it's a issue possibly with your valve stem seals, piston rings or both? If so, my bad. If you do decide to do it remember to disconnect the tci and remove your air filter. I'm wondering if you might have broken "springs" under the buckets.

 

That's an important clue. One coil fires 1/4, the other coil fires 2/3.

 

Agreed.
So far, I know the petcock is fine.
Opening fuel cap doesn't help
Getting spark in all the cylinders
Spark plugs are ~1000km old?
Spark plugs were gapped when installed and checked and still correct 2 days ago.
Rotor on the left side crank thingy plus sensors where cleaned up with sand paper lightly.
Air filters are good
Oil level is good
Battery is good
Getting enough power for ignition

Last night, I decided to f*** it and rebuild the carbs again. floats are good, everythings good.

I don't know how to test the sensors in the left crank case cover

I also don't know how to test the module that collects the info from those sensors and send signals to the ignition module

And I also don't know how to test the ignition coils

I checked the resistances in the wire caps and all is good. Connection from wire to cap is good.

I am debating pulling my ignition coils off and swapping the 1-4 with the 2-3. That way if cylinders 1&4 gets hot while 2&3 doesn't then it confirm that the ignition coils and wires are the issues. If 1&4 remains the colder two then it means ignition coils and wires are definitly not the problem.

I'm starting to get pretty irritated and desperate so I also swapped plugs on cylinder 1 with cylinder 3. Didn't make a difference.

Also, Is it normal for the spark to be weaker at idle and stronger when you rev? or should it always be just as bright?

After rebuilding the carb, it's idling smoother but sounds like it's on 3 cylinders, and occasionally it'd just die, rather than hunt and try hard to stay alive before dying. It's misfiring at minimal throttle and full throttle even at 5000rpm. but all is fine at 1/2 to 3/4 throttle.

it used to misfire under all condition under 2000rpm and misfires only at wot until 3000rpm and then it's all good above 3000rpm


How does oil contribute to my problems?
Would good, clean, synthetic oil and a nice oem filter make any difference?
Or should it run just fine as long as it's got the right amount of oil regardless of what oil it is?
I'm just using normal castrol motorcycle 4 stroke oil and i'll admit it's a little dirty and imo overdue for a flush. But I want to sort out this problem first partly because if dirty oil does make the symptoms worst then i want to fix it properly rather than having clean oil mask up the issue, and also that I might have to pull the engine appart or this or that.


I need help from experts at this point. this issue is just pissing me off

 

First let me say I've been there, done that on the pissed off part. I completely understand and it's normal-you've put in a lot of time and your ready to just say F&#! it! One BIG plus is you have a running engine and that's more than many have had so it's a starting place.

What your describing could hardly be an oil issue, so forget that. I know my bike runs better with clean oil but your issue is not lubrication related-it's ignition or fuel and I'll bet ignition since you've been through the carbs-and to make sure, you did go through the pilot circuit completely right? If so let's suspect your ignition.

Do the coil swap as this is an excellent test to find a failing coil. You can also check primary and secondary resistance in your coils and this would let you know that either all is good all the way from the pick-ups (left side cover) to plugs or not. If all four are firing, and all four carbs are behaving and your compression is solid, you shouldn't have any misfiring at any rpm unless your gas is bad. Start with all four firing at idle because there is no point in revving it up if they aren't.

The spark will be marginally more intense at higher revs because there will be additional voltage charging the coils magnetic field above 2000rpms, but from a visual perspective this shouldn't be noticeable-at least not by much. This tends to point towards a failing coil-or a faulty TCI. And your symptoms have suggested the same.

You test primary coil resistance btn the wires coming from the TCI to the coil at the coil. Secondary is tested btn each plug wire coming from the coil at the plugs but before the resistance caps (so unscrew the plug caps and test there). Not certain of your specs for the 750 but you can test them, post your #'s and the specs will be given. At this point I'll bet you have a faulty coil.

Don't give up yet, and don't let it piss you off (as hard as that is) because whatever the issue is, it can be solved-it's only a matter of finding the gremlin and destroying that offending bitc!

 

Float levels precisely, individually wet-set to spec?

Although the "pattern" of the problem cylinders sharing a coil does point to an ignition problem. Have you swapped coils yet to see if it changes which set of cylinders misbehaves? That's a good troubleshooting step.

DO NOT switch to synthetic oil, you'll just cause a whole new set of issues; Castrol 4T is fine. Your issue isn't oil-related.

YOU NEED A SERVICE MANUAL. It will cover all the above tests.

But start by swapping the coils.

 

I agree with the duck. Re check those float levels again please.

 

I cleaned whatever I could clean and made sure all the holes were flowing properly....
not sure what the names are.
So I don't know which one is the pilot circuit....
Would someone point it out to me?

I also didn't do a wet float adjustment..... but i noticed cylinder 1 was slightly off compared to the other 3 so i adjusted it. Now i don't understand how it'd be a problem when i seem to be running well on cylinders 2 and 3 only and all the floats are set the same. Either ways, I will level out my carbs by tilting my bike as needed, then plugging in a hose and checking the float levels with the carb on my bike.

I have the hayes manual. I guess I should try harder in finding the info i need in there...

I'll do the float and the ignition coil swap first thing tomorrow.

Seems like i'm almost out of possibilities, which is a good thing because i'm bound to hit some sort of an answer soon.

Thanks guys.

 

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.