running last night. won't start today

Running perfectly last night


won't start today


got no clue wtf is going on

new plugs couple months ago

got fuel

air filter is good

oil level is good






might the starter motor gear be stuck and not releasing causing too much load and thus not letting the motor run????? i got NO clue and this is my best guess

 

Flat battery. Unless you still have the stock fusebox in which case it mighta bit the shed.

Pull the battery; check the water levels and add distilled water if needed; fully charge and reinstall.

Install a brand new set of properly-gapped NGK plugs (yes I know do it anyway if you want it to run.)

Start the bike.

How many miles on it? We'll go from there (especially since it will probably fire right up.)

Report back.

 

i hooked up jumper cables. definetly not a lack of electricity

i got brand new set of properly gapped NGK plugs in there. not the problem

tried to start the bike. Still won't start


just under 50xxxkm

81 xj750

 

just so it's out there. I'm an apprentice auto mechanic and i've owned this bike since september and have done a fair amount of work to it.

Oh and the fuse system have been replaced with updated fuse system.

one year old battery with good fluid level.

took the petcock out a couple weeks ago, fuel system is feeding the carbs perfectly.

 

You checked to verify spark? The engine cutoff switch s in the run position and making a complete circuit?

 

While there are many reasons for a "No Start" after a the Bike was running just-fine, ... the first thing to check would be the Side Stand Switch Activating Rod.

Chances are it's stuck from being dirty or dried-out crud on it is keeping it from moving like it should.

 

Just hooking up jumper cables isn't always a solution with the XJ system. My battery has been low before, bike won't start, hook up the charger and put it on 50amp 'start', bike turns over fine but won't start-but charge it for 2 hours at 10amps and try again it fires right up. I realize this seems weird considering jumping should override the battery, but somehow it doesn't work like it should.

Anything get wet on your last ride? I would pull your plugs and see if they are getting good spark. If so then prime your carbs and try a bump start to get it running. Then prepare yourself for a carb cleaning, you probably have some fuel delivery issues. When the bump start works but the E start won't it usually means some pilot circuits aren't flowing right or your battery is weak.

 

That circuit has been bypassed and working fine for a long time

 

Hooked it to my car battery via jumper cables. don't see how the bike can understand the difference between a car battery outside of the bike or a real motorcycle battery thats inside the bike.....

I ride in the rain all the time and it's fine. But last night was dry. carbs have been running good lately.
what do you mean by bump start?

 

Oh and yes i did trickle charge it last night

 

Push it downhill, second gear, pop the clutch, full choke, no throttle.

Would be very surprised if it didn't start if all the other ducks are in a row.

 

Oh yea I did that. Which is why it's now 2 blocks down the road and i cudn't push it back up the hill myself and the hill ended there.

I gotta get my buddy to help me push it back to my garage after work.

 

Maybe the kickstand switch went on you? Pull the safety start relay and see if that gets her going.

 

please read before you comment.

the kick stand system has already been bypassed.

 

Well sounds like you don't have a battery issue, have you checked primary and secondary resistance on your coils. They might have failed.

And your carbs may be fine, but they can go from fine to clogged pretty quick. You could test this theory by spraying starter fluid into the intakes and see if it kicks over.

'Bump start' is a rolling start-using the added compression with no voltage drain sometimes works where the Elec won't. Have you tried talking to it nicely after cursing it for not starting?

 

check the brushes and rotor rings, make sure they're clean and copper-bright...

 

Starter fluid?

I'm pretty sure i'm getting fuel. It had enough fuel in the exhaust to go bang..... plus smells like gas. But worth a shot if i've got something in my garage that works. wd40?


Oh and this morning it wudn't start and i got a buddy to help me push it up the hill to my garage. tried for half an hour. even tried when we took a break at the middle of the hill. No luck.

Got into garage, hooked up to charger, set at startup amperage. and BINGO. Just one touch of the button and it was instantly on. felt like i'm missing a cylinder untill it warmed up. Then it started running fine.



Rode around for half an hour. Everything was good. Parked it. Shut off. Start again. All good.

Rinsed it down (salt on roads), dryed her up and cleaned her up. By then she was nice and cold. 3 degrees here.
NO START.

Pulled the coil and pluged in an old spark plug.
Got spark in every cylinder.

Can someone describe to me exactly what the spark should look like?


Still no start at this point. Bike obviously hates the cold.


Oh and sometimes the starter motor makes a huge clunk as tho gears are smashing...... any clue?


and talking nice doesn't work. My bike likes the dirty rough talk. Shes all about being dominated by a real man

 

HUH?

 

Oh and yes i did measure the resistance in the coils a month ago. everything checked out great

i do know that my valve shims are JUST barely out of specs and that IS on my list of to do once things are sorted out here.....

unless valve shims can cause all this.....


I am also under the impression that even these old bikes are supposed to fire right up first shot with only a second of cranking even when it's cold as long as chock is on.....
I want that....... i can't figure out what's going on........ I'm probably gonna pull my carb and send it out to be rebuilt but i wanna make sure that's what the problem is first which means i gotta fix everything that isn't perfect and in spec
cuz i don't even know if the carb needs cleaning at all.....

 

He's talking about the alternator. Alternator brushes and the rings on the rotor that "brush" against them. Just under the alternator cover, easy to check. I'd think it's just cold weather killing your battery, I had to put mine on the charger after I came back for the holidays. Wouldn't even bump start(but mine was on the street, not a garage).

Edit: Oh, and I wouldn't use WD-40 as starting fluid! "Instant start" as it's commonly called, see the sticky about it in this forum, is basically ether, or some other highly flammable gas. I wouldn't use it at all, myself, but if the motor is *really* stubborn it can work.

 

NOT when they're cold!
These babies are a bitch to start ... COLD!
Late Fall and Winter cold.
It took me 25-minutes to get my 750 Max to pop, this week.
I resorted to Starting Fluid shot right into the void behind the Air Filter.

 

Would be interesting to know what the voltage drop is between fully charged and when you turn the ignition over. I woud throw a voltage meter on the battery and turn it over - see what the voltage drops to under load. Of course this woud not account for why it wouldn't start when trying to "bump start" it, but could be two separate issues. Coud be a combination of lower battery (voltage drop) and dirty / clogged enrichment circuit - I would want to rule out battery first. I am sure someone on the forum much more experienced then I could tell you what the minimum "voltage under load" when turning ignition over should be. I know I read it some where in the forum posts but can't seem to locate it now.

I know there is a fine line between what is believed to be a fully charged and functional good battery and one that will start these bikes.

 

That's way too cold to be starting an XJ. The starter is going to draw some serious power away from the battery and not leave enough for the ignition to work. Are you actually riding this bike in this type of weather? If the roads are full of salt that's going to eat on all your metal parts big time.

MN

 

like the others have already mentioned, I'm just reiterating the fact that these bikes are cold-blooded. unless you have a real reasoning to be riding in temperatures like that you may as well work on anything else besides trying to start the bike. winter season is a good time to disassemble carbs for regular maintenance, clean engine covers, and other seasonal maintenance. its been in the 20's and 30's for several weeks here in Ohio, so I took the battery out. not worth fighting against mother nature

I've also been told that random starts on an engine in temperatures that cold does more harm than good; unless you fully warm the bike for 20 minutes of riding. the temperature effects cause condensation but don't quote me on that. anyone else know more about this?

 

This will be the last I comment on this thread...

Please read what *I* posted before you make yourself look like a jack@ss... I said to remove the relay, not bypass JUST the kickstand switch.

You've got a weird way of accepting help.

I'm out.

 

Doh.....

must be the cold weather then..... I ride until it's icy out. I even rode on the snow. Lots of fun! Just wash the bike after.

I suppose the battery being on the weak side is probably one of the problems as well as the cold.

my enricher system is working fine.


it'd be nice to figure out what's a reasonable voltage drop when i'm cranking over.

 

http://www.xjbikes.com/Forums/viewtopic/t=27543.html

The above link might help - Chacal (supporting Vendor) authored "The Utimate Relay, Switch, Sensor, and Diodes Guide" -- the last post very bottom speaks to testing / and specs required for a good strong battery. Required load voltages are aslo specified.

 

You are absolutely correct and for the reason you stated. Starting the bike in really cold weather without fully warming it up (as in a good 20-minute ride) to burn off all the resultant internal condensation can wreak havoc in the engine and exhaust system. I can't think of a quicker way to ensure your mufflers rust out.

 

Yea I usually start it because i have to ride it...... unless it's to make sure i didn't f*** something up cuz i'm working on it in which case i'd have the portable heater on in my garage so it's somewhat comfortable

And yes i'm very very well aware of it being extremely bad to start and shut off without being warmed up.

 

what is this "brushes" people talk about? is it actually wire brushes? how much are they approximately?

 

Brushes are located under the altenator/ generator cover and recharge your battery and provide electrical power to lights, indicators ect.

Your bike will need a good sound battery to start the bike, any abused or old battery is unlikely to hold sufficient charge.

Use chacal's guide and check your batteries output and measure voltage.

 

They're little carbon blocks; like the "brushes" in an electric motor. They're located IN the cover and run against the face of the rotor. They wear down. They have little "wear limit lines" in them; once you can't see the lines, they're less than 11mm long (the "service limit") and need to be replaced. The factory books claim they'll need to be replaced at 10K miles; they tend to last twice that provided everything is clean, dry and oil-free in the alternator housing.

Generally, a new brush/holder assembly is available for around $20. Check with XJ4Ever (chacal.)

 

I'm suspecting that a new juicy battery, fresh starter brushes, plus fresh alternator brushes/parts would really help crank the motor over better....


time for some tests to see how my charging system and battery are doing

 

rd337,

What does your starter button look like? Might check inside the control switch to ensure the wiring to your contact plate is still soldered solid.

Gary

 

i'm not having problems with the button..... unless you're telling me the power that goes to the starter goes through the button thus a poor contact on my button means insufficient voltage going to my starter.....

 

rd337,

There's a contact plate inside the control switch behind the button/spring. When you push the button a signal is sent to the solenoid at which time the large charge necessary to start your bike is sent to your starter. If the wiring soldered to that contact plate is loose or not connected the signal will not happen. I had this problem; took the switch apart, cleaned all the parts, stripped and re-soldered the wiring (I had ONE thin wire connected to the contact plate), new button and spring...varoooom. Hope this helps.

Gary

 

but the starter is cranking just fine. if the button flips a relay and the button is faulty then the starter shud be either on or off, not week

 

"Cranking just fine" is automobile speak. These XJs have fairly robust starters that are able to crank even when there isn't enough left for adequate ignition to start -- i.e., starter cranks, engine won't fire.

Do yourself a favor. If you want to ride this thing close to zero degrees, get a new AGM maintenance-free battery from Chacal, enjoy the benefits of higher cold-cranking amps and longer life (double or triple) and put the battery question to bed. Then you can move on from there. I know I'm never going back to an acid battery for mine.

 

It has a new yuasa battery as of this past spring.... it's holding up at around 13V

I cleaned up the contacts in the start button and the switch. no problems with it before, and didn't make a difference after.

Would the ..... i don't know what you call it..... the part which the key goes into to turn it on and off..... would that possibly be an issue?

I got some valve shims as a couple of mine were a hair out of spec last time i checked a month ago.

Gonna pull everything apart, seafoam into the gas, bomb the carbs with carb cleaner spray, do whatever i can to clean up the carbs a bit more without having to tear her apart. replace the valve shims, seafoam into oil before a nice oil change.

I want this all done within one night. I really don't think the carbs were dirty at all. I always use the best gas and it's been running fine so far.


A couple questions.

Is there only one drain plug? i heard there are two but do i only bother with the one under the filter? or should i find the second one and drain from there too?

And would an inline fuel filter be a good idea or is it unnessisary?

 

.... it's holding up at around 13V

I am assuming this 13V is standing voltage - no draw or load on battery, but what is the battery voltage while turning engine over ??

The ignition switch (where the key goes in) would have no bearing on your issues, based on your previous posts that the bike is turning over but just not firing - is that correct ?.

As far as your question about the need for an inline fuel filter ..Yes, it is highly recommended if not a must.

 

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.