Electrical Issue - Won't Start XJ750 Seca 1981

If anyone can offer some wisdom I would greatly appreciate it. I have been trying to tackle this for a couple of weeks now but this is my first bike and first real mechanical experience so I'm at a loss for what to try next. Thanks!

The bike came in working order. It had to be driven an hour and a half from where I picked it up and it continued to work for a week or two afterwards. Without warning it failed to start. Power would drain from the lights as the ignition rolled over and after several attempts the battery was drained. Mechanically the bike seems fine. I charged the battery and ran a friend's bike on it without an issue. I put it back into my bike and the bike started up perfectly. I shut the bike off and tried to start it again but it only rolled over and eventually after several attempts wouldn't do anything. The bike can be bump started with no problem.

Here's what I have done so far:

-Checked the battery by charging it and hooking it up to a Voltmeter.
-Checked all of the connections on the battery and they are clean. (it's almost brand new)
-The fuses under the seat seem good but I have an inexperienced eye. They are not black or burnt. Most of them have been rerouted through more modern arrangements.
-Replaced the brushed in the AC "generator"
-Electrically tested the Rotor, Stator, and the Regulator/Recitifier
-Solenoid clicks when battery is charged and there is no obvious corrosion at its connections
-after one start from a charged battery I turned it off and the battery read 11.5V in the OFF position
-Even if the ignition won't roll over the battery drains power for as long as the starter button is held in

I thought at first that it was a charging issue but I couldn't find any obvious culprits there. Still, as I said I can get it to start from a fully charged battery but for some reason it doesn't seem to replenish the battery while running which leaves me still thinking that it must be an issue in the charging system.

My next course of action is to recharge the battery and hook it up to a voltmeter to see what it reads while the engine is running/being revved.

I can't figure out what to trouble shoot next and to be honest I just want to ride. I have been waiting for a long time to finally own a bike and this starter issue is really putting a damper on the experience. If you could point me anywhere in the right direction or at least eliminate some things for me that would be great. Thanks!

 

Check the voltage at the battery terminals. Check at idle, at 2,000 RPM, and at 3,500 RPM. Your symptoms sound exactly like there is a problem with the regulator.

 

Thank you for the feedback. Today I charged up the battery and tested it with a multimeter. Here are the results:

- Battery was charged to 11.8V before start.
- Bike started perfectly and continued to idle
- At 3,500 RPM the meter read an average of 14.2V
- At 2,000 RPM the meter read an average of 14. - 14.05
Here's the strange part
- At Idle the meter can't get a consistent reading. It quickly flips numbers between 14-19V
- After all of this I shut the bike off and it read 12V

New findings:
- The bike started again after the previous process and ran the same voltage readings
- Two hours later the battery had a good charge in the Off position, started easily, and showed the same readings for Idle, 2,000 RPM, and 3,500 RPM.

Needless to say this gives me hope but also confuses me even more. Despite these events I'm still not confident that the bike will continue to start. Is this still a Regulator issue?

Hopefully these results will help to further clarify this predicament. Thanks!

 

The charging circuit appears to be fine, aside from the occasional very high voltage at idle, which is concerning. At idle the regulator output shouldn't be more than 13 volts, and is usually lower than 12. That it jumps to 19 is a serious problem, as that can damage the battery. Can you retest and check if it ever jumps that high at higher RPMs?

When you park the bike, do you lock the forks? If you do, are you careful that you aren't turning the key one stop further to the left? That would turn the parking lamp circuit on, and drain the battery.

 

I have tested it a total of three separate times now. All of them yield the same results. I have been sure not to put it into park even when I do lock it.

This is what's happening with the voltage.

- higher RPM gives a stable reading. No drastic fluctuation at all.
- idle RPM: The multimeter starts flickering random readings before I can even touch the probes to the terminals. This happens whenever I get the multilmeter and probes anywhere close to the middle of the bike.
- when the probes do contact the terminals during idle the numbers continue to flicker sporadically, so quickly that it never pauses on one number for more than a fraction of a second. The range of 14-19V is just what I see popping up as the numbers keep changing at a high rate of speed.

Is it possible that a problem with the regulator could be affecting the battery only at low RPM?

 

Possably, but I'm not sure what that would be. Do you happen to have an analog meter that you can do the test at idle with? I'd like to eliminate the possability that your meter just isn't settling down enough to always give you an accurate reading. Wiggling the probes a little can sometimes change the readout on a digital meter, even when reading from a regulated power supply on the bench.

 

Okay so it has been a while but I am still fighting with this issue. I recharged the battery again and then for some reason the bike started working. Starts up with no problem. Then I randomly started having times when the starter button wouldn't even cause the bike to turn over. The bike eventually refused to start while I was out. I rode it there, parked it, came back and couldn't get it to start for anything. I couldn't even get it to bump start this time. It would start, the rpms would fluctuate up and down and then the bike would die. I got it back home eventually.

Since then:
-Put a new Regulator/ Rectifier on it.
-Charged the battery and got it to run twice but then it died.
- found that if I jump it from another bike it runs every time
- When I press the starter button the battery voltage drops drastically even when there is no turn over.

Some sources have suggested a carb cleaning but I don't want to take apart the whole thing before the end of the season if I am still going to be left with a bike that doesn't run because of an electrical issue. Is there anyway to test the starter button? Why does it start just fine when jumped from another bike?

 

At this point I can suggest that the only way to solve this is to start at the battery and thoroughly go through and clean/rebuild every electrical component that has not already been replaced. You'll keep chasing your own tail otherwise. Sure it takes longer to do this, but once done you will have a reliable machine.

 

It sounds possibly like a loose electrical connection at the MAIN fuse in the fusebox or at the key switch electrical connector....

 

I read back through your post, and I don't see a voltage reading indicating the battery charges fully, even with the external charger.

From Len's catalog:

How do I know if my battery is good?:

Is it your battery, or your charging system, or something in-between?

The best way to know for sure is to use a multimeter (voltmeter) attached directly to your battery positive and negative terminals, and observe the following:

1) with the engine and all electrical accessories off, the battery should read a minimum of 12.8 volts DC. If not, the battery is either not fully charged, or it is bad (it is incapable of holding a full charge). Charge the battery fully and check again; if the reading is less than 12.8 volts, the battery is bad and should be replaced.

NOTE: most manuals describe checking the specific gravity of each battery cell electrolyte (fluid) as the preferred method of checking the condition of the battery. This reading should be between 1.2650 - 1.280 per cell. If a fully charged battery cannot reach these levels in all cells, then that cell is bad and the battery should be replaced.


2) If the first test above passes, leave the multimeter hooked up to the battery terminals, and press the starter button. While the starter is engaged (but before the bike starts), the battery voltage should be 9.5 volts or greater. If not, then this signals either a bad battery, very dirty or weak electrical connections, or it could be a incredibly problematic starter motor (not likely; it's probably the battery!).

Another indication the battery is bad, or not being charged. The numbers look good on the charging system so the battery is still the likely cause of the failure.

 

Are the valves in spec and the carbs fuel levels correct?

Gary H.

 

Hi all, I know it's a late reply to the thread but I dug it up looking for a solution to another problem. I had what sounds like the same issue. The fix for mine was surprisingly simple after trying just about everything else. I took apart the regulator and gave it a good clean. The inside seemed to have a thin coat of oil on everything. My guess is that the bike had tipped over at some point. I used glass cleaner to try and not leave any residue behind, then gave the commutator a quick polish with a fine emery cloth. Since then there has been no issue with recharging and starting. At the very least it's worth a try. Good luck.

 

Welcome aboard.

Sounds to me like you did not take apart the regulator (since it's essentially non-serviceable). What you did was remove the alternator cover. Any oil you found in there is from a leaking oil seal or o-ring. Cleaning the oil out is a temporary solution. You should have also checked the wear marks on the alternator brushes, but that can be done when you go back in to replace the o-ring and seal.

 

Thanks for the additional info. I definitely did mean alternator not regulator! I'll get back in there and replace that o-ring and seal.

 

there is a thread about replacing the seal think it is for the xj700

Replacing Alternator Seals in XJ700N with Pictures

 

The procedure is identical for the XJ750/650.

 

I have a 1981 xj750 seca, got it for free owner said it ran when he parked it. I have cleaned the carburetor, spotless and correctly. The wiring though is a mess.... I removed the headlight and as much stuff as possible as I would like to make a cafe racer. There's are multiple wires snipped, missing, and simply unplugged. The start button will not crank it over as do I not hear a click either, but I CAN get it to crank over if I bypass by applying power to the starter solenoid, I am getting no spark either. But it does crank at the starter. Please help? Lol

 

start your own thread include bike and problem in the title , it will make it easier to help you.