Help, Bike starts then dies. Any help please

My girlfriend has a 1981 seca 750. It will only stay ruinning with the battery charger hook up. After I disconnect the leads the bike will stay running for about 30 seconds before it dies. If i keep the RPMs above 2000 it wont die. Once it hits idle it quits and wont start up until I charge the battery up. The battery is about 1.5 year old I am very new to the bike world. I tried looking for a similar thread but no luck. Thanks for any info.

 

Sounds like you might have two problems..first sounds like you might need a new battery you can put it on a charge for a few hours and take it to an auto parts house (assuming you don't have a battery tester yourself) .they can tell you if the battery is good or bad.
Second it sounds like the charging circuit or some part of it is not putting out voltage to charge the battery. If you are lucky it could be just a bad connection somewhere, that is the first thing I would check, see if there is any corroded wires, or if any wires are broken or shorted. Maybe someone here will help you troubleshoot the rest of the charging system

 

I'm going to guess that this is a new purchase and you have not done anything to the machine since buying it. Stalling is symptomatic of maintenance that has been left undone.

Begin reading here: The Information Overload Hour

The specific problem that you are having could be the result of a faulty battery, or a faulty voltage regulator. Do you have a multi-meter so you can measure the voltage at the battery when the bike is running? You should also take the battery to an auto-parts store ane have it load tested.

 

I guess I will rule out the battery 1st. I will post the results in the next few days. Thanks.

 

When there is a charging problem, I always look for the cheapest fix first thing. After checking the fuses I would next pull (unplug) all the (big multi-pin) connections under the seat and see if there is damage or corrosion at those connections. The culprit is often the rectifier connections, they sometimes get wet and tend to corrode. Do this checking with the battery disconnected, of course.

If you find anything burnt, broken or any corrosion at the (big multi-pin) connections that could be the reason why your battery isn't charging. Don't worry about the little one pin connections too much they are to the turn and brake lights. If no problem there at the connections, next I would check the rectifier, it's the next cheapest fix. I would check the stator and other parts last.

By the way, if the headlight doesn't go out when you push the starter button, then the starter button may not be working properly. The headlight is supposed to go out when you push the starter button and come back on when it is released. It is designed that way so all of the power from the battery goes to the starter when you push the starter button.

If the headlight doesn't go out when you push the starter button then, again ...there is probably a problem with the starter button and the headlight is taking starting power away from the starter when you try to start the bike. this is especially a problem if you have a weak battery.

 

Slow down. Voltage checks first. We have yet to confirm that it is a charging system problem and not just a case of a faulty battery. Your method could lead the OP down the road to unnecessary parts swapping (though I do agree that disconnecting, cleaning and applying dialectric grease to all electrical connections is a good idea on any old motorcycle). The methodology is sound, but you left out the details about how to test each component.

Secondly. The headlight on a Seca 750 does not go out when the starter button is pushed. What happens is that it does not come on at all until the engine fires.

 

Okay, thanks..
From reading his first post, I figured he most likely has a charging problem.... As far as the headlight working in connection with the starter button...sorry, I thought other bikes worked very much the same as my XJ, but you are obviously correct with regard to the Seca 750. I was just trying to help... but, I'll keep my opinions to myself from now on, and leave all advice on the details about how to test each component to the experts. There 's usually no shortage of people on any forum quick to give people much better advice than my own...BTW it's called dielectric grease, and I hope I'm not nit-picking, nobody likes that.

 

I understand that you are trying to help, but jumping to conclusions often does more harm than good. Troubleshooting requires thoroughness, and far too often people chase their tails when only given part of the methodology; which is why I tend to go one step at a time when possible.

Thanks for pointing out the typo. I make a lot of them, but people still seem to figure out what I mean.

We help each other here, and we also take each other to task when we give bad or incomplete advice (I've given my fair share). It's not personal; it's just good shop practice.

 

Yep, I would call that nit picking.

 

Well I cleaned the points on the stator, fully charged the battery. I got a voltage reader and it reads 14.7 volts while the bike is running at 2k RPM. So far the bike has stayed running, beside the idle being low where is wont stay running with a little help from the throttle. Thanks for all the input guys.

Anyone got a thread on how to adjust the idle? or a picture?

 

Check your battery voltage tomorrow and see if it is holding a charge.

In between the two middle carbs is a knurled knob about the diameter of a dime.
Your idle speed should be around 1,100 RPM's.
Turning the afore mentioned knob will change the idle speed, in is faster, out is slower or is it the other way? Little fuzzy this evening, you will find out when you turn it.
Recommended that when the engine is warm you turn it an 1/8 of a turn in the desired direction and then blip the throttle and see where she settles.

Do you know the last time the carbs were rebuilt?

 

Clean stator brushes and rings are important. Can't set the magic pixies free if they are dirty; very good catch on your part.
Did you happen to look at the length of the brushes when you had the cover off? There is a wear mark that will show you where the service limit is.

To help Stumplifter out (I'm less foggy this evening than usual) turning the idle adjustment knob clockwise raises the idle speed.

 

Well I messed with the idle screw and still wont stay running. Maybe the carbs have to be cleaned. I will look for threads about my problem.

 

There is one. Have a look at the second reply in this thread. There is a link you should look at.

 

Does this engine have a earth ground separate from the battery ground? If so make certain it has good contact with the frame (gently file the paint from the contact point).

Gary H.