94' cb400sf Several Issues need help sorting

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NATcb400sf
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94' cb400sf Several Issues need help sorting

Post by NATcb400sf » Sat Jun 23, 2018 12:48 pm

Hello all,

Did post some background to the issues faced on my 94' cb400sf, here are just the main ones:

1. Bike not idling, if i keep giving the bike abit of throttle it keeps running but if i let go it shuts off after a few seconds.
2. The rectifier keeps getting really hot, changed like 5 of them, still the issue remains along with heating up the battery.
3. Removed the air filter so the bike can go above 100 kph, otherwise with the original air filter in place the bike does not rev above 5000 rpm or 100 kph.
4. Rear shocks are finished, no idea which ones to buy in a budget of $200.
5. Bike sounds like its misfiring below 3500 rpm, once you go above that it starts firing and running properly.
6. Wiring for the rectifier and bike do not have the 6 pin connectors, need wiring diagram or help to setup the wiring again.

cb400f1
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Re: 94' cb400sf Several Issues need help sorting

Post by cb400f1 » Sun Jun 24, 2018 6:11 pm

1st things 1st. Get the electrical problem sorted. Search the forum for NC31 wiring diagram. There is a link there for you.
Battery should not get warm and suggests a wiring problem. Have you got use of a digital multimeter? Very useful for checking charging voltage not exceeding 14.4 Volts DC. Make sure the 3 ac wires from the alternator are connected to the correct ac input to the rect/reg. On my bike they are 3 yellow wires.
If when that is sorted, you still have the slow running problems? Sounds like the carbs need a thorough clean. If that fails, has anyone tampered or replaced any of the jets? I've had problems with pattern parts causing similar problems. Keep to Genuine Honda if you can.

NATcb400sf
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Re: 94' cb400sf Several Issues need help sorting

Post by NATcb400sf » Mon Jun 25, 2018 7:53 pm

Looked at the wiring today, i'll post the pictures to give an idea of how they were done, still don't know if the wiring is correct as some of the wires are connected to different colours that are coming from the rectifier.

1. All of the wiring currently with any proper connectors https://ibb.co/jJycVT
2. One of the Red wires from the bike going to the red rectifier wire https://ibb.co/gQCt4o
3. The three yellow wires from the alternator to the rectifier https://ibb.co/fDDuAT
4. Other red wire combined with the orange wire joining to the black rectifier wire https://ibb.co/h0hnVT
5. Green wires going to the Green rectifier wire https://ibb.co/mgXRPo
6. All wiring different angle https://ibb.co/c5dY4o

As you see in the pictures, the alternator wires are also three yellow ones, the order of which i dont know so connected them as they were to the 3 yellow wires from the rectifier.

There are two green wires connected to a single green wire to the rectifier. The odd thing was that the two red wires coming from the bike are separated between one going to the red wire on the rectifier and the other red wire joined with an orange wire (also coming from the bike) which is connected to the black wire on the rectifier.

Also since the battery is dead, ordered a new one to test starting the bike and see if the rectifier and battery are still heating up. Will also check with the multimeter.

As for any tempering to the jets, there hasnt been any because the bike still has all its OEM parts and the carbs were cleaned/tuned last year when i got it, along with new spark plugs, engine oil and a valve adjustment (since the bike used to take forever to start).

Maybe its time for another service?

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Re: 94' cb400sf Several Issues need help sorting

Post by cb400f1 » Tue Jun 26, 2018 9:45 am

Before you install the new battery, check the old batteries terminal voltage with the engine running at 4,000RPM. IF it is higher than 14.4V do not connect the new battery, you could damage it by warping the plates inside. Wiring seems to have been added by a former owner, are there any accessories on the bike?

Your fuelling issue could be dirty fuel from either the bottom of the tank on the bike or from the filling stations underground tanks. If you find the carbs have got dirty so quickly, consider fitting an in-line fuel filter if Honda haven't already done so.

NATcb400sf
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Re: 94' cb400sf Several Issues need help sorting

Post by NATcb400sf » Sat Jun 30, 2018 4:19 pm

Have not started the bike in weeks, the old battery is dead by this point, i still have to check the voltage readings with the bike turns over. As for the wiring, no accessories on the bike but it was an auctioned Japanese police bike (says CB-400KP under the seat) so there is wiring of sirens or extra lights but those were not on the bike when the previous owner had it or when he sold it to me.

The fuelling and carbs i have not looked at yet, i am thinking to take off the tank, drain it and add new fuel along with checking the carbs and cleaning if need be.

Will keep posting pictures and a video (to sort with the running and meter readings) for better view of the situation.

Thank you for the support and help so far.

NATcb400sf
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Re: 94' cb400sf Several Issues need help sorting

Post by NATcb400sf » Mon Jul 02, 2018 2:53 pm

Checked the voltage today on the old battery which was showing 15.5 volts and the new battery showed 14.5 v. I initially tried to start the bike with the old battery but it would not start and the neutral light would go out. I fitted the new battery to see if it would start, would do the same and not start. When i went to unplug the battery, the battery connecting wires were really hot so i disconnected the battery immediately.

No idea what the issue is here because the bike started and ran 3 weeks ago but now doesnt even start.

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Re: 94' cb400sf Several Issues need help sorting

Post by Superjack44 » Mon Jul 02, 2018 7:44 pm

It would appear you have a direct short somewhere ,disconnect the power lead from the starter motor/ solenoid to see if that stops the wires getting hot.
When you fit the battery make sure everything is switched off, fit the + lead first then fit the - earth lead there should be no reaction ie sparking,
there maybe a little if it runs with the lights on but no major blue flashes.

NATcb400sf
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Re: 94' cb400sf Several Issues need help sorting

Post by NATcb400sf » Sat Jul 07, 2018 7:36 pm

Superjack44 wrote:
Mon Jul 02, 2018 7:44 pm
It would appear you have a direct short somewhere ,disconnect the power lead from the starter motor/ solenoid to see if that stops the wires getting hot.
When you fit the battery make sure everything is switched off, fit the + lead first then fit the - earth lead there should be no reaction ie sparking,
there maybe a little if it runs with the lights on but no major blue flashes.
Update so far, disconnected the leads and the bike was still not turning on, i connected the starter motor leads manually to see if the bike would turn. There were small sparks and i heard the starter motor make a click sound but not like it how it normally tries to turn the crank. The lights would also go out when it would connect the starter motor leads.


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