GSXR750 Srad lights causing rough idle

[Mullan]

Hi all, 

First of all so glad to see OSS up and running again, was delighted when I discovered it was back by chance yesterday. Couldn't have built my 7/11 without the help from a lot of great minds on here.

So now to the main problem, have a GSXR750 SRAD that when the lights are switch on the starts to run rough. Originally thought it was when the bike was hot and the fan came on but can replicate the problem when bike is cold. Charging at over 14v no lights and 13.1v with lights on, and it starts to almost drop a cylinder.

Originally thought it was air leak when hot, changed intake rubbers as one was cracked, balanced carbs, set mixture screws, bike runs better than before until you are idling with lights on.

Then I tried charging system as when it was dropping to 12.5v volts with lights on at idle and 12.1v with lights and fan. Changed battery and reg/rec which improved the charge to the originally stated figures but still as soon as the lights are switched on it starts to run rough. Genny check out according to workshop manual. 19v per phase at idle, 55volts per phase at 5k rpm, nothing is earthed and all have continuity between each other. 

Have checked the headlight wattages both are 60/55w. Have even changed the bulbs incase one was shorting but same thing. 

Really stumped at this point and running out off ideas. 

Anybody ever come across this before?

 

[Captain Chaos]

most electric problems are because of a mechanical failure. Have you checked all the plugs/connections are clean? Not just the generator and reg/rec ones, also the handlebar switches etc.

[jameskat]

4 hours ago, Captain Chaos said:

most electric problems are because of a mechanical failure. Have you checked all the plugs/connections are clean? Not just the generator and reg/rec ones, also the handlebar switches etc.

Totally agree, dirty connections act like resistors dropping the voltage to the next component in the circuit.

[Mullan]

16 hours ago, Captain Chaos said:

most electric problems are because of a mechanical failure. Have you checked all the plugs/connections are clean? Not just the generator and reg/rec ones, also the handlebar switches etc.

Thought the same, have been through all the block connectors and can't find any substantial corrosion. Just trying to get my head arround how the lighting circuit could/can affect the ignition circuit???

[Captain Chaos]

On 4/24/2017 at 7:06 PM, Mullan said:

Charging at over 14v no lights and 13.1v with lights on

it's affecting the charging system, low voltage means weaker spark. Ideally it should charge 14,5V with or without lights on.

[Mullan]

22 hours ago, Captain Chaos said:

it's affecting the charging system, low voltage means weaker spark. Ideally it should charge 14,5V with or without lights on.

Yeah with the lights on the voltage going into the cdi and also into the coils is closer 11v than 12v. Have inspected the stator and it looks perfect and also checks out according to the Suzuki manual, have tried a new reg/rec and no change. Can only assume the lighting circuit is drawing a large load than it should, but can't see why.

[jameskat]

If you are confident that the charging system then with the motor running and light on start with one volt meter lead on the battery and then run the rest of the system starting with the starter relay, regulator rectifier, ignition switch, fuse box, ignition module, side stand relay and switch gear looking for a voltage drop, if nothing check the negative side of the of circuit for a voltage drop.