hi this is my first post (probably of many).
i have a 1990 cbr 100f cracking bike but there is 1 issue that has got the better of me so far as i can only bump start it.
i try to start it off the button and it cranks really slow as if the battery is flat so here is a list of the things i have tried
new battery
new starter motor
new earth cable
new oil
ive tried buypassing the solinoid by putting battery cable from the battery straight to the starter motor.
and ive had no luck. ive taken out the plugs and turned it by hand and its fine.
i put a multimeter to the battery and it shows just above 13v then when i start it drops down to 7v!

if anyone could help or even some suggestions they would be greatly appreciated

if you need to know anything just ask and ill get back to you asap

 

Do you have a multimeter that can measure DC voltage? I would suggest doing a voltage drop test on the power & earth cables from the battery to the starter/frame to rule out a possible cable issue. Specifically the power cable since the earth has already been replaced.

The battery voltage dropping when cranking is normal, but 7v does seem low to me. Might also try jump starting it from another battery or vehicle and see if it cranks over better.

 

hi thanks for the reply i do have a multi meter to check which i will do over the weekend. i did try jump starting it from another battery with the same results for the first few times then fired up twice then went back to slow?? quite annoying really

 

Yeah that is a bit odd unless you have a bad/corroded connection at the battery or a cable with excessive resistance which could cause something like that to happen. Perhaps it is a bad battery even though it is new.. doesn't happen often but I've seen it occasionally over the years as a tech. Anyway the voltage drop test is a quick and easy way to determine if the cabling or connections have built up resistance that shouldn't be there..

 

Just use the ol' electric equation, V=IR. Voltage equals Current x Total Resistance. If the battery voltage drops it usually in one of two things.
1. The battery is worn and cannot provide enough current (CCA's) to turn the starter, so the system voltage drops.
2. There lies some other resistance somewhere in the circuit (battery, cables, etc).

 

I meant to say lack of resistance in the circuit.

 

ok quick update had the battery checked and he sais its fine, changed the power lead and all fuses and still no luck so im gonna give up and take it to a shop

 

it didnt the first 3 attempts but the 4th and 5th it started like it should then went back to slow. ive just been fiddling about and took all 4 plugs out. turned it over and it spun really fast as it should. then put 2 in and tried again and managed to start it up but then put the other 2 plugs in and back to square 1!!! so fustrating. if anyone knows what it could be from that or any suggestions then please speak up as im going out of my mind

 

hi guys spoke to mate who goes to bike meetings and his friends have all said the same thing.. its the valves playing up which is causing to much compression. just thought id let you all know incase someone is in my situation in the future

thanks for your help though