Yamaha 100 600 hours loosing power

Hoping some one can help with my engine fault

traveling out to the 70s last week and I lost power while at half throttle one gauge blacked out and the tachometer numbers  went hay wire on the other gauge

i returned the motor to idle and all returned to normal.had a look around and couldn't see anything wrong.put the throttle back into gear and throttled up at around 2500 the engine started to shake and miss and lost power and the gauges did the same thing again one blacked out and the tachometer went haywire.return to idle all good again

i did notice before the gauge blacked out that the battery voltage dropped to 8 volts when under revs but returned to 14.6 at idle

i swapped the battery's over and tried again and all was good.Reset the batteries to the original position and could get the fault back

turned and headed in and the fault never returned 

what's my next steps as the faults not there now and I don't want to head out thinking I may get stranded 

cheers for any sugestions 


The Saint's picture

Posts: 455

Date Joined: 30/01/13

 Have had a similar problem,

Sun, 2022-03-13 08:29

 Have had a similar problem, was a loose connection on one of the batteries.

Worth checking that first up.

The Saint's picture

Posts: 455

Date Joined: 30/01/13

 Have had a similar problem,

Sun, 2022-03-13 08:30

.

Posts: 821

Date Joined: 22/07/10

 If it's older model yammy

Sun, 2022-03-13 13:15

 If it's older model yammy could be the voltage regulator, get hot and loses power.let it cool down then returns to normal.

my old 80 carb model 4 stroke did exactly what you described.

Posts: 1084

Date Joined: 21/05/12

fact it gets good when u swop

Sun, 2022-03-13 13:34

fact it gets good when u swop batteries over means 1 battery is cactus or got loose connection as mentioned before,  more likely than  explanation  regulator /alternatior ,cdi

when last have u checked electrolyte level in batteries?

a lot of "maintenance free" batteries never get electrolyte levels checked /filled

should be called "less maintenance"  yes there are hidden screw tops under that nice flat cover ;)

 low electrolyte is main reason for battery warranties being declined at places like Ba... world etc.

 

have a reputable mob check your battery/ies - have a load test done - a certain battery mob does it for free

if all is ok with batteries, check voltage across battery terminals while at idle and at revs should be 14.7 ish, if it aint, it might be regulator if not check charging circuit

little johnny's picture

Posts: 5329

Date Joined: 04/12/11

Power

Sun, 2022-03-13 17:18

Pack . On way out my guess

Posts: 54

Date Joined: 21/09/11

Thanks for the suggestions

Sun, 2022-03-13 20:28

Thanks for the suggestions  gents 

stab testing the batteries sound like a good start point  and a through check of all connections 

heading to steep point for a week in a few weeks time so keen to get this sorted

thanks again