88 fzr 1000 rpms going crazy??

[88FZRMAYHEM]

i have a 88 1000 runs fine. but the tach reads way high at times and then it will drop back down to normal .....

it reads about 7-8k in 5th gear at about 55mph ..... which normal rpms at this speed in 5th gear are about 3700 rpms .....
it doesnt happen all the time ... im leaning towards the VR ....which is inside the alternator correct?

voltage at the battery under load is about 15.8 or so .. so imma say the VR is shot .... what are your thoughts

and is there a place to get a rebuild kit for it??

thanks

[willandrip]

Sad to say;this is one of those instances when it is far more cost effective to scrap the alternator and buy a used one unless; A ,you enjoy hobby electrics and circuit building or B,You are mates with an auto electrician. Iirc the factory v/r is over £100 sterling.!!!

[DonTZ125]

15.8vdc is HUGE; you are killing everything electrical in your bike. Park it until you get this sorted!

W&R is correct, these things are silly expensive. The 1k models used car-style variable-field regulators, vs the shunt regulators seen on the smaller models. You might see what the local automotive alternator rebuild shop can do for you.

[88FZRMAYHEM]

so say i find a "ricks rectifier" for a 88 fzr1000 .... that is what i need . correct? i found one fairly cheap.

[88FZRMAYHEM]

its listed as "THIS GOES INSIDE THE ALTERNATOR ON ALL THE OLD ND FAN COOLED ALTERNATORS"

[88FZRMAYHEM]

ok so i got another alternator off a 88 1000 .... took mine off put the other on , cranked the bike and put a volt meter at the battery, reved in up a bit and holy hell it was putting out right at 20volts ...... way higher than before , so i took the new voltage regulator i got un soldered the old one (question the VR is the half moon shaped thingy on the inside of the alternator cover with the three copper wire and a red soldered to it isnt it?) so i put it on and checked voltage again and now it back to runnin at about 15.7 - 16.0 ....so whatt now ?? im lost , what else should i check ????? help me out here please!

[DonTZ125]

If you've just installed a new VR and you're still getting overcharging, you need to have a serious chat with the guy who sold you the part. Make sure all the wires are connected, most especially the engine ground wire (from the battery to the engine).

[willandrip]

If a "known to be good replacement" alternator and a new correctly rated R/R are both giving these readings I would be firstly checking your meter calibration itself.!!
I would; as a simple test; run battery down by leaving lights on full for 10 minutes max or until they start to dim.start bike,rev it and watch h/lamp glow brighter at circa 2/3 K rpm.
If it seems massively bright start checking for shorting wires on the 3 phase part of the alternator.
With these voltage readings you should theoretically have already blown most fuses and bulbs!!!!! if not started to melt wiring,buckled battery plates or boiled it dry.
Get the tank off,r/h side by carbs ,airbox off,look at main harness here.
Once and only the once mind ;I found a bike that all and sundry had failed to repair/diagnose with "similar" symptoms and at this point found SEVERE verdegree in harness and plug connector.Once cleaned it was perfect. IIRC some have no plug connection here but check harness for overheat or pinch marks .slim chance but worth a try.
If your meter is correct the geny/R/R is trying to compensate for a short/very poor earth in wiring by overcharging.This WILL lead to burnout or even fire.!!!!
Voltage ouput on a 12v system should never exceed 14.2 volts even when system is trying to charge a duff battery .
This runs alongside your tach craziness theory.

[88FZRMAYHEM]

the day this all started i remember going to crank the bike and it let off a loud back fire pop ..... then it fired up and every since then ive had high voltage reading and the tach reads way high

[88FZRMAYHEM]

okj so after swaping parts back and forth from the 2 alternators i know have a steady voltage , it runs at about 13.7 under load .... seems a bit low but id rather see that than 20 volts...... but i still have the rpm issue .... the tach reads WAY high ... like if it should normally read 3k its read at 7 or 8 k .... so i still ahve some sort of issue here .... thoughts????

[DonTZ125]

13.7 is on the low side; you may have issues when the fan kicks in. Check your wiring and connectors for damage, corrosion, or security.

I think you've let some magic smoke out of your tach.

[reelrazor]

I would be firstly checking your meter calibration itself.!!

Yep.

Most analog meters will have a dial wheel.....set to 'ohms' scale, cross the leads (red to black) and 'zero' the needle(using the dial wheel).

Digital meters have varied calibration procedures....some will just zero themselves if you pick a scale and cross the leads, some you need to cross the leads and push down on the rotary switch.

And, I'm with Don..I think a component or two is fried in your tach. It should be fairly obvious by eye

[willandrip]

Hi reelrazor,
Mind that Douglas Adams knew what he was talking about. !!