Drop rpm idle when hot

Cocoloco

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Ok so i encountered this problem twice and i cant seem to find whats causing this.
The bike ran fine no jerking or sudden power loss .
Bike revs fine and no delay when i twist the throttle
It only happens when its hot outside
How ever when i let the bike rest for a minute or so, it comes back to normal idle rpm (1200-1300)
Heres the video
can a bad R/R do this? Although its new but its not genuine yamaha
 

Gary in NJ

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You definitely have a charging issue. That restart was barely completed. As to whether that same problem would cause a poor idle - I just don’t know - but it is certainly possible. It takes about 10 to 11 volts for the ECU to operate. If at low rpm the output of the RR is below spec and the battery doesn’t have enough reserve then I would expect to see such an issue.

Have you checked the output of the RR? Have you checked the AC output of the Stator? Have you conducted a load test on the battery?

I’m on vacation this week and I don’t have access to the FSM, but if I were home I’d be reading the Troubleshooting section to see what it says about a hunting idle.
 

Cocoloco

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You definitely have a charging issue. That restart was barely completed. As to whether that same problem would cause a poor idle - I just don’t know - but it is certainly possible. It takes about 10 to 11 volts for the ECU to operate. If at low rpm the output of the RR is below spec and the battery doesn’t have enough reserve then I would expect to see such an issue.

Have you checked the output of the RR? Have you checked the AC output of the Stator? Have you conducted a load test on the battery?

I’m on vacation this week and I don’t have access to the FSM, but if I were home I’d be reading the Troubleshooting section to see what it says about a hunting idle.
Yes ive checked my stator 3 white wires AC with in spec 70-80v at 5k rpm
14.4v at R/R voltage (red/black wire)
Im thinking maybe that RR is overheating and not function as it should, i havent tested the R/R while the rpm is dropped like in the video.
Are MOSFETS any good?
Since i have doubts about my chinese R/R im thinking a upgrade is not a bad choice.
 

Gary in NJ

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A switching regulator (FET based) is a superior design. The output is more consistent and they produce less heat. In the US I always suggest using Ricks.
 

Cocoloco

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A switching regulator (FET based) is a superior design. The output is more consistent and they produce less heat. In the US I always suggest using Ricks.
I saw someone in my local market that sells surplus mosfet R/R which is from bike breakers and its selling like hotcakes mostly installed to honda cb400
I'll give it a try.
Perhaps you could give me some tips what to look for.
Parts number or codes maybe?
 

Gary in NJ

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The difference between the various models of mosfet R/R is not the circuit, but the connector. If you get a unit that was made for a Honda, and if it has a harness and connector, you will need to modify the connector to work with the FZ6 connector. There’s no real magic, there are the three yellow AC power lines, and then the red (+) and black (-) output lines (some have an additional green wire for an indicator light).

If you current aftermarket R/R has a harness and connector, then modify that to work on the new one.
 

Cocoloco

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An
My first thought is this is not related to the voltage regulator.
Any thoughts about this?
I was out looking for parts on my new project when this happened
I plan on tackling this when i finished rebuilding the engine.
 

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Cocoloco

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Update
I let the bike warmed up and turned the idle screw all the way to highest rpm it could get, and slowly turned it out until i reached 1300rpms and left it set , so far the problem hasn't occured yet
 

TownsendsFJR1300

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Did you check the "base" screw on the block used to sync the TB's?

It should be about 3/4 -7/8" a turn out... A throttle body sync wouldn't hurt either


Pic will expire in 48 hours
 
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Cocoloco

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Did you check the "base" screw on the block used to sync the TB's?

It should be about 3/4 -7/8" a turn out... A throttle body sync wouldn't hurt either


Pic will expire in 48 hours

I cleaned the sync block and the throttle bodies before, and yes i set the base 3/4 out and sync the TB's using vacuum gauges. Revving it steady at 3k rpm it all seemed to have the same vacuums.
 

Cocoloco

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Update
It happened again i noticed when im at slow traffic and sometimes get stuck in traffic light it occurs.
when im cruising at a good speed and the weather is cold it does not occur.
I tested my IAT sensor for resistance when its hot and the problem occurs it shows very low ohms and jumping to OL in my multimeter which should not happen
Making the A/F super lean AFAIK
But no CEL in the cluster.
Heat soaked or failing IAT sensor
I'll try putting resistor equivalent to the specified resistance at 20°c 2200ohms just to confirm my diagnosis.
 

Cocoloco

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I
Sounds like the culprit. How did you test the sensor?
I lift up the tank then unplug the iat socket while running(problem occurs). CEL Lit when i unplugged the socket
Put multimeter set to ohms and poked the probe to the 2pin sensor.
Thats how i got the ohms reading
 

Cocoloco

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Another update!
I did the resistor trick. Runs well and no CEL
But problem still exists
Im still thinking why i didn't do TPS test when the problem occurs
Well it turns out my new chinese TPS is affected by heat soak
Tps reading when
Cold engine 16
When hot 25
Before replacing the tps, i will try to replace my throttle cable i can feel resistance when twisting the throttle when hot.
 
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