Rough Idle when hot......Again. New battery voltages. Help.

My carbs are clean. My tank/petcock are clean. Knowing that...........

So, yesterday on my way home my '93 VFR started acting strange once warmed up. The idle starting giong bad/rough at stop lights and in traffic. When I pulled away from a light or accelerated it ran as though it was starving for fuel unitl about 3K rpm at which point it ran fine on the highway all the way home.

This morning on my way to work same issue. Started fine. Warmed up fine. First 50 miles of my drive it was fine. Got to the gate on base and while waiting in line to get on base the idle got shitty and actually died once but started right back up. Same thing on the way home. Started fine but got the bad idle in traffic but fine above 3K rpm.

I just got home and though WTF!!!!! I tested battery voltage while bike was off and its 12.1v

While ideling the voltage is at 11.8v

At 4500-5000 rpm it read between 9 - 12v

Am I to assume my R/R or stator as craped out and I should started searching through the 100000000 posts on here about it?

 

Its probably the r/r. I just replaced mine with a FH010 and connectors and better wiring from eastern beaver.

I misdiagnosed the stator and ordered a new stator. Found out later my stator fine.

Check the voltages between the 3 stator output wires with the multimeter set to read AC volts and if they read about the same between all three and are around 20v at idle and go to around 70v with revs the stator is fine.

I mounted the new r/r at the stock location but I plan to move it to a cooler place near the rear of the bike.

 

While running, voltage on battery should be ~13.7 V or so. Good battery should measure ~12.5 when bike is off ....
So, it is fair to diagnose this as toasted R/R. However, I would still check for blown fuses and fried wires, although this is less likely ....

 

Under 14V when running near idle speed is fine for stock type (shunt type) r/r. If you are only getting 13.7 v through out the rev range there is too much resistance in the wiring and connectors or the r/r is getting weaker and the probability of it stranding you is high. I installed a FET r/r with heavier gage wiring and its a steady 14.3 v from 1000rpm thru redline. I think my multimeter reads a couple 10ths lower than actual( I have to double check with my dad's Fluke) but the notable part is the voltage was steady and the r/r runs much cooler!

 

You say "New battery voltages". Are you saying these are voltage tests on a new battery or these are new voltage tests on an old battery? If this is an old battery charge and test the battery first. If this is a new battery check wires and connectors and buy a new R/R.

 

Sorry, Not a new battery. New readings from awhile ago in a different post.

Thanks for all the help. I figured the R/R was on it's way out. I will test the stator also.

 

I did a quick test before I came into work this morning. Tested resistance on the 3 yellow wires at the r/r to test the stator. Alll were ~.1 so that is good, where it should be. Someone mentioned to test the 3 yellow wires while the bike is running (AC) should be around 20VAC at idle? I assume you put the pos. test lead of the multimeter on the yellow wire and black to ground?

Just to clarify your thoughts, would the dying R/R be the cause for the rough idle when it's hot? I know with electronics, something can work/test good when cool but once it heats up the item can loose resistance or have other issues. It makes sense to me but I'm no pro with this stuff.

I'm giong to go with a dying R/R as per my initial results and get one on order with a VFRness and go from there. Thank God I still have my pretty '86 VFR to ride. I'd go nuts with no bike. It's suppossed to be in the 70's all week and sunny.

 

Inspect the plug connector on top of the starter relay for burned wires, also the 3-wire plug between stator and r/r, both common trouble areas.

 

measure ac voltage between two yellow wires, not between yellow and ground. The alternator voltage is/must be isolated from the chassis.

 

Thanks for the help. Hope to have more time to work on it tomorrow.

 

Update:

Fully charged the battery overnight. Brought it in to get tested and it tested fine. Plugged it into the bike. Let bike warm up. Here are the readings:

Idle = 12.30V
5000 rpm = 13.40V (it takes a few seconds to climb from 12.3v to the 13.4v and it kinda sits there. Maybe will climb a lil higher if I hold it at 5Krpm longer.

Turn bike off. Check resistance at 3 yellow wires. A, B, C and back and forth and they all read 1ohms or less. So that's good.

Turn bike back on and check ACV at 3 yellow wires. Each read 20VAC at idle and 50VAC at 5000 rpm.

Aside from my DC readings at idle and at 5K rpms everything checks out. Should I assume my R/R is weak and heading on it's way out?

 

Another update.

After all that I decided to put on a new fuel filter just before the pump. I hooked it up on the inlet and wanted to test flow. Turned the tank on and it flowed really well for a few seconds, then it slowed to a trickle and I was hearing a hissing sound from the tank cap. It's plugged and won't flow fuel!!!!

So, guess the whole issue I've been having is from a clogged fuel tank vent. I sprayed some carb cleaner into the key hole in hopes it would break loose whatever is in there. Anyone experience this? How do you fix this?

 

Your stator checks out fine. So the issue is definitely with the r/r. I would recommend getting a used Fh012 or similiar from ebay off a R1 or zx10 or another newer bike(should be able to get it for under $50 from ebay, like this 2005 Kawasaki ZX10R ZX 10 Regulator Rectifier 04 05 | eBay) and get either a VFRness modified for R1 r/r or get the the connectors and wiring from eastern-beaver(R/R Connectors) or somebody else selling it. part A and part B from eastern beaver r/r page is what you need to use the R1 r/r.

The total cost should about the same as getting new stock type (shunt type) r/r and the retrofit shouldn't take half an hour more than just swapping the stock one and the retrofit should last much longer than the stock unit and the stock wiring/connectors.

For the fuel tank issue :
The vent is either under the cap where you should be able to see with cap open or under the tank connected to the evap emissions stuff. Don't remember exactly how the venting is on vfr. carb cleaner followed by compressed air should clear it up. Some times removing the fuel cap and cleaning the passage thru the fuel cap is required. Shouldn't be too hard to figure out what needs to be done when looking at it.

 

Smack - you might have to thank your slow fuel flow for making you check your voltage readings.

Get that R/R outta there and replace it. Its doomed.

 

+1
and connect the battery to a tender every night till you get the r/r replaced to avoid getting stranded. Atleast the VFR is easy to push start. I think the mass(lots of K.E.) of the bike makes it easy to start it with just a walking pace. My old ninja 250 needed a lot more speed to be bump started.

 

Thanks guys. Yeah, bike will be on the tender nightly and I'll be looking more into the newer R1 and ZX10 R/Rs. Hopefully I'll have it all on order in the next week. Again, appreciate the help.

 

Remember a bad R/R can ruin a good Battery and Stator so do it ASAP. It sure looks like your on your way to happy motoring!

 

Don't you just love it when you ask for a little help and things work out!

 

I know!!! I love these darn forums. I have it parked until the new r/r gets here. I'm also going to order a vfrness. Guess I'll be putting some miles on Ms. '86 while Ms. '93 is out of commission.