660 not liking the choke

[ranmafan]

Hi all,

So my 660 (97+ YZF600 rods, carbs, etc.) has been running for a while now, and I'm fairly happy with it.

One problem, though. It really doesn't like running with the choke on, any position (typically cuts out after a second or two). That is, from a stone cold start, the procedure is:

- Open choke all the way
- Crank for ~5 seconds before it even starts firing (all the while playing with the throttle)
(bike now sounds like it's running on 2 cylinders)

- A second or two later, close the choke (still holding the throttle)
(running noticeably smoother)
- Baby the throttle for a few more minutes until it's warm enough to idle.

The valves are adjusted. Carbs are as clean as they could be, choke plungers move fine, and there aren't any obstructions I could find. While it's anything close to warm, it starts "half-kick" - no issues.

I've tried replacing pilot jets (#40 with 1 turn out now), playing with the IMS, to not much effect. I don't think it's too rich at idle, either - closing the throttle at speed, there's always a fair bit of popping, and it won't start cold without choke.

So... any ideas where to start digging? Weak spark, perhaps?

[Camala_Pillion]

Hi all,

So my 660 (97+ YZF600 rods, carbs, etc.) has been running for a while now, and I'm fairly happy with it.

One problem, though. It really doesn't like running with the choke on, any position (typically cuts out after a second or two). That is, from a stone cold start, the procedure is:

- Open choke all the way
- Crank for ~5 seconds before it even starts firing (all the while playing with the throttle)
(bike now sounds like it's running on 2 cylinders)

- A second or two later, close the choke (still holding the throttle)
(running noticeably smoother)
- Baby the throttle for a few more minutes until it's warm enough to idle.

The valves are adjusted. Carbs are as clean as they could be, choke plungers move fine, and there aren't any obstructions I could find. While it's anything close to warm, it starts "half-kick" - no issues.

I've tried replacing pilot jets (#40 with 1 turn out now), playing with the IMS, to not much effect. I don't think it's too rich at idle, either - closing the throttle at speed, there's always a fair bit of popping, and it won't start cold without choke.

So... any ideas where to start digging? Weak spark, perhaps?

Hi,
I seem to remember Y_Geo saying the FZR has an enrichening circuit not a choke as such, I have not had George tell me to clean out carbs so I am a little hazy on this but I would make a guess that set up has a jet and that needs to be smaller. Since no jet works alone you will need to look at the idle jet overlap to smooth out the throttle response.

I will mention your problem to George and see if he has anything to say except "get me outa here" LoL

[ranmafan]

Hi,
I seem to remember Y_Geo saying the FZR has an enrichening circuit not a choke as such, I have not had George tell me to clean out carbs so I am a little hazy on this but I would make a guess that set up has a jet and that needs to be smaller. Since no jet works alone you will need to look at the idle jet overlap to smooth out the throttle response.

I will mention your problem to George and see if he has anything to say except "get me outa here" LoL

Thanks, and yeah, "choke" is a misnomer here (albeit a very common one) - otherwise, I could just write it off to dirty carbs.

All the other circuits are fine - picked the mainjet after a few dyno runs, and the rest after some riding. At any rate, neither mainjet nor needles should have much effect at idle. Not even the float height, I'd think....

Oh, and leaving the choke on does actually seem to flood the engine - that is, liquid fuel visible in two of cylinder intakes. Perhaps it just works too well?

[CJD]

At any rate, neither mainjet nor needles should have much effect at idle. Not even the float height, I'd think....

Believe me float heights & needle position have a profound effect @ idle/low RPM. Mine when I got her were float heights 19mm needle position 4th position from the top = running very rich. The bike would start cold without the choke, when the engine was warm she was a b#@ch to start. Not the problem you have though.

So... any ideas where to start digging? Weak spark, perhaps?

You may be on to something there, take a reading of your battery voltage, then check the coil input voltages (red/white wires), are they battery voltage or very close I.E. less than 0.5V difference ? if not when you hit the start button (Starter engaged) the voltage to the coils drops around another 2V causing a weak spark and a poor start. Better still check the coil input voltage's while your attempting to start the engine, should be no less than 10V.

[DonTZ125]

"Too rich" and "weak spark" are different problems, yet they can compound each other. The FZRs do NOT like a weak battery, as the starter and coils are all very power-hungry; the starter always wins, sometimes leaving the coils out of luck - and out of spark. A too-rich mix needs a stronger spark.

Your comment that it fires 'half-kick' when even silghtly warmed up strongly suggests to me that this is valves, not jetting. A warmer engine will run WORSE if too rich; rich = happy when cold. Check your valve clearances.

[ranmafan]

"Too rich" and "weak spark" are different problems, yet they can compound each other. The FZRs do NOT like a weak battery, as the starter and coils are all very power-hungry; the starter always wins, sometimes leaving the coils out of luck - and out of spark. A too-rich mix needs a stronger spark.

...And after running for a bit, the weaker battery would now be fully charged... making it start easier. Plausible?

Your comment that it fires 'half-kick' when even silghtly warmed up strongly suggests to me that this is valves, not jetting. A warmer engine will run WORSE if too rich; rich = happy when cold. Check your valve clearances.

Valves were my first guess, too - but I did VCA when putting the YZF head on, then another one ~1000k later (i.e. just recently) - not much difference (had to reshim two valves that weren't set quite right the first time, but that's it - I think they're barely under factory shim sizes). The timing is bone stock, as well. And yes, it's definitely not running rich when it gets going - if anything, it's a tad on the lean side at idle and top end...

Will be trying to test coils/leads/battery today, hopefully...

[ranmafan]

You may be on to something there, take a reading of your battery voltage, then check the coil input voltages (red/white wires), are they battery voltage or very close I.E. less than 0.5V difference ? if not when you hit the start button (Starter engaged) the voltage to the coils drops around another 2V causing a weak spark and a poor start. Better still check the coil input voltage's while your attempting to start the engine, should be no less than 10V.

So, a bit of testing:

Off:
Battery: 12.29V (rather low)

On (but not cranking):
Battery: 11.65V
Coils: 10.55V (on all inputs - not good...)

Taking out the coils:



Found:
- a bumblebee corpse lodged between the soldered coil terminals and the mount
- a broken upper coil mount
- 2.3Ohm at all primary winding terminals (OK)
- 30.6kOhm at 1+4 secondary, 31.6kOhm at 2+3 secondary (EDIT: Oops. I guess that should have been measured without the caps)

I'm suspecting the kill switch: red-white/red-black wire measures ~0.5-1Ohm between coil inputs and TCI, occasionally jumping to 20-30Ohm after flipping the switch a few times. That would explain the drop on that wire, at least.

I'll try cleaning the switch and jumping it from a car battery next...

[ranmafan]

Cleaned all contacts and the switch, rechecked the secondary windings (12.6kOhm each) and caps (~9kOhm).

The difference is noticeable - 0.2V higher at the coil inputs, starts firing after a few turns, and spends another second or two in high idle before dying.

Here's a video of what happens with a car battery connected:


The symptoms are the same, but less pronounced, and it even idles properly (with choke on) towards the end (see the annotations). The idle is set a bit higher than normal, ~1400 RPM warm, and this is at 20C and ~1km above sea level.

[CJD]

The coils are permanently live when the ignition is switched on regardless of the kill switches position, take a look at your ignition switch connection block close to the radiator cap. Wire colors are red brown blue, corrosion there will cause a voltage drop, I assume you checked the coil connectors for corrosion the white and yellow blocks?

[DonTZ125]

I have to disagree with you there, CJD - the coils are fed by the kill switch, which is in turn fed by the 10A Ignition fuse, which is switched by the key.

I agree completely with following the wires back and checking for corrosion absolutely everywhere!

[CJD]

I have to disagree with you there, CJD - the coils are fed by the kill switch, which is in turn fed by the 10A Ignition fuse, which is switched by the key.

I agree completely with following the wires back and checking for corrosion absolutely everywhere!

Just to clarify is this a FZR 600? if so take a look at the wiring diagram http://fzronline.com/wiki/lib/exe/fetch ... iagram.gif

Note the coils are fed VIA the ignition fuse, take a closer look.

The red white wire from the ignition fuse branches to the coils, and to the kill switch. The kill switch has no effect on the voltage delivered to the coils whatsoever. Unless the diagram here is wrong or this isn't a FZR 600.

[DonTZ125]

Yeah, that's NaeSLaS's wiring diagram. I'm looking at Yamaha's diagram in the manual. There's a few errors in his version...

[CJD]

Yeah, that's NaeSLaS's wiring diagram. I'm looking at Yamaha's diagram in the manual. There's a few errors in his version...

So this diagram must also be wrong http://imageshack.us/f/215/fzrwiringdiagram1.jpg/

The haynes manual also shows the ignition fuse feeds the coils directly your certain that all 3 diagrams are wrong?

[DonTZ125]

I just double-checked the Yamaha manual - I hate it when I screw up!

[ranmafan]

The coils are permanently live when the ignition is switched on regardless of the kill switches position, take a look at your ignition switch connection block close to the radiator cap.

Ah, that is correct, and it does make sense if you look at the diagram closely. And yes, this is (mostly) a 1991 FZR600 - my bad.

I did check/clean the rest of the connections, they all should fine (southern Alberta is a pretty dry place, anyway...). I'm now getting a voltage drop of about 0.8V between the battery and coil inputs with the key on. I've no idea how TCI outputs look like, but that sounds about right for, say, one silicon p-n junction...

Also fixed a few possible air leaks that I stupidly missed before... Now, it seems I'm starting to get somewhere.

Unlike before, it fires right up with its own battery and choke on (everything else is about the same). Once it's warm, however:

(choke on all the way)
- goes up to ~3k RPM
- a moment later, slowly starts to drop back down to ~2k
- at the same time, cylinder #2 exhaust temperature starts dropping like a rock, from ~220C to below 100C, while the rest stay around 180C
(choke off, all cylinders idle at around 220-240C)

I'm guessing #2 plug is not gapped correctly....