'91 FJ1200 won't rev past 5k rpm under load PLEASE HELP!

[red]

.
I hate carbs!

{rant on} . . .The only thing I hate worse than carbs would be trying to get the air/fuel mix right with carbs,
without having an Exhaust Gas Analyzer (rich/lean), and maybe a dynomometer. . . .  {/rant off}

[racerrad8]

FYI I ping'ed Randy....
He will be able to get an answer for us next week

Looks like David already did it.

As Robert already mentioned, as well as David, the needle and emulsion tube need to be identified before recommending jetting changes.

Randy - RPM

[Troyskie]

Luckily I have Pete nearby.....

[Pat Conlon]

As Robert already mentioned, as well as David, the needle and emulsion tube need to be identified before recommending jetting changes.
Randy - RPM

Yep, according to the Yamaha GFSM for the '91, the needles and the needle jets (aka:emulsion tubes) are different.

JDM needles = 5FZ74-2
Usa needles = 5FZ74-3

Needle jets:
JDM = Y-0
USA = Y-2   Do these USA specs sound right Randy?

[racerrad8]

As Robert already mentioned, as well as David, the needle and emulsion tube need to be identified before recommending jetting changes.
Randy - RPM

Yep, according to the Yamaha GFSM for the '91, the needles and the needle jets (aka:emulsion tubes) are different.

JDM needles = 5FZ74-2
Usa needles = 5FZ74-3

Needle jets:
JDM = Y-0
USA = Y-2   Do these USA specs sound right Randy?

The stock, non adjustable needle we see in USA carbs is 5FZ72

The emulsion tube is 378 Y-2

So, if the JDM carbs use different needle and emulsion tubes, the jetting we use in the US will probably not work correctly. I have never seen a set of JDM carbs, so I do not know what the difference is to be able to offer advice.

FJ12IRL, it might be worth snapping a couple of photos and verifying the part number you have on your parts.

Randy - RPM

[T Legg]

I see a set of FJ1200 carburetors on e-bay for $195.00

[FJ12IRL]

Hi all, the new jets arrived today and I installed them. The bike now will rev out to the red line with no load, it wouldn't do that previously.
I'll take her out for a spin tomorrow to see how she's performing.

[FJ12IRL]

Hi All, Just been out for a test drive and I'm proud to say that my JDM FJ is able to access ALL the ponies!
She pulls well all the way to the redline in every gear now, no flat spots, idle is a little off but I will balance the carbs later.

I can say without doubt that the main cause of my troubles were the main jets sizes.

Thanks to all of you who helped me out with this, I can finally enjoy riding my beautiful FJ

[aj52]

Hi All, Just been out for a test drive and I'm proud to say that my JDM FJ is able to access ALL the ponies!
She pulls well all the way to the redline in every gear now, no flat spots, idle is a little off but I will balance the carbs later.

I can say without doubt that the main cause of my troubles were the main jets sizes.

Thanks to all of you who helped me out with this, I can finally enjoy riding my beautiful FJ

Good for you.
What jets did you put in.
Is it still OEM exhaust system.

Hannes

[FJ12IRL]

Hi All, Just been out for a test drive and I'm proud to say that my JDM FJ is able to access ALL the ponies!
She pulls well all the way to the redline in every gear now, no flat spots, idle is a little off but I will balance the carbs later.

I can say without doubt that the main cause of my troubles were the main jets sizes.

Thanks to all of you who helped me out with this, I can finally enjoy riding my beautiful FJ

Good for you.
What jets did you put in.
Is it still OEM exhaust system.

Hannes

I replaced the 87.5's with 112.5's..
stock exhaust system.

[red]

Hi All, Just been out for a test drive and I'm proud to say that my JDM FJ is able to access ALL the ponies!
She pulls well all the way to the redline in every gear now, no flat spots, idle is a little off but I will balance the carbs later.  I can say without doubt that the main cause of my troubles were the main jets sizes.  I replaced the 87.5's with 112.5's..  stock exhaust system.

FJ12IRL,

Sound good, man.  I'd keep the stock exhaust, unless you want to re-do the jetting again.  An aftermarket exhaust system may get you a few extra ponies (if even that much), but I've never seen results that justify the money and trouble of an aftermarket exhaust.

My $.02 worth . . . 

[aj52]

Hi All, Just been out for a test drive and I'm proud to say that my JDM FJ is able to access ALL the ponies!
She pulls well all the way to the redline in every gear now, no flat spots, idle is a little off but I will balance the carbs later.

I can say without doubt that the main cause of my troubles were the main jets sizes.

Thanks to all of you who helped me out with this, I can finally enjoy riding my beautiful FJ

Good for you.
What jets did you put in.
Is it still OEM exhaust system.

Hannes

I replaced the 87.5's with 112.5's..
stock exhaust system.

Thanks a lot.
The ABS one also had stock exhaust,going to open it up when the other carbs are finished and back on the non ABS one.
If it still have the 87's in,I am going to swap them out with the 112,5's then.

Hannes

[aj52]

Main air at 9 o'clock.

Pilot air (removable) at 1 o'clock

Thanks Pat,will check tomorrow.
I didn't know there is also a jet in that hole.
The ones at 1 o'clock are 157.5

Hannes

Ok,got a chance today to look at the main air jet.
It is also a fixed jet,can not remove it.
I measured it with nozzle cleaner set and use a micrometer.
It is 0.60mm. It goes in quite stiffly with that tip.

Hannes

[racerrad8]

Mikuni Jet sizing...?

As far as the fixed main air jet, my Hanson number drills fit the #49 (.073") almost perfectly in the fixed air bleed jet. 48 won't even try and 50 is sloppy.

Based on my other post above, the .073" converts to 1.8542mm and that is no where close to the listed size of 45 for the US market as well as the JDM. That would make it a 185 jet size if it was based on the holes size.

If I'm way off base please let me know...

Randy - RPM

[Pat Conlon]

...and that is no where close to the listed size of 45 for the US market as well as the JDM.

I didn't know that the GFSM lists the USA carbs as having a #45 main air jet.

The listing of a #45 for the JDM sounds logical with the goofy #85 main jets.

This Mikuni jet numbering is getting weird. Could the numbering on air jets be different than fuel jets?

Randy, do the 155 pilot air jets actually measure 1.55mm? (0.060")