Carburettor Question......

[fazerscotty]

A question for the FOC-U fonts of knowledge.


Gen 1 1000 FZS. Pilot Air Screw setting. In both the Good Book of little fibs (Haynes!) and the genuine Yamaha service manual, the pilot air screws are set at 2.0 turns out. Have I seen on here that 3.0 is recommended and if so why?
I've currently got mine set to 3.0 and it seems very rich and will start from cold with no choke.


Answers please, not on a postcard 

[Falcon 269]

Set at 3 turns out to richen the mixture at idle and just off idle.  In fact, 3.5 to 4 turns is better still.

If it starts from cold with no choke, possible that it's been 'Ivanized'.

I assume you're saying very rich because you can smell fuel at idle.  You will.  However, once you crack the throttle, you'll be glad you have that little extra richness.  It's not excessive, either.

[Gnasher]

Set at 3 turns out to richen the mixture at idle and just off idle.

Turning the air bleed screw out will lean a mixture off, not richen it. Unlike and not to be confused with a mixture screw, which is the opposite out to richen i.e. more fuel.   The pilot air circuit, has no effect on fueling above 1/4 throttle (3000 rpm) as fueling is switched over the the main circuit.    

[fazerscotty]

Set at 3 turns out to richen the mixture at idle and just off idle.  In fact, 3.5 to 4 turns is better still.

If it starts from cold with no choke, possible that it's been 'Ivanized'.

I assume you're saying very rich because you can smell fuel at idle.  You will.  However, once you crack the throttle, you'll be glad you have that little extra richness.  It's not excessive, either.

Didn't used to start from cold without choke and I can't see any evidence that it's been "ivanised". In fact getting one of the kits was on the shopping list this winter just gone, but a lack of funds dictated otherwise!
I'll have a play this weekend and see what results I get 

[Gnasher]

I've currently got mine set to 3.0 and it seems very rich and will start from cold with no choke.

As mentioned by Falcon, it's possible your bike has a Ivan's kit fitted, which will richen up the mixture at idle and requires a 4 - 4.5 turns out to lean off the mixture to obtain a smooth idle.  If the bike has been running fine for a good while and has recently started running rich, it's possible the air filter is now restricted and needs either cleaning (K&N) or replacing, so check that.

The above will happen if it's Ivaniased or not. 

To find out whether your bike has a kit fitted will require you to, pull the carbs off and check the main jets, needles and if the air bleed holes have been drilled.  Many are now Ivanised which is a big improvement, unfortunately owners often don't tell, new buyers/dealers and/or they've been sold on a good few times and the info is lost.     
     

[Falcon 269]

The reason Ivan took the unusual step of enlarging the pilot circuit bypass holes was to allow more fuel to pass through them just off idle.  In his testing, he found that turning the mixture screws out as far as they would go (about 5.5 turns) wasn't enough to give him the richer a/f ratio he wanted ... the size and placement of the holes was the limiting factor.

To check if Fazer carbs have been 'Ivanized' simply remove any carb top and look at the slide spring.  If it has been cut at one end to shorten it, it will be obvious.  If you go on to remove the slide and inspect the needle, you'll find that Ivan's needles have changes in taper that are visible to the eye.  Stock needles are straight-edged along the whole length of the taper.  If you remove the needle from the slide, you'll find that stock needles have SD-130 or SD-129 stamped around the top.

[fazerscotty]

Apologies for the delay in responding (been working away).
Many thanks for the info - hopefully, I'll get more than a few minutes in the garage to investigate and play with the carbs.


Thanks guys.

[fazerscotty]

So, whipped the carbs off, set the screws at 3 turns out each. Whilst carbs were out of the sockets, I had a quick look and I can see no evidence of Ivanising. That'll be next years treat to myself (or this years Fathers Day  )
Carbs back on - starts with a whiff of choke and settles down nicely.
Planning on a 50 - 60 mile whizz when it stops raining to settle everything down and then back on the ramp for a carb balance.


Thanks guys.