FJ1100 Carb problems

[Nickomac]

Hi there, I have a problem with my FJ1100 Chop. It is constantly running rich. The settings are needle on 2nd groove from the top. Main jets 114, Filters K&N and the air jet (Non removable one) drilled out to 1mm and custom one off 4 into 1 pipe. The pick up performance is fine, high revs is good too but mid range response is crap, it really doesn't like low revs in a high gear. for example i'm trundling along in 4th gear and have to slow a little in traffic, when I open it up again without changing gear it sounds like its flooding or something and is definitely not firing right, then after some gurgling or if i change to a lower gear it runs ok. plugs are always black. I am going to drop the needles to the 1st groove and considering dropping the main jets down to 110. will this help? Also it is stage 3 dyna jetted (or so i'm told) I have put new slides and diaphragms in as the old ones were naff.

[Nickomac]

Also if it has been Dyna jetted as I have been told then the jet sizes are as for that make...

[the fan]

Why did you drill the main air jet? That's a new one for me, not sure how that will affect things.

DJ kits tend to run a bit rich.  1 or 2 sizes down from suggested is common. I would go down to the 108 if I were in your place and leave the needle alone. While in there check the float level and adjust to factory spec.

I would set the mixture screw at 2.5 turns out and adjust from there.

Your application is going to be a bit different from the norm based on the carbs hanging out in the breeze and the custom pipe.

[Nickomac]

Hi mate, thanks for that. I didn't drill the main air jet out the guy I bought it from did that, i obviously didn't help with the mix though as its running too rich still. When you say go down to a 108 is that mikuni or dyna jet size?

[Klavdy]

Geezer,
An FJ Chop?
Cor.
You have to post pics of yer motor.

[Nickomac]

Already posted lol
http://www.fjowners.com/index.php?action=gallery;sa=view;id=1049

[andyb]

Strikes me that there's some strangeness here.

If you're certain that it's rich at lowish revs, the mains and needles have a minimal effect on that portion of the revs.  A DJ114 is likely just a pinch rich, but is close enough to start out.

If you're at low rpm in a tallish gear (say 2500 in 4th) and hit the gas, it'll go jerky and make all sorts of "not running right at all" sounds.  First guess is to check the fuel height/float level.  If you've got leaking orings at the needle seats, the float height will be right but the fuel height will be way too high, but it will run okay up higher on the tach.

If it's through the midrange (3k-6k at 1/4-1/2 throttle), then I'd suggest pulling the emulsion tubes (needle jets) out and seeing if they're still actually round.  As they wear, they make you untunably fat.

What's the pilot jet?  Guessing you need a 37 (stock) or a 40.
Where are the mix screws at?  Should be between 1.5 and 4 turns out someplace.

As per usual, this should be your tuning bible for carbs. 

You could possibly drill further into the air jets and tap them for jets, if you want to reduce the orfice size.  Don't really know what to  expect with those though, conventional wisdom would say that would lean things out.

Do be sure that you're rich though, before you work too hard at it.

[the fan]

Hi mate, thanks for that. I didn't drill the main air jet out the guy I bought it from did that, i obviously didn't help with the mix though as its running too rich still. When you say go down to a 108 is that mikuni or dyna jet size?

That would be the Dyno Jet size.  not sure on how that relates to Mikuni. I only have a chart converting to Keihin.

[andyb]

This post has a comparison of jet sizes for reference.

[Nickomac]

If you're at low rpm in a tallish gear (say 2500 in 4th) and hit the gas, it'll go jerky and make all sorts of "not running right at all" sounds.

Yep thats the problem. I believe that the mixture screws are 2 1/2 turns out. I haven't checked the emulsion tubes or float levels yet, but I will be seeing the guy who fitted the original dynajet bits to the carbs so hopefully he can give me some answers.

Watch this space and thanks for the help lads.

Nick

[Klavdy]

If you're at low rpm in a tallish gear (say 2500 in 4th) and hit the gas, it'll go jerky and make all sorts of "not running right at all" sounds.

Yep thats the problem. I believe that the mixture screws are 2 1/2 turns out. I haven't checked the emulsion tubes or float levels yet, but I will be seeing the guy who fitted the original dynajet bits to the carbs so hopefully he can give me some answers.

Watch this space and thanks for the help lads.

Nick

Can you have your motor off the frog and toad for a fortnight?
Pull the carbs off and send 'em to our carb gurus, is it Randy or Andy that sells a complete set for bugger all?
Or, stop faffing about, get 'em to sell you a whole new set.