Shakedown run jetting issues.

[TheRadBaron]

I took the first ride on my FJ this morning.  I've never ridden the bike before, so I don't have anything to compare the results to.  Here's my setup:  It's an '84 FJ1100 with a V&H SuperSport 4-1 exhaust and the dual carb UNI pods.  Other than that, the bike is stock.  Based on what I've read here, I have #40 pilots and #125 main jets, and the adjustable Mikuni needles from Randy.  Needle jets are stock and not worn.  I started with the needle clips in the #3 position and the pilot screw 2.5 turns out.  It was about 30 degrees out when I was doing this.  The bike started and idled well while I was synching the carbs.  However, it would hardly move under its own power because as soon as I gave it gas it would bog down and die.  I lowered the clips to the #4 position and this improved the problem, but the bike was still barely rideable.  I lowered the clips to the #5 position and gave the idle screws another 1/2 turn out (3 turns out total).  Now the bike runs pretty well.  The idle quality is good and the off idle power seems okay, the top end feels good, but there's a bad stumble at part throttle, mid-RPMs (I don't have the tach on the bike yet, so I can't give more meaningful RPM figures.
Based on some other posts by Pat Conlon regarding the jetting, it seems like everything should be right with my jets.  Maybe I could step up to a 127.5 or 130, but full throttle feels good, anyway.  According to him, the needle shouldn't have to be richer than the #3 position, so I'm curious as to why mine wouldn't work in the #3 spot at all.
Anyone have any ideas?  Thanks.

[SlowOldGuy]

I think you're too rich on everything.  Are you sure the carbs are clean?  Sounds like you're compensating for a dirty/lean idle circuit with massive over jetting.

I have an '85 with Wiseco 1200 kit, stock exhaust, degreed cams, UNI replacement filter in stock airbox, with a DJ kit.

I'm running #40 idle jets and mixture screws out about 2-3/4 turns
#110 DJ Main jet
Needle position at 1.5 groove.

Great carburetion with this setup, but it smells a little rich at idle.

I don't think you're going in the correct direction.  Something else may be wrong.

DavidR.

[TheRadBaron]

I'm sure that the carbs are clean.  I gave them a very comprehensive cleaning before putting them back on the bike.
Thanks for the input and the fact that something else could be wrong is a very real possibility.  I'm far from an expert on these carbs and their jetting, but based on what I have read here I think the differences in our bikes would make for a very different jetting.  Yours being a 1200 with stock exhaust and stock airbox, and mine being an 1100 with a 4-1 and pods.
I think that Pat's bike is set up similarly to mine and he's using 130 main jets and says that it works well, though 127.5 would also work well.  I think his needle is in the #2 or #3 position.  He'll probably chime in here. 

[racerman_27410]

did you change the air correction jets ?  they help a lot with a 4/1 mid range stumble.

the jet numbers can be confusing what brand are your jets ?

[TheRadBaron]

I'm using genuine Mikuni jets.  Tell me more about the air correction jets.  I haven't read anything about those.  They're the ones in the carb intake throat that are the same jet type as the mains, right?
What size did you use to help your stumble?

[Dan Filetti]

I think you're too rich on everything. 

Damn, I wish that were true for me....

Dan

[andyb]

What do the plugs say?  You should be close on that jetting for cold weather, it'll be a pinch fat when summer's full-on. 

I'd double check for vacuum problems, mis-assembled bits, etc, before tearing the carbs off again.  And ffs man, it's too cold for this crap, you're gonna make me feel bad for not getting mine up and going! 

[SlowOldGuy]

I'm far from an expert on these carbs and their jetting, but based on what I have read here I think the differences in our bikes would make for a very different jetting.  Yours being a 1200 with stock exhaust and stock airbox, and mine being an 1100 with a 4-1 and pods.
I think that Pat's bike is set up similarly to mine and he's using 130 main jets and says that it works well, though 127.5 would also work well.  I think his needle is in the #2 or #3 position.  He'll probably chime in here.  

The biggest effect pods have is on the needle position.  
Yes, a 4:1 will make a difference, but does it really require a 20% jetting difference??  I think NOT.   The main jet mainly affects the top end at WOT.  What you're explaining has practically nothing to do with the main jet.

Are you sure the diaphragms don't have holes in them?

DavidR.

[andyb]

According to FactoryPro, the pipe is less important (at least on the FJ) as the pod filters.  They recommend a 132.5 main jet on a comparably equipped FJ, albeit with their bespoke needles.

Randy, who successfully races, builds, and maintains cars using this engine suggested 122.5's to me, in a comparable configuration to the original poster.

I personally have run a 125 and 122.5 main in testing at the dragstrip with no real noticable difference in mph (read, average power put down through a 1/4mi pass).  I've also run a vastly ridiculous jet that caused the engine to nose over hard when the needles topped out, either smaller mains or a needle with less taper would have corrected that, the former is how I fixed it, the latter is likely why FP is getting away with such large mains in their kits.

The main jet has a fairly minimal effect at small throttle positions/idle (low demand).  So that's undoubtedly not the problem for a bog on initial throttle application. 

Without a tach, it's going to be difficult to assess where the problem is.  I agree in part with David though, this is going a bit outside the box on the usual tune for clip position.  In fairness it is cold as shit out, and that's going to make it pretty hungry for fuel.  The other issue is multiple adjustments at once. 

-Compare what happens with and without the choke on.  If it improves, you're still lean.  Note that this is only for the low-rpm and around town sort of speeds. 
-Read the plugs. 
-Check the carb spring/slide assemblies.  Make sure that they move with very little resistance in either direction (a little oil helps on the slide sometimes).  Check to make sure the diaphrams aren't torn/pinholed, either.
-Get a tach on that thing, it's useful.  Despite the need to vroom around to check your work so far   Know the feeling though!

With the cold weather, it wouldn't shock me to see you run the mix screws a full 5 turns out.  It'll run like crap in the summer, but with things so cold that'd be closer for a winter tune.  The main jet you don't want to really fiddle with until you have a tach on the bike.  Basically, it should try to rip your shoulders out of joint from 7k to a bit into the redline, if it's nosing over or getting flat, it's not right.  I'm also in northern IL and I had to use a 42.5 pilot to get the mix screws under 4.5 turns out, so don't sweat things too hugely.  If the needles are right, you shouldn't feel them transition.  Job done.

[TheRadBaron]

Thanks for all the info.  My carb diaphrams aren't in the greatest shape.  There are some cracks but I looked at them very closely and held them up to the light and didn't see any spots where light came through.  I'm putting some money aside for new ones in the future.
I guess that I could try turning the pilot screws out a bit more to see if that helps.
Racerman made mention of changing the air correction jets and that it helps a lot with a 4-1 exhaust.  I did a search here and found a bit more info, but not much.  I gather that I should reduce the air jet size to make the idle circuit richer.  How much smaller should I go? Anyone have any jet numbers?
I should have the fairing on the bike within the next few days, so I'll have some useful RPM readings.  In the meantime I'll double check everything to make sure I haven't missed anything.  I'll check out the float levels, as well.
I can't wait to get this sorted out.  Once I got past the mid-range stumble, the high RPM power was unlike anything I've ever experience.  Man oh man.

[Yamifj1200]

"the high RPM power was unlike anything I've ever experienced"


Welcome to the FJ world... wait till she's just right,  You aint seen nothing yet..


Eric M

[SlowOldGuy]

I guess I should temper my recommendations and observations witht he fact that all my experience is with DynoJet components.  Although I have experimented with mixing in some Mikuni jets with the DJ needles, couldn't really tell much if any difference.

And, to tell the truth, I don't really exercise my main jet all that much.  I don't find myself needing much full throttle response when riding the twisties.

DavidR.

[racerman_27410]

IIRC they were the 155? air correction jets


i had a nasty mid range stumble with my supertrapp exhaust and installing the ACJ's fixed it right up.

Kookaloo!

[TheRadBaron]

I think the stock size is 155.  I went through some other posts and it sounds like a DJ 144 jet was an option in some Dynojet kits.  Is that what you installed?
According to the jet comparison chart this translates to a 135 Mikuni.
Another thing that occurred to me is that I'm not sure if the slide springs are the stock ones.  The bike had what I think were Dynojet components (needles and main jets) in the carbs when I got it, but the needles were too worn and corroded to reuse.  Is there a way to tell if the springs are stock or not?

[racerman_27410]

I think the stock size is 155.  I went through some other posts and it sounds like a DJ 144 jet was an option in some Dynojet kits.  Is that what you installed?
According to the jet comparison chart this translates to a 135 Mikuni.
Another thing that occurred to me is that I'm not sure if the slide springs are the stock ones.  The bike had what I think were Dynojet components (needles and main jets) in the carbs when I got it, but the needles were too worn and corroded to reuse.  Is there a way to tell if the springs are stock or not?

that sounds about right on the air correction jets..... it's only been about 12 years since i did that job 


did you replace the emulsion tubes that had the corroded needles in them ?


KOokaloo!