low end heasitation

i am new to this site, but i have had my 81xj550r for a while now, and lately it has had a low end heasitation, it idles fine and the top end is awesome, but from off idle to about 4k it just won't go, it feels like it is getting too much fuel cause i have to hold it wide open from off idle and it heasitates till about 4k and then takes off like a rocket, it has a custom made free flow exhaust and pod filters, and the only jets i changed were the pilot jets cause they were the only ones that were beyond repair when i first got it and i went from a #35 pilot (stock) to a #50 pilot ( the closest the local shop had to a 35), i am wondering if that might be my problem and what exactly the pilot jet does, and also, what the heck does yics mean, it has just been something that has been bugging me, thanks for your help

 

That's your Problem.
The Pilot Jets are too Rich.

Pull the Plugs and examin their coloration.
If they are extremely dark to almost black ... you have to turn IN the Pilot Mixture Screws to present a less Rich Mixture to the Cylinders during Off-Idle and the transition to Main Jets.

I'm surprised you aren't Fouling Plugs.
Turn the Pilot Misture Screw IN until they bottom out and try them at One and a half taurns out for those over-sized Pilot Fuel Jets.

 

thanks for the info, but i was wondering if anybody knew where the pilot jet screws are located on the mikuni carbs

 

i have had the same problem you come out of idle it wants to die at 1500to 2100 and not much till 4000 all i had to do was sink the carbs better and it runs like a dream
as said before it could also be the mixture but it could simply be the sink

 

The fact that he went from a 35 to a 50 Pilot Jet and is requesting the location of the Pilot Air Screws on those Mikuni's is a good clue that the Bike is running way too Rich.

The Pilot Mixture (Air) Screws on Mikuni are on the top, front, centered above the Intake in a cylindrical housing ... sometimes with Plugs preventing actually viewing the Screws hidden below the Plugs.

If your Bike has Plugs preventing access to the Screw Heads the Plugs will have to be removed.
Drill a small hole partially through the Plug being extremely careful not to allow the drill bit to contact the soft brass top of the screw.

Use a drywall screw ... screwed into the small drilled hole to extract the Plug by holding on to the drywall screw and impacting the Plug out.

Not drilling through the Plug and damaging the top of the Pilot Mixture Screw cannot be over-emphasized.

 

i must have read it to fast i completely missed the 50 jet part

listen to rick he knows his stuff

 

ok i found the screws, i had to take the caps off to get to them and i turned them all the way down and 1 1/4 up and it still heasitated, so i turned them down 1/4 at a time and it progresivly got better, now they are all the way down and it is almost gone,it will cruise at highway speeds without having to have it at a higher rpm, my fear is it is running too lean and it will damage the motor, the exhaust is pretty much a custom straightpipe with pod air filters, but i have noticed something else after a cruise down the highway for a few miles and coming to a stop, it will idle fine but when i try to take off again it feels like it is flooded and i have to hold it wide open so that the motor can catch up to the fuel in the carbs, then it will go back to normal... but i do love riding and my girlfriend loves it too, i just don't want to cause any engine damage if it is too lean

 

All you have to do is pull the Plugs and look at them. If they are Clean and look like new ... you're too Lean.
Now that you have some control ... try to get the Bike to Idle smoothly without too much Throttle-on at the Idle Adjustment Rod.

You got your work cut-out for you because you got Pods and that normally means re-jetting the rack.

First things first ...

Make sure you aren't burning too Lean. Adjust the Pilot Mixture Screws for a strong Idle.
The hesitation might be worked-out there ... but, with the Pods its anybodies guess.

I don't have an answer for you on what to do or try. I don't get involved in trying to tune-up an XJ-Engine that's got Pod air cleaners because what I'd tell you would probably be wrong, anyway!

You are going to have to deal with taking advice from the Membership that has swapped-over to Pods and made good.
Not everyone who had Pods or a performance exhaust gets the satisfaction out of riding a well tuned-up bike.

There are sacrifices to be made in performance and from what I have learned not too many successful work-arounds.

The Pods Society will be along and give you some advice on what you should try to do.

If you were my brother I tell you to get and airbox and boots and tune the thing up right!

 

I gotta agree with Rick.. 50's might be a tad much. 35 to 50 is a pretty big jump. That would also explain the stumbling on take-off once the bike is warmed up.

Are the main jets and needles stock?

 

yes the main jets and the needles are stock, the reason for sucth the big jump is the pilot jets were beyond repair, and the closest ones the local shop had were 50's for $4.50 each, i could have ordered the stock replacements but they wanted $17.00 for each one

 

With those BIG Pilot Jets in there, you are going to be running very Rich at Idle and off-Idle.

You will have to adjust the Pilot Mixture Screws IN to lessen the amount of Fuel the Air is dragging along. I don't know what a thumbnail setting would be ... but, I'd try One to One and a half and see what happens.

They might be all-together too big for the application, in which case you'll have to revert back to something closer to a 35 or so.
You'll just have to turn them in, listen to the Idle unless you have a Colortune Plug, and hope to be able to get the Pilot Mixture Lean enough so that its not snuffing-out the spark during Ignition.

That's what's happening now, I'm pretty sure. The Mixture is too Rich to Ignite during the Power Stroke.

But, that's only half of your Problem. With the Mods in place, you still need to worry about the Main Jet having enough supply for the additional air that the Pod Filters supply.

 

ok, i noticed that the last time i had the carbs apart that the main jets had a washer between them and the carb, just out of curiosity, if i was to take that washer out then would the transition from the pilot jet to the main jet take place at a higher rpm being that the needle would have to lift up further to get fuel, or would that mess with the top end power too much

 

That washer holds the emulsion tube in the carburetor. If you remove it, it could wonder up into the body of the carb, at a minimum wrecking the air:fuel mixture.

 

oh ok then i definently won't be doing that, thanks

 

That washer needs to be there. It holds down the Emulsion Tube, which could vibrate loose and cause you to have to pull the Carbs again to replace it.

If you weren't aware of that, I might suggest you examine the Emulsion Tubes.

They press out the Top of the Carb after removing the Main Jet and Washer plus the Carb Cover, spring and Diaphragm assembly.

If the Emulsion Tubes have clogged Air Holes the whole Mid-range and Top-end Fuel Supply suffers greatly!

 

oh the tubes are free and clear i just wasn't aware that the washers held them in