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XLT 34mm Mikuni pilot jet?

Tuning

 
 
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  #1  
Old 11-09-2009
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Default XLT 34mm Mikuni pilot jet?

have a 1994 XLT580 with 34mm Mikuni carbs. runs good but at very start of thumb throttle travel (between 1800-2500/3000rpm), have a slight 'bog'. RPM still increases but not a 'snappy' response. Once past 2500-3000 rpm, goes like hell. I don't know if I would call it a hesitation as the rpm still rises but doesn't respond like I think it should. would this be the pilot jet? do I need to increase the size of my pilot jet to allow more air hence allowing more fuel at beginning of throttle?

Last edited by xlt580 : 11-09-2009 at 09:47 AM.
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  #2  
Old 11-09-2009
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Hold on, so is the sled engaging and moving at 1800-2500 RPM? Or are you just noticing a hesitation on the tach?
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  #3  
Old 11-09-2009
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no, not engaging the clutch until about the point the engine starts to respond the way i think it should(3000 rpm or so). also have an Ultra700 in my shop(bro-in-laws) and it is really snappy right off the getgo. On his machine, if you quickly mash the throttle to the hand grip and let go, increases rpm enough to engage the clutch. Mine, do the same, not even close to engaging the clutch. almost have to sqeeze a little slower it until the revs come up, then pin it. Tends to react much slower until around 2500-3000 rpm at which point it really comes alive and seems to run correctly. Really runs good once it gets past 2500-3000 rpm.
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  #4  
Old 11-09-2009
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depending on how you define 'hesitation'. RPM does not drop at all it still increases as you squeeze the throttle, just not quickly until about 2500-3000 rpm. I guess this would be considered a hesitation of sorts. Removed airbox and replaced with pod filters but this is not the problem as it did the same with the airbox on.
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  #5  
Old 11-09-2009
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Your pilot will affect your idle and low end. The needle jet will affect the mid range. And the main jet is the top end.

To be honest I would check the carbs for plugging before you start changing anything. If they look good and clean then I would set the carbs back to the factory defaults and work from there.
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  #6  
Old 11-09-2009
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one thing that did change since removing the airbox; will start with choke engaged but will not continue to run unless I feather the throttle and/or turn choke off. after about 5-10 seconds machine will run on its own. not a major issue, still starts easily, just need to run throttle a little until running smoothly.
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  #7  
Old 11-09-2009
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To be honest there aren't many sleds that won't do that. I know on my 2005 600 HO if I leave the choke engaged she'll puke out. But if and when you take those carbs apart makes sure those chokes are moving freely in there. I've seen those chokes on the older triples develop corrosion on em and they'll stick up or down and make for a bitch to start or a sluggish performing machine.
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  #8  
Old 11-09-2009
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have had the carbs apart and cleaned (were actually very clean already), replaced needle and seat in all three carbs. Have set the air screw back to factory(1 turn out from lightly seated). Adjusting the air screw did not seem to have any effect on the bottom end hesitation. Went to 1 1/2 turns out, seemed more responsive after about 3000rpm. With pod filters, was told introducing more air, need to introduce more fuel to keep AF ratio at safe level. Haven't ridden the sled yet since adding pod filters. may need to re-jet after inspecting plugs after first hard run.
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  #9  
Old 11-09-2009
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just was expecting a little more snap at the bottom end. As I mentioned, Ultra700 responds very quickly. XLT580, not responsive at all until 3000 rpm.
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  #10  
Old 11-09-2009
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Sounds like you did exactly what I would have done.
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  #11  
Old 11-09-2009
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not worried about the choke thing, starts good, will run on its own after a few seconds. would really like to solve the bottom end hesitation issue though. would larger pilot jets allow more fuel at bottom end?
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  #12  
Old 11-09-2009
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Yes, you may also want to play with the needle jet, cause it will have 3-4 settings where you can have more or less fuel coming at certain times.
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  #13  
Old 11-20-2009
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Ok fellas, I am confused now, really need some advice. Ran engine for about 10 minutes, running same as before, low end response is lacking but comes to life after about 3000rpm. Removed the spark plugs and they were soaking wet. This indicates too rich? How can it be too rich? Idles perfectly, no major smoke from exhaust but as soon as I start revving the engine(3000-6000rpm), very smoky, shop fills up very quickly. what the hell is going on? Removing the airbox should have created a lean situation? So, thinking rich, I moved my jet needle down one notch (moved clip up one notch) to lean it out a little. No noticable change. Have replaced pilot jet with stock new part. Have stock 200 main jets in 34mm carbs. Any suggestions? I understand that I am trying to tune the machine at about 0 degrees celcius, will be riding at about -15-20 degrees celcius. This will make some difference but I would like to be close though so as to not be standing in the cold tuning my sled. I am sure most of you have been there...

Last edited by xlt580 : 11-20-2009 at 06:41 AM.
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  #14  
Old 11-20-2009
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Choke plunger stuck open?
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  #15  
Old 11-20-2009
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Removing the airbox won't create a lean condition. I agree with IBS check that choke plunger and cable.
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  #16  
Old 11-20-2009
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I thought about that as well, have already removed all 3 choke mechanisms from carbs, cleaned and re-assembled. Were not dirty and looked OK. To rule out the choke problem, could I remove the mechanisms from the carbs and manually plug the choke orifice on the carb? I checked the action of the cables and plungers and they appear to be closing. I do have a little slack at the choke lever on the console but this can be interpeted 2 ways; either set up to close completely with a little slack at the lever to ensure closing completely or sticking slightly and not pulling cable tight at the lever.
With regards to the lean condition, I am only repeating what was indicated to me, that replacing the airbox with pod filters introduces more air flow into the motor thus creating a 'lean' condition. Was told to be careful, run for 10km then check plugs for color, may need to use larger jets. Now, this makes no sense to me as the plugs were wet when I removed them which means too large of a main jet? Have stock 200 in carbs now, seems backwards to go smaller?
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  #17  
Old 11-20-2009
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Oh I see yeah typically replacing with pod filters will net more airflow. Sorry its been a while since I saw this thread. But your main jet shouldn't come to play at idle. Pilot is going to be the one you need to be concerned about, and the needle is for the mid range and main is for the top end. Even still I'm not sure even running at idle if you can tell whether you have too rich of a pilot or not. I've always changed them based on the performance of the sled, never tried to inspect the plugs at low end because they always seem wet.
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  #18  
Old 11-20-2009
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ok, so plugs being wet may not be out of the ordinary? sorry but bit of a newbie with these newer sleds. It is from 0 to about 1/4 or 1/3 throttle where the sled lacks power or response. To me, this indicates pilot jets as you mentioned. I replaced the originals with new OEM, same size as from factory. Surely this sled wouldn't have been tuned to have this little low end response? And it runs great at idle, no smoke idles smoothly, only when applying throttle does the machine start to create smoke and the lack of responsiveness is noticed. Once past 3000rpm or so the old 580 absolutely comes alive, still creating some smoke but the response is good. I guess after ensuring choke plungers are actually closing all the way I will try larger pilot jets. I have to add that the sled had a lack of low end response with the airbox still installed on the sled too.
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  #19  
Old 11-20-2009
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In the mid range you would adjust by moving the needle clip up or down.
Have you set the air screw at 1 turn out? You can turn it in to make it richer if needed, usually I have found that the Poo tends to like 3/4 turn out best.
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  #20  
Old 11-20-2009
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If you're going to get some pilot jets get a size smaller as well, if I remember right the XLT's were always a touch fat from the factory on the low end. I feintly remember my brother putting 40's in his XLT down from the stock 45 if I remember correctly.
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  #21  
Old 11-20-2009
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I started with the air screw at 1 turn out, tried half a turn in and out, not what I would call a noticable difference on bottom end. shouldn't there be a noticable difference? seemed to affect start of midrange more than anything. My stock pilot jet is a 35, maybe first I'll try 30's before going larger as it seems awfully rich on the bottom end.
Just to clarify, turning the air screw in makes it richer? I was told opposite, that opening the screw allows more air into the pilot circuit thus allowing more fuel to leave the carb. Similar to drinking from glass bottle, you can suck all you want but unless you let some air in beside your lips, no fluid can leave the bottle. Sorry, lame example, this is how it was explained to me, made sense at the time. Now, it seems that you are saying that with the screw closed all the way, nothing but fuel is entering the engine, no air? Opening the screw allows air to mix with the fuel before it enters the engine? I was under the assumption that the air the engine needs to operate at idle was still coming thru small opening at bottom of the slide. Learning every day....
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  #22  
Old 11-20-2009
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Try this thread:
http://www.slednutz.com/showthread.p...light=airscrew
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  #23  
Old 11-20-2009
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94 xlt 580 stock is 200 main ,jet 35 pilot jet , air screw 1 turn out, jet needle third place down, if one of the needle and seats leak you will be boggy on the low end as well.( may be caused by a plugged vent line) If your carbs are synced and in good condition then i would move onto the primary clutch. I have in the past had boggy start off the line due to a worn clutch. Let me know if this helps
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  #24  
Old 11-26-2009
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have already replaced needle and seats, the original owner says he put in a new clutch only about 120km ago. Clutch appears to engage nicely and does not engage too early. As far as carbs sync'd up, all sliders move at same time. The original owner also stated that the sled had a tuneup same time as new clutch. For a relatively fresh tune-up, machine runs really rich.
For jet needle, you are referring to the e-clip location (third place down), correct? I had moved the clip to the second position to drop needle lower in the needle jet in an attempt at leaning out the sled a little but have moved it back to stock location.

Rubi-
Thanks for the tip on the thread referring to carb operation. It is all clear now, crystal clear.
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  #25  
Old 03-10-2010
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Default What was the problem?

Was this sled fixed? If so why aren't any threads added so the solution is posted for the next poor sucker who experiences the same problem?
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