air leak at airbox?

[piet]

i have a problem with my xs1100 idle mixture it is a bit lean,the airfilter is in place with on both side foamtape,the airbox is put thogether with a good rubber seal on the edge around,two carb vent. hoses are connected on the box and the crankhose too,and all rubbers between the box and carbs are correct fitting no leakage there,and at the bottom of the box there is a drain foamfilter in place.
now i'm asthonished that the engine keeps running when i totally close the intake hose,i noticed doing that that there was bilding up a vacuum when turning the trottle but where the heck is all the air leaking through the box,it is a puzzle for me
ther is only one cillinder getting the correct mixture number 4,there are cap's placed over the pilot screw's ,and the can't therefore turned to the correct mixture,i have to take them off to make the right turn out giving better mixture allthoug my repairmanuel advise me not to do that

[xssiveone]

No idea where the air would be coming in, could be a lot of places. I think you will have to just hunt it down. Take a propane torch and open the valve slightly, but don't lite it, and hold it next to the air box at any place that looks like it might be leaking. When the idle of the motor changes, you will have found your leak.

You didn't mention how long you've had the m/c, or how long it sat before you got it. Since only #4 is getting the correct mixture, maybe the carbs are dirty inside and need to be cleaned. This is especially true if it has sat for an extended period of time without proper prep. The gas evaporates and leaves behind a mess inside the carbs.

As for the caps on the mixture screws, the only way you are going to adjust them is by removing the caps. They are set at the factory to comply with the polution standards in effect at the time. To properly clean and tune your carbs, they must come out.

Drill a small hole thru the center of the cap. CAREFULL NOT TO GO TOO DEEP!! They are only thin metal and you will damage the tops of the mixture screws if you go too deep. Once you have the hole drilled, screw in a sheet metal screw. Then just pull on the screw and pop the covers out.

[piet]

i've got the xs1100 yust a week and i replaced the engine with a bad exhaustvalve for a good one from one of mine other five xs's ,i didn't checkt the carb's for dirt inside i forgot
on top of the pilotscrew's there is a white plastic cap what makes it impossible to turn the pilot's out because of the little tip that blocks against the carb's outside
so the pilotscrew's are not sealed but have a cap meant to turn by vinger

[rover]

You can gently pry these off by putting a flat blade screwdriver under them. Do a little on one side, then the other side until they come off. After you are satisfied with the adjustment, you can replace the pointers, but put them in the center of their travel, then later you can fine tune in either direction. Just to the left side of this screen, click on TECH TIPS, and you will fine a lot of information on how to get your XS running well, and keeping it that way. Happy riding Oh, when you are adjusting these idle screws, DO NOT tighten them very tight, it is quite easy to break off the end of the small needles. Lightly seat them, then back off about 1 and 1/4 turns for an initial setting. If you only want to enrichen one or more carbs, turn that one out (counter clockwise) 1/4 turn at a time, until you get where you want to be. C U l8er

[piet]

thanks monday i will rip off those whithe cap's and turn the screw's 90 degrees out all three of them and see if the engine run's at normal idle rpm,at this moment i have to keep the rpm above 1500 else the engine stops,this lean mixture probebly is the reasen that the original engine #3 exhaustvalve burned away.
i also found a piece of metal in the airbox that didn't belong there,it was the metal from a ripped out airfilter that was clued at the bottom and when placing a new filter on top of that the airboxparts didn't close 100% when the 4 butterflyscrew's turned thigt,this also can/has be/been dissassteres for the valve's

[rover]

Well, Piet, after re-reading your posts, it sounds like you are overdue for a good carb cleaning. Check in the tech tips for instructions how to do this. Read every post that you can find on cleaning carburators, then do a complete job. Do EVERYTHING at this time, or you will be chasing little problems for a long time. If that engine burned a valve, then you WILL NOT fix the problem by adjusting idle screws. Just make sure that you clean every single hole, passage, and jet, and get your floats all set correctly and evenly. EVERY tiny detail IS important. And if you can follow directions, you CAN do this job properly. Everything you need to know is on this web site. Find it, read it, understand it, and DO IT.Happy wrenching, and later, happy riding

[2fast]

Just a couple of comments. When you take off the plastic caps, be VERY carefull when you turn the adjusters in to the seat. They have VERY sharp and fragile points that like to break off in the carb body. Then the tips can be impossible to remove with out damaging the original hole size. I think that may one of the reasons that Yamaha put the limiting cover caps on in the first place, other than emission concerns.
Second, it is fairly popular for owners to drill holes in the air box thinking that it will help air flow. If that was done to yours, it could be an air source as well.

[piet]

don't worry i won't turn them totally in no need for that the engine is allready running so its need's fine tuning(a little more out).
i was wrong about the bad exhaustvalve in engine i had replaced by another one,this night i took off the head and found a bent peace of metal next to the#3 compressionchamber,it is the seal for the camchaincompartimend,probebly the headgasket at that #3 spot leaked and the high pressure made the metal bend.
after seen that i had a good mood and sleeped well,now i only have to place a new headgasket and put it all back together.
where the heck can i find a explanation how to put a photo in my reply,i didn't find it at the F.A.Q.