what is this tube for?

my friend said that it's not necessary to hook it up since he doesn't notice air coming in or out of the tube. but i'm not so sure. the petcock runs out of gas if i drive on ON. i'm wondering if it might have something to do with this. if so, why is there no air closing from the tube or the little "nubbin thing" (is that the technical term? ) that it seems to suppose to hook up to. the pic is below and the tube is just northwet of the fuel filter in the pic.

can somebody tell me the purpose of this and how it is affecting my bike by not being connected? thanks![/img]

 

if you're talking about the vacuum line going to the petcock, then you definitely need to hook it back up to that brass "nubbin thing" on the manifold (right behind your filter). When you start the engine, the vacuum from the manifold engages the petcock if it's set to "ON" or "RES" positions.

also, if that "nubbin thing" isn't capped off or attached where it's supposed to be, the bike will suck air through it and run very lean on that cylinder, which is bad news.

 

If you are referring to the tube just behind your filter - there is a vacuum line that goes from the nipple on the manifold (next to the tube in pic) to the petcock. It serves to open the valve when engine is running. The other vacuum nipples should be capped.

Your engine should not idle well with them not capped....

 

wow, Bill.. get outta my brain! :mrgreen:

 

That's the vac line to your Petcock. The petcock is vacuum operated, so that only fuel flows when the bike is running. It should be connected to that "nipple" on the intake.

If you're running it as is, the left cylinder (from seated position) will be running extremely lean.

You will only be getting fuel when in the PRI (Prime) position the way ti is. UNLESS, you have a non OEM petcock that doesn't operate from vacuum.

If this ithe case, then you need to buy a rubber cap for that nipple so it's not suckin in air!

Put that tube back on if it's an OEM petcock!!

 

Bah i type slow hahahah

 

okay. i guess i gotta stop at the store some new tube then since the one in the pic is old and broken. btw, dont know if the petcock is OEM, but it does have ON, PRI, RES, and something else. i assume it is the original one though.

i figured it might have something to do with the petcock problem i was having. but if it is the vacuum, shouldn't i feel air coming in or out of the tube or nipple when i put my fingers over it?

thanks!

 

i've been riding on this for a couple months (maybe 5-8hrs a week). how do i know if it's running lean? the idle seems to sound okay. but keep in mind, being that it's my first bike, maybe i don't know what "okay" is. how can i tell?

 

take the spark plugs out and look at the ceramic insulator. if it's bone-white or barely has any color to it, that cylinder is running lean. if it's a darker tan color, you're safe. If you're unsure, post pics of the plugs. Do a search on "plug chop" as well.

Lean = hot. Critically lean = slowly disintegrating cylinder walls, valves and pistons.

You should have some vacuum on that brass nipple when the motor is running... This is the same vacuum that pulls fuel/air mixture from the carbs. Get a vacuum gauge and hook it up to be sure. If there's no vacuum, then you have another massive air leak somewhere (not likely, as it probably would not ever run like that), or that brass nipple is stopped up somehow.

 

okay...stupid me. i guess there is some suction coming from the brass nipple. and the idle sounds different when i plug the nipple with my finger. i guess this is good, since i may not have to by a new petcock. but...when you say "critically lean=slowly disintegrating cylinder walls" how slowly are we talking here? i mentioned before i've only ridden it 5-8 hours a week for the past couple of months. (i'm thinking we may have not have plugged it in when i took the carbs apart to clean and maybe the previous owner had it plugged in)
would there be any tell-tale signs of permanent damage? any thoughts?


btw...thanks to everybody for the answers. i can always count on this site for help, and i really appreciate it.

 

You didn't hurt anything by riding it a little with the vacuum line disconnected just stop doing it. Hook the line back up, ride for a couple of weeks, and look at your plugs. Yes it's been "sucking wind." Most likely didn't do any serious damage. I'd put in a new set of plugs, though.

 

Those "Tubes" are Vacuum Ports on each of the Intake Manifolds. Normally, three are "Capped-off" with a Rubber Stopper and one (of them) usually #-3, used to supply Vacuum to the Vacuum Operated Petcock.

Be sure it is actually opened to atmosphere and not sealed-off by having been filled with a Sealant.
(It's hard to imagine your bike running very well if this Vacuum Port was Open to atmosphere.
The ensuing air leak would have made the Engine not Idle too very well and created a Lean condition with Throttles Open.

Block-off with Vacuum Tube Plugs (AutoZone) three of the four Vacuum Ports and connect the Vacuum Line from the Petcock to the one remaining Port not Plugged-off.

If you don't have a Vacuum Operated Petcock ... Cap-off all 4.

 

wooooohooooo!!! i hooked up the vacuum hose like you guys said, and now it's running in the on position. i guess i don't have to buy a petcock. i can just leave it on ON without having to worry about the fuel leaking into the oil (which it was doing due to faulty float needles), am i right? i was getting tired of forgetting to turn it from PRI to ON and then having to change the oil. (three times in the past month!)

boy...with each problem i fix on this bike, the more and more i feel like a man. i swear i see some new chest hair growing in.

 

btw...just took it for a spin and she's running like a champ. (other than the chain knocking on the chain guard which i'll be switching that out next). she sounds louder and more powerful on idle, like Rick and some others may have mentioned. i assumed that she was running optimally before, but now i see that shew wasn't. man i can't stop smiling.

 

Congrats it is a good feeling to slay the dragons

 

sorry to up the post but one more quick question about this. ever since hooking the vacuum tube back up, after riding around, i noticed that it runs hotter quicker. also the idle seems to be running high RPMs. I don't have my tach cable hooked yet, but i can hear it sounds a bit higher pitched. is there a way to adjust that? i think I remember seeing my friend adjusting it with a screw driver on the right side of the bike somewhere around the clutch. but i could be wrong. any ideas?

 

Idle adjust should be between the carbs down near the bottom of the bowls.