Petcock only working when it leaks

[nikiforova]

So I decided to ditch the vacuum petcock and went for a normal one. It was working fine, but then I noticed it wasn’t flowing when turned to “on.” I went to take it off and removed the hose and though, “let me see if it will flow” and when I turned it to “on” it worked. Put the fuel line back on and no flow. Wiggle the fuel line so that air is coming in where it sits on the nipple and it flows, seal it off and nothing. What’s going on here? I have the vacuum ports on the carbs capped off and sealed

 

[jpdevol]

Perhaps fuel cap not venting? Pics please....

 

[nikiforova]

Perhaps fuel cap not venting? Pics please....

Not the fuel cap. Fuel will flow with the cap closed if the line is disconnected

 

[jpdevol]

So that's an unfamiliar looking T fitting at the bottom of the fuel line? Also, are the float valves working ok?

 

[Exploding Coffin Emporium]

I’d check my carb setup, could be a stuck float or some shit building up internally blocking flow. Old bikes contain more grit and grime inside than we often realize if they haven’t had a complete overhaul and sometimes swapping out a few parts like a petcock that has been attached for 40 plus years will jar enough garbage loose to turn the tides against you.

When you say “it was working fine” what do you mean by that? Like started initially and idled for a bit, or took it on a good run and she had no issues until you parked?

 

[nikiforova]

I’d check my carb setup, could be a stuck float or some shit building up internally blocking flow. Old bikes contain more grit and grime inside than we often realize if they haven’t had a complete overhaul and sometimes swapping out a few parts like a petcock that has been attached for 40 plus years will jar enough garbage loose to turn the tides against you.

When you say “it was working fine” what do you mean by that? Like started initially and idled for a bit, or took it on a good run and she had no issues until you parked?

I just cleaned the carbs out, re jetted, adjusted float heights, and changed the T connector with one from mikesxs because the rubber on my old ones disintegrated.
I had it up and steadily idling for about 15-20 minutes. Went to sync the carbs and this happened before I could adjust anything.

 

[jpdevol]

Young'in; you're into weird problems again.lol

 

[jpdevol]

So if you open the float bowl drain, then turn petcock to ON or RES, you get no flow?

 

[gggGary]

Leave petcock on, open a float bowl drain does fuel run then? An air "bubble" in the line is normal if the float bowls are already full.

 

[Exploding Coffin Emporium]

Isn’t anyone going to say “you do have gas in the tank, right”, had to say it. As I was typing it both you guys pop in haha.
So at this point we’re assuming it’s venting properly and not causing an air lock, check. There’s not an obstruction in the petcock filter, petcock, barb, or fuel line significant enough to block flow, check. Our next logical suspect has to be the carb. I do understand that you just went though the carb, but if it were me I’d do it again, just seems like the sensical progression that something is either blocking or locking within the carb at this point.

 

[Wingedwheel]

Just my 02 but if it flows with the line disconnected but not the other way around we always move downstream. Next component in line is the float needle. It may well have gotten stuck after that run session. Perhaps the clip fell off and the needle is just sitting there independent of the floats.

 

[nikiforova]

Alright, so I checked up on a few things. The petcock has no obstructions and will flow when there’s no line connected. The float needles are in place and the floats are moving as they should. I’m at work, so I don’t have my gauge, but I set the height last week at 22mm for the 83sk model. The diaphragm on my right carb is a bit sus. It seems to not be sealing properly. No matter how I sit it, it will not fit all the way around in its groove. When I gently lift up on the brass diaphragm tube with the needle, it falls with little to no resistance unlike my left carb. Could this be the issue?

 

[Wingedwheel]

That might not be the flow problem but it’s def a problem. Perhaps using a little lightweight grease around the groove can help stick that edge down And hold it in place until you can get the cap on. Review the carb guides in the tech section before putting everything back together. They’ve kept me from missing a lot of things with my carbs.

 

[nikiforova]

Alright, so I checked up on a few things. The petcock has no obstructions and will flow when there’s no line connected. The float needles are in place and the floats are moving as they should. I’m at work, so I don’t have my gauge, but I set the height last week at 22mm for the 83sk model. The diaphragm on my right carb is a bit sus. It seems to not be sealing properly. No matter how I sit it, it will not fit all the way around in its groove. When I gently lift up on the brass diaphragm tube with the needle, it falls with little to no resistance unlike my left carb. Could this be the issue?

Wrong, the petcock itself isn’t flowing at all. I have fuel, won’t flow set to “on” or “reserve”

 

[jpdevol]

You have some investigating to do......

 

[nikiforova]

Alrighty y'all, every time I think I fix something another problem shows up. Replaced the 0 rings on my float needle seat and that helped! its flowing and will idle for as long as I will let it. I rejetted one size up on the pilot and mains as well as shimming the needle with two washers on each. So I am running 45 pilots, 135 mains, and two washers on my needle. I leaned my mix screws and idle screws to accommodate. I believe they are around 2.75 turns out and whatever brought me to 1.2k for idle on the idle screw.
BUUUUTTTTTT WAIT, it dies the second I start rolling. Its as simple as rolling backwards in neutral with the bars dead center. I think its probably electrical, but I it sounds like the engine is dying of no gas. Sometimes itll start right up, sometimes it wont. Also, when this happens my petcock seems to not flow any until the bike is running again.

 

[nj1639]

Eh, no mention of air filters.......let me.
Some aftermarket air filters can strangle air flow, especially the ones who's mounting rubber covers over the small holes in the bellmouth. Make sure there's no issue there.

 

[jpdevol]

Its as simple as rolling backwards in neutral with the bars dead center

Well, don't do that!

 

[nikiforova]

Eh, no mention of air filters.......let me.
Some aftermarket air filters can strangle air flow, especially the ones who's mounting rubber covers over the small holes in the bellmouth. Make sure there's no issue there.

I was running those k&m tapered filters, but I switched to the non tapered uni pod filters. I’ll check to make sure they’re not covering those holes when I’m off work

 

[nikiforova]

Update:haven’t gotten it solved. The bike seems to be dying in the flat spot just off idle. It’ll slump and I give it gas and it just dies. I’ve got the slide needle shimmed with 2 washers. Could this be where the problem lies?

Edit: checked cam chain tensioner, not moving back and forth. (Warm engine)
Edit 2: don’t want to rule out electrical. A main fuse just blew outta nowhere