Bubbles in fuel lin

I thought I had licked this issue.
I had bad fuel flow issues where the float bowls were filling REALLY slow and solved it by changing the filters at the float needle as well as the float needle.
First off, I've done church of clean rebuild of the carbs.
Since I thought I have licked this issue, I had put nearly 300 miles on the bike taking 30-60 minute rides averaging 35mph. Bike has a manual petcock on it now and translucent fuel line and a rock filter. Every time I'd ride the bike, I'd turn on the petcock and watch the fuel flow to replace any evaporated fuel from the bowls. I could see when the fuel stopped flowing at the rock filter, then when it stopped, I'd see no air in the fuel line and then start the bike and ride.
Yesterday, I turned on the petcock and then waited a little bit but did not look at the filter and started the bike and took off. After 5 miles, I was running lean. Then started to come home and it stalled on me. Pulled to the side and I could see the air in the fuel line. Squeeezed the air to purge up the petcock, waited a little bit then went home. I squeezed out any remaining air out before a ride today and went on a short 20 minute ride. came back and no air in the line.

I have got to figure out where the air is getting in cause this is annoying.
I wish I had a tiny camera to put on the fuel line and see if any bubbles are coming from the carb or at a junction in the fuel line

Any ideas?

 

Try and re route the line so that bubbles cannot get trapped in the inverted U section like they are. As short a line as possible and routed so any bubbles can get up to the tank. Run it below the bar that links the carburettors and point the fuel inlet on the carburettors towards the petcock.

 

Yep. reroute the fuel lines. I think you are getting an air block that impeding the flow. I have air in my lines fairly often, especially the Rebel 250, but it causes no problems as long as the air can go up, back into the tank.

 

great suggestions.
Went on 45 mile ride with last 15 miles on a local 4 lane. All was good till then end then was starving fuel. But this time, no air in the lines.
Stopped for a little bit then after waiting 5 minutes or so, it was fine for a few miles, limped home. Not sure now if ignition issue or fuel so I"m swapping out a spare set of carbs I have to see if its the carbs.

 

A lot of that sounds like the classic plugged gas cap, but I seem to remember you rebuilding that? It would still be worth popping it open if you duplicate it again

 

When I stopped, I did open up the gas cap. Could not tell if that was the issue or not. But even after doing that, it only ran well for another couple miles. I'll take the time to pull that thing apart and check it.
Thx

 

I don't know if this will make any difference but you should push that fuel line onto the stub more and try a screw type retaining clip. Is there a direction arrow on the fuel filter?

 

Disconnect the fuel line from the engine side of the filter and see if it flows strongly. If so, you probably have a problem with the carb needles or, more likely, the filter screens if you have them installed on the carbs. I'm not a big fan of the filter screens if you have a good inline filter and a clean tank.

 

I put the carbs back in w/o using the spare set. I removed the rock filter. I then ran the line before the support bar as suggested.
Rode 2 miles around the neighborhood but that's not such a great test. Small air bubble in the line but the bubble formed right at the petcock.
Will have to take a longer ride.

 

I always have a little bubble of air.... but keep the line aiming down hill all the way and the air bubble can’t block fuel from flowing

 

Next time it happens watch the fuel line and then open the cap on the tank to see if fuel flows in. In your last photographs it looks like the petcock is set between on and reserve. Does the lever point downwards for on and vertical for reserve?

 

Its currentlyl oFF which is long part faces left.
UP is REServe, DOWN is ON, LEFT is OFF

 

So not a stock petcock then——as a reminder for those just jumping in here.....

 

Hmm, I have my opinions on what to do next but would like to hear from the collective

I took video of the fuel line
video is sideways , up is to the right where tank is. carb is to the left


@ 10:00 I stop by Highs and bike is idling
@ 10:38 I shut off engine
@ 12:10 I start engine
@ 12:30 you can see fuel flowing down replacing the air
@ 13:28 you can again see fuel flowing down replacing air
fuel flowed down thru the air bubble for most of the rest of the ride as I travel at about 45mph

 

Put an opaque black fuel line on…solved!

Your symptoms sound like a fuel cap vent issue, if air can’t get in to “make up” the space made by displaced fuel it won’t flow out.

You’ll always have an air bubble unless the petcock is the highest point. Air will rise up from carb when needle opens, when bike sits and carbs dry out etc. My bikes all have it, won’t affect it as the gas will run through the air space/around the bubble. Pretty normal for a non pressurized fuel system. If there’s fuel between the bubble and the carb then no issue with fuel delivery.

 

I personally would not use the type of fuel line , you maybe getting vapor lock , the line you use is not a hight temp type of line . Just my two cents

 

Fuel line is never near anything hot. If and when I fix this issue, I may switch to different type.
I don't see any bubbles coming up from the carb, so I feel the air is getting in at the petcock.
I put in a vacuum style petcock like what was on it when I got it. I am not running the vacuum line initially and will set it to prime to run the bike for now.
I emptied the entire tank that was nearly full w/ the gas cap all the way closed. Fuel flow to empty the tank was pretty darn good.

 

If the air bubble is actually preventing or restricting proper fuel flow - then it's a problem.
If it's not, then it's not.
The fact that fuel is present on the lower side of the bubble means that more than the carbs need is getting by - so it's not a problem.
The only thing that really matters is the fuel line is on a downward-enough slant to rule out the probability of a proper air lock - ie, far too high a hump in the middle.
As mentioned above, fit a black rubber line and forget about it.

 

FYI, the video was from a short ride. Prior to moving the fuel line, I took longer rides and I got fuel starved after 45 minutes with the last 15mins on the highway @65mph.
Proof that its not a problem or not, is coming the next time I ride it.

 

Did 70 miles just now, mostly 60-65mph on a 4 lane going back and forth 6 mile stretches at the exits closest to my house.
No issues at all. Now, there was a number of things that were different than the last time it gave me trouble:
Started @ full tank of gas vs 1/2 tank
Removed BB in the tank cap for the vent
Removed rock filter (has about 300 miles on it but that started with a tank derustification and I wonder if tank had gunk still in it?)
Re routed fuel line as recommended above
Different petcock.

I had stopped at about 8 miles into it and the bubble was about 2" long. At the end of the ride, the bubble actually went down to 1/2" and was not even taking up the full diameter of the tube.
I have not taken this bike on long rides and just back country roads @ 35mph for an hour so I think I'll leave it as is for now and do those rides with it a couple times a week and see how it goes.