Air bubbles

I have a streetmate. I got air bubbles in my fuel line. Had it since I bought it. On long rides I will have to stop and let the gas refill the line because it sucked it all out.

Everything attached to the carb(and the carb itself)/fuel line/petcock is sinched down.

I also changed the fuel line and filter. Filled the line with gas. Rode it half a mile and the bubble came back. Did that 3 times. Same problem.

The bubble is half as long as the fuel line.

Anyone else have this problem? I tried doing some research, couldn't find anything.

Re: Air bubbles

I have had this problem before. For me it was caused by a vacuum in my fuel supply. This can be caused by several things. I inline fuel filter in the fuel line adds a lot of fluid resistance, as does a clog in the petcock. I would also check to make sure you tank vent (usually located on the fuel cap) isn't clogged as that will also cause a vacuum to occur. If it isn't any of those, then I have no idea, maybe get a bigger fuel line?

Re: Air bubbles

Try running with gas cap off to see if it is a vent problem, if not take petcock off and look in tank for blockage, if you cant see it pour some alcohol in to check for flow, a pint does not cost much just dump it in and watch how fast it runs out, it wont hurt to run on the ground or catch it. While you have petcock off check it for blockage. It does not take muck to block things up.

Re: Air bubbles

Bubbles in the line do not actually mean the fuel isn't flowing. Bubbles can remain stationary as the fuel moves past them, but what you describe is a fuel flow issue.

I agree that fuel flow from the petcock, or a clogged tank vent are your issues. I would point to the tank vent because you mention that it happens after riding for a while and stopping allows it to continue running.

If this happens again, try cracking the fuel cap loose for a moment and see if the problem doesn't immediately clear up.

Re: Air bubbles

Robie Osborne /

Thanks for replies! I checked the petcock, tank (very light rust) and tank vent. All clean. I'm going to take it to school tomorrow with the gas cap off and see what happens.

Re: Air bubbles

You don't need to remove the gas cap......that can be dangerous. Just fold a piece of cardboard and wedge the fuel vent by the headset so it's pushed in. That will vent your tank.Much safer. don-ohio (:^)

Re: Air bubbles

I meant just a test run with a pint in it, should have spelled it out more. Sorry.

Re: Air bubbles

Robie Osborne /

I turned a gas can nozzle upside down and it fit perfectly in the tank vent. No splash back, gas tank was half full (so the nozzle wasn't touching the gas) and plenty of ventilation. Rode it 4 miles. Air bubble is back :/

Re: Air bubbles

One more time, one. Bubbles in the line do not matter. Fuel will flow with bubbles. You have another issue.

Re: Air bubbles

DPC Ryan Wrote:

-------------------------------------------------------

> One more time, one. Bubbles in the line do not

> matter. Fuel will flow with bubbles. You have

> another issue.

Re: Air bubbles

Robie Osborne /

Gotcha Ryan. 4 miles in today, not long enough to see if anything noticeable happens performance wise.

It will flow okay when I’m riding it, but it takes about 10 kicks to get it started (it will start up first kick when I get the bubble out).

I’m going to take it for a 8-10 mile ride this weekend (got work and a few tests this week) to see what happens.

Also, 3 things.

1) I forgot to mention that the petcock is lower than the carburetor. From what I know it helps if it's the other way around? The carb is already touching the case, can’t lower it anymore.

2) When I come from an idle I will have to twist the throttle somewhat carefully or else it will die (that happens whether or not the bubble is there). It runs fine besides that. Not sure if that’s a separate issue or if it’s related.

3) I just hooked up a longer fuel line and put a fuel line splitter for a fuel gauge tonight for the heck of it (not sure if that information is useful).

Re: Air bubbles

The petcock should be higher to get all the gas tank otherwise you will never get all the gas, The gage idea wont help there but may give you a buffer. I run a similar setup to the gage. I will attach my gage setup.

15.15 SHA, gas gage 002.JPG
15.15 SHA, gas gage 004.JPG

Re: Air bubbles

Your petcock must be higher than carburetor, see my poor illustration. Gas feeds by gravity. This is part of your problem the weight of the gas is diminished. (edited)

IMG_0101[1].JPG

Re: Air bubbles

Vibration of gas in lines causes air bubbles.It's just vapor,and gas flows around usually just fine.

Lower the bowl of the carb to check for actual flow.

don-ohio

Re: Air bubbles

Why is your petcock so low?

Re: Air bubbles

Robie Osborne /

I haven't riden it since I last posted.

But to clarify, they start out as little air bubbles that don't matter. Then they clump together to make a 6 inch long bubble that encircles 90% of the line. It leaves very little available flow. Ill be riding and every now and again twisting the throttle won't do anything because it's not getting gas. I will take a picture when I get the chance.

I can't lower the bowl either :/ it's already hitting the engine. And to be specific, the petcock outlet is about a half an inch or inch lower than the fuel inlet of the carb.

I'm making a mock external gas tank out of a dish soap bottle (cleaned with hot water, paper towels and rinsed with gas) that I'm going to hook to the side of the false top tank to see if it is a gravity issue.

I got rid of the bubble last time I posted. The bike has been sitting since (petcock open for flow) and the bubble came back. It is an inch long. Not sure if that hints towards anything.

Re: Air bubbles

My A35 on my Tomos TX-50 has a large air bubble in the line and doesn't seem to effect anything.

Re: Air bubbles

Mars™   Wrote:

-------------------------------------------------------

> DPC Ryan Wrote:

> --------------------------------------------------

> -----

> > One more time, one. Bubbles in the line do not

> > matter. Fuel will flow with bubbles. You have

> > another issue.

Re: Air bubbles

Probably Fred /

Re: Air bubbles

Robie Osborne /

"But to clarify, they start out as little air bubbles that don't matter. Then they clump together to make a 6 inch long bubble that encircles 90% of the line. It leaves very little available flow. Ill be riding and every now and again twisting the throttle won't do anything because it's not getting gas. I will take a picture when I get the chance. "

Mind you, the throttle thing doesn't happen when I take the bubble out. I understand bubbles aren't a problem. I've had them before and you guys are right. They arent a problem. This isn't just a bubble. ITS A BIG BUBBLE. The line eventually becomes 4 inches of gas --> 6 inches of pretty damn near all air --> 2 inches of gas.

"I'm making a mock external gas tank out of a dish soap bottle (cleaned with hot water, paper towels and rinsed with gas) that I'm going to hook to the side of the false top tank to see if it is a gravity issue."

Finished it. Gonna try it out tomorrow and see what's up. If it works then I'm thinking theres something wrong with the petcock. If it doesnt then air is getting blown back up thru the carb into the line again. Doesn't reversion from the exaust do that? I do hear clinks when I tap the pipe.

Also, if I'm just being stupid, let me know. And if you would be so kind, hint me towards the right direction. I think I've tried every suggestion posted. I appreciate them btw!

The problems I have seem to be directly correlated to the presence of the huge bubble.

Re: Air bubbles

While you have petcock off check it for blockage. It does not take muck to block things up

Re: Air bubbles

Steve's right....you aren't getting enough flow to keep air from backing up the line.

don-ohio

Re: Air bubbles

barney gierer /

Try a larger diameter fuel line maybe. Long runs need to be bigger tube.

Re: Air bubbles

What are your meter valve and float doing when flow stops? Check to see if valve is opening properly. This is a copy of a meter review ( I did not write). Its for a Dellorto spring loaded meter valve here. https://www.treatland.tv/v/vspfiles/photos/phbg-float-needle-116680005-2T.jpg .

Top end Fuel starvation issues performance tuning September 17, 2013

taco eater: Hugh Goldspiel from San Jose, CA United States

I've worked on motorcycles and vespa scooters before, and whenever you do a kit, fuel and air flow changes. On a motorcycle or Vespa I know what fuel starvation sounds like, on this crazy moped it sounded like- muuuhhwawww!!!. And last kit seized when it made that sound . So, from what I've learned In The past float needle affects fuel flow so I opted to upgrade the float needle to this from the one that comes in a new Paco carb. As soon as I put it in, issue solved . I watched all the air bubbles in the line go straight away. Now i can stand hard on the throttle. I didn't even have to upjet again on my new malossi kit. Use this if you're doing any kit with a SHA carb. Get this before you even buy jets for a more accurate tuning . Word up, you will be stoked you did .

Re: Air bubbles

my fuel flow issue was caused by a spider making an egg sack in the banjo on the sha carb.. it would let fuel in.. but starve it at WOT..

took me so long to figure that out.. had the pet cock out and cleaned.. shortened the fuel line.. then i finally just said fuck it ill make the float not float as much so it over fills.. thats when i found it.

you may just need to adjust the float..

the float needle idea sounds good too

Re: Air bubbles

Robie Osborne /

I think I found the problem. I was checking out the line tonight and watched a small drip fall on the engine. I felt up the petcock and it was wet. Soooo... Leaky petcock. I have a spare. Gonna switch it out and ride it around when I get the chance.

Re: Air bubbles

Robie Osborne /

Well. That wasn't it. I ordered

https://www.treatland.tv/ProductDetails.asp?ProductCode=phbg-float-needle-116680005

Won't be able to adjust the float tonight (the bike is at a friends house). Will be able to update by Thursday.

Re: Air bubbles

Keep at it! You're sure the gas cap is venting,right? don-ohio (:^)

Re: Air bubbles

Robie Osborne /

Yessir. I blew in it, sucked at it, and even ran water through it a couple of days ago to double check (since I missed the leaky petcock). Totally clear. With all the ideas being thrown my way; I'm getting a strong feeling it's the float needing to be adjusted.

Re: Air bubbles

Robie Osborne /

Well, I was wrong about posting Thursday.

Last night I put the new float needle on. All it did was blow gas into my air filter and prevent me from starting the moped. It's shorter and its spring tension is higher than the stock one (see pics).

I twisted the heads on both to see if it adjusts that way. I don't think it does. I put the stock needle back on. It will at least start with that on.

My jet size is 52. From what I remember stock jet size is 54-56? The guy I bought this from was messing with the carb before he sold it to me. Could this just be a jetting problem?

Float needles.png
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