air lock in fuel line :(

So... the deeper I dig into this bike, the more I find.

One of the issues with her appears to be an airlock in the fuel line. The tank is a norton-style fibreglass unit with twin taps, running to a T piece, then a single line runs to a fuel filter, then to the carbs. I'm getting air building up in the fuel filter preventing any more fuel going through. The fittings are all tight, the fuel line that's been used is in good condition, fittings are tight.

Can anyone make any suggestions as to how to nail the cause of the problem - and more importantly, how to solve it?

Sounds like your fuel filter is too small,had the same issue switched from the cheapo small ones to the K+N filters, no problem anymore...

I'd be surprised, it's a big chunky unit - BUT - it looks like it's a cheap unit. I'll try changing that.

My fuel line filter looks like it's one of these - anyone else riding a "boober"?

http://www.ebay.co.uk/itm/IN-LINE-FUEL-FILTER-IDEAL-FOR-CHOPPER-BOOBER-CUSTOM-CLASSIC-MOTORCYCLES-/390979453629?hash=item5b083102bd:geUAAOSwnDxUbILd

Khaos said:

I'd be surprised, it's a big chunky unit - BUT - it looks like it's a cheap unit. I'll try changing that.

My fuel line filter looks like it's one of these - anyone else riding a "boober"?

http://www.ebay.co.uk/itm/IN-LINE-FUEL-FILTER-IDEAL-FOR-CHOPPER-BOOBER-CUSTOM-CLASSIC-MOTORCYCLES-/390979453629?hash=item5b083102bd:geUAAOSwnDxUbILd

Click to expand...

do you have a external plastic tank to test your setup WITHOUT any fuel filter?maybe there´s a carb or petcock issue...

is the fuel filter installed in the right direction, normally there is an arrow that should show the fuel flow direction!

I don't have a separate small tank - I'll see about getting one - it'll be a handy piece of kit. The filter is installed in the right direction.

Gravity fed systems can be a bit wonky if they have a clogged or partially clogged tank vent, what happens if you open the cap?

Did you actually pull the fuel line off to see if fuel is flowing? A lot of inline filters will not fill up all the way with fuel and look like they're not flowing when in fact they are.

Likely Coyote13 is right. Most if not all gravity feed bike fuel systems will perpetually have a lot of air on top of the fuel in the lines going to the carbs. Try some clear lines on most any gravity fed system and you will see the lines immediately start to fill up when you open the petcock, but stop the instant the needle and seat assembly closes leaving a giant air space above the fuel. This is super common and I've never seen it be a problem as fuel immediately flows in to replace that used by the carbs. I suspect it is caused by the petcock which fills first through the valve and then into the bowl - then flowing up through a screen to the tap(s). That way dirt is left in the petcock bowl and helped to stay there by gravity. It also lets you take off the bowl with the valve off to clean it. Perhaps the air can't be forced downward past this "trap" so some air stays perpetually trapped in the line(s). For what it's worth, I have never had a use for filters as long as the petcock has a screen in good condition. The petcock should be plenty good enough as a filter if it is in good shape. Most have an internal screen that filters the fuel in both the main and reserve positions, and an additional filter screen on the reserve inlet which feeds from the bottom of the tank where most of the likely crap will be. I've ridden bikes all over this country (and others) and seen my share of bad gas, but I've never had an old crusty tank that couldn't easily be sufficiently cleaned or had a sediment/contamination problem that filters would have helped. Of course if your petcock screens are damaged or missing you probably will need inline filters, but manufacturers make the petcocks like they do for good reason. If they clog up, you just remove the bowl, clean the screen and you are on your way again in a few minutes. In line filters not so much, even if you carry spares.

yeah, I had flowing fuel. Please note the HAD - as the bike died on me in heavy traffic on the way to get the carbs set up properly.

A friend picked me up and trailered the bike there - she's in expert hands (two wheel engineering services in Bridgend). While she's there being fixed I'm going to get her serviced, get the clearances checked, and get a bit of welding done - the rearsets are off an R1, and shaped to fit the frame, which shows. I'm going to get an indent filled, and the brake pedal altered to fit me properly.

When she comes back to me, she'll be in fine usable trim. I've only just got back online, after discussion between the three of us at the garage the inline filter is gone anyway. It looks flashy, but it's a pointless item since both petcocks have gauze filters. The battery that had been fitted would be ok for a 125, but for a 306 twin it's just not meaty enough - so I'll up the size to a bigger battery.

When she comes back, the basics will be there - a safe, reliable (with maintenance - GPZ305 after all...) bike, from there I can think about moving forward and making the changes I want.

frogman said:

Gravity fed systems can be a bit wonky if they have a clogged or partially clogged tank vent, what happens if you open the cap?

Click to expand...

I have to agree with frogman. The vent for the tank must be plugged. The pressure in the tank becomes less than the atmospheric pressure and is preventing any more fuel to flow. Check your tank vent, or try running the bike with on the stand and then loosen the cap.

www.precisionmoto.com
www.timeinthegarage.com

sharperdill said:

I have to agree with frogman. The vent for the tank must be plugged. The pressure in the tank becomes less than the atmospheric pressure and is preventing any more fuel to flow. Check your tank vent, or try running the bike with on the stand and then loosen the cap.

www.precisionmoto.com
www.timeinthegarage.com

Click to expand...

Tank vent's fine. Crap filter in the end, from the look of it.

Cheap filters can inhibit fuel flow (most are designed to be used with fuel pumps).


Get a good quality paper element filter.....or a low pressure fuel pump.

hillsy said:

Cheap filters can inhibit fuel flow (most are designed to be used with fuel pumps).


Get a good quality paper element filter.....or a low pressure fuel pump.

Click to expand...

The fuel taps have gauze filters, so I'm going to ditch the additional in-line filter. The subject of fuel pumps came up when I was going over the bike with my friend Paul (who rescued me when she died on the way to the tuners). Certainly it's under consideration.