Fuel starvation issue?

[nik_the_brief]

I'm back to pick your brains again, apologies if this has been done before but I did have a good search before putting up a new thread.

In the past two five mile runs I've done commuting to work I've had what seem to be fuel starvation issues shortly into the journey.  The MIL light and the fuel light come on with the other symptoms but disappear when it clears itself, I lose power as if I've a fuel fault but then it kicks back in although the first time I had to nurse it about a mile like that.  The rev counter also sweeps quickly to the top of the dial and back when the symptoms become more extreme.  Obviously I can't ride it safely with the possibility of it losing power, part of my journey is a short treacherous piece of motorway full of foreign lorry drivers desperate to get to the port. 

I may have narrowed it down to a blocked fuel tank vent as I think the symptoms are similar to those mentioned in a few of the steamer threads.  It just feels like the fuel pump hiccoughs.  I've noticed that the symptoms disappear if I open the cap and then lock it again.  I did that on my way home tonight less than half a mile into the journey and the remainder if the 4 1/2 miles she didn't cough or splutter but I was anticipating it doing it for the whole journey back. Perhaps it would be wise to have the key in the lock when riding to see if opening it cures the symptoms when they occur.  Is that a good starting point? 

If it is, then what do I need to do to resolve it as I'm not too familiar with all this.

Cheers in advance for your collective wisdom.

Nik

[Timbox2]

The rev counter/ MIL light issue would have me looking for electrical gremlins, charging circuit etc. But one simple thing to check is the fuses, especially the main fuse on the side of the battery box, look for any signs of arcing,  melting etc. A blocked fuel tank vent doesn't explain the MIL light either. Oh, and put a voltmeter across the battery, before starting and with engine running and report back

[nik_the_brief]

Thanks Timbox2.

I am as certain as I can be that it's not a charging system issue. I've had one of those already. New Motobatt battery, uprated  new MOSFET reg/rec AND a new stator all within the last 1,000 miles!

[Timbox2]

Ok, still check the fuses though. That one on the side of the battery is known to cause all sorts of weirdness.

[Bixxer Bob]

IF it is a blocked tank vent the MIL light will come on to warn of low fuel pressure.  You say you've already proved it's a blocked tank vent so:

Step one.  Unblock the tank vent.

[nik_the_brief]

Ok, still check the fuses though. That one on the side of the battery is known to cause all sorts of weirdness.

Cheers, I'll give a good look over this bank holiday weekend.

[nik_the_brief]

IF it is a blocked tank vent the MIL light will come on to warn of low fuel pressure.  You say you've already proved it's a blocked tank vent so:

Step one.  Unblock the tank vent.

And that's where my my shortcomings become apparent! Is the tank vent in the fuel filler cap or elsewhere? Will I need to remove the tank or can I sort it in situ? Sorry to sound like a numpty but it's not immediately apparent from Haynes Book of Lies.😀

[Bixxer Bob]

Lift the filler flap;  inside you'll see two holes.  One is the vent, the other the drain.  They lead to the two rubber tubes on the rear left underside of the tank next to the fuel pump plate.  They should both be clear.  If the vent is blocked you get fuel starvation.  If the drain is blocked, you get water in the fuel.  I disconnected both tubes and used a clean bit of tube to blow up them.

The drain is usually the one that gives trouble and may need a very small drill working up through the crud that's hardened in the bottom reaches. Once you break through you'll get a small amount of skanky water from it so putting your mouth near is not a good idea.

I do mine regularly so don't get issues but the first time I ran a piece of fine wire all the way through and gave it a through clean.  I imagine in your case the vent tube is the same.

[nik_the_brief]

Brilliant, cheers Bixxer Bob, I wandered over to the garage and spent a few minutes poking an old WD40 straw down the holes.  After a little initial resistance it cleared nicely and hasn't displayed any symptoms since though I've yet to give her a good blast to make sure.

I very much appreciate your sage advice as always.

[Bixxer Bob]