Anyone Experienced This Problem?

I can't deny that fuel starvation was one of my first thoughts. I tried switching from main to reserve a couple of times even though I knew that I had quite a bit of go-juice in the tank. I will check the breather etc. and see what they are like.

 

Sorry to hear you are having health problems @mpllineman and hope you get better soon. I am starting to suspect that either it's actually an air or fuel supply problem in my case although I am not going to rule out the Ignition sensor going 'open circuit' when it gets hot. I am a little dubious of this as it's a very simple device, somewhat akin to a guitar pickup and really just a small coil of wire around a magnet that has a current induced in it as the protrusions on the rotor pass through it's magnetic field sending a timing signal to the igniter. Given that the coils are recent and have barely done a few hundred miles and the plugs were replaced at the same time as the coils I would probably rule them out for now. So if it's not an intermittent fault with the igniter or the ignition sensor that points to it being fuel or air. I will check the fuel supply as advised by folks above and then, if nothing stands out there, I will possibly take the Igniter, and maybe the coils off my other 2001 Bonnie plus the few neccessary tools and take a ride out once it stops raining in Argyll (it does occasionally) where I can replace these parts should she conk out on me again and, if that doesn't sort it then it will point straight at the Ignition sensor.

 

OK, could it really be this feckin @&*%$^ bleedin' simple?!!!

I pulled the tank off to check the fuel and breather hoses. The breather hose was a swine as it is fed through a slot under the spine of the frame and is tight but, down near the bottom, I came across the item pictured with a further piece of hose after it. On inspection it's a one way valve. Obviously it is meant to stop anything getting up the breather but, sucking on it (no sniggering in the back) to imitate a moderate vacuum in the tank it is sticking shut and requires quite a blow to open it again of course, given time and the right conditions the weight of the metal ball, or slide or whatever weighty lump is in the valve will cause it to drop naturally due to gravity allowing the vacuum to clear.

Has anyone else found this valve on their tank breather pipe? My genuine Triumph Workshop manual (that cost a freakin' arm and a leg) doesn't even detail the breather at all on the tank and gives sod all in the way of detail of the carbs and tank assembly and the Haynes is no better. The Triumph workshop manual is disappointing and definitely not a patch on the ones that I used to have on my Suzuki's. Those fellows had everything down to a microscopic level on their bikes!

Unfortunately as it's ten to three in the morning here and I do have neighbours I can't get out and test the machine out no matter how much I want to.

 

Just checked on the Fowlers website and it's given as the 'Roll over valve' and they cost twenty two quid to porder so I guess it is a standard part of the system. I don't recall ever having any sort of valves on my tank breathers in the past. Is my memory failing me or is this a fairly unnecessary item?

I recently replaced the original fuel cap and I am now wondering if the original wasn't sealing and therefor there was no vacuum build up whereas the new fresh one is sealing and hence allowing vacuum to build up.

 

Ach I am rarely in my bed before four in the morning due to being a bit of a night owl/insomniac. I've just been doing a little research and, apparently this little valve is meant to stop fuel escaping from the tank via the breather in the event that the bike ends up on it's side on the road and so is unnecessary if you don't plan to lay your bike down. I have found one thing online which states that is was suspected of causing fuel starvation due to vacuum build-up in the tank. If you didn't buy your machine brand new perhaps a previous owner had removed it because it was causing problems?

 

I can report that the problem seems to have been fixed and, it would seem at least, is the fault of this little roll over valve gizmo. I have retained it for the moment. After trying to flush it out with methylated spirits and then acetone it still seemed to be sticky so I dosed it with GT85 with the idea in mind that the Teflon in that would hopefully make it non-stick. When out for a tentative run and ended up taking her for a few miles and she is running well and hasn't missed a beat. I don't believe the airbox being restrictive was a direct cause although I think that it compounded the problem as the engine was being starved of fuel and then what fuel did get it was being starved of air to burn it with. If it becomes sticky again I will be junking the thing as I do think that it's an essentially pointless and unnecessary item and has the potential to cause greater problems that it's meant to solve.

 

I took another run out tonight, covered maybe 15 miles and she never missed a beat so it looks like the valve was definitely the cause. I will be checking my other two Bonnie's as well to make sure their Roll-over valves are in good working order although I must admit that I am tempted to pull them off myself as they have little worthwhile purpose.

 

A little further piece to this tale of woe which, I think proves the cause is the aforementioned roll-over valve which is going to be removed from the system.

I went out on the bike today and, after perhaps four miles she suddenly lost power just like in the past and I pulled in the clutch and coasted to a stop. To see if it was fuel starvation due to vacuum in the tank I twisted the fuel cap off and back on and she fired right up. I carried on my way and, perhaps another four miles or so farther on and hitting around 70mph I suddenly felt the same loss of power, reached down and gave the fuel cap a screw and she instantly perked right up. In a journey of perhaps forty or so miles she did this a half dozen times and each time it was remedied by twisting the fuel cap open a little. On the return journey I actually just left the cap screwed out a little so it wasn't sealing and she never missed a beat.

Clearly the answer is fuel starvation due to vacuum building up in the fuel tank and I am 99.9% certain that little valve is the culprit and will be removed.It really is no loss in my opinion and, to ensure the breather also stays fee of gunk that may block up the end of it (cut at an angle as recommended ) I think I will shorten it so that it is out of the way of gunk and moisture that might block or somehow airlock it as well.