Vapour Lock

[Flip]

Out for a ride yesterday afternoon after having a fiddle with my suspension and taking the bike for it's MoT (which it passed) and while riding through some heavy traffic in the afternoon heat my bike starting spluttering and coughing until it died completely.

Now it has done this on two previous occasions, once on an even hotter day (yes really) while riding in London way back in about 2003 and another time more locally a couple of years later.

So up until yesterday it hadn't done it for over ten years including some pretty hot filtering while in Europe last year.

Anyway, while road side I did the usual check of opening the fuel cap- no hiss, and trying starting it with the cap open (needed some choke to pull some fuel through) but still no go.

Once the thing had cooled down (about an hour later) I tried again and with some choke it farted into life and got better as I turned the choke off and with the early evening cooling air it ran great all the way back home.

So I am thinking it is the dreaded vapour lock that is said to plague 900's from time to time.

Anyone else had similar or know a 100% cure short of fitting an electric fuel pump?

Cheers Peeps!

[DrD]

You can get the vacuum pump repair kit from Allen's Carbs.
That and new hose from the inlet to the pump.

[Flip]

Cheers DrD, I have a spare vacuum pump so I'll clean it up and buy a repair kit for it (although I am not sure there is anything wrong with mine but it is the original) and fit it on.

I'll order up a new vacuum pipe too as I need to place an order with Luke at Moto Rapido so some bits and bobs anyway.

[Flip]

O.K. I dug out the spare vacuum pump I have and with it a spare vacuum petrol cock, I had a look through the Haynes book of B*llocks along with a factory manual and they say there is no way of checking the pump and it should be referred to a dealer.

In the Haynes manual they don't even mention the vacuum petrol cock, only listing it as a tap type which I think the original bikes had.

Now, assuming I fit the overhaul kit to the vacuum pump how do I know that the problem isn't the vacuum petrol cock and if it isn't working as it should would it simply flow fuel permanently to the pump?

[utopia]

.....Now, assuming I fit the overhaul kit to the vacuum pump how do I know that the problem isn't the vacuum petrol cock and if it isn't working as it should would it simply flow fuel permanently to the pump?

I wouldn't have thought so.
Well not if the diaphragm is underperforming anyway because surely that would cause it to OPEN less effectively .. ie it fails closed rather than open (just as it closes when the engine stops and there is no vacuum applied to the diaphragm).
On the other hand if the sealing element fails it would presumably dribble (or open fully).

...if that's what you're getting at, though it sounds a bit suck eggsy to me so sorry if I've got the wrong end of the stick.

As it happens, I'm going to fit a tank with an internal, electric pump to my 750.
The external "tuna can" pump is untidy and disrupts airflow to the rear cylinder in my estimation (sits right in the flow that my airscoop collects actually).

[Flip]

No I wasn't sure if it would flow less or flow freely if the diaphragm was faulty in the petrol cock part- it seems a bit of an odd arrangement to me, to have two vacuum controlled metering parts.

I guess to remove any doubt I should order a new one to go with the repair kit for the pump?

[FLATTOP]

This happened to me once whilst filtering for about 8 miles down to the Brighton burn up, I was on my M900 and it was a scorching day I managed to get to where my group of friends were parking and it totally give up the ghost it was like fuel starvation my mate put it down to the petrol evaporating due to the heat.

A few hours later and cooler conditions and it was fine it never happened again.