vapor lock

[al_roethlisberger]

The later(2002+ ??) bikes all have the manual petcock, not electric. While the electric petcocks may introduce their own set of additional problems, my bike was more than happy to "vapor lock" with just the manual petcock installed

 

al

[Gio]

Thanks Al - the fewer variables the better in this case.

 

Hoses are now replaced and heat-shielded, as is both fuel pump and filter. Just waiting for two 3/4'' FI hose clamps (the stock ones are crap / worn out) and I will be ready to see if this has any beneficial effect...

 

Gio

[callison]

Well, it seemed like I got hit by the dreaded vapor lock problem today. Maybe. I did refuel last night and immediately started having some surging symptoms as the engine ran. So I suspect the vapor pressure rating of this tank of fuel at the least, or the probability of water from the bottom of the station tank in the fuel. Either/or. Doesn't matter, because the engine died in traffic on the way home. Twenty seconds by the side of the road and I had it running and happy again. The fuel line, which has been re-routed and has too much slack in it, is pushing hard against the newly installed manual petcock. So much so, that as it heated up (or the gas formed a vapor bubble - take your pick) the gas line kinked and shut off the fuel. Something more to check I suppose.

[al_roethlisberger]

...yeah, that sounds like a slightly different cause, but in the end similar results

 

Kinked fuel-lines will do that

 

The trick with "vapor-lock" thing is that if you can get it running after it sat and heat-soaked, it will probably run.... but that is the trick. I've never heard of the "vapor lock" happening one running, or if the bike is in motion = being cooled.

 

al

[twhitaker]

The surging may be a symptom of the charcoal cannister soaked with fuel from overfueling.

[Gio]

Hey guys,

 

I agree (with Al) in that (as an experienced vapor-locker!) the problem has never occured whilst in motion, only after stopping for a while and trying to re-start.

 

Also, if experiencing mild pre-vapour-lock (spitting and coughing) one can sometimes ride through it - once the air-cooling/and or fuel-cooling gets going things seem to be fine (this happened to me a couple of times this summer whilst riding in ~30c temperatures)

 

The other point I note (callison) is that you were able to re-start after only 20 seconds. I have had to wait for up to an hour (eg the last two experiments I did - both vapour locked at 48 mins) before the bike would re-start. So that would make you todays lucky winner!

 

Stay tuned - I have results from the heat-shield experiment #3 coming up.

 

Gio

[Gio]

Vapour-lock update - Expt #3

 

Just to re-cap the fuel delivery system (at least on my V11S), from the left side (LHS) to right (RHS) of the bike we have petcock/supply line/fuel-pump/filter/injector branch/return line/regulator.

 

Following the results of the previous two expts (see below), I replaced both the main supply (petcock to pump) and pump to filter hoses and wrapped them both in a combination of both Thermo-shield and sleeve. I also shortenened the main hose by ~1 inch and routed it between the throttle body rails (rather than under) so that it was further away from the LHS cylinder (by at least one inch at the closest point). I also thermo-shielded both the filter and filter to injector branch hose (ie all components of the fuel delivery system that are directly above the cylinders were now shielded).

 

I repeated the test run used in expt #2, using the same map (V11TomH) :

 

Ambient temp = 48F

Cylinder temp at end of run = 228 - 231F

Supply line (LHS)* =104F (?)

Fuel pump* = 96F (?)

Return line (RHS) = 82F

 

(* Now covered in reflective thermo-shield so may not be comparable to previous)

 

So peak cylinder temp is a little higher than previously....?

 

After 15 mins, supply line (LHS) = 126F (previously 123F) and fuel pump = 106F (previously 130F). So the pump appeared to be significantly cooler*.

The shape of the cooling curves for each measurement location is similar to before.

 

And so for the acid test at 48 mins - any vapour lock?

 

For the first 30 seconds the motor started right up and ran ok, then began to splutter and die in classic vapour-lock style. Several expletives were issued...!.

 

So the best I can conclude from this is that whilst heat-shielding may (?) have reduced the temperature of the fuel-pump in particular, vapour-lock still ensued at the end of the test (perhaps to a slightly lesser extent....?)

 

So whilst I'm not ruling out any benefit to heat shielding, I am still on the hunt for a primary cause for this problem.

 

Any comments, thoughts or ideas would be most welcome.

 

Gio

[al_roethlisberger]

Well, IMHO the problem is in low-pressure supply line that runs too close to the left cylinder. Everything past the pump is less likely the problem I believe.

 

A couple points:

 

1) Fuel in the supply line is under no(other than atmospheric) pressure, so boils/vaporizes easily. And in fact may be under reduced pressure when the pump first kicks-in creating some vaccuum effect, then in combination with the heat may combine for a quick vaporization. Although I've shielded the other hoses, filter, and pump as you have done, I think the primary culprit is this line. In the case of everything post-pump, it is pressurized and much less likely to vaporize at the temps experienced.

 

2) It is interesting to note that in your test the temperature of your supply line is not only unimproved, but actually worse. I would run this test again, but try to route the supply line as far as possible from the left cylinder. With my pump relocated, my supply line is now some 5 inches further away from the cylinder, as well as shielded.

 

Also, out of curiosity... how are you getting this to vapor-lock in Winter? Where are you located?

 

I ask because, although I have experienced vapor-lock, it's been very very rare... and although we've had some awfully hot days here this Summer, I haven't fallen victim to it since last year.

 

So I wonder, if you are in a mild climate, and you are vapor-locking consistently.... something a bit more acute and significant must be going on with your bike??

 

Just curious...

 

al

[dlaing]

I imagine unless a fuel line is resting directly on a cylinder head fin, the hottest place in the fuel system is right at the fuel injectors.

Could that be the problem?

[Gio]

Al

 

Thanks for the feedback. I agree with your reasoning re the main fuel line - but how did you manage to re-locate this to give 5 inches of clearance - is your airbox removed? Did you transpose the locations of the pump and filter? The clearance I now have is the best I could manage with stock pump location and air-box body still fitted. In response to your questions :

 

Temperature measurements - may have been compromised by the reflective material (I'm using an infra-red thermometer I believe flat black is the best surface to test..) As for as location - I'm in southern BC, Canada. We enjoy a reasonably mild climate so I ride throughout most of the year.

 

When the bike (V11S) was completely stock (and running very, very rich as all seem to) I only ever had vapour lock on very hot (25 to 30c) days. With time I have made various modifications (Mistral cans, PC, K&N, airboxlidtomy) and with each of these the prevalence of vapour lock seems to have increased - particularly the airboxlidtomy which has resulted in reproducible vapour lock in otherwise cool conditions. Many of these mods leaned out the mixture.

 

So I still think that the leaner = hotter engine theory is a good one although running a richer map does not seem to help. Plugs still look fine also (nice tan colour) - I have always run the std CDN model plug (NGK-BPR6ES)

 

So I also agree with your last thought that there may be some other factor in play. For example - I still have a suspicion that the temp sensor in the air-box now gets much hotter than previously (with the snorkels removed but drilled lid still fitted - hot air can now easily fill the roof of the air-box - less so for those of us with the lids completely removed perhaps...?). I'm planning to do a test re-location of this outside the airbox.

 

dlaing,

 

I'm not sure I understand why other than the main fuel line or pump that the injectors would be the hottest place..? I will try make a couple of measurements in this region in my next test.

 

Keep the conspiracy theories coming please - I would really like us to solve this problem.

 

Gio

[al_roethlisberger]

Yep, my airbox is long gone, and the fuel-pump relocated on top of the spine.

 

I completed "Phase I" .... some months back, which was just relocating the pump and shielding everything. "Phase II" is some replumbing, and dressing it all up a bit better past the prototype/proof-of-concept first stage, and installing a "balance tube" for the tank.

 

Here is the link to that discussion:

 

Relocating Fuel Pump Thread

 

 

al

[Gio]

Sorry - I remember the thread now...

 

I just re-loacted the temp sensor from the air-box and will report shortly (with those repeat measurements you suggested)

 

Do you have any way of measuring the fuel line/pump temperatures with your new set-up?

 

Gio

[Gio]

Expt #4 - Temp sensor

 

It was a hunch I had to test. But remote location of the temp sensor from the air-box did not help. Here are latest results which were obtained under otherwise the same conditions as expt #3 :

 

Ambient = 50F

Cyl temp = 203 to 207F

Supply line (LHS) = 132F

Pump = 182F

Return line (RHS) = 87F

Oil cooler = 147F

 

At t= 15mins

 

Cyl temp = 170 to 177F

Supply line = 121F

Pump = 151F

Return line = 84F

Oil cooler = 99F

 

I charted the results in excel but was unable to post the graph...?

 

At t=48 mins the motor started, ran for about a minute (best so far!) and then spluttered and died as previously....

 

I would prefer not to remove the airbox, but unless anyone knows of a much smaller filter I don't see any easy way to re-position both pump and filter above the spine. As a compromise I will try reversing the positions of the pump and filter to see if this helps (at least the pump should be cooler above the spine, and the supply line a little further from the LHS cylinder.....

 

Gio

[dlaing]

dlaing,

 

I'm not sure I understand why other than the main fuel line or pump that the injectors would be the hottest place..? I will try make a couple of measurements in this region in my next test.

 

Keep the conspiracy theories coming please - I would really like us to solve this problem.

 

Gio

During normal operating the injectors should stay rather cool, as the air flows throught, but I imagine after sitting for a while the heat from the engine will be retained in the intake manifold, trapped between the throttle valve and the intake. The heat will move from the engine to the throttle body.

How much? I have no idea....

[al_roethlisberger]

...or you could put the pump "out in front" like most late '02's have, and as was the standard on the Sport 1100 and Centauro. I think most folks with this setup have avoided the "vapor lock" syndrome that have this arrangement.

 

al