X Flow with Over Fuelling Webers

[Marden]

Hi - I have a 1700 X-Flow that has a mechanical pump running at 5psi. This appears to allow the carbs to send unspent fuel out through the air filters onto my o/s rear wing ! I have just replaced this pump, but with no difference, and set the Webers up as indicated by all factory settings, confirmed today from Caterham. They also say the webers would work better around 3psi. The physical restriction of the fuel line by means of a partial clamp is the only way to stop the leakage!

Were X-Flows installed with mechanical pumps in the first place ? Should I fit regulator and electric pump to resolve this ?

Anyone faced the problem before ?

Any thoughts appreciated on how to solve this issue.

[Drumster]

I'm no expert on Webers, but my x/flow ran perfectly well for 13 years using the standard mechanical pump (no idea what the psi was though) and twin 40s so I'm not sure that the pump is the problem. Having said that I now have a Zetec (still using the same twin 40s) and that does use an electric pump and fuel regulator. Regulator is set to 3psi which seems to suit it fine.

 

AFAIK x/flows were originally installed with mechanical pumps.

 

 

[Roger King]

5psi is a little on the high side, but nowhere near enough to cause fuel to come out of the ram pipes and into the air filters unless you have other problems.

 

It sounds far more like you either have stand-off problems or there is a problem with the general health of the engine.

 

Stand off is a situation that can arise with certain engine specifications where at specific revs the air going into the carbs bounces out again and leaves a cloud of fuel vapour hovering around the ram pipes. It is caused by combinations of tuned lengths of the inlet and exhaust tracts and cam profiles and there isn't much to be done about it other than changing something about the spec of the engine.

 

Assuming your engine is (exactly) to a standard Caterham spec, it would definitely be worth carrying out a health check - compression test, set valve clearances, check ignition timing (throughout the rev range), change spark plugs, check for a healthy spark etc.

 

Finally, but probably most importantly, you need to check the condition of your needle valves, make sure your floats aren't punctured (the later, black plastic ones don't puncture, but the earlier brass ones do regularly) and then set the float height. if there is anything wrong in this department you could easily have fuel flooding out of the float chambers into the venturis.

 

 

 

 

[millsn]

post made redundant by others'

 

Edited by - millsn on 26 Aug 2011 19:41:52

[Pezky]

My xflow would do this if the carb balance was out.

[oldbutnotslow]

I stripped down a set of 40's that had been leaking in just the same way and found that that someone had tried to seal the venturies with silicone sealant!!!!!

 

As Roger says

Finally, but probably most importantly, you need to check the condition of your needle valves, make sure your floats aren't punctured (the later, black plastic ones don't puncture, but the earlier brass ones do regularly) and then set the float height. if there is anything wrong in this department you could easily have fuel flooding out of the float chambers into the venturis.

the needle valves would be my first port of call. They wear over time and can stick hence the flooding. It is vital that the float height is also set correctly.

 

The mechanical fuel pump was never great when used with 40's and if the carbs haven't been serviced for some time the pressure can overcome the needle valve.

In its original Ford guise the fluctuating pressure wasn't a problem as the ford car was fitted with a return pipe that bled excess fuel back to the petrol tank. 40's obviously dont have this provision.

 

Facet solid state fuel pump and a Filter King with a pressure regulator will do the job but dont neglect the rebuild if its not been done in the last 5 years.

[Marden]

Thank you everybody for your advice - there seems a measure of agreement that I can act upon which is much appreciated. I will get back to you all when the work has been done next week.

 

Any images of tidy installation locations for the following appreciated!

Facet solid state fuel pump and a Filter King with a pressure regulator will do the job.

[Eugene]

I have a set of 45's on my Zetec, with a fuel regulator, but have to set that to 5psi to enable the carb's to get enough fuel when on full-chat...

 

Never have a problem with over fuelling...

 

But, I did have a problem with my old VeganTune with fuel stand-off when some engine builder put the cams back in miss-timed once!

 

Drove all the way to Le Mans band back like that. I think the amount of fuel vapour I swallowed will have seriously cut short my life expectancy!