Yet another VW question!

johnlear · Post by **johnlear** » Sun Jul 17, 2011 5:47 pm

Mike,

Thanks for your blunt observations, I've had the aircraft for 25 years and have always maintained it myself, including engine strip down and overhaul, structural maintenance etc... so I'm not really an ignorant numpty...but the PHN carb is something even VW experts seems to know little about...and yes I have all the manuals that I have been able to download from the internet..however when things go wrong I think it common sense to listen to what anyone might say that may throw some light on a subject.
Thanks for yours!!

mikehallam · Post by **mikehallam** » Sun Jul 17, 2011 8:26 pm

Fair enough John,

But your innocently fiddling with the pilot fuel mixture did make one wonder. Though I admire your frankness.

So what other maintenance has your carb had in 25 years ?

Mike hallam.

Nigel Ramsay · Post by **Nigel Ramsay** » Sun Jul 17, 2011 9:08 pm

Mike may have a point John, but if you've survived this long......!

As a matter of interest, Barry Smith reckons that there is no better carburettor for a VW than a Stromberg CD150. I bought a New Old Stock CD150 for £40 from Ebay! It would of course mean fabricating a new inlet manifold etc.

These carbs do have needles and as such tuning them is reasonably straight forward. There's no specific jet/needle combination for a VW of course, but there were a number of 1600cc cars using stromberg CD carbs so that would provide a good starting point.

Steve Brown · Post by **Steve Brown** » Mon Jul 18, 2011 12:26 am

Hi John - what does your inspector think could be the trouble?

Since it has just suddenly started to occur, it does sound like perhaps a mid range / second stage jet / mixer is blocked and hence failing to deliver sufficient fuel at higher speeds.
I assume you haven't made any other changes that may have caused this. This cut out at higher revs indicates that it happens as it comes off the idle circuit and onto the second stage - pumping the throttle likely results in the accelerator pump giving a brief extra flow of fuel to sustain higher speeds for a while.

I'd see if your inspector has any ideas - much easier to diagnose on site than remotely.

Regards
Steve

G.Dawes · Post by **G.Dawes** » Mon Jul 18, 2011 8:04 pm

When I have problems that suddenly appear with carbs, I strip them and put them through an ultrasonic cleaner which removes All the muck from all the places that you might be surprised at, Then careful rebuild with new gaskets.
If it worked before then it probably will again.

Rob Swain · Post by **Rob Swain** » Fri Aug 19, 2011 3:26 pm

G.Dawes wrote:If it worked before then it probably will again.

I can see the attraction of this philosophy, and have used it myself, but it falls down when the failure is due to wear.

I'd agree with the strip, clean and new gaskets, (for the carb as well

) but I'd include careful inspection of butterflies and their spindles/bushes, careful inspection and possible replacement of diaphragm (assuming Stromberg carb) and the replacement of the main jet and needle (only a few quid).

This does rather assume you know what the needle was, of course. It might have an identifier on the end of it, assuming the fixing screws haven't chewed the markings to illegibility.