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MG MG Y Type - Overflow pipes - overflowing!

Guys

I need your help and advice please.

Having driven over 900 miles on before and after the Brittany Run with no problems other than a leaking rocker box gasket (which I had set aside late afternoon today to replace) I went down to MGB50 at Blenheim on the 23rd September. The weather was awful and when I arrived there were droves of B's leaving.

However, one of the BP staff advised me that the car smelt of petrol. Sure enough and the overflow pipes on back and front float chambers were pissing out fuel. I tended to the matter in the pouring rain and then was advised that the RAC were on site and as I was a member I thought I may as well use their services. Float chambers were chaecked, the valve checked and everything put back together and all seemed fine. As I came to leave an hour or so later I thought that I would check out the problem again - and sure enough it was still leaking. So back to the RAC guy and again he checked it over. I then left and about 2 miles out of Woodstock on the A44 I pulled into a laybye. Once again petrol still overflowing but principally from the rear chamber overflow (nearest to the petrol pump). I switched round the top of the float chambers and then reconnected the system. There was a leak but this was from the union so I tightened this up. I aslo checked the front union and of course lost the fibre washer! It was still raining so I called the RAC out again as I had no replacement washer - a couple of B owners kindly stopped but they too had nothing.

I had to wait some while but the RAC came out having been mystified when I mentioned that I was on the A3400, fogetting that it morphs into the A44 at Chipping Norton! The guy was very helpful and fabricated a rubber 'O' washer in place of the fibre one that I had lost! He tightened it up and then followed me to the next service station about five miles on and checked everything and it was all fine and dry (the float chambers - not the weather, which was still nasty).

I acquired a new set of gaskets and a rocker box gaskets from Octagon and set out to replace the neccessary bits. When I collected the car from my garage I checked and noticed that overflows (both) were leaking.

I then replaced all the gaskets and switched the float chambers round so that they were correctly postioned. Leak from rear overflow but not front. Changed the floats once more -still a slight overflow from the rear chamber through the overflow pipes.

It was then getting late and I was working in the road so I drove the car to the garage about 250 metres away and it was still overflowing from the rear chamber o/flow. I then put away, switched off the battery and came home.

Any ideas? Could it be the effect of 95 fuel In France (5% ethanol) or Super (again in France and 5% ethanol). Should I replace the floats with ethanol resistant types which I believe SU now make? Maybe a new float chamber top(s).

Your thoughts would be most appreciated.

Thanks

Jerry
J P BIRKBECK

Jerry could it be the metering valves, my one is constructed with a plastic sleeve and loose fitting spring loaded steel needle, is the needle jammed or tight, or even worn out? also I think the float arm should have 3/8" clearance from the chamber lid. Sorry I have no more ideas Bryan
B Mellem

Firstly Jerry, check the distance gap on the forks and that they are correctly set per the workshop manual. If you do not have a workshop manual you can get it on CD from YZ Publications.

Secondly, take out each float and check that when you shake it you cannot hear any fluid - if you can dump them in the trash and buy a pair of unsinkable floats - NTG sell them.

Third, check the float pins slide up and down smoothly and freely in their sleeves and that the sleeves are correctly installed and done up properly ... and that you have the correct sleeves and pins. I have seen some pretty poor fits in my time and also wrong pins and even wrong sleeves.

Finally, inspect the top of the pin (the pointy end) and if you can see a waer ring on them, toss them and fit new pins and sleeves.

On reassembly check all your gaskets are in good condition and are fitted in the right order, and that the gasket around the lid rim is also in place, not torn or twisted or crimped.

Paul
Paul Barrow

It occured to me that the ethanol is causing disintegration in the fuel lines and fragments are jamming the metering needles open. I think that you should find particles in the bottom of the float chambers. Have you an in-line filter fitted, I have one just before the carb so that any deposits can be seen and trapped, although I'm told that the ethanol is disolving some makes of filter! Happy times Bryan
B Mellem

Hi Jerry, I too had a similar problem earlier on. This followed an extensive re-build of the Carb with new parts from Burlen, as a result of hot starting problems (now resolved??). This including re-bushing the throttle spindle and replacing the float chamber valve. The replacement valve was the modern type with a plastic centre. Eventually, the problem of overflow was narrowed down to this valve, the float chamber lever that links the float to the needle valve was pushing the needle off centre and jamming causing the flooding. The valve was replaced with the original and a new spindle for the lever cured the problem as the lever would stick due to wear in the spindle. So, have a look at the spindle and the shape of the lever. As Paul suggests, the shape of the arm is important. Also, if the needle valve is longer than the original this may also be a problem causing a jam. Maybe a Grose valve would be an alternative.

Also, regarding Ethanol in fuel, Read the Book by Rivers-Fletcher "MG's past and present" there he details problems he had in 1947 with his racing N type, mixing up special "brew" of petrol, methanol and other ingredients. To investigate, I mixed a brew similar to his, using petrol, methelated spirits (methanol) and red wine (12.5% Ethanol/water mix) and let it stand. After a few weeks, the mixture has clearly seperated into three distinct bands, petrol on top, red wine/water at the bottom. So, a run every few days to stir up the mix, (bouncy rear springs!!)
Regards
Dave

D P Jones

Are you running a standard fuel pump? I had an identical sounding problem with my MGBGT a few years ago. The cause was my petrol pump, a replacement electronic unit which I had fitted in lieu of the original SU. It was operating at a higher pressure than the old SU, and the fuel was forcing its way past the needle and seat of one carby. I fixed the problem by fitting an in-line pressure reducing valve to knock the line pressure back to about 2 PSI. Probably too obvious a solution to your problem, but one never knows!
N Wakeman

Well the YT was fitted with an electronic pump, though I also have a new pump that I bought about 18 months ago when I owned an XPAW engined TA.

I have ordered replacement valves and a set of new floats from Burlen.

I'll keep you informed of the progress.

Thanks for all your advice

All the best

Jerry
J P BIRKBECK

This thread was discussed between 03/10/2012 and 06/10/2012

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