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MG MGB Technical - weber45dcoe-

I recently had a new 1950cc engine fitted to my 1973mgb roadster,together with a weber45dcoe carb.This does not allow closed circuit brething and the car fills with fumes.We have tried taking a hose from the breather on the top of the engine and letting it vent down by the gearbox but,this has not helped.Also the carb leaks petrol copiously at tickover,maybe it does at speed but,it is difficult to test this.
The problem is so bad that I have just had the SUs put back and I already miss the holigan effect!
Any ideas,advice,or even better a solution would be welcome
Will Hazell

Will,
I too enjoy the holigan effect of a 45 DCOE! but it sounds like you need a couple of things;
1. Oil catch tank for the breather to go into this can be a nice shiny alloy tank or an old 1 litre drinks bottle it really doesnt matter!
2.Do you have a malpassi fuel regulator fitted? if not you really need one as you are probably over pressuring the carb andd thats why its losing that expensive fuel all over the place.
3. A session on a rolling road to set everything up correctly. A weber is a much harder beast than SU's to get right.
If you need more details please email me.
TJ
T J Nicolson

I'd second what TJ is saying but would add that if you have a standard SU fuel pump, check the inlet needle valve as the pressure should not be excessive. Actually, I'd just go ahead and fit a new valve and a gasket set as I hate to see fuel leaks from any carb, epspecially when it's dripping onto a red hot exhaust manifold.

You can see a few shots of a catch can at http://spostins.photosite.com/GT/. The rocker cover is vented to it, along with the tappet chast cover, and a large bore pipe runs from it to under to gearbox. That said, I'll bet most of the fumes come from all that petrol vapourising in the engine bay.
Steve Postins

Will,
Catch tanks won't help the fumes, what you need is one of those ugly Rectangular air filters with the hole in the backplate that you can run one of your crankcase vent hoses to. Thus creating negative pressure in the block again and the fumes are burnt by the engine.
As for the leaks. I'd start with putting a kit through it if it's not new and yes a fuel pressure regulator is handy, but I've never used one and raced with Webbers for years. Check what pressure your fuel pump is. If it's 4-6PSI then yes regulate the pressure if it's the 2-4 range then your probably OK without one.
I'm currently using a 3psi facet one like this
http://www.fuelsystem.co.uk/web-facet.pdf with no problems.

Kit's etc are available at places like this.
http://www.fuelsystem.co.uk/weber%20jets.pdf

Lastly I find Webbers far easier to tune than SU's once there right they stay that way also.
I've put together an extensive list taken from this source but added Moss and S/T book info also.
http://www.teglerizer.com/dcoe/index.html
If you want a copy email me and I'll send it over.
I'm know expert, but all the info is out there.

Hope this helps
Cheers
<MARK>

http://freespace.virgin.net/marka.hester/index.htm
Mark Hester

I'm with Mark.

Somehow route the breather hose to the aircleaner
and let the engine burn up those pollutants. The
slight negative pressure it'll impart in the engine
block is more pro-active at evacuating
post-combustion by-products and acids, and it
helps to make life a little easier for the oil seals
and gaskets.

The pressure from a standard SU fuel pump is not
excessive and a Weber carb should be able to
handle it without an added pressure regulator.

The engine tends to shake a bit during tickover.
Because the Weber DCOE is mounted far
outboard of the engine, this sort of magnifies any
s-s-shaking and v-v-vibration effect to the carb.
If the fuel chamber in the carb isn't fully filled
at tickover, a worn needle valve may have a bit of
difficulty seating itself during all this commotion
and excess fuel will slosh out through the fuel
chamber breather port (next to the forward
ram trumpet).

Renew the float needle valve assembly, and be
sure to adjust the float level.

Before winding up the engine (tickover), switch on
the ignition and wait a second or (two or three) to
allow time for the fuel pump to fill up the carb fuel
chamber and the float needle to fully seat itself.
Check for leaks.

Then, spin the starter and...go man, go!
Daniel Wong

This thread was discussed between 11/05/2005 and 12/05/2005

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