38 DGAS fuel problem, any ideas?

[hallsie]

Hi All

today I started project GOLDMEMBER's engine for the first time, and she ran beautifully.

However, I noticed that after 30 seconds I started to get fuel up and out of the holes on the top of the carb from the ones pointed out in photos below, and it started to spill over the top of the inlet manifold.
Needless to say I shut it off pretty quick, but has anyone got any ideas as to what may be stuck or blocked?

Thanks






Stu

[RCK974X]

It might just be the float valve isn't shutting off ? If so, have to take the top off and clean out the valve.

Would make sense if it's been stood for a while....

[prideaux]

RCK974X said:

It might just be the float valve isn't shutting off ? If so, have to take the top off and clean out the valve.

Would make sense if it's been stood for a while....

On Reflection I think that's the problem the floats do sometimes stick mine did at Silverstone last year looks like I would either strip and clean that carb or get someone to do it.
A

[chris52]

Yes agree it will be the float fuel cut off valve. If you get a rebuild kit it usually includes a new valve.

Chris

[hallsie]

Thanks all

Ive rebuilt the carb recently so Ill strip it down tomorrow and have a play with the float,

Stu

[Grantura MKI]

Be sure the float is working...meaning no holes, etc. and is actually floating.
Cheers,
D.

[RCK974X]

Er... my memory tells me (so it might be wrong) that -

1. the float valve on those style of webers had a small rubber cone on the top to seal them, and they are easy to damage...and then they don't seal properly.

2. the valve had a wire spring clip thing to hold it in place, which can also cause problems if it's not put back dead right...

(Or do I have the wrong carb connected to these memories ?)

[bluezeeland]

Hi Stu,

Have a look at this

http://www.poustusa.com/weber_carb_pages_pix/weger...

grtz

[hallsie]

Right,

with the carb top upside down, floats putting pressure against the rubber cone top of the valve, im getting a measurement from the housing to the floats of 40mm.

The valve is new and seating well as I can blow through the inlet valve and raise the floats (upside down) to get iir fow, and when I let them back down to rest on the valve the ir flow stops and goes out of the fuel return pipe.

However, what I have noticed is that there is not much air coming out of the return pipe, (again whilst blowing) as if there is too much restriction there which is causing the fuel pressure to build up and for fuel to continue into the float chamber, past the valve?

Will there be a problem with opening up the fuel return outlet orifice a bit to help with the pressure relief?

Ive got a new Mechanical fuel pump which may be a bit too powerfull as its new?

the only reason I can see for the return pipe to be restricted is to act as a basic kind of pressure regulator, or its blocked??

Any thoughts?

Thanks

Stu

[hallsie]

Adrian@ said:

The float is set vertically with light contact of the pin ball, including the gasket and then the travel is 12.5 mm (change the body to vertical and set on the rear lug ), the outlet is a restrictor, for back pressure. Check that the floats do not touch the power valve.
Adrian@

Thanks Adrian.

Ignore the steel rule you can see, the angle of the camera makes it look wrong.

Just resting on the ball of the valve the floats are at 40mm from the casing

And the second photo shows 52.5mm.

Ill be out after the children ahve been put to bed to play again!






Stu

[bluezeeland]

1 The float looks tatty, are you sure it is 'floating' ? If it is leaky it will cause symptoms as described. Burton' does them (plasticy ones, that is)
2 the little lip actuating the valve looks not to be enough down to close the valve (in the picture, might be deciving)
3 to state the obvious, but is the complete return to the tank free/no blocks/kinks, iow is petrol gettin back to the tank ?

[hallsie]

bluezeeland said:

1 The float looks tatty, are you sure it is 'floating' ? If it is leaky it will cause symptoms as described. Burton' does them (plasticy ones, that is)
2 the little lip actuating the valve looks not to be enough down to close the valve (in the picture, might be deciving)
3 to state the obvious, but is the complete return to the tank free/no blocks/kinks, iow is petrol gettin back to the tank ?

Hi Frank

The float only looks tatty because Mr Gray didnt get to polishing it and it floats nicely in the sink!
The valve is definately closed in the first photo as blowing through the supply connection only gives air through the return pipe.

and the return pipe, albeit a bit more restricted then I would expect, definately lets fuel return.

once I have refitted this weekend and tested, if it still doest the same I will be opening the return pipe orifice to allow better return flows, and if this causes problems I can always fit a pressure regulator to compensate.

Stu

[hallsie]

Adrian@ said:

Opening the return will screw the whole carb up, and finding a replacement expensive (another carb), this IS a simple as set up IMHO...which version of the kit did you buy into, as the valve tips now match the current fuel, it should be orange, set the float and try again.
Adrian@

I bought the Webber kit, and yes the tip is orange.

I havent tested it since setting the float correctly so Ill wait until Ive re fitted it this weekend and get back to you.


Thanks

Stu

[bluezeeland]

Stu,

As said, think you should re-measure the 'fetch' of the float in the vertical, re-adjust the actuating lip if need be (play around a bit, I do realise its a bit of a faff....)The float obviously needs to close the valve through its buoyancy......
Just a thought, is the gasket of the power valve on all of the three screws ?

Think you should not 'enlarge' the return, can of worms and all that !

F

[hallsie]

Bought a 'New Old Stock' 38 DGAS this morning.
couldnt be dealing with messing around!!

Put it on and still have the same problem!

Im now going to put on the old pump and see if it still does it, I now suspect not.

Then Ill try an extra gasket on the new fuel pump to give it less actuation from the cam and see if that works.

Until tomorrow.

Stu

[hallsie]

Sorted

The new fuel pump is a bit efficient!

Ill put another gasket on the new pump and see if that works, if not Ill stick with the old pump!

Garage is full of fumes, so Ill leave it for an hour!

Stu

[bluezeeland]

glad you nailed it !

Do seem to remember that on my mecha pump there was some 4/5 mm of gasket/spacer, went to elec afterwards...