Fuel issues - 2.25 with Weber carby

[Shonky]

Ambrose is still being uncooperative.

I had thought that my issues were supply issues - namely that the fuel line was leaking air somewhere between the tank and the pump.

I have duplicated the line with a one piece jobbie, bypassing the fuel tap and various other connections along the way that mil 2As have

There are no leaks that I can fathom, and on hand priming there seems to be plenty of fuel getting up to the inline filter before the carby. When running though, there is but a trickle into the bottom of the filter and the filter doesn't fill.

I put low pressure compressed air to the inlet on the carby, and I noticed that air was freely escaping from just above the fuel bowl (there is a join there).

Now one thing I have noticed with the fuel pump, if the carby end of the line is stopped up, no more fuel will pump out into the filter.

My question is, could the fuel bowl be full, and not permitting much more fuel to come up the line, while the carby sucks mostly air and some fuel from the bowl? Or - should the pump keep pushing fuel up into the filter, and subsequently the bowl?

I guess it could be a piece of crud blocking something, but the lines and pickup have all been apart multiple times now and all are clear. Maybe a flake in the bottom of the tank - but you would think it would be intermittent, not constant. Besides, the tank has been in regular use for about a year.

I wouldn't think that the cam shaft is worn and hence not activating the pump properly...

The pump is new, and the problem is the same with the old one (which appears fine in retrospect)

[Blknight.aus]

could be a blocked needle and seat.

first off confirm the pump and filter arent the issue by dropping the fuel line off of the carby and then turning the engine over on the starter for about 10 seconds you should pump about 100mls into a container.

once youve got that checked the problems got to be the carby.

[Shonky]

I think I've got it!



Had a sit and a think, and tried to get my head around how carbies work (This is my first foray into the nitty gritty of their operation)

I concluded that the carby was indeed sucking air, and running on vapour whiffed off the top of the bowl. This explained why it was fine on idle, but quickly died when running. It also explains why revving it wouldn't recreate the same issue, as of course when you rev, it squirts a shot of fuel straight down the throat.

The leak site as found with compressed air:


So I decapitated the carby, and found evidence of leakage on the gasket. A straight edge showed the body of the carby (forgive my lack of correct terminology) was level and true, as was the mating surface of the 'top bit'.



The obvious culprit seems to be a manufacturing defect. This roundy 'bit' has a raised surface which sits on the gasket seat and obviously is not allowing the two components to mate properly.



If you look at the first two pics you will see some brown gunk stuck around the leak site - fuel and dust no doubt. It seems that this has been happening for some time, but the extra heat endured last weekend may have made for thinner air/lighter fuel and hence acutely exaserbated the leak.

So: I am going to level out the surface and hopefully this will solve the issue.

What a bloody wild goose chase!

[Shonky]

could be a blocked needle and seat.

first off confirm the pump and filter arent the issue by dropping the fuel line off of the carby and then turning the engine over on the starter for about 10 seconds you should pump about 100mls into a container.

once youve got that checked the problems got to be the carby.

Just missed your post Dave - was typing mine.

The needle and seat seem fine, but we'll see how we go. The fuel line is definately okay, and the pump seems to be behaving properly (as you say, it is pumping what I guestimated to be a normal amount into a jar)

[Chris Fehrenbach]

Just discovered a similar problem but I have the CD175 Carby.
The pump is working until the fuel line to the carby is connected. Lots of crud in the bowl (cleaned out) I can see why you need an apprentice now that I discovered the bolts holding the bowl on were in the inside, got them by myself though.
I am hoping that there may not be enough fuel so I will put another 5 litres in tomorrow before removing the carby to dismantle, check and clean.
Glad I enjoy it! Particularly when the nuts kept falling from the socket while I tried to bolt the bowl back on.

[JDNSW]

I am not familiar with the operation of a Weber - never had one, but your analysis may be partly correct - an actual leak from the outside air into either the carburetter throat (it is above the venturi) or the float bowl (it is somehow connected to the outside air pressure anyway) should have no effect. But the various small passages between the top and bottom of the carburetter do need to seal properly, and this may well be your problem. I would be very cautious about filing off those raised rims without understanding exactly how everything is supposed to work - perhaps they are to locate the gasket, which is supposed to be thicker and have a hole large enough for the rim to go through?

John