27 replies to this topic

[Tonylamb]

The A+ engine I bought didn't have a fuel pump so I decided to fit an electrical one. For a bit of security I've added a switch in the line. basically you get whats in the bowl and that you done. However a couple of times I've forgotton to switch on.

Problem is when I switch back on the engine just won't start. First time I could hear the pump clicking like mad so assumed it was an air lock. fiddled with the pump and all good.

This time I just can't get it to start. there is fuel at the filter in the engine bay and right up to the carb is pumping strongly. The plugs are dry as a bone? I'm wondering after the fuel starvation if the float is stuck. That doesn't make sense to me because the fuel valve would be wide open? Is there a way of checking fuel is in the carb without taking the bottom with the float all apart?

[nicklouse]

most likely some crud blocking something.

[Tonylamb]

Its wierd that its done it twice when the fuel pump has been previously switched off though? Is there any way of seeing if theres fuel in the bowl without taking the bottom off and spilling fuel everywhere?

[cal844]

Do you run an inline fuel filter before the pump? Sometimes these case issues

[Tonylamb]

yes there is a filter before the pump and a filter and fuel pressure regulator before the carb. I've just taken the needled assembly out of the carb and switched on. I know there is fuel pumping at decent pressure to the carb inlet. there is no fuel coming up through the needle jet??? So presumably the float is stuck shut not letting any fuel in?

[Tonylamb]

Is there a certain amount of pressure needed to open float chamber? There seems to be decent pressure?

[Tonylamb]

Looks like the carb is going to have to come off

[cal844]

You need 3 psi MAX at the carb.

[nicklouse]

Is there a certain amount of pressure needed to open float chamber? There seems to be decent pressure?

nope it opens as the float drops. if it is crudded up it may not be opening.

[Spider]

Where is the pump located?

If it's in the engine bay, some pumps don't draw too well, particularly if a filter is fitted before the pump. Never a good idea with Diaphragm Pumps (like an SU).

[Tonylamb]

I fitted the pump on the sub frame under the tank, seemed like the obvious place. there is plenty of fuel from the fuel pipe at the carb it fills a cup in 2 seconds. But it doesn't seem to be going anywhere or into the choke from the float chamber. I can only imagine that the needle is stuck and not letting any fuel in or something is stuck in the float chamber needle.

[Tonylamb]

Perhaps theres too much pressure would that force the float needle shut?

[nicklouse]

Perhaps theres too much pressure would that force the float needle shut?

nope, too much would blow it open.

[nicklouse]

https://sucarb.co.uk/technical/

[Tonylamb]

I've taken the carb apart, the float bowl in particular. nothing seems to be amiss but I did notice that if I blew in the inlet pipe it seemed to be blocked. Checked the little filter under the float needle valve, that is clear. So putting it all back together I cant get the rubber ring that seals the bowl back in. It just too big. I've stuck it in the freezer to try and shrink it to size. may need a new one which will delay putting it all back together. The float valve all seems to be working and a little fuel came out but the bowl certainly wasn't full with fuel which is should be.