18 replies to this topic

[DUF2]

Duffy is fitted with a 1275 A+ engine which runs a HIF 44 carburettor.

where and how should the overflow pipe terminate?

I realise this is so overflowing fuel does not drip on the exhaust, but know that this pipe allows air into the jet so don’t want to terminate it where it could drag dust etc into the float bowl.  Currently there is a rubber pipe which terminates on an open end over the head steady.

 

 09CFEB03-70BE-4228-A30E-349AC959A393.jpeg   126.29K   12 downloads

not sure why the photo is coming out upside down, it is the correct way up when I upload it!!

[Chris1275gt]

On my hs4 I run the overflow along the top of the box section then down the side of the rad next to the rad overflow and terminated it 150mm from the road.

[Ethel]

It won't suck. there 's no flow it just lets pressure equalise with atmospheric.

[DUF2]

It won't suck. there 's no flow it just lets pressure equalise with atmospheric.

If I put my thumb over the end of the pipe the engine stops, so there must be a bi5 of suction there.

[Dusky]

If you’re bothered by it, add a fuel filter in line. ( or a vacuum filter like on all American cars)

[PACINO]

Hi friend. By the way, I put the photo correctly, would you be so kind to tell me what you have the crankcase breather hose double connected to? A picture of that ... that would be great.
Regards!

[3VILC]

Hi friend. By the way, I put the photo correctly, would you be so kind to tell me what you have the crankcase breather hose double connected to? A picture of that ... that would be great.
Regards!

On mine one goes the rocker cover vent the other goes to the crackcase breather

[GraemeC]

I'd suspect one to the timing case breather and the other to the carb.  Standard set up on a A+ 1275.

[DUF2]

GraemeC is correct, one pipe comes off the breather shown in the pic, the other pipe comes from the breather on the timing case.

I am still not sure where and how the overflow pipe is to terminate. This pipe will have been a standard fitting on the ‘90-94 cars before going to fuel injection

As Dusky says I could always put a fuel filter on the end of it.

[cal844]

Your car should have a metal pipe that goes along the top and front of the wok, the wok bolts hold it in. I took mine off and just used a length of fuel hose

[Chris1275gt]

It won't suck. there 's no flow it just lets pressure equalise with atmospheric.

If I put my thumb over the end of the pipe the engine stops, so there must be a bi5 of suction there.

If you put your thumb over the end of the pipe your stopping atmospheric pressure getting to the top of the float chamber which will cause a slight vacuum and stop the petrol flow to the carb.

[GraemeC]

The pipe is as Cal describes - I might have one somewhere....

[DUF2]

Thanks for the info, I was just wondering where it was supposed to terminate. Clipped to the wok and terminating near the front of the car, that is fine for me.

 

GraemeC don’t worry about the pipe, I will have something I can use. I think the fuel filter will be a good idea, just in case things are a bit dusty. Gaiter was fine thanks.

[Ethel]

 

 

It won't suck. there 's no flow it just lets pressure equalise with atmospheric.

If I put my thumb over the end of the pipe the engine stops, so there must be a bi5 of suction there.

If you put your thumb over the end of the pipe your stopping atmospheric pressure getting to the top of the float chamber which will cause a slight vacuum and stop the petrol flow to the carb.

 

 

The Venturi between the piston & the bridge creates lower pressure, allowing the atmospheric pressure in the float chamber to push fuel out of the jet (like the levels a U tube barometer). Fuel then flows through the float valve to replace what's been fed to the engine.

 

Yes, a small amount air has to be free to enter the float chamber as the fuel level drops, but it comes out the same way when you let off the throttle and the float level returns.

 

Air entering the end of the vent pipe will never get as far as the float chamber. Blocking the vent just allows the air pressure in the float chamber to drop as low as the depression over the jet: the "U tube" levels are then equal and below the jet, so no fuel flows. 

[cal844]

The pipe is as Cal describes - I might have one somewhere....

Quite easy to make with some 6 or 8mm microbore and a couple of P clips