6 replies to this topic

[TomConroy24]

I have a 1991 mini with a 998cc engine with what I believe is a SU HS4 carburetor. Since I was getting petrol in my oil and I have an electric fuel pump, my idea was to replace the needle and seat in case the float bowl was flooding.

 

I removed the carburetor, removed the cover on the external float bowl and replaced the needle/seat. (the new needle was an upgrade part with a rubber tip) I reinstalled the carb with new gaskets and the car starts up and idles fine, but when I try to drive it sputters and will not build RPM's like it is starving for fuel. It's seems like there is not enough fuel getting to the float bowl.

 

It didn't seem like there was an adjustment on the float bowl. I can hear my electric fuel pump run when I turn on the ignition and then it stops once pressure is built up and the float bowl is full.

 

Does anyone have any ideas as to what might be the problem? 

 

[cal844]

Petrol in the oil is usually a mechanical pump failure, check the flow rate of the pump :)

[gazza82]

From the float bowl it has to get to the needle so check the flexible hose at the bottom of the float bowl to the jet for kinks/perishing.

[TomConroy24]

I took these photos of the pipe from the float to the jet. It looks ok to me. Does anyone see an issue with it?

 

https://goo.gl/photo...H2VmKLT3ih9bXf7

https://goo.gl/photo...Pvo2UUA8bvf3go9

https://goo.gl/photo...nDkMDh3avDtjdH6

 

Any ideas would be greatly appreciated.

Edited by TomConroy24, 26 July 2016 - 01:39 AM.

[carbon]

The pipe from float chamber to jet looks OK in the photos.

 

You could try refitting the old float needle and seat. If you do this check the gap between the float and chamber lid with both combinations.

 

 

It's not easily adjustable on the HS4, but if there is a bigger gap with the new seat and needle then fuel level will be lower and mixture slightly weaker.

 

And fuel getting past the needle is often because of dirt/rust coming through from the tank. Do you have a fuel filter installed?

[TomConroy24]

If the fuel level is slightly lower in the bowl is there a way to compensate for it by adjusting the jet?

[carbon]

The jet height affects the mixture, most important to get this set right at idle.

 

The float height does not have so much effect, but if fuel level is low then you may get poor engine pickup. Also with single carb set-up if you go round sharp corners (such as roundabouts) quickly the engine may go 'flat' when on part throttle (right hand corners if float chamber is on lhs of the carb when looking into inlet, and vice versa if float chamber is on other side).

 

It is best to get the float level exactly as specified by SU, but the late HS4 float level is not easily adjusted.

 

Where did you get the replacement float needle and seat? It may be different to original, check if float sits at different height when you refit the original parts.