SUs and pumps

[Richard McDonel]

Since  first firing my rebuilt 2.4 engine back is September, I''ve probably run it for about 20 minutes.     But now it won't start, and the problem seems to be that the new,  Kyosadenki mechanical pump has stopped pumping.  There is fuel to the filter side, but none comes out the carb side.  Anyone know of any reason why a new pump would fail?  I  took if off the car and bench tested by pushing the lever while hold a thumb against the inlet.  Sounds OK.  Also, when I removed the pump, it appeared that some fuel may have back-flowed into the engine - likely oil change time.  Any thoughts  or suggestions would be appreciated. 

With respect to the carbs, both the SU book and the Haynes manual call for setting the float level by holding the top upside down and measuring the gap between the rim and the lever.  But all the comments here seem to concentrate on measuring the fuel depth in the bowl.  Any particular benefits one way or the other.

Thanks

 

 

[7tooZ]

 

 

 

Sent from my iPhone using Classic Zcar Club mobile

 

[240260280]

Some tips:

- fuel rail only flows one way, as well as pump and most filters, make sure flow is correct through all.

- you can quickly prime carbs by pouring fuel through fuel bowl vents to get it running quickly.

- run outlet of fuel rail to container to verify fuel flow into container when cranking.

 

[Richard McDonel]

240...

Tried priming, but it would only run as long as the primer fuel would allow.  

I ran a short length of hose from the pump into a container and twice spun the engine on the starter for a good 10 seconds, and not a drop came through.

Based on that, it  is logically the pump, but if I'm questioning it's because I haven't had a mechanical fuel pump fail on me since April 1968 ('57 Chev BelAir four-door hardtop, wedding night - story for another night)

[Patcon]

I have found that the fuel pump valves in the pump can stick and prevent the pump from pumping

[Captain Obvious]

15 hours ago, Richard McDonel said:

both the SU book and the Haynes manual call for setting the float level by holding the top upside down and measuring the gap between the rim and the lever.  But all the comments here seem to concentrate on measuring the fuel depth in the bowl.  Any particular benefits one way or the other.

I'm no carb expert, but I believe that flipping the lid upside down and measuring the position of the float is to be used as a preliminary "ballpark" setting only. Just to get you "on scale". It only has a little bearing on exactly where the fuel level will end up because the final level is dependent on other factors such as the design of the needle valve.

A direct measurement of the dependent variable is always preferred when compared to an indirect "inferred" relationship. Put simply:

Q - How do you get the fuel level set correctly?
A - Check the fuel level and adjust the float tang accordingly.

So I suggest that the mechanical measurement of the float position with the lid upside down is a good way to start, but after you have done that (just once), you should always refer to a direct measurement using the clear tube method after that.

If you get lucky and happen to hit the target level on the first try using only that mechanical method, then that's excellent! But just don't count on it!

[siteunseen]

15 hours ago, Richard McDonel said:

With respect to the carbs, both the SU book and the Haynes manual call for setting the float level by holding the top upside down and measuring the gap between the rim and the lever.  But all the comments here seem to concentrate on measuring the fuel depth in the bowl.  Any particular benefits one way or the other.

The newer needle valves won't support the weight of the float when you turn the lid upside down.  Find something .55" and blow through the fuel inlet on the lid pushing up on the float until it stops your breathe.  When it stops your breathe the top of the float should be .55" from the lid.

I do this with the lids upright, in front of a mirror.

Yes, this is a ballpark, first step thing.  I used the clear tube off the very bottom like in this picture.

 

Edited March 27, 2018 by siteunseen

[Captain Obvious]

15 hours ago, Richard McDonel said:

when I removed the pump, it appeared that some fuel may have back-flowed into the engine - likely oil change time.

What do you mean by this?

If you're saying that fuel came out of the back of the pump and ran down into the crankcase, then you've obviously got a bad diaphragm in the pump. That would explain both the lack of fuel, and the oil in the gas. Somehow, I don't think that's what you meant, but it's my job to check.     

[Captain Obvious]

1 minute ago, siteunseen said:

blow through the fuel inlet on the lid pushing up on the float until it stops your breathe.  When it stops your breathe the top of the float should be .55" from the lid.

And that should STILL only be used as a preliminary set-up method.

A direct verification of the level is the only way to be sure, and is the gold standard for accuracy.

[siteunseen]

5 minutes ago, Captain Obvious said:

and is the gold standard for accuracy.

I did all three. 

Edited March 27, 2018 by siteunseen

[Captain Obvious]

Zactly. In the end, I don't care how far the float is from the lid is when things are dry.

In the end, I only care about where the fuel level is when things are wet.

[Richard McDonel]

Cap't.

Yes, that's what I mean.  Fuel came out the back as I removed the pump and gasket from the head,  I disassembled the pump, and to my untrained eye, the diaphragm looks OK, but there is no way I'm putting that pump back in.  I hope I get a better lifespan out of its replacement.  Might want to pack a spare when travelling.  Anyone else had a fuel pump fail after 20 minutes?