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General Tech Using Fuel Pump Lever When Setting SU Floats

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KVH

KVH

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When adjusting my floats I’m having an issue on the front, leading carburetor. I installed a new seat and Viton tipped needle. I set the gap to lid at about 3/16. I filled the bowls using the manual pump lever. I had fuel running out of the jet into the intake manifold. Clearly not right. I’ve tried two even larger gaps, 1/4 and 5/16. Same thing. The level in the jet is too high, spilling from the top. I checked by removing that piston of course.

I’ve checked the needle and seat out of the car. It closes and seals properly.

Is the problem likely that I’m using the manual lever to refill the bowls? Does the manual lever push too much pressure into the line and cause a bypass of the needle?

PS. I have HS6 carburetors on my vehicle.
 
Shot in the dark: Is your float compromised?
 
The correct adjustment for TR3 and TR4 SU floats is established by using a 7/16-inch diameter rod (I use a drill bit).

Any excess fuel should run out the float bowel overflow tubes, not the jets.

On both the original and the aftermarket fuel pumps for my TR3a, the priming lever appears to stop working at some point; meaning I stop feeling that moving the lever is doing anything.
Maybe this is because it feels a resistance when the float bowels are full and the needle and seat are closed. I don't really know.
But once I feel it is no longer pumping, I just start the car and go on my way.

Have you tried starting the car to see how it runs
 
My float is also new. I’ve checked it and see no evidence of cracks or leaks. That 7/16 spec for the lid gap is actually for a different model SU, usually the one with the brass fork closing lever under the lid. It’s shown in the SU instructions, but that’s not for HS 6 carbs. The instructions for HS 6 is 1/8 inch, but the SU website says you can increase to 3/16 inch.

I think I need to experiment running the engine to fill the bowls, rather than using the pump lever. That means I can’t verify or check fuel level in the jet without dismantling the carb housings each time. A bit of a hassle but, oh well.
 
When the pressure comes to spec (about 3 psi), the fuel pump lever should not pump any more. It goes "limp". It does sound like maybe your pump is overpowering the float. If you have an old vacuum gage, it also has a fuel pressure side to it...so it can be used to test your pressure is below 3psi.

All above are also correct...if your float has a leak it will not float, and therefore will not close the valve.
 
I just rechecked it. I’m surprised. It’s registering almost 4 psi. I have a spare pump that I’ll put on. I sort of hope this has been my problem.
 
Last edited:
KVH said:
I just rechecked it. I’m surprised. It’s registering almost 4 psi. I have a spare pump that I’ll put on. I sort of hope this has been my problem.
Click to expand...
This is why I have electric fuel pumps and Holley regulators on all my old cars. On my Bugeye Sprite, I found that my fuel pump had an outlet pressure of 4.5 PSI, and it was forcing fuel past the float valves. I now use an electric pump with ~6 PSI outlet pressure and regulate it to ~2 PSI. The higher pump pressure probably provides a little resistance to vapor lock and gives the regulator a little headroom to operate.

I suppose you could reduce the output pressure of the mechanical pump by trimming the spring a little shorter. I've never tried that, but I'd be interested to hear how it worked from anyone who did.
 
Could I use a pressure regulator in connection with my manual “standard“ fuel pump?

Do you also change over from a generator to an alternator for more reliable current supplied the vehicle and accessories?

Just reading the material online from Moss, it seems that the change over to an alternator is almost too simple. Surprisingly, if I read the instructions correctly, the voltage regulator becomes obsolete, a relic left bolted under the hood.
 
KVH,
I have an aftermarket original-style mechanical fuel pump on my 1959 TR3a, without a fuel pressure regulator.
I have the original generator in my 1959 TR3a, although I rebuilt it.
I have the original SU carbs in my 1959 TR3a, although I rebuilt them.

A couple of weeks ago, I completed a 1500 mile road trip in my 1959 TR3a without any problems.
Apparently, 66-year old technology still works just fine.
 
I’m inclined to stay with my mechanical fuel pump and add a pressure regulator/reducer right before the carburetors.

It’s a little tight in that area, especially if I want to keep my fuel filter. Would anyone see a problem with my using one of those very tiny universal fuel filters? The one I’m thinking of using is barely 2 inches long and maybe an inch in diameter. At least it seems to fit.

I have a feeling I’ll be revisiting electric fuel pumps in the future, but for now I think this is the direction I’d like to go.

It appears I’ll have to make a little support brace for the regulator to sit on. I’d like it to be secure and to look as “professional“ as possible.

I do realize Moss has a reducer/filter all in one. I’m not ready to go with that model just yet.

Thanks all.
 
Sarastro said:
This is why I have electric fuel pumps and Holley regulators on all my old cars. On my Bugeye Sprite, I found that my fuel pump had an outlet pressure of 4.5 PSI, and it was forcing fuel past the float valves. I now use an electric pump with ~6 PSI outlet pressure and regulate it to ~2 PSI. The higher pump pressure probably provides a little resistance to vapor lock and gives the regulator a little headroom to operate.

I suppose you could reduce the output pressure of the mechanical pump by trimming the spring a little shorter. I've never tried that, but I'd be interested to hear how it worked from anyone who did.
Click to expand...
Steve, how did you run the fuel lines to your regulator, and where did you mount it? I’m thinking of mounting very close to the location of the “stock” line, fitting it in place with a very small fuel filter. It’s possible, but I could also mount it on the passenger wheel well, a cooler location temp wise, but then I’d be running a bit more than two extra feet of rubber fuel line (over to the wheel well and back). Not sure I like that. Seems a bit cumbersome but I’m wondering how others have done it. Thx
 
KVH said:
Could I use a pressure regulator in connection with my manual “standard“ fuel pump?

Do you also change over from a generator to an alternator for more reliable current supplied the vehicle and accessories?

Just reading the material online from Moss, it seems that the change over to an alternator is almost too simple. Surprisingly, if I read the instructions correctly, the voltage regulator becomes obsolete, a relic left bolted under the hood.
Click to expand...
One of the alternator mfrs offer a dummy regulator to take its place.
 
Gutting an old regulator is easy to do , then just use the common connections as a buss. This
will leave some spots blank ,but it looks pretty nice if you do it carefully.
Mad dog
 
KVH said:
Steve, how did you run the fuel lines to your regulator, and where did you mount it? I’m thinking of mounting very close to the location of the “stock” line, fitting it in place with a very small fuel filter. It’s possible, but I could also mount it on the passenger wheel well, a cooler location temp wise, but then I’d be running a bit more than two extra feet of rubber fuel line (over to the wheel well and back). Not sure I like that. Seems a bit cumbersome but I’m wondering how others have done it. Thx
Click to expand...
It's all here:
 
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