TR4/4A New to forum - Rebuilt Fuel Pump and weeping float bowl

[Federalees]

Hello!

I am new to this forum and wanted to make my introductory post. I recently acquired a 1967 TR4A IRS and this forum has been a wealth of information. Thank you for that! In this post I figured I would relate a problem that I resolved that seems pretty common based on other posts that I have searched. However, the resolution to the problem was one that I had not seen.

I recently smelled gas in then garage and noticed fuel seeping from the fuel pump, so i decided to rebuild it. Easy enough, but once I reinstalled the pump and started the car, I noticed a lot of gas weeping from the vent hole of the back carburettor. Assuming that this was the actual cause of the gas smell and I hadn't notice it before, I checked floats on both carbs for adjustment and leaking but they were fine. I replaced the needle and seats on both carbs along with the floats for good measure and none of this solved the problem. This was driving me a bit bonkers. I spoke to everyone I could find that was an expert on SU HS6 and searched this forum for the answer but was unsuccessful. So, back troubleshooting 101. What changed? The only thing was the rebuilt fuel pump. I checked the pressure from the pump and it was at 7 PSI !! Instead of pulling it apart again, I replaced it with a new pump. Problem solved! (face palm). So now I am wondering what I did wrong in rebuilding the pump that would cause such high pressure. Any ideas? Has anyone had this problem? The kit came with the diaphragm gaskets, and check valves, which I have double checked and they are installed properly as far as I can tell.

 

[DrEntropy]

This is just a W.A.G. on my part, but about the only things I can think of that might affect output pressure on those pumps is the springs. The diaphragm spring may be weakened over time, the aftermarket check-valve replacements may have less-than strong enough springs.

But again, just a guess.

 

[Federalees]

Thanks for the response @DrEntropy . I think you might be correct. I guess it will remain a mystery for now.

 

[TRopic6]

The closer the pump is to the block (& the cam), the more stoke it will have. Was there a thick gasket (or several) between the pump body and the block? I had to use a non-AC replacement pump for my TR6 and the output was ~5 PSI. I cut a gasket out of 1/8 material and brought it down to ~3. It worked OK but I did rebuild the original AC pump with a kit from Then & Now. They use really good check valves (+1 on replacement valves leaking).

 

[charleyf]

The "weep" hole you refer to is actually the overflow from the float bowl. So if fuel was coming out of that hole it means that your float valve or float on that carb was not working correctly. A piece of debris in the fuel line above the float valve can cause the valve to not operate correctly or they could have been defective.
I would not get rid of that fuel pump just yet.
Charley

 

[Federalees]

The closer the pump is to the block (& the cam), the more stoke it will have. Was there a thick gasket (or several) between the pump body and the block? I had to use a non-AC replacement pump for my TR6 and the output was ~5 PSI. I cut a gasket out of 1/8 material and brought it down to ~3. It worked OK but I did rebuild the original AC pump with a kit from Then & Now. They use really good check valves (+1 on replacement valves leaking).

Interesting, and this makes sense. But mine had/has a thin paper gasket only.

 

[Federalees]

The "weep" hole you refer to is actually the overflow from the float bowl. So if fuel was coming out of that hole it means that your float valve or float on that carb was not working correctly. A piece of debris in the fuel line above the float valve can cause the valve to not operate correctly or they could have been defective.
I would not get rid of that fuel pump just yet.
Charley

Thanks Charlie,
Yep. I am aware of the overflow hole’s purpose. This is why I checked and replaced the needle valve and float first. As stated in my original post, this was not the problem and I was surprised by that. It was definitely the fuel pump, but I am still keeping the old one.

 

[Popeye]

Just curious, how are you guys checking fuel pressure?

 

[Federalees]

Just curious, how are you guys checking fuel pressure?

I used a fuel pressure tester tool. Super easy to use. Connect the vacuum line from the tool to the output side of the fuel pump and crank the engine for a few seconds.

 

[Popeye]

I used a fuel pressure tester tool. Super easy to use. Connect the vacuum line from the tool to the output side of the fuel pump and crank the engine for a few seconds.

Thanks!