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1976 Jensen GT  Rate Topic 
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 Posted: 10-24-2018 04:06 pm
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CongletonService
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Hi Guys,
I am new to the forum. I am working on a 76 gt for a customer. It has a mr gasket fuel pump under the vehicle. I am wondering if it the correct location and what style pump should be used. He would like to use a SU pump he bought off the web store but it will not fit or mount there. So I am trying to figure out what the correct style pump is and location. Thanks.

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 Posted: 10-24-2018 07:21 pm
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Esprit2
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Does the Jensen GT's owner have the manuals for you to reference, or are you working in the dark?

The original fuel pump was an SU, so your customer is moving in the correct direction. In a Jensen-Healey roadster, it would be located in the rear boot, to the left of the fuel tank. I don't know how that might have changed in the Jensen GT since there is no rear boot separate from the hatchback interior.

In the original system, there is a T-fitting a short distance from the pump's output. The main branch goes forward to the carbs, and a T'd-off fuel return line goes to a hose fitting on the tank, near/ a part of the filler neck.

There's a metal restrictor orifice with a 0.046" ID in the return line. With the stock pump, plumbing, and elevation difference between the pump and carbs, the orifice's inside diameter is sized to result in the correct fuel pressure 'at the carb inlets'. It's a 'dumb' fuel pressure regulator. It bleeds off just enough fuel to yield the correct pressure at the carbs. Change anything in the system (like an aftermarket fuel pump) and the pressure at the carb inlets may change.

If a non-standard pump is used, then it's best to eliminate the T-fitting & return line, and cap-off the spigot on the tank's filler neck area. Delete the whole 'dumb regulator', plumb a direct line from the pump outlet to the carb inlets, and install an adjustable pressure regulator as close to the carbs as practical. Set it for 2.5 psi.

I'm sure a JGT owner will chime in with more specifics about the pump's correct location.

Good luck,
Tim Engel

Attachment: JH Fuel Tank, Pump & Plumbing - Factory OEM.jpg (Downloaded 114 times)

Last edited on 10-24-2018 07:25 pm by Esprit2

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 Posted: 10-24-2018 07:28 pm
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Esprit2
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The attached photo shows the 0.046" ID restrictor that is inserted into the fuel return line. It's not my photo, but I've forgotten who originally posted it where. I hope no one is offended by me recycling it.

Regards,
Tim Engel

Attachment: Fuel System - Return Line Restrictor 0.046 Inch ID.jpg (Downloaded 113 times)

Last edited on 10-24-2018 11:31 pm by Esprit2

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 Posted: 10-25-2018 12:59 am
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Esprit2
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The Workshop Manual specifies an SU AUF 300 pump as standard. That pump's pressure output is 2.7 psi 'minimum' (2.7-3.8 psi range). Flow losses through the plumbing, and an elevation difference between the pump outlet and the carb inlets will result in a slightly lower pressure at the carb inlets. The carbs, both Zenith-Stromberg & Dellorto prefer 1.5 - 2.5 psi. 2.7 psi is a little high for a Dellorto. Z-S carbs can tolerate 3.8 psi, but they work better at ~2.5 psi.

Regards,
Tim Engel

Last edited on 10-25-2018 01:00 am by Esprit2

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 Posted: 10-25-2018 08:27 am
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NigelK
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There is no dedicated workshop manual for the Jensen GT. The GT parts book shows the fuel system components, but not the mounting point of the fuel pump. It is mounted on a bracket welded to the vertical bulkhead behind the right hand (looking towards the front of the car) seat. I have highlighted the bracket in the image below (acknowledgement - Tim Hatcher GT restoration thread on the JOC forum). Hope this helps!

Attachment: Fuel pump location.jpg (Downloaded 106 times)

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 Posted: 10-26-2018 12:14 pm
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CongletonService
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That is where the aftermarket pump was mounted. The SU pump is very large and I did not think it would fit there. At least not easily.

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 Posted: 10-26-2018 02:21 pm
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NigelK
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Here is an image of the fuel pump in situ. It's not the same as the fuel pump as fitted to the J-H. Jensen part number 91434 for the J-H pump and 98065 for the GT pump. I'll try to find an SU part number from the pump on my GT but it won't be until next weekend I'm afraid...

https://www.motoexotica.com/listings/images/4877/122321.jpg

Last edited on 10-26-2018 02:42 pm by NigelK

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 Posted: 10-26-2018 09:26 pm
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Tim Murphy
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Nigel, in the photo, is that heat shield above the exhaust system stock on the GT? Any idea how effective it is? Thanks.

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 Posted: 10-26-2018 10:03 pm
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Sander
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My 2 Jensen Healeys and 2 GT's all use the same SU fuel pump. The GT pumps are mounted under the car as pictured.

Off topic a bit but both of my GT's have that heat shield. I don't know how to answer as to it's effectiveness .... I imagine it does something until it too heats up and eventually transfers heat to my butt!

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 Posted: 10-27-2018 10:29 am
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NigelK
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Tim, I think that heat shield was only fitted to GTs which had catalytic converters. My GT is UK spec and never had one, so I can’t tell you how effective it was. Best wishes, Nigel

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 Posted: 10-27-2018 01:45 pm
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Brett Gibson JH5 20497
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My JH5 had that heat shield as well, the car was one of the last JH's to leave the factory and had a number of GT features. when I replaced the drivers floor pan it didn't dawn on me that the pan was not the same as a regular JH, it had a indentation in it to allow the shield to recces and fit. So when I went to re-fit it with the regular flat pan, it wouldn't work, still have it in the garage collecting dust. It' kind of a metal sandwich with a layer of asbestos matting as the middle layer, probably very effective.
Brett.

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 Posted: 11-13-2018 08:37 pm
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NigelK
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The GT fuel pump is indeed an SU AUF 300 type. Not sure why the Jensen part number is different for the J-H and GT fuel pumps, maybe different variants of the same SU pump type?

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 Posted: 11-14-2018 12:59 am
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chrisl
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That is where the aftermarket pump was mounted. The SU pump is very large and I did not think it would fit there. At least not easily.

I replaced the SU fuel pump on my GT not long ago; as far as I can tell it's identical to the Jensen-Healey. The mounting point is under the car as indicated by Nigel.

It wasn't too large or overly difficult to fit (although idiotically I forgot to clamp one of the fuel lines and got a shower of fuel...). I wonder if you have the correct one? Let me know if you are still stumped and I'll crawl under mine and take a photo.

And don't forget to fit the non-return valve.

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