Stitebunny Posted May 14 Report Share Posted May 14 (edited) Is there any reason you can’t unbolt the top of a oem mechanical pump and ‘re clock’ it so the inlet and outlets point in a more desirable angle? I got a new pump and did do this. this new pump puts out the same 1.5-2 psi. I replaced it in hopes of higher pressure. Shouldn’t this be higher? Im running DHLA 40’s and need a little more pressure. Don’t want to go electric pump if I don’t have to. Most things I read say stock pump should be okay. It does run okay, but I’d like to get everything as spot on as I can. Edited May 16 by Stitebunny 1 Quote Link to comment
Slow Loris Posted May 17 Report Share Posted May 17 @Stitebunny Great idea, please advise how it works out…I think you asked my question before I even knew I had it. 1 Quote Link to comment
datzenmike Posted May 17 Report Share Posted May 17 On 5/14/2024 at 11:00 AM, Stitebunny said: Is there any reason you can’t unbolt the top of a oem mechanical pump and ‘re clock’ it so the inlet and outlets point in a more desirable angle? I got a new pump and did do this. this new pump puts out the same 1.5-2 psi. I replaced it in hopes of higher pressure. Shouldn’t this be higher? Im running DHLA 40’s and need a little more pressure. Don’t want to go electric pump if I don’t have to. Most things I read say stock pump should be okay. It does run okay, but I’d like to get everything as spot on as I can. L16/L18 pump 2.5 to 3.4 PSI L20B pump 3-3.9 Both should deliver 1 liter per minute or less volume. Quote Link to comment
Stoffregen Motorsports Posted May 17 Report Share Posted May 17 While you have the pump apart, you can tap the inlet/outlet threads for different fittings. I tapped one for 1/4 NPT and installed adapter fittings to use AN hoses. No reason other than I wanted to. 1 Quote Link to comment
Stitebunny Posted May 17 Author Report Share Posted May 17 16 hours ago, Slow Loris said: @Stitebunny Great idea, please advise how it works out…I think you asked my question before I even knew I had it. Worked fine. No issues. Other than the low pressure. But that was not affected by rotating the top. 1 Quote Link to comment
Stitebunny Posted May 17 Author Report Share Posted May 17 3 hours ago, Stoffregen Motorsports said: While you have the pump apart, you can tap the inlet/outlet threads for different fittings. I tapped one for 1/4 NPT and installed adapter fittings to use AN hoses. No reason other than I wanted to. That’s a good idea. The fittings it came with are suitable so I used those for now. Will keep in mind for the future. 1 Quote Link to comment
Stitebunny Posted May 17 Author Report Share Posted May 17 16 hours ago, datzenmike said: L16/L18 pump 2.5 to 3.4 PSI L20B pump 3-3.9 Both should deliver 1 liter per minute or less volume. I have a few different pumps. Including a new Nikki ( from Thailand, if that’s an issue) and none are above 2.5. Quote Link to comment
datzenmike Posted May 17 Report Share Posted May 17 That's from the '73 620 FSM for the L16/18 and the '78 620 and '76 710 FSM. You say it runs fine as is why fix something that ain't broke? Quote Link to comment
fiveoneO Posted May 18 Report Share Posted May 18 How are you measuring your fuel pressure? If all your pumps are showing low pressure, maybe your pressure gauge is incorrect. 3 Quote Link to comment
Stoffregen Motorsports Posted May 18 Report Share Posted May 18 If it ha a return, the pressure reading may also be off. Really depends on the size of the return orifice. Quote Link to comment
datzenmike Posted May 18 Report Share Posted May 18 If there is a drain, such as a return, then the pump regulator simply increases the flow to keep the pressure side of the pump constant. The return would have to exceed the pumps output volume to lower the pressure. The return orifice has to be small so that the pump can push against this restriction and build pressure or fuel will simply flow the easier path... back into the tank. The orifice is just over 1mm? Can't see one liter getting past this in a minute at under 3 PSI When a T is inserted in line and the output of the pump is directed into a container it should deliver 1 liter or more per minute at 1,000 RPMs. That's a lot of fuel. 1 Quote Link to comment
Stitebunny Posted May 19 Author Report Share Posted May 19 No fuel return on it. Mechanical pump to adjustable regulator with a gauge mounted. I can get the pressure lower by the adjustment, but won’t go higher. I could try a different gauge or may take the regulator out and see if that’s the issue. Quote Link to comment
Stoffregen Motorsports Posted May 19 Report Share Posted May 19 What regulator are you using? If it's one of those cheap dial types, it can't be used before the carb as it will restrict the flow, not just the pressure. Those need to be used on a return line. A Holley type adjustable regulator with the set screw adjustment does not restrict fuel flow. Quote Link to comment
Stitebunny Posted May 19 Author Report Share Posted May 19 It is a Holley. Will try with out it just to see. Quote Link to comment
datzenmike Posted May 19 Report Share Posted May 19 You may not even have a problem if it runs. Quote Link to comment
Stitebunny Posted May 19 Author Report Share Posted May 19 25 minutes ago, datzenmike said: You may not even have a problem if it runs. I know. It does run. I’m trying to get it to run well! Everything about tuning carbs starts with pressure, volume and float level. So I want to get all that sorted. I used a different fuel gauge with the Holley regulator removed. It’s now at 3.5 psi. So it seems the regulator can’t bump it up enough. Quote Link to comment
datzenmike Posted May 19 Report Share Posted May 19 I don't think a regulator can add pressure it can only attenuate pressure. 3.5 is about max for the L series fuel pump. Quote Link to comment
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