Hello,
I think I once read that Dellorto carbs (on S1 1,3S engine) should have 4 psi fuel pressure, can someone please confirm or tell me what the actual reading should be?
I think of surcing one regulator that comes either in 1-4 psi or 4,5-9 psi, so I need to know if the actual value is a minimum or a maximum.
Best,
Thomas
fuel pressure on Dellorto carbs
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tim
Re: fuel pressure on Dellorto carbs
I believe 3psi is about optimum. As your series one doesnt have a fuel return pipe a higher pressure will cause flooding and wear out the needle valves. I fitted an electric pump and a fuel king filter /regulator and did some tests and didnt see any difference from as low as one psi upto 4psi. At the time I was trying to sort a 1600 on 35mm delortos which ran out of steam at c 5k's. You should put a pressure gauge on the mechanical pump - even with a regulator it is much more variable due to the nature of the pump.
Tim
Tim
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Huib Geurink
Re: fuel pressure on Dellorto carbs
I agree with Tim. About 3 psi is correct for Dellorto's.
The mechanical fuel pump should give a constant pressure. The membrane is pushed down with infinite pressure by the rod operated by the auxiliary shaft. The return of the membrane is done by the spring inside the pump and thus the same force at any rpm. It is the return of the membrane which supplies the fuel to the carbs. If it the fuel pressure from the pump is not reasonably constant there is something wrong which needs to be corrected. It is an early warning for a failing fuel supply.The pressure from the mechanical pump should be about 0.3 bar which is 4.2 psi. This is optimum pressure for most Solexes.
The mechanical fuel pump should give a constant pressure. The membrane is pushed down with infinite pressure by the rod operated by the auxiliary shaft. The return of the membrane is done by the spring inside the pump and thus the same force at any rpm. It is the return of the membrane which supplies the fuel to the carbs. If it the fuel pressure from the pump is not reasonably constant there is something wrong which needs to be corrected. It is an early warning for a failing fuel supply.The pressure from the mechanical pump should be about 0.3 bar which is 4.2 psi. This is optimum pressure for most Solexes.
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Jay Hinton
Re: fuel pressure on Dellorto carbs
Thomas-
Huib and Tim are both right this time. I fit a adjustable fuel regulator with a electric pump as well. One thing, try fitting a fuel pressure gauge between the regulator and carbs and actually measure what pressure is really arriving, I tuned my 1300 S1 ( 818.302) with Dells to 2.7 lbs and felt it was best. Haven't mounted the Dells to the other Fulvia 1.3S (818.303) yet, so don't know about that one.
I did measure the pressure with the original mech pump and it was something like 4.4 lbs .
Tim- when you were sorting the 35 mm Dells to your 1600, did you inspect the full power jets size and possibly experiment with these. They can have a tremendous influence on power output at higher revs. Its one of the reasons that some manufacturers (Lotus) did actually use Dells on production turbo four cyl engines, sort of a fuel enrichment device.
Jay
Huib and Tim are both right this time. I fit a adjustable fuel regulator with a electric pump as well. One thing, try fitting a fuel pressure gauge between the regulator and carbs and actually measure what pressure is really arriving, I tuned my 1300 S1 ( 818.302) with Dells to 2.7 lbs and felt it was best. Haven't mounted the Dells to the other Fulvia 1.3S (818.303) yet, so don't know about that one.
I did measure the pressure with the original mech pump and it was something like 4.4 lbs .
Tim- when you were sorting the 35 mm Dells to your 1600, did you inspect the full power jets size and possibly experiment with these. They can have a tremendous influence on power output at higher revs. Its one of the reasons that some manufacturers (Lotus) did actually use Dells on production turbo four cyl engines, sort of a fuel enrichment device.
Jay
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tim
Re: fuel pressure on Dellorto carbs
Jay
Further to my 1600 dellorto experiment.... These were fitted to my 1600 Sport by its previous owner who tuned it on a rolling road (also fitted exotic exhaust manifold, and holbay cams) and achieved 113bhp at the wheels equivelent to c132bhp at flywheel!!! at 5700rpm. I have the graphs which were "calibrated" against Martin Cliffe's Racing Fanalone which was close to the nominal 158bhp.
When I drove my Sport with the dellortos they were fantastic. I overhauled the carbs and noted the jet sizes (mains 118, idle 48) but didnt note the power jets size.
I fitted them to my 1600 HF to take down to Turin (to gain some extra mpg) and they were horrible running out of steam at 5000rpm. I didnt leave them on for long! General consensus was the Dellortos were too small for the 1600. Now.... My sport has just returned to the road after an extensive restoration - the ardenne trip was in effect its shake down run - and so it was interesting to critically drive it again with the 35 dellortos. Absolutely no complaints and achieved over 33 mpg at quite high speed over 1000 miles!!!
BTW I definately agree it is worth investing in a 0-10psi fuel pressure dial guage!!
Tim
Further to my 1600 dellorto experiment.... These were fitted to my 1600 Sport by its previous owner who tuned it on a rolling road (also fitted exotic exhaust manifold, and holbay cams) and achieved 113bhp at the wheels equivelent to c132bhp at flywheel!!! at 5700rpm. I have the graphs which were "calibrated" against Martin Cliffe's Racing Fanalone which was close to the nominal 158bhp.
When I drove my Sport with the dellortos they were fantastic. I overhauled the carbs and noted the jet sizes (mains 118, idle 48) but didnt note the power jets size.
I fitted them to my 1600 HF to take down to Turin (to gain some extra mpg) and they were horrible running out of steam at 5000rpm. I didnt leave them on for long! General consensus was the Dellortos were too small for the 1600. Now.... My sport has just returned to the road after an extensive restoration - the ardenne trip was in effect its shake down run - and so it was interesting to critically drive it again with the 35 dellortos. Absolutely no complaints and achieved over 33 mpg at quite high speed over 1000 miles!!!
BTW I definately agree it is worth investing in a 0-10psi fuel pressure dial guage!!
Tim
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Geoff Goldberg
Re: fuel pressure on Dellorto carbs
I know this is a Fulvia forum, so forgive the digression to older cars - but the issue of fuel regulation is really important for all Lancias. We have spent a lot of time here with a couple of Aurelias, setting up fuel pressure. Both the electric and mechanical pumps are to give between 2.5 and 4 psi, and the electric pump is setup to the same pressure as the mechanical pump - so the carbs know no difference when it is turned on. The electric one pumps through the mech'l and is switch operated for starting, or high volume needs.
On the Aurelia motor (and likely on many other Lancia motors) the mechanical pumps are very sensitive to setup: a few thicknesses of thin paper gasket can change the pressure for 0 to 7 psi on the Aurelia. Truly. Most surprising.
Add to that the changes in pumps in different series of the model - there are three different pumps in the first three series of B20's, for example - and the likelihood of getting the pressure right without fiddling is pretty slim.
Setup of fuel pressure is highly recommended. Without that, too much pressure will push gas through the needle valves, and possibly wash the cylinders, with impact on long term wear.
On a Nardi equipped B24 convertible, the carbs got so hot when the car stopped (on hot days) that they were percolating out the gas. The addition of a fuel return line (located up by the carbs) to the gas tank has remarkably fixed that issue - and the car starts hot perfectly. Noticeably cleaner oil too. Highly recommended for any "improved" engines.
Geoff
On the Aurelia motor (and likely on many other Lancia motors) the mechanical pumps are very sensitive to setup: a few thicknesses of thin paper gasket can change the pressure for 0 to 7 psi on the Aurelia. Truly. Most surprising.
Add to that the changes in pumps in different series of the model - there are three different pumps in the first three series of B20's, for example - and the likelihood of getting the pressure right without fiddling is pretty slim.
Setup of fuel pressure is highly recommended. Without that, too much pressure will push gas through the needle valves, and possibly wash the cylinders, with impact on long term wear.
On a Nardi equipped B24 convertible, the carbs got so hot when the car stopped (on hot days) that they were percolating out the gas. The addition of a fuel return line (located up by the carbs) to the gas tank has remarkably fixed that issue - and the car starts hot perfectly. Noticeably cleaner oil too. Highly recommended for any "improved" engines.
Geoff
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Thomas
Re: fuel pressure on Dellorto carbs
Gents,
thank a lot for your valuable insights. I have the pressure gauge and will fit a regulator 1-4 psi type during winter works when I change out the head. On anothe rmatter, it's awkward that despite utterly erratic vacuum measurements (even when lines choked, there's simply too much dirrerence between the cylinders), the car actually drives very nicely.
Thanks again,
Thomas
thank a lot for your valuable insights. I have the pressure gauge and will fit a regulator 1-4 psi type during winter works when I change out the head. On anothe rmatter, it's awkward that despite utterly erratic vacuum measurements (even when lines choked, there's simply too much dirrerence between the cylinders), the car actually drives very nicely.
Thanks again,
Thomas
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Huib Geurink
Re: fuel pressure on Dellorto carbs
The thickness of the gasket inluences the stroke of the rod pushing the membrane down and thus the compression of the coil spring under the membrane. The return force of the spring is proportional to its compression.
If the fuel pressure is higher, the float needs more upward force to keep the needle valve closed. The float thus needs to be immersed more in fuel. The float level goes up.
When you reduce fuel pressure by adding gaskets, the stroke fo the membrane is reduced and thus also its capacity to supply fuel. I would imagine this is not noticeable when the engine is running (unless the stroke is really near zero) but it would seriously increase the time to fill empty float bowls.
Ideally one would want a fuel pump with a pressure at the higher end of the "green range" for carbs and then reduce the pressure to its correct value with a pressure regulator. It ensures fast priming and correct pressure by easily adjusting the regulator.
If the fuel pressure is higher, the float needs more upward force to keep the needle valve closed. The float thus needs to be immersed more in fuel. The float level goes up.
When you reduce fuel pressure by adding gaskets, the stroke fo the membrane is reduced and thus also its capacity to supply fuel. I would imagine this is not noticeable when the engine is running (unless the stroke is really near zero) but it would seriously increase the time to fill empty float bowls.
Ideally one would want a fuel pump with a pressure at the higher end of the "green range" for carbs and then reduce the pressure to its correct value with a pressure regulator. It ensures fast priming and correct pressure by easily adjusting the regulator.