Does anybody with experience running twin 40 Dellorto's know what kinda of fuel pressure is best to run them at? I believe I am finally choking out of fuel at high rpms (old cheap fuel pump) and am planning to get rid of the stock mechanical pump in exchange for a nice electric setup w/pressure regulator, but I need to know how much psi Dellorto's like to run at. If anybody has experience and recommendations let me know. I already know what the stock fuel pumps run at, but with a hotter setup (cam, ignition, headers, etc) I figured it'd need to pump a little higher pressure/volume in there. Let me know!

-Andy
Little Rock, Arkansas

You're not gonna believe this the fuel pressure
is 2.5-3.0 psi if it is higher it must be regulated.
This I know. Although I have seen some up to 8-10 psi its just they seem to use more fuel and run too rich. Really its not the pressure its the amount of fuel the pump flows. The fuel has to flow quickly to keep the fuel bowl level right. If you pressurise the fuel bowl it gets too rich. If you are sure its fuel starved from the pump then a better flowing pump is required. But also consider the size of the fuel lines and if the fuel filter is blocked, you never know what else it might be.

yeah, the weber side-drafts are low pressure as well. It's high flow you want, not high pressure.

Well I spent a pretty penny and got the Holley Red fuel pump, a low pressure regulator, new filter, and lines. I found some websites advertising not going over 4 psi on the Dellorto's, so I'm running about 3.5 or so and not having any problems. I couldn't find a place to put the fuel pump near the tank, so I installed it at the very bottom of the right front strut tower, below where the original fuel filter went. Gravity still seems to feed it where it's at, so I don't think I'll run into any problems. Anyway, I went from the stock 1/4" fuel line going into the pump, to 5/16" coming out of the pump to the regulator, filter, and carbs. The pump is rated to like 7-9 psi and 95 gallons per hour, less with the smaller line and regulator, but still way better than stock. I noticed a nice difference in power and driveability with this new setup. I've still got to get a blanking plate and remove the old mech. pump, which will free up a little horsepower as well, but it pulls a lot harder through all rpm's, most notably mid range (3500-6500). I'd recommend tossing the stock mech. pump for a setup like this to anyone, it runs great! And there's no black smoke or over-richness either...A/F ratio guage stays in the richer part of ideal (stoich) at full throttle. I want to take it to a quarter mile track to see the difference really bad...it'll probably be a couple weeks before I can do that, but I'd guess low 16/ high 15's. Last year with same setup minus lightweight flywheel, heavy duty clutch, dual valve springs, exhaust cutout and electric fuel pump it ran 16.5 and it feels much stronger now than it was then. We'll see!

-Andy

Good to hear how this turned out. High 15s would be very respectable!

Well, until I can get larger main jets, idle jets, and 36mm chokes I'm limited to low 16's. It's weird, but the carbs are going lean at high rpms, it doesn't do it at all in 1st gear (redlines 7300 rpm), but drops off super lean and a well felt power loss occurs. It didn't do this a couple weeks ago right after I put in the new valve springs and ported the cylinder head...it pulled great through redline in all gears, but now it dies off at about 6400 rpm. I think maybe it just needs to be re-tuned with different jets and such??? I did beat my best ever 60 ft time, 2.3 seconds, only to get better with more practice w/the heavy duty clutch/lightweight flywheel. It doesn't roast the tires like it used to with a high rpm launch...the engine more bogs down then picks up speed. This is where I can finally notice the difference between heavy vs. light flywheel....much better! Now to figure out this high rpm lean spike.....

-Andy

Sound like it might be the air jets, rather than the fuel jets?

Check your fuel pressure is still at least 2.5 Psi under sustained load. As the engine is held at longer periods of full throttle as you go up the gears the carbs can starve through insufficient pump capacity or too small a fuel lines.