350xfire

iTrader: (1)

I rebuilt my Dellorto 48, installed the Mallory fuel pump and set the pressure to 4.5 psi. Turned the engine over and it acts like it wants to run. There is however an issue. While trying to start it fuel dripped out of the open header. I took the air filter off and while looking into the carb I am seeing fuel dripping when the engine is sitting without cranking.

Was wondering if anyone knows what can cause this? Could I have improperly adjusted the accelerator pump causing it to stay partially open at all times? If so, how do I properly adjust it?


Thanks

rwatson5651

iTrader: (5)

Sounds to me like either your needle valve is stuck or the float is not adjusted properly, causing the fuel level in the bowl to be too high and allowing fuel to overflow.

350xfire

iTrader: (1)

I measured the float levels and they were about 14.7mm and about 24mm closed and open. This is what the manual said... About 15 and 25mm...
The needle valve is brand new as well. I used the 300 needle valve.. I did notice that the needle valve fitting looked different than the one I originally had. The 300 I got had holes on top of the fitting that goes into the carb. The one I took out had no holes.

snivley whiplash

iTrader: (4)

drop the fuel pressure no more than 2.5 psi deflood the engine, add a small amount of engine oil in the plug holes and start it up. go to Gruntled.com - Home and look at my set up info this will help you,..

joe

j9fd3s

iTrader: (3)

either the float is too high, or the fuel pressure is too high.

i would drop the fuel pressure as low as you can, start it, and see if its still dripping at idle. if yes, lower float, if no then fuel pressure can go up.

with the webers we basically run as high a float level as possible before it drips at idle, and on a race car, it might need to drip a little.

peejay

Bear in mind that what the manual says to set the float to is always a base setting that may or may not reflect what will actually work properly. If the float is too high then the float is too high. It makes no sense to ride theory down in flames if the carb is not working right and everything else checks out.

However the possibility still exists that the needle isn't sealing, or fuel is leaking past the seat. My experience is more with Holleys, but "new" usually means No Experience Working (or Never Ever Worked) and you can't assume that it doesn't have some minor manufacuring defect. I usually don't change them unless I have a really good reason to. (And half the time, a bad N&S is really a bad sealing O-ring, on the Holleys)

350xfire

iTrader: (1)

The reason I changed the N&S is because I read the RB used a 300. The carb had a 2xx seat in it. Also, I am using a Mallory pump and using the internal regulator to get 4.5 psi. I will have to add another regulator since that's as low as it goes.
Thanks

350xfire

iTrader: (1)

Can you guys recommend a pressure regulator? Also, should I do a return style or a dead head? The pump has an internal bypass so I guess it could be the return... right?

Jeff20B

iTrader: (13)

RB recommends the Mallory 4309 fuel pressure regulator. Mallory 4309 Fuel Pressure Regulator for RX7 1975-1985 - Racing Beat

j9fd3s

iTrader: (3)

you could try lowering the float level too. i'm running 4.5psi with my weber, and its happy

peejay

Larger needle and seat means more force pushing against the float for a given pressure, so you either need to lower the float level or reduce fuel pressure to compensate, relative to the smaller N&S, if you want the same fuel level as before.

t_g_farrell

iTrader: (1)

Your running too high fuel pressure. It won't tolerate more than about 2.5 psi. Get the holley 1-4 psi fuel regulator and jusy dead head into the carb and you should be good to go.

350xfire

iTrader: (1)

Ordered it yesterday! For some reason I thought Dellorto could take 4.5... I guess not!

t_g_farrell

iTrader: (1)

A lot of folks get told the Dellorto is a Weber clone, which it is, but its requirements
are different. Once you get that pressure dialed back you will be happier I'm sure.

350xfire

iTrader: (1)

Cool, thanks. Can't wait to get the parts in. It actually tried to run and ran for a few seconds but was soooo flooded that it actually spewed fuel out the headers. Plus I didn't have the throttle cable installed yet so I couldn't open it up. I still need to figure out how I'm going to tie it in as I don't have the original brackets and linkage.

350xfire

iTrader: (1)

Another Dellorto question. How do you guys adjust the accelerator pump? Is there a nut threading distance for proper engagement? Do you just work the linkage while adjusting until you see it engage fully?
Thanks

350xfire

iTrader: (1)

So I finally, got my FPR, got the fuel pressure to 2.5 psi and still leaked. Took the floats out and readjusted, also backed off the accelerator pump adjuster just in case. I adjusted floats to recommended 15mm and 25mm. The leak is about a drop per 2 seconds or so. So I have made progress. I went ahead and took the float from 15mm in the closed to about 17mm to see if that fixes it.

Am I on the right track?
Thanks

lwrobins

There should be no leaks. How old is the dell? Throttle shaft bushings? I rebuilt mine and run 2.5 psi runs great! There is a specific measurement for the accel pump important for less stumble just can't find the measurement right now!