Weber Conversion ?

[phish1270]

Guys,

I am new to this forum & recently bought a 1981 Plymouth Arrow truck with the 2.6l. It has been a nightmare so far with one problem after another but $1200 later & a laundry list of new parts I think things are looking better. I just did the Weber carb conversion yesterday. The truck seems to be running pretty well but I have a few questions. 1st (& most important) is what to do with the 2 "OUT" lines on the stock fuel pump. The Mikuni original carb used both lines but the Weber only needs 1. The Weber Tech guy told me to hook the return line, that ran off the driver side of the Mikuni & went back to the tank, to the extra fuel pump line. It seemed logical. Is that what other guys have done? I noticed that my fuel tank is building up a lot of pressure now. I did not have the truck very long before the motor came apart for a new head gasket thanks to a previous owner hiding it when I bought it so I don't know if the tank did this before. I thought about venting the gas cap but really would rather figure out what is causing the pressure. I also added an inline fuel filter between the pump & Weber to help lower the fuel pressure & it seems to be fine. How crucial is hitting the 3.5 psi that the Weber calls for? Can I keep the stock fuel pump & add a regulator? How do I know if I am getting too much pressure to the carb? Any help at all is greatly appreciated. If possible, someone could PM me for my phone # & I will call if it is easier. Thanks guys! Great site!

Glenn

[Acuta73]

Buy a Carter P4070 fuel pump and a pressure regulator. Blank out the old mech pump. Will save much headache...

[phish1270]

Buy a Carter P4070 fuel pump and a pressure regulator. Blank out the old mech pump. Will save much headache...

I already have almost $1200 into what was supposed to be a daily driver when I bought it & I have been out of work for 3 months now. I can't keep putting money into this truck until I find a job. The Carter 4070 is close to $100 & then another $25-40 for a regulator. That is not happening unless it absolutely has to.

[Acuta73]

Do understand that!

I know some guys on here made do with the stock mech. pump til they got an electric. Hopefully one or 2 of em will pop in with some kernels of wisdom as to yer issues. When my Weber went in, so too did the electric and regulator. If it helps any (and I doubt it does), the regulator burst and I never did replace it...running fine straight off the pump.

[camoit]

Plug off the return line and check fuel pressure to the carb. 3 is just fine, 4 is plenty, 5 on the high side, 6 no good. You can always just use a regulator if necessary. Just make it work and take care of family first. Cars are just things. It will only produce as much pressure as the spring in the pump is what makes the pressure. They normally can only build 5psi max. older pumps have worn springs and loose there pressure and flow rate. The needle and seat will control the flow rate into the carb. I have a feeling it will be just fine. What does the paperwork on the carb say the max pressure should be?

[Fordubishi]

You could always just get one of these at "most" parts stores http://www.summitracing.com/parts/MRG-9710/

[phish1270]

Thanks for the help guys. I understand the pressure going to the carb. The Weber wants 3.5 according to the instructions. I am going to go buy an inline pressure gauge first & see what I am getting; if it is above 3.5-4 than I will add an inline regulator.
I am still concerned about the pressure building in my fuel tank. I am not sure if our tanks are vented but my tank is actually building up pressure even when the truck is sitting & hasn't been run. I will start to dig deeper into the issue this week.

[camoit]

It should vent out through the charcoal canister, in through the cap.. But you can fallow the hoses from the tank to there and make sure there not plugged. Or blow through it. Don't use compressed air. I'm not sure but I think there is a 1 way check valve at the tank mounted by the filter. If it's bad it will cause excessive back pressure. Some pressure is normal.

Take a look in the manual section in the first gen factory manual for the fuel system.

[pennyman1]

The issue is the mechanical pump is pressurizing the tank as it is sending the pressure not being used by the carb to the tank. Using a regulator won't help, as the pressure will still end up in the tank. Since the tank is not meant to be pressurized, something is going to fail eventually. The real solution is to eliminate the mechanical pump and install an electric one. Because of the close proximity of the pump to the carb, if you do put a regulator in, it will kill the pump from excessive back pressure. Facet makes an electric pump that sells for 35 - 50 dollars that will work until you can get the good pump. I have had several D-50s and my friend has an 81 Arrow and they have been setup with electric pumps - my 1980 D-50 Geronimo has had one on him since 1983. There are threads in this forum that will help you through this, or contact me if you have further questions. I have been where you are and I know how frustrating it can be.