Stock fuel pressure and weber 34/34 tuning problems

I did a search and didn't find the answers I'm looking for.

First, How much pressure does the stock, in tank electric pump put out? I put a Mr. Gasket adjustable fuel pressure regulator and fuel pressure guage on my Maz tonight, and the stock electric pump is only putting out 2 pounds. I'm thinking this is part of my problem, which I will get to in a minute. What do I need to do to get the pressure up to 3.5 psi or above (I can use the fpr to fine tune the pressure) so the Weber is getting what it needs. Extra inline pump?

Here's what's going on. I have a Weber 34/34, it works ok, but not the greatest. I can get it tuned to where the truck isn't sputtering or falling on it's face in town, but the highway is another story. While holding speed, say 65 mph, the truck will start sputtering and loose speed, BUT if I let off the throttle ever so slightly the engine will smooth out and slowly loose speed. Roll back into the throttle ever so slightly the truck will start sputtering again unless I put the pedel to the floor, then it will pick up speed. Then the process starts over again. WTF is going on?? I thought maybe since I didn't have a fpr that maybe the carb was loading up because of too much pressure, but that doesn't seem to be the case, now I'm thinking the carb is starving for fuel and leaning out. Your thoughts???

Maybe someone with a 34/34 will read this. How many turns out (from seated all the way in) does the "off idle" screw need to be??? Since this screw seem to be the only adjustment on the carb, other then choke and idle speed. MAybe I'm missing something and there is other mixture screws I'm not seeing.

Sorry for being so long winded here.

According to Alldata. . .

FUEL PUMP PRESSURE

Mechanical 3.7 - 4.7 psi (26 - 32 kPa)
Electric 2.8 - 3.6 psi (20 - 25 kPa)

You might need to change your fuel filter.

Stock pumps should be fine for what you are doing.

I forgot to add the truck was given a full service a couple weeks ago. Fuel filter was changed, new spark plugs, dizzy cap, dizzy rotor, plug wires, oil and oil filter. Thought about changing the air in the tires for winter air, but got lazy. LOL I thought maybe a vacuum leak, so I resealed the carb adaptor plates, and replaced the vacuum caps for new ones, also checked the timing, it was alittle off so I brought that back to where it's supposed to be. I even have my dad stumped, and he's a an old mechanic from back in day everything had a carb.

If I can't get this think running better by spring, there will be a 34/34 for sale, cause it will be replaced by a 32/36 (wish I would have bought that one instead)

Dude, you have a 22 year old truck.

It is likely the fuel pump has gone weak.

All it takes with electric pumps is someone running the vehicle out of gas. Since it isn't likely you have owned the truck for the entire 22 years, you don't know whether that might have happened, maybe more than once. So now you get to play detective. It is obvious at 2 psi from your testing that it is way below spec. 30% or more.

An electric in-tank fuel pump is supposed to be cooled by the fuel surrounding it.

Or maybe the fuel lines that are made out of rubber have gotten swollen to the point of constricting fuel flow. The early fuel lines were not resistant to alcohol. Sometimes owner's manuals even include warnings not to use methanol-based additives. Ethanol in the gas is almost as bad.

Or the inlet is clogged.

You might let the truck sit overnight, then pull the drain plug on the gas tank. . .it's a 14mm headed bolt.

Let about a half a gallon out into a pan, and look at it.

Maybe that will provide some clues.

What did the filter look like internally when you changed it?

Now i have a 32/36 but Linn just explained to me how to tune that properly and i understand much better than the mazda truckin How to. Mabye this well help you.


If your factory fuel pump is only putting out 2 psi mazda tweaker is right there is a good chance your
fuel pump is dying a slow death. Also check the pickup i know that they can deteriorate and enter the pump. This happened to some one else on here

Hope you get it figured out

The filter was clean.

When I seen 2 pounds I thought that was alittle low. It snowed today so the truck is buried again, so when the snow goes away alittle bit, I'll pull the bed off and change the fuel pump. I pulled the plug as you said, the gas came out clean, no dirt. So clean the gas went into the snowblower.

I picked my dad's brain again. He said to try to adjust the choke so that it's staying on about 1/4 of the way, see what that does. He says if it gets better then the carb is too lean and needs rejetted. If it's worse then it might be too rich. I duuno.

I know this is vague but do you think there could be an internal problem with the carburetor?
How old is the 34/34?
whens the last time its been rebuilt?

That's one thing that is going threw my brain, deffective carb. It was purchased from Webercarbsdirect 4/18/09, less then a year old. I sent Weber an email asking if they will exchange this one for a 32/36 (me paying the price difference). Told them what's going on with it, explained my reasoning behind wanting to exchange it. Now it's a waiting game to see what they say.

I have a 34/34 and a modified engine and my only issue is the carb has a habit of running rich. If u lean it out a tad, runs fine.BJ

Don't be suprised if they tell you that "it is impossible to ascertain a defective carburetor independant of verification of correct operating parameters."

If you had a completly blocked air filter (oil soaked), you would be experiencing one set of problems with fuel / air ratio.

You couldn't blame the carburetor for that issue.

In your case, you are running inadequate fuel pressure, which equates to lack of pressure to push the fuel into the carb.

You cannot blame the carburetor for that, either.

The easy "fix" for this is get a stock mechanical pump, and mount it on the head, and use it in conjunction with your wishy-washed out electrical unit.

Stop blaming the carburetor. The problem isn't there.