I've got a Weber 32/36 feeding the 20R in my '75 pickup and I'm having problems with it. It's been running rich for a while and I started having trouble getting the truck to start a couple weeks back, this went on until it wouldn't start at all. This turned out to be (mostly) a spark issue, I had a bad ground and a Pertronix unit that was going bad. Replace the Pertronix, cleaned up the wiring, still had issues with starting and now also with the keeping running- when I could get it to start it would drive ok for a few minutes and then start to spit, pop, and lose power and then it would die and refuse to start unless I let it sit a couple hours.
I got a rebuild kit and cleaned the carb, it looked ok, not too messy and I didn't find any issue but I didn't have air to blow out the jets so I did the best I could checking by eye and blowing by mouth. Put it back together and I'm having the same issues- it will start and idle (I have to run it a little rich to get it to keep idling) but then when I try to drive it it misfires and dies.

Here's the weird thing: I can rev it in neutral and it sounds great, ramps up and back down to idle, but if I put it in gear it will misfire and die. If I catch it while it's starting to misfire and jam the clutch back in and goose it a little it will catch and run ok, then the moment I put load back on it I get a misfire. Even weirder is that usually it will drive ok for a few minutes, like 3 minutes maybe, 3-10 blocks, before it starts to do this misfiring thing and dies, and then it won't start again, it will turn over and fire once or twice but not start up and I have to let it sit for a while to get it started again.

I don't know much about carbs but I'm wondering whether it could be a fuel starvation issue, where it's getting just enough fuel to fire and turn the engine over but not enough to move the truck? Or could it be that my main jet is the problem and the idle jet is carrying enough fuel to idle and even rev in neutral but the main isn't providing fuel for driving?

When I rebuilt the carb I used this guide: http://www.mk3supra.org/topic/561-gu...236-dgav-carb/ and messed with the float balance a little to try to get it to the 35mm recommended here, with 2mm of travel on the pin. It seemed way off however it was set up but I also had trouble getting it to those specs, I think I got it to 32mm with a little less than 2mm of travel, any higher and it was bottoming out on the power diaphram. Not sure if that's relevant, seems like this wouldn't affect anything to the degree I'm seeing unless maybe I really mucked something up with the float so that the bowl is running dry?

Fuel pump seemed fine, when I took the hose off and pumped it into a quart jug it filled in a few seconds. Don't have anything to test the pressure with.

Having some suspicions that this is a knock-off weber and not the real thing, the last owner told me he got a great deal on it on the internet and wonders if he bought a knock off, but it was working in the truck for 6 years.

 

You did remember to replace your fuel filter correct

 

Sounds like ignition more than fuel, unless like imhousing said the fuel filter is getting bad. Carbs usually aren't intermittent, they either work, or they don't. Is the choke working? It's not closed, or going closed as you drive it is it? Check your ignition condenser, and check the coil.

 

Been too busy to really work on this, but I have a little new information. Today I took the air filter off to see what was going on with the keys. If I turn the key on and open the accelerator linkage wide I get a squirt of fuel out of the left barrel of the carb (left looking from the front of the truck) that lasts less than a second and stops. If I work the linkage again I get another squirt. Holding it open seems to have no effect. I'm not seeing any action in the right barrel regardless of what I do.

Am I right thinking I should be getting a steady stream as long as I hold the throttle open?

My first thought was that I really messed something up when I put the carb back together but I was getting the exact same symptoms before I pulled it and before that it was driving fine.

Haven't had a chance to replace the fuel filter but I did pull the line after the filter to test flow and it filled a quart jug in a few seconds.

I was also suspicious of ignition because of previous problems with the pertronix but if it was ignition problem why would it only be happening when I put the truck in gear? Like I said I can fix the stumble and keep it from dying just by putting the clutch in (at least for the first few minutes of run time).

Choke seems to open ok.

 

That squirt of fuel is just from the little accelerator pump on the front end of the carb. You should see it move when you operate the throttle lever on the other side. One squirt per pump is all you get, never a steady stream.

 

What else have you done besides clean out the carb? You mention Pertronix - assume it's converted from points?

I would try checking the timing and the carburetor settings per the instructions here on YT or on Weber/Redline website. Do you know what size jets are installed right now? On my 75, the stock jets in the Weber were too lean and I had to go up a size on the primary idle jet.

Also, while I was reading about the Webers on 20r, I saw several mentions regarding fuel pressure and the possible need for regulating it. PO of my truck went through all the fuel stuff, so I've got a nice fuel filter, pressure regulator and a gauge. I think mine's set at 3psi.