Weber DFEV cuts out at 3-4000RPMs

[ebrown0104]

In general, my car (77 1800 engine) is running great with the Weber 32/36 DFEV carb. I'm having a little bit of an issue during a specific situation, though. When I'm in 3rd or 4th gear going up a long incline it feels like the car is running out of fuel. After accelerating uphill about 10 seconds, it'll cut out and buck until I either back off the throttle for a second or pull the choke knob out (which clears it up for a second until it starts to choke out). After 4000 it picks up and runs fine up till redline, and before 3000 it runs fine. Also, in first and second gear uphill (or if I'm on a flat surface) it'll run fine in the 3-4000 range. It just seems to happen when I'm in an area where there's a specific load on the engine - I'm assuming it has something to do with the secondary butterfly opening up since my throttle is about 5/8-3/4 open. I'm guessing that the secondary is opening but there's no extra fuel being added until you're at almost wide open, when the main jets take over. I tried going from a 50 to a 60 secondary idle jet, and it helped maybe a little bit but not much. I also opened my mixture 1/4 turn and that helped, too, but now it's a little rich at idle. I'm just kind of lost as to where to go next, and it's tough finding tuning tips, since it seems most people just bolt these carbs on and they work fine.

Thanks for any help!

[bradartigue]

You're on the right track, the transition is from main idle jet -> main jet -> secondary idle jet -> secondary main jet. In between there is assistance from the accelerator pump. It is unlikely to be even using fuel from the mixture screw at the stage you are in; I'd set it to a good idle and forget it.

First I'd check the float level. Since this is happening on an incline I'm wondering if your float is closing itself too much. It should be 6mm - 7mm, and I'd set it to the smaller end (6mm) which allows more fuel in.

If this does not cure the issue I would be suspicious of my fuel pump and filter and not of the carburetor jetting. Once I eliminate the pump and filter as sources I'd move onto the carburetor.

[ebrown0104]

I had just cleaned the carb out a month or so ago, but just to be safe I took it back off and gave it another good cleaning. I ran a wire through the secondary idle passages and blew compressed air through them to make sure they were free. Checked float height and it was at 1-1/2 inches when vertical. Put it all back together, reset idle and mixture screws, and took it for a drive. I pulled a long, fairly steep grade for about a half a mile in 4th gear at 3500 and it never hesitated, so I think it was just clogged up.

[BeachBum]

I'm having the exact same problem you described. I rechecked the timing numerous times and am certain is right. Car cranks and purrs like a kitten and I can run through all 5 gears with no problem. But when I get on a slope and push it, I can wind out 1 and 2 and get most of the way through 3rd (about 3500rpm) and it starts bucking and then it loses all power. Sometimes I can save it and downshift to 2nd or 1st and continue. Yesterday, I couldn't save it and had to pull into a neighborhood. It never cut off but when I tried to rev it up, it would rev to a certain point and then start fading out again. I'm heading out this morning to see if I can at least get it running and back home.

Did cleaning the carb fix the problem? I'm not much of a mechanic and carbs scare me. How difficult is it to do what you did?

[bluespider262]

When my spider did this it was because the fuel sock in the tank was a solid lump of rust. It's amazing it ran at all but it did...until I hit 3rd or 4th gear, only under load.