Weber Carb problem

[Randog]

Hello.

When I took my '73 620 on its maiden voyage, it ran great! I drove it to town and back, total 16 miles, and aside from some electric issues I posted under the electric section of this forum, I had no complaints. Then last night I went to drive it to a little town 20 miles away for bible study, and it started really acting up. It was fine downhill, okay on level ground but uphill it coughed and spit and backfired and generally bucked like a bull and lacked power pretty badly. There was also a whistling noise. If I pumped it would stop. I asked my father about it and he says that its starving for fuel, maybe plugged jets? He says the reason it stopped if I pumped is because when I pushed it down over and over I was engaging my accelerator pump, therefor putting more fuel in. The problem is, there's a big difference between pulling the head off a rig I don't particularly need and doing carburetor work, on a rig I'm gonna need tomorrow. I'm not particularly knowledgeable about carburetors, although I did rebuild one once. Is it gonna hurt it to drive it like this? Is it an easy fix? Its a Weber the the previous owner put on, the the previous owner seemed to underestimate the the value of cleanliness when working on engines, and my very highest suspicion is that the jets are indeed plugged.

[ggzilla]

If the jets were plugged, it wouldn't run good on the level.

 

These syptoms can be caused by more than one thing. Some of the most common are:

* Partially clogged fuel filter

* some crud/water in the fuel bowl which is intermittently blocking the main jets

 

However with the whistling noise, I would suspect something is loose (air leak). Remove the the four weber bolts, lift it up a couple inches and re-tighten the two adaptor bolts.

[Randog]

Thanks for the information. I took the carburetor apart and cleaned it, the adapter plate seemed tight, and adjusted the idle and lean/rich, and then I took it for a drive. Although I didn't discover any obvious problems, the truck suddenly ran great. So I went ahead and drove it to a basketball game 40 miles away. When I went to drive home, it had some trouble getting going, but once I got up to speed drove home fine. Stopped for fuel on the way home and it drove wonderfully again. It still whistled once or twice for a second, but not at the same time it was running rough. So I guess I'll just drive it. Maybe there's some sort of contamination in the fuel that I need to burn out, the truck sat for many years. Or maybe its just coldblooded.

[Tucson620]

The whistling noise sure sounds like a air leak.

 

 

When you're up to disassembling again (and I doubt the problem will go away on its own), check the adapter plate AND the carb bottom for flatness. Put a straight edge along/across and you might one or the other or both are warped. When I encountered intermittent air leaks (off idle for me, wouldn't happen at idle), I discovered Weber flange and adapter plate were all warped. I flattened by sanding on a granite surface plate and solved the issue.

[EricJB]

I am Assuming it's a DGV progressive 2 bbl. If your having a normal drivability problem, the possible jet problem will be on the primary side. But let's backup, First you have to look at fuel delivery, and fuel quality. If the truck has been sitting for a while, The tank could be contaminated. Or the fuel pump diaphram could be cracked. The fact that it ran better after you put more fuel in it tells me you have a bunch of crap in your tank. You can clean the carb everyday and not solve the problem.

 

Drain the tank into a white bucket. There is a plug in the bottom of the tank. look for rust and water. Water will look like a air bubble on the bottom. If the fuel pump has been sitting dry, just replace it. The diaphram has been soaked in fuel and being dry will make it brittle, crack and lose its' ability, Also the check valves can be sticky or dirty and not sealing.

 

Put clean fuel back in, disable the ignition. Pull the hose off the carb and pump fuel into the bucket to check output. If all is well, move on to the carb.

 

The DGV has an idle, or pilot jet at the side of the carb. close to the bowl if I remember correctly Llook for a brass screw. That is the jet holder. I'm sure its fine, because it wouldn't idle if it was plugged. This is the circiut it runs on from Idle to about 2k at light throttle. The Idle mixture screw is only for idle, not for anything else. It works just a faucet. In is lean, out is rich. I usually slowly turn it in till it started to run unevenly, out till it smooths out, than out another 1/4 turn. If you had a vacuam leak at the base or due to a loose connection, you would see it more at an idle than anywhere else.

 

The main jets are in the bowl,down in the bottom. One is for the primary side, the other is for the secondary side. If you drive carefully you can feel it go from pilot,to primary main, and then secondary main with more throttle. If it doesn't run right at any throttle position, the jet you are on is the problem. Pull the jets and blow or spray them out, NEVER use a wire to push crud out.

 

The needle/seat/float assy is just like a toilet. Pull the top off the tank and flush, It's the same thing. The Weber carb is simple and works great. Feed it clean filtered fuel and drive it, Good luck.

[Randog]

Drove it to church and back this morning, no problem. The fuel filter has been sitting, but not dry. It did whistle some, but just maybe three times today, for a few seconds at a time.

 

I'm really not sure what happened that night, but I know that its running like a top, just humming along like a dream. I'd say "like a Cadillac" but it doesn't ride as smooth and rattles, "Old truck syndrome" my father calls it.

 

If it keeps running this good, I ain't gonna touch it. No need to look for a problem when you don't have one.

 

Thanks for all your help, I'll definitely be taking you advice if the truck starts acting up again.