Bay Area folks, help! Carb problems!

[copacetickid]

I'm having fuel delivery problems. I have a weber I bought off of ebay last year and rebuilt (never do this). The main problem is that I can't cruise; the engine pulses -- pulls strong for a second, coughs the next, repeat. When the engine is working, even slightly (i.e. going up a slight incline or accelerating), it pulls strong no problems. The truck has been at my parent's for a year and I just rebuilt the engine. I didn't have these problems last year, I only had a problem with the choke which I've since fixed. What it feels like is that the main circuit just isn't working at all.

 

There are some really strange symptoms, especially when tuning the idle: after I get the mixture screw to the point where rpms just slightly start dropping, I try to turn the speed screw in a tad and the rpms drop instead of increasing. The only way to get stable idle is to take the mixture screw out to the point where the speed screw doesn't even touch the throttle stop at all. This is weird, and has something to do with the problem I'm having for sure.

 

I know the idle circuit has a strong effect for up to 1/2 throttle, and since it seems like the main circuit isn't working I turned the mixture screw way out to compensate -- no effect. I also turned it way in thinking it was starving for air not fuel, but still no effect.

 

I don't see how it could possible be an ignition problem, and I just did a compression test: 185 190 195 190. One thing that would make sense is that there's a vacuum leak, but I can't find one! The only thing connected to the intake manifold is the break-booster (plugged the hole to the air-cleaner hot-air intake diaphragm). The vacuum advance and the gas tank evaporator are the only things connected to the carb. When idling well (with the mixture screw out a bunch) it has a solid 20 mm hg...

 

What's going on???

 

I'm in the bay area for the next day or two on my way up to washington. If anyone here has an l20b carb that works and would like to sell it to me, it would help me out a ton.

[copacetickid]

Took the carb off at a friend's house and soaked the jets and cleaned all the passages off. Put it back on and found out that the bottom of the carb was warped a bit, so I threw on some right stuff to seal it up. Whatever the problem, that cleared it right up.

[Lozer]

so take the carb back off and slap it on a belt sander for a few secs and measure for flatness w a straight edge.

 

i love rightstuff but its not supposed to be used in direct contact with gas.

 

it will probably leak in one week when you need it to work in the middle of a snow/hail/rain/thunder/tornado storm. (yea thats one hell of a storm)

[racerx]

Took the carb off at a friend's house and soaked the jets and cleaned all the passages off. Put it back on and found out that the bottom of the carb was warped a bit, so I threw on some right stuff to seal it up. Whatever the problem, that cleared it right up.

 

1). sounds like when the base of carb was tigthen, you tigthened it too much. This probably created a vacuum leak.

 

2). Idle jet should not be adjusted more than 1.5 turns out, if so then you may need to go up a bit., usually they are 55 or 60 and go up in increments of 5 so the next one is 65. You can try this..they are very easy too change. Check out Pierce Manifold located in Gilroy. Go on line. They also have tech assistance by phone and on line and have tons of diagram on webers.

 

3). you said you sealed the bottom of carb. Typically you don't need to seal it, except for gasket. Be careful since the "seal" can melt and get in the carb and will cause more problems later.

[Orange620]

Sanding the base on a sheet of fine sand paper glued to a sheet of glass would give it a flat surface.

[copacetickid]

How could tightening down on it too much cause a vacuum leak? Am I missing something? The idle mixture screw is definitely out more than 1.5 turns... but my feel like my engine shouldn't be any different than most people's L20b's that use webers, so there's got to be some problem I can fix. The main circuit idle jet is a 60.

 

The next 600 miles were better than the first 400, but it still showed the same symptoms, just less severely. I'll sand down the bottom on a piece of glass like you suggested orange.

 

Didn't know the Right Stuff couldn't stand up to gas. It seemed like it got gradually worse over the coarse of the drive from the bay area... maybe that's why.

[agentalpha]

Just like over tightening a chevy stamped steel valve cover bolt.

You DISTORT the metal, causing warps, dips and bends.

Gaskets don't like that.

Plus, you can pull the threads out, even in cast iron, doing that.

 

Did you know that just torquing head bolts down, even to specs, the cylinder bores distort a few thou?

Yes, even thick cast iron distorts!! Are your lugs over tightened to 200 ft lbs? You can warp your rotors as well!!

 

BUY a QUALITY torque wrench SOON and USE it if you haven't yet learned how to tighten bolts and nuts by "feel" yet.

And ALWAYS use it on precision torqued parts like lugs and headbolts.

Use oil to overcome friction for more accurate readings.

Edited January 4, 2009 by agentalpha

[mike]

On finnicky/problematic bolts (manifold, carb, valve and timing covers) I use just one or two fingers to pull on the wrench or ratchet. Shorter wrenches help too. Go easy and try and get them all even. Craftsman makes some short thin wrenches that are great for carbs and little stuff. They are about the size of the wrenches youd get with an assemble yourself entertainment center or something. Make sure that everything fits right before you tighten it down.

 

I had a weber on a generic aftermarket adapter from I dont know where (came with a parts truck) and the studs were too long and bottomed out on the base of the carb body when I would tighten it. It was the back two studs, it took me forever to figure it out. Shaved the studs down with a file and it works like a champ, went together WAY easier too.

[racerx]

How could tightening down on it too much cause a vacuum leak? Am I missing something? The idle mixture screw is definitely out more than 1.5 turns... but my feel like my engine shouldn't be any different than most people's L20b's that use webers, so there's got to be some problem I can fix. The main circuit idle jet is a 60.

 

The next 600 miles were better than the first 400, but it still showed the same symptoms, just less severely. I'll sand down the bottom on a piece of glass like you suggested orange.

 

Didn't know the Right Stuff couldn't stand up to gas. It seemed like it got gradually worse over the coarse of the drive from the bay area... maybe that's why.

 

 

Yes that's true but sometimes the 32/36 got to be jetted for a particular engine. If for, example, the cam was changed or that you built it up from the inside the jets will more than likely need to be changed. When you say webers are you saying you have side drafts or a 32/36 down draft? Because it does make a difference if adjustment.

[copacetickid]

Thanks for the tip mike, I'll check if they are bottoming out.

 

racerx, what do you mean "built it up from the inside"? I just rebuilt the engine... Anyway it's a 32/36 downdraft.

[racerx]

What I meant is that if you build up the engine or mod it with cam, new crank, pistons, the jets may need to be changed because the engine tech. is bigger in displacement and will require more fuel. A lot of track cars will do this to customize the need of their engine but typically a stock 32/36 is good enough for your engine.