Just bought a 521

[d.p]

Man I still think you need rubber (or thicker?) isolators? I thought I mentioned it before and you said it was just a thick gasket?   For what miles I have on mine since building it bolts all along the carbs and heat shield have worked themselves loose (among other places) but most of them have been centered around the carbs.  Lots of vibrations I guess. 

[mainer311]

Yes indeed. Everything cooks and settles.

I threw my colortune on the truck tonight and had a look. Idle was pretty lean. I cracked the idle screws open another 1/4 turn and it was much better. It idles a touch rougher, but there’s next to no popping back out the carb. I’m at 1-3/4 turns out, so good enough. Nice orangey rich burst comes through from the accelerator and then it leans back out. 
 

Looks like bigger exhaust is next.

[Charlie69]

12 hours ago, datzenmike said:

 Put a level on the head. The firewall is almost always higher than the rad support so the engine will look like a sinking ship at the back.

That only works if:

The height of the front and back of the truck is stock and not sagging

The wheels & tires are all the same size

The truck is parked on level ground

 

Edited May 8, 2021 by Charlie69

[d.p]

9 hours ago, mainer311 said:

 

Looks like bigger exhaust is next.

Yeah I am going 2.25” with a vibrant resonator and magnaflow muffler.  Not sure where I am to exit it though yet.  Behind the a rear wheel? Straight out the back? 
 

Have an appointment on the 19th to get it done.  

[datzenmike]

6 hours ago, Charlie69 said:

That only works if:

The height of the front and back of the truck is stock and not sagging

The wheels & tires are all the same size

The truck is parked on level ground

 

I don't think it really matters much to the carburetor. What happens if you are climbing a 13% grade? Or accelerating at warp 7.

 

 

1 hour ago, d.p said:

Yeah I am going 2.25” with a vibrant resonator and magnaflow muffler.  Not sure where I am to exit it though yet.  Behind the a rear wheel? Straight out the back? 
 

Have an appointment on the 19th to get it done.  

 

I believe it must exit out from under the body if in front of the axle and anywhere if behind. I have a 45 down bend and the tip just misses the front of my axle. A side exhaust in front of the axle would be hard to plumb.

[Charlie69]

I am talking when you are welding motor mounts to the frame and modding transmission mount for an engine swap.

 

If you do not get the engine centred and the proper angle, yes most engines are installed with a 6 to 12 degree angle to the back of the engine.  This helps to drain oil out of the heads.

 

Next time I level my 66 520 chassis I will take pictures of a level on the L20B valve cover and on the intake manifold carb mount area.  The engine is tilted back and the cab mount is level.  The center of the crankshaft is also in a perfect straight line all the way to the center of the pinion flange which is the center of the pinion gear shaft.  I am talking looking straight down or striaght up on the drive train of the truck.  There is a 3 degree pinion angle also set after the truck was lowered.

[mainer311]

Makes me wonder if people just run the fuel level in the bowl a touch high, and then just try to throttle back on the jetting to the rear. As it sits right now, I have #1 idle screw turned about 1/8th more than the other 3.

[datzenmike]

Again acceleration, braking, cornering, climbing or descending steep inclines would affect them if this was true. For the most part it does not. As long as the main jets are submerged....

 

 

[mainer311]

1 minute ago, datzenmike said:

Again acceleration, braking, cornering, climbing or descending steep inclines would affect them if this was true. For the most part it does not. As long as the main jets are submerged....

 

This isn't true at all. In fact, one of the tests in determining correct tubes is to find a steep sweeping corner in the opposite direction that the carbs are mounted on. Fuel level in the emulsion tube plays a huge part in mid-range mixture.

[datzenmike]

May be true for what you have but the down draft carburetors and the R-1 carbs I have has no noticeable effect. It would be a poor design if the previously mentioned forces affected the carburetor mixtures. So it's tuned for level driving how does it affect this tune it you change it for hard cornering? It would seem you can't have it both ways and there is a compromise.

[mainer311]

Hard cornering is a lateral tilt, which the carbs already have anyway. This doesn’t affect mixture changes between the two sides like a linear tilt does.

[datzenmike]

7 hours ago, mainer311 said:

Makes me wonder if people just run the fuel level in the bowl a touch high, and then just try to throttle back on the jetting to the rear. As it sits right now, I have #1 idle screw turned about 1/8th more than the other 3.

 

Both carburetors are inclined at the same angle so front or rear are the same in every way. 1/8 of a turn is nothing in the scheme of things. 

[mainer311]

Here’s some proof that the bowls are definitely not level. I really dialed in lean best idle today with the tach function on my timing light. The idle smoothness drastically improved.

 

1 and 3 (higher tubes of both carbs) are 1.5 turns out. 2 and 4 (lower tubes) are both 1.125 turns out. That’s a pretty big difference, and I didn’t even realize the pattern. I was tuning each tube individually for max rpm.

[mainer311]

Well, I've been fighting with my Webers the past few days. Finally figured out that the butterflies are not nearly open enough to be in the correct position directly under the 1st progression hole. It's such that it's causing a lot of lean stumbling and backfiring out the carbs during very light throttle cruising, since the butterflies need to travel extremely far to uncover the 1st hole. I'm starting to read online that DCOE 40 151's and DCOE 45 152's typically need an extra hole drilled closer to the butterfly such that the delay is much shorter. Why Weber never correct this, I'm not sure. Drilling holes in a new set of carbs is not something I look forward to. 

[Crashtd420]

9 minutes ago, mainer311 said:

Well, I've been fighting with my Webers the past few days. Finally figured out that the butterflies are not nearly open enough to be in the correct position directly under the 1st progression hole. It's such that it's causing a lot of lean stumbling and backfiring out the carbs during very light throttle cruising, since the butterflies need to travel extremely far to uncover the 1st hole. I'm starting to read online that DCOE 40 151's and DCOE 45 152's typically need an extra hole drilled closer to the butterfly such that the delay is much shorter. Why Weber never correct this, I'm not sure. Drilling holes in a new set of carbs is not something I look forward to. 

I thought this was corrected with the newer webers?

I believe the older ones only had 2 holes verse 3..... 

I thought that mod was only for older models....

 

[mainer311]

7 minutes ago, Crashtd420 said:

I thought this was corrected with the newer webers?

I believe the older ones only had 2 holes verse 3..... 

I thought that mod was only for older models....

 

 

Everywhere I look, people are drilling a 4th hole into the 3 hole Webers. I can sorta understand that these carbs would work better on some cars vs. others, and that the holes are generally placed, but in my case it's just not going to work. 

 

There are basically 3 options:

1. Drill extra hole.

2. Retard timing (not good for a Weber setup) to get idle lower, then screw throttle stops in further so that the butterflies are in the right place.

3. Open air bypass screws enough to disrupt the idle, then set the butterflies using the throttle stops. 

 

The extra hole option seems like the best case actually, since you're not fudging any of the idle circuit, you're just allowing the progression to happen as designed as soon as the butterflies crack open. Getting all 4 holes drilled and accurately placed is going to be a damn nightmare.

 

I tried to "cheat" the system last night by installing super rich idle jets to try to jump the flat spot at throttle tip-in, and it was just a stumbling mess. Once the accelerator jet hit, things would get super rich and it would fall on it's face. One nice thing I did play with is the air bypasses last night. Both of the carbs had uneven flow within each other, so I got that sorted out. I need to reset lean best idle tonight and then start looking into the best way to drill these 0.8mm holes.

Edited May 11, 2021 by mainer311

[Crashtd420]

What about changing the throttle plate?

Do you know which way it needs to go? I believe it says you want the first progressive hole about half exposed?

 

 

[Crashtd420]

I'm sure you are reading similar info...

 

 

[mainer311]

It would basically need to close at a shallower angle, so less than 78 degrees. The throttle stop screw needs to turn almost another one full turn in to put it in the right spot, which is well beyond the 1/2 turn that Weber suggests. It just doesn't make any sense to me.

 

[mainer311]

I've been using these pictures as reference:

 

 

http://www.alfabb.com/bb/forums/attachment.php?attachmentid=49116&stc=1&d=1162670319

[mainer311]

http://www.alfabb.com/bb/forums/attachment.php?attachmentid=49116&stc=1&d=1162670319

Edited May 11, 2021 by mainer311

[d.p]

Damn dude what a headache and I feel your pain.   

 

I don't have shit to add other than that I hope you get it figured it out.  

[mainer311]

Here's where people are putting the extra hole. This makes it such that the butterfly position doesn't need to change, and then the circuit starts as soon as the butterflies begin to open.

Edited May 11, 2021 by mainer311

[Crashtd420]

6 minutes ago, mainer311 said:

It would basically need to close at a shallower angle, so less than 78 degrees. The throttle stop screw needs to turn almost another one full turn in to put it in the right spot, which is well beyond the 1/2 turn that Weber suggests. It just doesn't make any sense to me.

 

 

Just trying to understand.... 

One reason I hate trying to help online, it can get confusing describing things, I'd rather have eyes on to understand.. .

 

I'd hold off on drilling the extra hole unless you really believe its neccessary.... 

I didnt have an issue with my throttle plate location.... 

 

I know your very thorough and meticulous but there could be other things causing your issue, not sure what but its possible... I just wouldn't wanna see you modify the carburetor and create more issues...

 

Tuning sucks but you can tell the difference when you get it right...

Goodluck .. 

[Crashtd420]

10 minutes ago, mainer311 said:

Here's where people are putting the extra hole. This makes it such that the butterfly position doesn't need to change, and then the circuit starts as soon as the butterflies begin to open.

Is this you carburetor or an online picture?