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Just bought a 521


mainer311

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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. 

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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.

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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

 

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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.  

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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.

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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.

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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.

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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....

 

 

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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.

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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.

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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. 

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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.

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