cannon manifold 821

[yoloSun]

I had a really hard time bolting on the manifold - I used a wrench on the two bottom ones in the middle. Just getting them threaded was an ordeal, and in the end it leaked coolent, and I'm pretty sure it's getting sucked into the intake - It sounds funky and steam is coming out of the upper pcv.

 

I guess I'll have to do it all again with some...red atv? How do you guys tighten these bolts, don't say 12 mm shallow swival socket. I refuse to buy a set. 

Rather buy headers, that's a swell idea.

[yoloSun]

Alright I learned how to assemble that manifold with relative ease, no more leaks.

The gasket I used was listed as for the lb20, but the exhaust cutouts were square, and the two middle exhaust ports were just one big rectangle - whereas the original gasket had round ports and the two middle were not joined together. So now I'm wondering if this can cause some kind of backfire...or is it helpfull scavenging?

[datzenmike]

3, 4 or 5 speeds (in 4th) all go the same speed.

 

4-5K above 80k is probably the home wired tach. At 80k you would be under 3K. That RPM you'd smell the stench of the burning clutch.

[yoloSun]

3 hours ago, datzenmike said:

3, 4 or 5 speeds (in 4th) all go the same speed.

 

4-5K above 80k is probably the home wired tach. At 80k you would be under 3K. That RPM you'd smell the stench of the burning clutch.

Thanks mike, I'll try rewireing the tach, I have not smelled the clutch so thats good. 

[yoloSun]

Update: This post has gone far off topic. The rpms are where they should be now, more like 3 - 3.5 at 80k though. However  I still can't get a perfect idle, just a tiny bit rough. I recorded the sound of the engine under load, I'll post it. Doesn't sound right, missing some power.

[yoloSun]

 

I think it may be the "power valve",  since all other circuits are working. Can you guys tell me what part of the carb id be looking for?

Edited April 24, 2019 by yoloSun

[yoloSun]

Function of brass jet on the right?
Right Jet: Idle,   Left Jet:No idea

Middle Right/Left 😛Primary/Secondary

The power valve... it's in the center, the brass piece moves up and down when pushed, and so does the aluminum rod. 

 

Question: How to know if power valve is working?

 

Oh, and what's that diaphragm in the bottom left for? It's not holding pressure if I put my thumb on it.

Edited April 25, 2019 by yoloSun

[yoloSun]

Help me understand how this part meters gas. I understand that when manifold vacuum drops, a rod is pushed down onto this part by a spring. I know that this vacuum is supplied by a hollow screw at the base of the carb and that it must not be mixed up with the other long non-hollow screw. What I don't understand is this single tiny hole? How does it work?

[yoloSun]

Crickets chirpin' over here...perhaps all the enthusiasts toss their hitachis? Anyways, Lucy, you've got some splainin to do!

 

Check this out, I have a rebuilt carb that never worked right, next to the original.

There's a stamp, one says K4, and the original says K3. Dufuq? I tested the vacuum response of the power valve rods, and the original did not respond well unless I sucked super duper hard. The one with the spring sucked up easily.

I had the original on the car because the rebuilt one didn't work right. If my valve wasn't responding well to vacuum, then shouldn't I have been running rich all the time, making it not the reason I lacked some power?

[yoloSun]

Well, if anyone could tell me why one carb has a solid brass blocked port, and the other a metered port - It would be greatly appreciated.

 

Don't want to tear it down again.

Edited April 26, 2019 by yoloSun

[datzenmike]

When the tach jumps around like that the points need cleaning or replacing..... assuming that there is no loose wire. Point gap is about 0.022". Ignition timing is 12 degrees. Firing order is 1, 3, 4, 2 in a counter clockwise order. Set the valve lash to 0.010" (intake) and 0.012" (exhaust). These need to be checked and set first before tearing into a carburetor.

 

 

The Hitachi power valve is held closed by intake vacuum against a spring. Under heavy throttle and the resultant lower intake vacuum the spring pushed down on the power valve opening it and letting more fuel flow making the mixture richer. The vacuum for this travels up a long hollow screw in the carb base.  The front and back screws can accidentally be interchanged and I've had this. Someone had my carburetor apart and the power valve did not work. Swapping the hollow screw to the front fixed this.

 

 

 

Above...This is the underside looking up into the secondary. The screw to the right is on the left or driver's side. The top (front) and bottom (rear) hole between the primary and secondary are the ones that take the longer screws. You can see the top one has a hole and is hollow, to bring intake vacuum to the power valve.

 

Below is similar but has a trough and a hole up to the power valve. This is a later 720 carb.

 

 

 

This is the underside looking up into the secondary. The screw to the left is on the left or driver's side. The top (front) and bottom (rear) hole between the primary and secondary are the ones that take the longer screws. You can see the top one has a trough cut to bring intake vacuum to the hollow screw head.

 

 

 

 

There is a small air bleed just above the plugged one near that screw head.

[yoloSun]

2 hours ago, datzenmike said:

When the tach jumps around like that the points need cleaning or replacing..... assuming that there is no loose wire. Point gap is about 0.022". Ignition timing is 12 degrees. Firing order is 1, 3, 4, 2 in a counter clockwise order. Set the valve lash to 0.010" (intake) and 0.012" (exhaust). These need to be checked and set first before tearing into a carburetor.

 

There is a small air bleed just above the plugged one near that screw head.

Thanks Mike, I've been creeping you guys for a couple years now so I already knew all about that screw and your carb, was very helpful for me.

 

I have an electronic distributor, so no need to set point gaps. 

Timing set to 12 btdc.

Firing order set 1,3,4,2 counterclockwise

Valve lash is set.

 

I want to make sure the plugged port I pictured is not a modification, and is factory set.  Is it?

 

Not sure if you read the first bit because you repeated what I had just said, I'm interested in the piece that the power valve pushes down on - the piece I pictured in my hand. It doesn't look serviceable. I'm curious how it meters gas with one tiny hole.

Edited April 26, 2019 by yoloSun

[datzenmike]

I was saying the carburetor with the plug is different from the other in that it has an extra air bleed hole just above it. (probably) they changed it.

 

The carburetor will run fine without the power valve working. What it does is add extra gas under heavy load when the secondary is open, forcing it to run slightly richer. Engines like to run richer under load and will make more power. My 710 was blocked off with the wrong screw. When I sorted it out it ran much better when floored and the secondary opened.

[yoloSun]

4 hours ago, datzenmike said:

the carburetor with the plug is different from the other in that it has an extra air bleed hole just above it. (probably) they changed it.

 

I had not noticed that in my original post, so thanks for pointing that out.  But that doesn't tell me if the plug is factory set or not.  Maybe I can google k4 vs k3, but I doubt it.

Another air of mystery...

 

So far I found 1 failing power valve, and one...failed diaphragm that was prabably a vacuum leak. It was in the...uhh warmup choke linkage thingamabob.

And by the way mike, those are pictures of two torn down carburators, one was a rebuilt $XXX carb, the other came with the truck. 

Edited April 26, 2019 by yoloSun

[datzenmike]

How do you know the power valve is failing????

 

I think it should be closed when that little rod is pushed down flat and open when up. 

[yoloSun]

23 minutes ago, datzenmike said:

How do you know the power valve is failing????

 

I think it should be closed when that little rod is pushed down flat and open when up. 

Closed

Open^

^You can emulate high manifold vacuum here with a piece of vacuum tube.

Edited April 26, 2019 by yoloSun

[yoloSun]

I know one is failing because - One responds easily when I suck on it, and the bad one does not.

[datzenmike]

According to the FSMs vacuum pulls the rod upwards against that spring, so valve should be closed. When floored, the vacuum drops and the spring pushes down on the power valve to open it.

[yoloSun]

4 hours ago, datzenmike said:

According to the FSMs vacuum pulls the rod upwards against that spring, so valve should be closed. When floored, the vacuum drops and the spring pushes down on the power valve to open it.

Ya thats what I'm saying, with pictures.  Oh I see now, I meant to say the rod mechanism that actuates the power valve was failing, because It wasn't responding well to vacuum. 

Sorry, I cannot tell if the power valve is failing, my mistake, derp. 

Edited April 27, 2019 by yoloSun

[datzenmike]

I've had them stiff or hard to actuate. Probably because they don't get much use. I pushed it up and down to free it and this will polish any place it rubs.

[yoloSun]

Yeah that's what I'd do if I didn't  have a spare. 

 

I was just putting the spring on the linkage for the vacuum actuated secondary, and I wonder...what would happen if I didn't? 

I wouldn't mind an early shot of go juice

 

Although it would probably just turn into a self feeding vacuum that never stops reving.

Edited April 27, 2019 by yoloSun

[yoloSun]

On 4/26/2019 at 5:53 AM, datzenmike said:

The carburetor will run fine without the power valve working. What it does is add extra gas under heavy load when the secondary is open

Hmm I was pretty sure the power circuit kicked in before the secondary circuit. 

[datzenmike]

Yes, sorry, it richens up the primary under low intake vacuum heavy throttle conditions. Confused it with the high speed enricher jet.