2F Carb Secondary Opening Issues

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ASO544

ASO544

Joined
Oct 21, 2020
Threads
60
Messages
400
Location
USA
I’m having issues with the 2F carb’s secondary not opening under load or WOT. I confirmed it with the paper clip test

I removed the vacuum assembly and tested it by sucking on the gold valve and the diaphragm retracted and held in place as long as the suction was held. Once released the diaphragm released as it should.

I then used a hose and blew through the black gasket area on the carb ( where the gold valve lines up to it ) and could hear air blowing into the carb so the passage is clear.

I also could see the gold valve and black gasket area seem to line up but not perfectly ( see pic with gasket outline) Maybe the gasket is possibly blocking the vacuum flow ??

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With the carb mounted and linkage hooked up, I made sure my throttle linkage is activating and freeing the secondary and it is .

So either the vacuum assembly isn’t lined up good enough and the vacuum can’t flow or either the carb isnt making vacuum to operate the secondary under load.

Both fully closed …. Zero throttle. I can see the primary blade ( top one) isn’t fully closed and has a slight opening. That correct ?

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Full Throttle / WOT. Is that too much opening on the secondary blade? Would that mater ?

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Full throttle /WOT and the secondary linkage fully opened.


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I’ve also attached a few videos of the linkage and butterflies operating. Anything look off ?

I’ve attached a few videos of the butterflies operating and the secondary linkage.

Secondary Linkage # 1

Secondary Video # 2
 
Is this a knockoff Aisin? Look at the gasket between the carb body and diaphragm body. I bet the gasket blocks that gold passage. The solution is an o ring that doesn’t have as much meat to it, but is still thick enough to seal.
 
The other thing to check is that you are actually getting enough pedal travel for the primary linkage to kick the secondary open. If not, the linkage tab needs bent so it “kicks” the secondary open sooner.
 
Here was a good thread that went over a lot

CruiserTrash

Thread 'Aisin secondary tuning ideas'

There are already several great threads explaining 2F/60 Series Aisin carbs and what the secondary does, I’ll link those in the second post. So what’s the point of this thread? To discuss tuning the secondary to make it more useful. I’m just going through this and some of it is me thinking out loud, so feel free to argue with me.

After noticing my secondary wasn’t working, I set about to fix it. I rebuilt this carb a year ago and found two issues: the diaphragm was installed incorrectly, and the vacuum passage to the secondary diaphragm was plugged with gunk. There’s some cause and...
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I had to work through this also, I'd recommend checking two things:

1) Are you using a gasket between the base and body of the carburetor? If so, make sure it fully seals the channels your vacuum air passes through. This is an issue both myself and @greenEFSI had with the SMP hygrade carb base gasket which doesn't fully cover the vacuum path and leads to an air leak.

2) As @Skreddy mentioned, double check that when the carburetor is installed and you press the pedal to the floor, the linkage is kicking open the secondary. My throttle position switch was limiting my pedal movement and I only found the issue when I had one of my kids put the pedal to the floor while I watched the carb. If I pulled the linkage at the carburetor, everything seemed fine.
 
Here is every piece to the secondary mechanical/vacuum operated system:

1. Verify secondary diaphragm opens by sucking on the brass port on the housing, it should easily actuate inward and hold vacuum until released.​
2. Ports - make sure the diaphragm vacuum port is clear through the body to the port next to secondary barrel. A spray of air or carb/brake cleaner will show you the track. THEN follow that track from the body of the carb to the two inlets in each barrel to ensure those are completely clear.​
3. Secondary kickup - mechanical. Carb needs to be fully assembled: 1. Rotate primary butterfly so that the primary butterfly kickup lever hits the secondary butterfly shaft. At initial contact you want the butterfly at 67°. Verify that angle is at least close, exact is not important right now. Less angle means secondary mechanical opening opens sooner on throttle pedal.​
4. Then fully open primary butterfly (ensure this is 90°) and that the secondary butterfly kicks open to 25° (USA spec) to 28° (Non-USA spec). Usually its about 1-2mm of opening​
5. Next while primary is all the way open and secondary butterfly is kicked open mechanically, rotate secondary butterfly all the way open to ensure its smooth, doesn't bind and opens to full 90°. If more, you need to adjust the mechanical stop on the opposing side of secondary butterfly shaft.​
6. Finally, ensure gaskets on carb body insulator are clean, flat and the body tightened down.​

No pictures, I just did this straight off memory real quick at work.
 
For WOT, if you’ve had the carb off and removed the bell crank linkage (from firewall to bracket on carb), it’s possible to install the backwards and you won’t get full throttle.
Here’s the bell crank (screwdriver pointing at it). Long arm is carb side, short arm is firewall side.
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From the gasket witness mark on the diaphragm body though, you can see the port is offset into the gasket.
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As far as the secondary issue I believe this is the problem as well. The flattened o-ring/gasket , once installed and tightened, is blocking the port and the vacuum. Looks like a slight manufacturing defect.
 
This is common with the aftermarket Aisin carbs you can get off Amazon and eBay.
 
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