AVS2 Tuning Woes...

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7milesout

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Guys,

I'm going to *try* to keep this short, and stick to the topic, no venturing to tributaries.

I finally installed my AVS2 (1905, manual choke) after having it on the shelf for a couple years. It has been nothing short of a PITA to tune. Finally I have got most of the issues sorted. Except 2.

It is a much different animal to start cold, than the 1405. It seems to need a lot less choke, but I think I can figure it out, or learn the way it prefers.

The main problem is, at WOT it is rich rich rich. it is running in the high 10's pulling from 3,000 to 5,000 rpm. And I"m running a teeny tiny 0.083" secondary main jet. It seems to run strong for that AFR, but I know a) there's more 12.5 to 13.0, and b) it doesn't feel quite as strong as I think it should.

BUT ALAS! I think I just figured it out. I was thinking in my mind with such a small jet, it must not be getting enough air. What would cause that? Forget the secondary flap, I've just about tuned that out.

I just had my son sit in the car and push and hold the throttle pedal to the floor. While looking down in at the secondary butterflies, they are not opening fully. That HAS GOT to be the issue. It is not getting all the air it should be getting. With my hand on the carb linkages I can pull it the rest of the way open. But with his foot, could not get it that far.

This seems like a simple enough affair to resolve, but right off hand, I'm not seeing how to get more throttle throw ... without effecting the throttle opening at idle.

Help me out here guys, surely you guys have ran into this issue before.
 
7milesout said:
Guys,

I'm going to *try* to keep this short, and stick to the topic, no venturing to tributaries.

I finally installed my AVS2 (1905, manual choke) after having it on the shelf for a couple years. It has been nothing short of a PITA to tune. Finally I have got most of the issues sorted. Except 2.

It is a much different animal to start cold, than the 1405. It seems to need a lot less choke, but I think I can figure it out, or learn the way it prefers.

The main problem is, at WOT it is rich rich rich. it is running in the high 10's pulling from 3,000 to 5,000 rpm. And I"m running a teeny tiny 0.083" secondary main jet. It seems to run strong for that AFR, but I know a) there's more 12.5 to 13.0, and b) it doesn't feel quite as strong as I think it should.

BUT ALAS! I think I just figured it out. I was thinking in my mind with such a small jet, it must not be getting enough air. What would cause that? Forget the secondary flap, I've just about tuned that out.

I just had my son sit in the car and push and hold the throttle pedal to the floor. While looking down in at the secondary butterflies, they are not opening fully. That HAS GOT to be the issue. It is not getting all the air it should be getting. With my hand on the carb linkages I can pull it the rest of the way open. But with his foot, could not get it that far.

This seems like a simple enough affair to resolve, but right off hand, I'm not seeing how to get more throttle throw ... without effecting the throttle opening at idle.

Help me out here guys, surely you guys have ran into this issue before.
Click to expand...

If you move the connection point on the carburetor linkage more toward the throttle shaft, it will open further.
 
If you dont have any slack in the throttle cable at idle you will have to do what RRR said. Find another point to connect the cable to that will give it more throw. I have an avs2 on one of my cars ,I can snap a pic of my setup for reference.
The only issue I fought with the AVS2 was a bad bog when the secondarys opened. The flap adjustment didnt seem to do anything no matter how it was adjusted. I finally got it sorted out after many combinations of the piston springs and jet changes. Its a nice carb once you get it sorted out. It fires up quick when cold and has been very reliable.
 
I did just that, only to come in here and read what you guys suggested. THANKS!

Picture below shows what I did. I moved the linkage from where it is pictured to the highlighted red hole.

It pulls the throttle wide open now. And when I let off, it goes right to the throttle adjust screw (stop) as before. I haven't driven it yet. I will in about an hour and report back. It will probably be too lean with that little bitty secondary main jet.


7milesout

View attachment 1715760147

upload_2021-7-4_15-19-20.png
 
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so, correct me if i am wrong, but it seems to me if the car is cold the edelbrocks have a lock out that prevents the secondary's opening up unless the car is warmed up. I was having an issue with a holley not able to get it open all the way using the acc pedal , I had to install a longer throttle cable. They can easily be found online. I tired moving the cable closer to the shaft but it did not solve my issue. the longer throttle cable did
I am too runing a avs2, i have not really done any real tuning with it yet, just have not gotten to it. It on a 408 and it seems like a good carb so far.
 
Pic for reference.
Note: no KD linkage because im running manual valve body.
20210704_150520.jpg
 
Early a body said:
so, correct me if i am wrong, but it seems to me if the car is cold the edelbrocks have a lock out that prevents the secondary's opening up unless the car is warmed up.
Click to expand...
I don't believe there is any such mechanism on the 1905 (manual choke).

MoparMike1974 said:
Pic for reference.
Note: no KD linkage because im running manual valve body.
Click to expand...
My red highlighted hole seems about the same place as yours.

So I went out and drove it. It does seem a bit faster, not as much as I exptected. But ... it is still on the rich side. It leaned out to around 11.5ish. Which makes me want to put a camera over the carb with no filter, and confirm the valve is opening wide open. It's hard for me to believe I'm running rich at WOT with the jets I'm running (.100" primary (75/37 MRs) & 0.083" secondary).
 
You carb has an adapter bracket on it. I think its installed backwards as well. You probably dont even need the adapter, its mainly so you can hook up to stock KD linkage.
As far as your jetting, I would go back to the stock one and tune from there. These are pretty close out of the box on jetting.
 
I'm running an AFR gauge. My tune is better than the stock one. The out of the box tune is ~20% richer at cruise and WOT than I'm currently running. I'm very close to the as shipped AFR in the Power Mode (which is too lean).

If you could point out what your talking about with the adapter bracket being backward, I would appreciate it. The only thing on there that is really not needed (as far as I know) is the bar to attach a cruise control. But since it's not hurting anything to be there, I've just left it.
 
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Im not positive but I think that circular cutout goes around the throttle shaft. In other words, the bracket needs to be flipped around. Its irrelevant since your not using the stock KD linkage. Thats the only reason to use the adapter. If everything is working just leave it like it is.
 
I just checked on a spare AVS I have on the shelf. You do have the adapter installed correctly.
 
I didn't mess with it yesterday. I'm still surprised about how small a secondary main jet I'm running is, and still rich at WOT. Not terribly, but I'm sure you guys know the feeling of not wanting to leave any hp on the table. Let's say some crusty ole 67 Moustang were to pull up next to me at a traffic light. I need to be able to pull every horse out of the livery, not leave a few in there snoozing. :D

From the tuning I've done on this AVS2, I can say that Edelbrock tunes it safe / rich out of the box. I can't blame them for that.

And I can say that IN MY EXPERIENCE the metering rod shapes are crap and they don't pop up quick enough even with the silver spring, to run the power mode rich enough (however, power mode is not easily defined). The only way to ensure the power mode runs rich enough is to fatten up the cruise mode. I just can't bring myself to do that. I can also say that my cruise mode AFR is speed dependent due to the high rpm cruising of my combo. 40 mph cruise is a bit rich, 55 cruise is hovering around stoich. Leaner from there on up, but not detrimentally so.

In any event, the car cruises around town and accelerates nicely from a light. I'll just keep fiddling with it to get my WOT AFR perfect then I'm off to the next thing. An RPM Air Gap intake. And probably have to tune a bit more with that. Then leaf spring relocation, then big wheels and tires, then etc, etc, etc. I'm sure you guys know that feeling too.
 
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