Progress Thread The next "big" project for my Cobra

[extra_stout]

I really doubt that the secondary side would have an effect on the AF ratio at cruise, but it IS possible that the throttle is opened just enough to engage the secondaries?

I'm with you. On the secondary side fuel should only come from the transfer slot circuit... which should not have an effect on cruise.
One thing to mention: if your power valve is "leaking" it will constantly drip fuel and make it rich everywhere. But I thought you have put in a new power valve since you installed the AFR gauge...?!
The 4777 is a race carb, which will add a lot of fuel with the power valve , so in my opinion you can even go near 14.5 in cruise...
But it sounds like you will require a really small main jet size, which makes me wondering. On the other hand, if you have a good "vacuum" signal at the venturi you also get a lot of fuel with a small jet size...
So if you are sure about your power valve you can go ahead in my opinion. But if you ever change the power valve, be vary careful after that because it could result in a lean condition at WOT.

 

[LILCBRA]

Funny you mention the power valve.... I was wondering about that as well. I did, indeed, replace it, but I think it might be a little too light. I think it needs a 7.5 but I used a 6.5 because, at that time, the vacuum wasn't getting to the point it is now. Now that we've brought that up I think I'm going to order one - hopefully I can get one overnight from Amazon so I can install that before going with a smaller jet.....

Just went back through the other thread and confirmed, I used a 6.5. Now that I have better vacuum, I'll need to increase the PV size.

Round 2: Took the carburetor off and installed the 6.5 power valve. Confirmed it's operation the same as before. Messed with the idle mixture screws again and ended up about 1/4 turn out, 14 in vacuum, idle about 750, a/f jumping between 14-16. Kept fiddling with the mixture screws just a slight turn at a time until I ended up bouncing between the high 13s to the low 15s. Gonna call it good right there until I get it out on the road. I'll play with jetting at that point.

 

[LILCBRA]

Couldn't get one from Amazon, but I could through O'Reilly's. It is supposed to be delivered to the nearest store to my house by tomorrow morning. Luckily it's actually walking distance....

 

[extra_stout]

Sounds like a promising weekend!

 

[LILCBRA]

Nothing big and exciting happened today. I got the power valve, the jets, and the discharge nozzle. I went ahead and got the discharge nozzle and the power valve installed and was reassembling the carburetor when 3 of the 4 screw holes stripped while I was trying to cinch the bowl down. I didn't even apply that much pressure! I hunted around for anyplace locally that I could get a 12-24 Helicoil kit and wasn't successful there either. So I ordered a kit on Amazon that should be here tomorrow.

After I did some cleaning and rearranging of my temporary work area, I got the carb ready to perform surgery tomorrow. I'm also going to try and readjust the primary accelerator pump arm since the spring is just about bottomed out. I have another arm from my pile-o-parts but it's identical, so I'm not sure what I'll be able to get accomplished. But I can't just leave that spring collapsed like that.

 

[2Blue2]

when 3 of the 4 screw holes stripped

are those blind holes?

 

[LILCBRA]

are those blind holes?

Yes, they're roughly 1/2" deep. But the screws only engage about 1/4" of the threads. So as long as the tap can give me enough new threads for the insert I should be able to get away with going this route.

 

[extra_stout]

I got the carb ready to perform surgery tomorrow

If your carburetor is at that stage. Check the transfer slots on primary and secondary side. If possible make and post pictures, would be interesting to so how they look like after your last tuning session!
And also try to make you secondary idle RPM screw free again with some WD40...

 

[LILCBRA]

Here you go.

The primary idle slots.

And the aftermarket secondary pump cam. If memory serves, I had to install it this way otherwise it was too tight.

Thanks for the suggestion about the secondary screw, I'll spray it down and see if it'll loosen at all. In all outward appearance it looks like it's just about right. The secondary throttle plates are completely closed when the shaft is at rest, so I don't think it'll need any adjustments to speak of.

 

[extra_stout]

You could close the primary side a little to get the transfer slot more square, and open therefore the secondary side a little.
Than you should get more control with the idle mixture screw...
e.g.: If you need a little more idle RPM in the summer because of high temperature, you will not have excessive exposure of the transfer slot.

 

[extra_stout]

I just saw that the throttle blades are not closed fully in this picture. At least it looks like the idle RPM screw is not in contact with the stop.
So please look for that, before you make any adjustments...
Perhaps it's not necessary to adjust something.

 

[LILCBRA]

I just saw that the throttle blades are not closed fully in this picture. At least it looks like the idle RPM screw is not in contact with the stop.
So please look for that, before you make any adjustments...
Perhaps it's not necessary to adjust something.

Yeah, I noticed that too. I think it's because it was sitting on the vise.

 

[LILCBRA]

Here it is now that it's clamped back up in the vise.

 

[extra_stout]

That looks perfect!

 

[LILCBRA]

After waiting all day for the Amazon driver, I get to find out that I had only THOUGHT I ordered a 12-24 Helicoil kit. Instead, I must've selected the 10-24 kit. So now this is all on hold until later this week or, most likely, next weekend....

 

[rednotch]

The cheap $30-35 multiple size china kits ain't too bad .. If they send ya what you ordered... Took 3 tries to get an SAE kit but worked fine when they stopped sending me metric kits. Fixed a few boogered holes on some cheap beat up cast intakes i had just to test them out.

 

[LILCBRA]

Yeah, I ordered the cheap kits not Helicoil brand. The 1/4-20 set worked just fine on my mower.

 

[LILCBRA]

Got the carb back together with the 7.5 power valve. Adjusted the warm idle mixture to about 14-15 inches and checking out the AF gauge it says I'm around 12.5-12.7. A rev and hold stays around the 13 mark. My phone's camera stopped working so I cant take any pics at the moment. But I think smaller primary jets are in order.

 

[LILCBRA]

Down to size 62 jets, vacuum still 14-15 inches, warm idle mixture 12.7-13.5, rev and hold is in the mid 13s. I'll try a video and share that at some point to keep an eye on the gauge while cruising, but I'm gonna leave it as it is for now.

 

[extra_stout]

Adjusted the warm idle mixture to about 14-15 inches and checking out the AF gauge it says I'm around 12.5-12.7. A rev and hold stays around the 13 mark.

Just for understanding: did you just check AFR with the Mustang in P or N? Jet size should not have influence on the idle mixture. Idle mixture should only react to idle mixture screw settings.
Main jet size can only be checked, when you are cruising...