Best way to check for vacuum leaks?

[Chryco Psycho]

I usually change jets by 2 sizes so you can feel the difference .
 I also back the choke waaay off , so it comes on very lightly or no even fully closed , once running it will drop open fast & not waste fuel or foul plugs

[74 challenge]

I usually change jets by 2 sizes so you can feel the difference .
 I also back the choke waaay off , so it comes on very lightly or no even fully closed , once running it will drop open fast & not waste fuel or foul plugs

By process of elimination (the carburetor learning curve I'm now calling it) this is what I am going for. I have had it on too much and have had it on too little. I need to find that sweet spot, every time I start it cold I turn it a hair till I notice a change. I never realised how much outside temperature can affect a carburetor. I have always heard it changes it but I was thinking it would be less obvious. I ordered a jet kit 60-70 jets so I will likely start with 66 than re-do the air fuel mixtures, curb idle etc...

I do have another general Carb question. On the preform unit there is a thumbwheel adjustment on top of the vacuum secondary portion just behind the choke. IT has an arrow pointing to an S and to a P and is an adjustment of some sort, what does it do? From my understanding the secondary's are controlled by a spring on the inside of the diaphragm where adjustment was done by swapping the spring?

[Bullitt-]

I'm reminded of a local guy with a mild 440 that would surge at idle.  the problem was traced to weak advance springs in the distributor. 
If you put a timing light on it does the timing stay stable at idle?

[Chryco Psycho]

do you have a picture of the S & P unit ?

[74 challenge]

do you have a picture of the S & P unit ?

I don't have a picture of the exact carb on my car but here it is from Summit.

http://www.summitracing.com/int/parts/pro-67207/overview/

Right behind the choke (on the top right hand side of the Vacuum Diaphragm) there is a small screw that can be adjusted, on mine right above it where it says 650 on the pictue above it has a two headed arrow and one end is an S and the other is an F (sorry not a P)

Here is an example of the S and F adjustment on a quick fuel carb (written in orange on the vacuum diaphragm) What does the S and F stand for and what does this tiny screw do?

http://dragpartsusa.com/images/F86999910.jpg

[Chryco Psycho]

it looks like it is a needle adjustment , this would slow how fast the diaphragm opens the secondary , interesting idea , I have not seen that before .

[74 challenge]

it looks like it is a needle adjustment , this would slow how fast the diaphragm opens the secondary , interesting idea , I have not seen that before .

Could it be opening the secondary too quickly causing my horrendous fuel mileage? I guess it is easy to check with the car in park. open the throttle and see when the secondaries open up. It could be plausible since it's using quite a bit of gas on the highway. 

I won't investigate this until I have my new jets as I still think that is my main culprit. One at a time, right!

I'm sticking with my theory that this is a good carb but for a novice, it has too many adjustable components.

[dougs bs23]

Quick fuel vac secondary adjustment. There's a whole section on adjustment at the quickfuel website http://www.quickfueltechnology.com/media/tech-blog/adjustable-vacuum-secondary


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[dougs bs23]

Would it also be possible to  gain results by changing up or down the hi speed air bleeds?


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[HP_Cuda]

I like the new features on the Holley Avenger line whereas you have 2 screws and you can change out the spring quickly from the top without having to take the vacuum diaphragm off completely.

[74 challenge]

Would it also be possible to  gain results by changing up or down the hi speed air bleeds?


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this is on the list too but it I'm tempted to swap jets before air bleeds.

I am going to need to check out this adjustable vacuum thing, my screw is pretty damn far out but that is how it came form the factory. I am quickly feeling like I got a carb that was returned because so many things seem excessively off.

1. my choke was 100% as far as it could go to the lean side
2. My secondary adjustment screw had already been turned around (turns from the top not the bottom)
3. Transition slots were not only completely exposed but by a good 1/8 of an inch above the end of the groove
4. the cam on the choke has a significant modification in it.
5. Accelerator pump was so loose it barely made contact.

I don't feel like ProForm would send carbs out like this? but summit claimed it was drop shipped right from them.

Anyways with lots of help and anger I am going to make it right.

[Chryco Psycho]

This is so cool , I like the screw adjustment feature  this will put u between springs fa more adjustability .
 Sounds like someone was out to lunch assy your carb work through the issues & you will get it & learn lots .
 jet bleeds will change things but if it goes rich & clears up the bleeds will not help