Ok, so as I posted here:
https://www.rx7club.com/1st-generation-specific-1979-1985-18/bundle-carb-questions-609749/
Im running into some questions about modding the AP on my carb.

So far, Ive just sorta winged it as to what I got out of the writeup. I extended the AP arm 1 1/4" and added sevral holes for adjustment. It is also bent slightly for the optimal angle.


I cut out 6 1/32" gasket spacers, put 3 against the AP plate, and tried to bottom out a diaphragm that still had the hard gasketlike material attached. The diaphragm would not move any more than it would without the gaskets. It just isnt flexible enough. I scratched at it a bit and noticed it has a teflonish inner structure, that definately wont strech at all. This made me think that the AP mod is useless except for adding gas it doesnt pump into the carb side and air space on the outter side. pics below:
without gaskets:

with gaskets:

Theres no more throw there which would equate to no more pumping action.

At this point I was sorta disappointed that I had made all this effort. I decided that there must be a way to do it so I tried scraping off the gasket material from the diaphragm. Then I was left with a bit more room to play with. I tried the same thing again, this time I could bottom the diaphragm out in the AP plate, but there is no way I could keep the outside from wrinkling, which may cause a leak.


I tried sandwiching it in the middle of the 6 gaskets, and it seems to look like it would work, as long as the wrinkles flatten out and dont leak.


Now, I feel like although this would probably work, I dont like the creases in the diaphragm, and 3/16" extra throw seems prety overboard.

If I am on the right track and doing everything right with the sketchy stripped diaphragm awesome, if now what the heck do I do???
If we really need all that extra fuel, is it possible to get a larger size pump diaphragm from a holley or something to accomodate the longer throw?

Just seems really weird to expect such a long throw out of the stock diaphragm doesnt it????

 

I was thinking about holley AP diaphragms, so I looked at a few on ebay. This style is offered in 30cc and 50cc. Other than needing to make up a new pushrod, I think this just might work. Im not sure what kind of volume the stock one pushes, but If you need lots of fuel pumping ablility this might be the way to go?

http://cgi.ebay.com/ebaymotors/Holle...ayphotohosting

 

I've had much the same thought regarding Sterlings AP mod. After rebuilding my carb, it seems that limit is the diaphragm itself, rather than the amound of room in the housing. Also, increasing the length of the AP arm would seem to actualy reduce the stroke of the pushrod so that the whole mod basically spreads the same amount of fuel over a greater motion of the throttle shaft. Of course I really don't have nearly the amount of knoledge about this Sterling does so I'd love to hear his thoughts on this. The Holloy diaphragm might be a good idea if it fits the housing and has greater flexability.

 

I seem to remember Sterling mentioning that the stock diaphram should be able to flex enough to do the trick. I wonder if you have an aftermarket part, maybe someone performed a rebuild on this carb in the past?

Mine came with the mod already done by Sterling, and it works great. Haven't tried to do it myself though...

 

i just cut my spring in half... it seemed to work car "felt faster" and got worse gas mileage so it must've been working!!

 

The coating on the mesh center of the ap diaphram is what seals out the fuel. If the coating is gone, or even has small tears, the ap leaks out of the slot for the lever.

 

Yah, I realize this. The only reason I scraped off the coating and mentioned it is because what I took from the AP mod writeup is that the original diaphragm will displace more fuel with a larger pumping chamber, which I cant see to be true due to the fact that the diaphram seems to use all its flexible range in the stock application.

As Dogbox and I said above, the pumping ability seems to be limited by the diaphragm, not the pumping chamber size.
I simply scraped off the coating to confirm my theory that the diaphragm wont strech out anymore.

If you are talking about the last 2 pictures I posted, I didnt scrape any of the coating off that diaphragm, just the solid gasketlike part to show how much strechier it would need to be to have the extra travel.

 

I find it unusual that no one else has noticed the AP issue.

Has anyone else actually modded their own AP, or is sterling the only one to have done it successfully???

 

The diaphragm needs to be new. If you work it back and forth, it will stretch a bit (like your photos illustrate).
The whole point is to be able to still deliver a shot of fuel while the secondaries are being opened. The gasket spacers need to be equal on both sides. I used to use a quarter as a template for the hole. A paper punch works well for the screw holes. I use 1/8 thick rubber for the gaskets (1 on each side)Longer screws are needed.
The hole(s) in the AP arm extention need to be elongated so that the AP adjustable rod doesn't bind.


I dunno WTF's up with this forum, but my IE6 is acting all screwy.

 

Forum's working fine. It's just you Sterling... Maybe you should mod IE6 for better flow too, eh?

 

Ok, so a new diaphragm it is!!!

I checked the maximum angle of the AP arm, and the holes I drilled dont seem to be a problem. I will double check once everything is installed but I have a feeling what Ive got will be just fine.

When I get the new diaphragm, do I have to really push on it to get it to strech?? I know I am dealing with tough old diaphragms right now, but 1/8" strech is easily acheivable???

Also, is there anything I can do to check if the diaphragm has enough throw once Ive streched it?


Thank you so much Sterling, I really appreciate the help!
I hope one day to let you do the tweaking for me, but I just dont have the $$ to dish out just yet.. haha