Ok, so here it is. I wasn't sure where to put this, so I'll put it here.

We have an '86 rx7 with a 13B that was converted to carb.

The carb is a Weber 45DCOE.

Now, here's the problem. On quick throttle snaps, it bogs and almost stalls until I let go of the throttle. Also, if I build it up slowly, once it gets close to the high end of the powerband (for lack of better word), it bogs and almost stalls until I let go of the throttle, but sometimes it will get past the "flat spot" and go into high throttle. It is almost like it takes a minute for it to level out.

Here's part of the setup that's in it (the numbers i can remember).

170 main jets
210 air jets
65 accelerator pump jets
65f8 idle jets (I think)
And I can't remember the venturis.

When we got it, it had 210 mains and 170 airs, which sounds wrong to me, so I'm not sure any of the other sizes are what they should be.

What I have heard is that the symptoms we're experiencing might be because the accelerator pump jets are way too large, so I'm gonna try some 45's to see if that helps.

What about progression holes?

Any ideas?

 

Correction, I think the idle jets are 65f9

 

Your life will be much easier if you beg, borrow or steal an AF meter. Weber's are great, but their are so many variables, you can get way off in mixture and have difficulty coming back.

 

How big are your venturies.

 

I'll check when I get home. I really forget.

 

Another question.

How should the main jets vs air jets be? I've heard some people say bigger mains smaller airs on a rotary, but everyone else says about 40-50 bigger on the air compared to the main.

 

*posted by ToySport*

Ok, swapped back the 210 mains, 170 airs, and put in 50 accel pump valves. Same problem.

Idle jets are 65f2....Haven't taken it off to see the the venturi size yet.

Maybe a clog somewhere? Something in the progression holes? It'll only go to high rpm if you crack it quick, at which point it momentarily hesitates and then goes. But if you try to ease up the throttle it flat spots pretty quick and then almost stalls until you let go of the throttle.


So here is what it has now:

Main: 210
Air: 170
Idle: 65f2
Accel: 50
Emul: F16

And I will have to check the other stuff in a little bit.

 

large air jets + small main jets will lean out @ top end. I run them a lil rich so I use a minimum 50 increments difference between main and air (ie, 150 air/200 main)

 

Ok, here's what I found out.

45DCOE

Centuri: 45
Choke: 40
Main: 210
Air: 170
Accel pump: 50
Idle: 65f2
Tubes: F16

Engine is 13B NA, heavily ported race engine with turbo internals.

 

How is the fuel pressure holding? With a so-so pump you might get great fuelpressure on idle, but on acceleration pressure drops like a brick.

 

I have a gauge hooked up to it, and it seems to hold steady under all conditions at about 3lb (where I set it). I think the pump is a Holley.

 

So we just did a little test, and when it's coming off idle, it's lean and almost stalls. Like right when it's going over the progression holes. I sprayed fuel in it and with a spray bottle and it picked right up. Idle jets maybe?

 

try a f11 emulsion tube, fuel jets will tune your bottom end, airs will tune your top end. when you snap the throttle open your going lean because air moves faster than fuel. possibly need to up the pump jets. work the bottomn end first.

 

With pump jets at a 65, it was doing the same thing. I have F11 emulsion tubes on order, as well as 65F9 idle jets (it has F2's now). Should be here this week.

Basically as soon as it comes off idle to throttle is when it leans out, but if you give it a quick shot, it'll rev right up.

 

Have you tried increasing your fuel pressure a bit? 3lb sounds a bit low to me, maybe try 4 and see if it makes any difference.

 

Tried it at 4 to begin with and it didn't work, then turned down to 3 to see if that helped, and it still didn't work.