Hello all,

I have a j-bridge ported engine (much to my dismay) and I've put a RB full exhaust (2into2) and weber 48 IDA on it. The weber is fueled at 3.5 psi by a holley red and regulator. It actually runs okay, but I've been told and can tell that it seems a bit rich. There's an obvious smell of gas and it definitely isn't running to it's full capabilities, seems a bit bogged down when going through the range.

I watched Rototurd's weber tuning video and he states the mix screws should be between 1.5-2.5 turns out of bottom. But I search elsewhere on the rx7club site for weber tuning (https://www.rx7club.com/1st-generati...er-ida-568448/) and it says 3/4 turn MAX.

Currently, I can go to about 1/4 turn and the engine still doesn't fumble when I'm tuning the carb. It only really beings to fumble when I'm almost all the way in and even then I can still turn out just a bit and the engine won't stall.

My questions is, do I need to go leaner on my jets so that I'm further out on the mix screw? Which of the advice above should I follow? And does anyone have suggestions on what jets should be changed below, and to what?

For info, I followed the RB site for jetting.
Venturi - 42mm
fuel jet - No 240
Air Jet - No 170
Emulsion tube F-11
Need valve no 300

PS. Bridgeports are fun, but I realize they don't suit my driving needs. So if anyone wants to engine swap, hit me up!

Thanks!

 

the idle screw thing is kind of a guideline, for two reasons. the first is that most of the adjustment range is in the first turn. the second is that if its all the way out (or all the way in) its telling you you need to change the jetting.

the screw is 2 turns out (or so), there isn't really anything wrong with that, and certainly if you're still tuning its totally fine, but you probably need a richer idle jet. if the screw is all the way in, it probably wants a leaner idle jet.

you can take out the main jet stack, and this will show you what the idle jet does, but roughly its everything under about 25% throttle.

 

Thanks for the good info. Given that I'm almost all the way in and still not getting to a good tuning range, I feel I need leaner Jets. Would you agree?

Which Jets do I change? Go down one step on all? I realize tuning is all about trial and error, but how big should my iterations be?

 

I have tried three different jet setting and my car feels the same with every set I have tried. Do you always need to mess with the timing when tuning a carb? I am new to carb tuning.

 

yep, if you picture a passage, the idle screw literally just screws into the side of it. so when you screw the screw into the passage, it gets smaller, so less air and fuel can go through it.

the idle mixture screw is after the idle jet, so you need to change the idle jet. the main jet is a different circuit, and isn't effected by the idle mixture screw

 

no. timing is adjusted by the distributor. carb tuning has no affect on ignition timing.