reeceb7

hi, i have a prob with my car, s2 rx7 with 13b large extend port with 48 ida.
it only seems to happen when i have a person in the back seat, it not happen
when i by myself anyway, above about 6000rpm ( third gear, did happen once
in 2nd when doing a skid) it makes popping sound, loud bad sound. i picking it is prob detonation, tho it seems stange to me it only happens with weight in car, fuel system been upgraded it getting enough fuel, and apparantly on dyno
air fuel was around 13.0 all the way up to 7000rpm. i wondering if someone may
be able to help me with what may be causing this? what do i do to fix it?
is it a timing prob?
thanks
reece

bumpstart

13.0 is still a little on the lean side , aim for 12.2 - 12.7 carbed NA
the higher rev nature of the miss indicates more fuel jet volume than air jet mid range response
up two on the fuel jet ( not down on air as your mid range seems fine )

you may also need to gap down slightly ( if gappable plugs ), and double check your air gap in the dizzy reluctor
[ if its a miss, and not a ping, this will help measurably ]

if your dizzy still has mech timing advance, lock it
( or limit the mech, if you know how to regraph )
22 - 25 BTDC is in the ball park for load timing


PS
what choke? what air jets? what emulsion tubes? what fuel jets?

reeceb7

it has 42mm chokes, f11 emulsion tubes, 170 air jet and 220 main fuel jet.
so i may need bigger fuel jet, what size do you suggest? 230? it still has the factory needle and seat or whatever that thing is which i think is 2mm, when i got mechanic to order jets etc he was unable to get me a 3mm needle tho he said the factory one should be fine.
i have ngk br8et plugs with three electrodes, can i close the gap on these?
mech timing advance? i have vacuum advance hooked up to manifold, mayb that
the prob i will search up on how to lock dizzy if you think that will help.
thanks heaps mate

bumpstart

the combo is good, the air jet very lean for cold times

for a very good extend port, or mild bridge, i would suggest 230 / 120 combo
but knowing what you have here, grab some 90, 120, 150 air jets to fiddle your 220 up richer, earlier
if it keeps improving things, try the 230 for fuel

the trick to summer winter variation is to grab a couple of sets of air jets around the numbers you have for minor fidleabilty

the #200 ball/ seat is rubbish, you certainly NEED to find a #300 or custom 3.5mm
you also need ( if you dont have ) a bypass style fuel circuit and reg set to around 4psi
( and a rotary vane pump rated to flow 70 GPH at 4 PSI , as the common 30 GPH cell ones don't quite cut it with a good weber )

the et plugs SUCK, but yes you can close them up
you really should go the plug spanner mod, and the B8/ b9 - EG / EV/ EGV bike plugs, set to between .60 and .70mm
way cheaper, way more sturdy under stress

remove the vac advance, there is no true partial vacuum port for the proper use of vac advance , webers don't need them
the combo of fat acell pump and fixed FULL timing fully negates it for a shittier idle trade

PS
go the DFI mod, using BIM024 modules for dwell shift , and HEC coil combo
definite winner for response, with clean high revs and for cleaning up a bad fuelling act

with these, combos that ran too fat before, come to life, a MUST

reeceb7

thanks bumpstart, lots of good info for me. so i will go the b9egv plug i think, and
get a #300 ball and seat and some different jets. found a good thread on ausrotary about DFI, of which you had alot of input so i will definately be doing that. then i will also lock dizzy if i can figure out how to, and then disconnect vac advance. i have already fitted a holley red pump and holly reg which i set at 4.5 psi, 3/8 fuel line to tank. One last thing i not sure of... by bypass fuel circut do you mean running a fuel return? my reg not allow it but i can do it the carb can i not?

bumpstart

if you search me on aus rotor you will find the definitions of dead head, bypass, and dead head with kick back at carb , and even dual deadhead/ bypass setups for weber carb
with diagrams !


- even dead head regs can be used as bypass regs in some instances
( though they generally have a smaller ball/ seat )

if you have a decent pump, the dead head style will work OK, though it seriously derates and works the pump hard
( if no internal pump bypass )

we need to rule out the bowl level dropping as we hit third gear, especially with anticipated higher fuel usage

reeceb7

thanks bumpstart, i understand that now, i will turn my deadhead reg around and tee off fuel feed to supply the carb and run a return like described in ausrotary threads. will do dfi mod also this week if have time, then sort out the dizzy.
unfortunately i need to rebuild now also , i been having other probs recently the oil in water and starting on one rotor and water spraying out of overflow bottle points to blown water seal dammit.... oh well time for bridgeporting, was always going to rebuild it as a bridgy and now i got reason to rebuild, blessing in disguise mayb!. thanks a heap for your help, with the pointers you given me my new engine will run decent i thinking,
thanks
reece