urquhartglen

please help anyone. i have a 1978 rx7 s1. i rebuilt a tall port 12a. new housings and seals etc. carbon apex. it is extand port primary and bridgeport on the secondarys. running points dizzy and factory tall port inlet manifold. the nikki carb is off a 6port cosmo 12a that been jetted to suit with venturis at 20.6mm etc etc. it idles at 1800rpm and revs nice to about 5500 when secondarys open (mecanal) then is starts missing (like having fouled plugs) i hav reset timing, tryed new plugs, point gap is .018" im running std fuel pump thats flowing 1.5 liters a min. do i have a elec prop or fuel? if it lack of fuel do they miss (badly) or do they just go flat? oh and engine got 100psi hot or cold

Aaron Cake

iTrader: (1)

Lack of fuel can cause missing quite easily, as can way too much fuel. Are you getting black smoke?

At the very least, I would recommend upgrading to the newer electronic dizzy. The points suck.

I'm not a carb expert but it sounds like you may be drowning the engine is fuel if it starts missing as soon as the secondaries open.

urquhartglen

ive tryed leaning it out eg working my way back to std jetting and tryed larger jetting didnt change were my miss starts. did a peak voltage test on it yesterday got 30.000volts at coil leads and 25,000volts at plug leads when cranking and 10,000volts at sparkplug when running. coils tested fine had 1.3ohms and ballast restors had 1.4ohm thats what its ment to have. put 12v strigaht to coils and rechecked peak voltage no change. when rechecking my timing tho (points dizzy) got no vaclum advance on it and i set timing to 8deg at 1100rpm and then gave it a rev trailing mark moves to bot 18deg and the leading mark moves to about 22deg and then at 4000ish rev when i get miss the timing mark fu#ks off on me. should i lock the weights in dizzy? or any ideas what elec prob would it b to make timing change like that. eg my 20deg timing mark just disappars unsure if it advancing or retarding to fast to tell and cant see it. sort of like it goes 180deg out?

Aaron Cake

iTrader: (1)

You're out of my realm of knowledge with the points dizzy. That stuff is far too old for me to bother with it. Though it makes complete sense that you timing mark is disappearing when you rev the engine because of the mechanical advance. When the engine is missing, it will be misfiring quite badly which will make the timing mark very hard to see.

urquhartglen

had it in at shop and they bored out and jetted my carb. set up holley pump and reg. rebuilt points dizzy and timied up etc and nothing changed. they said i have a elec prob? i applyed 12v to coils and bypassed key etc did not change. can you get the rotas 1 tooth out during rebuild?

Aaron Cake

iTrader: (1)

If you are referring to engine rotors, they can only be installed correctly.

The dizzy of course is easy to stab on the wrong tooth.

urquhartglen

thanks. dizzy isnt a tooth out. (was but not now) mayb its my secondary port size or overlap etc? doesnt matter if u stap secondarys at 3000rpm or 6000rpm. still miss the same. engine did the same thing when i bought the car 8months ago with std 6port 12a in it. i put in new plugs and it went well for 3000kms untill i put this engine in. then its got same miss back again

urquhartglen

and the endine rotas can only be fitted right? no way rear rota could b a tooth out without hitting rotor housing?

urquhartglen

i have a 12a secondary bridgeport. centre plate large street port and end plates large street port (we call street port, extand port) and end plates bridge ported aswell (secondary bridgeport). been to rotary workshop and had nikki carb bored out and jetted to suit. had holley red fuel pump and reg fitted. running points dizzy that they rebuilt with all new parts eg rota,points,cap,leads etc. new sparkplugs and they set timing up etc. only running mac advance no vaclum. engine done 1037km on complete rebuild eg new housings all seals (carbon apex) bearings etc. plates were milled and i lapped them and assbled engine. exhaust ports were ported by rota shop. engine is smokey round town but clears up on open road untill you slow down and vaclum is high eg round town or idling. then get a blue haze out back give it a rev and it clears then starts to build up again.???? maybe sucking oil past oil seals at idle as they havnt beded into new plates? they were tallport 12a r5 plates. anyway, as soon as you hit secondarys at any revs eg 3000 to 6500rpm it misses badly and wont rev through it(like having fouled plugs) will rev out to 6500 on primarys no prob. eng got 100psi comp and i tryed 12v to coils from battery to buypass my wiring loom and it didnt help. any ideas. do you think my ports to large or 2 much over lap on secondarys?? could it be crook coils. ohm test was ok 1.3ohm. when i bought car with std 12a 6port init it was doing same thing so i put new plugs in and it didnt miss a beat untill i built new engine and miss came back and i cant get rid of it.
have tryed 3 carbs with diffrent sent ups etc. mixture checked on dyno the best they could and its not lean or rich. help me please