13b misfire (with video)
 

hey guys, i've had a string of problems with my car recently (rx4 powered series 1 rx7), here's the rundown

car started misfiring really badly, and eventually crapped out on me on the side of the road. i pulled the plugs when i got it home, and found the ceramic core falling out the back of one of them. ok, i said, that must be the problem. replaced it, no change! the car would start but i had to pump the gas to keep it idling, and it wouldnt rev

so i moved up the chain and checked the distributor cap. found corrosion all over the contacts. ok, i thought, thats why replacing that plug made no difference. the contacts were eroded anyway, so i replaced the cap and rotor. still exactly the same problems

ok, i thought, i must have a bad coil then. so i swapped some coils over. still no change. then i got grumpy and came on here to complain. its a first gen so has the separate ignitors, but i havent had a play with them, other than to measure resistances between various points and found them to be identical (no concrete proof either way, but at least there's not a massive short in one or something)

the car starts just fine, it's got OK vacuum, fuel level in the front and rear glasses is fine (nikki carb), and ive recently replaced the fuel filter.

the only way to stop it from crapping out is to pulse the throttle at about 10%... any less than that, it dies. any more than that, it misfires and dies. for the first 3/4 of the video it's just me pulsing the throttle. at the end, i give it a fraction more gas, the revs try to rise to about 2000 but the engine misses like crazy. im starting to wonder if i've got a blocked jet, and by pulsing the throttle im runnning it on the accelerator pump alone, but i dont think i'm moving the pedal enough to make the pump work.


thoughts?

Did your timing possibly slip? You might try dead-setting it to TDC and re-stabbing the dizzy.

also, check you vac advance linkages & mech advance assembly in the dizzy, & make sure neither is stuck. If you had corrosion problems in the dizzy it may be stuck advancing the ignition too far.

Sounded like one rotor to me, but revs on both ok on the accel pump. Check carb jets.

dizzy advance is free, i've just reset the timing (20 BTDC - although i've got aftermarket pulleys, so perhaps the timing marks arent perfect?) spark checked the leads, everything is good on that front

i guess i'll pull the jets out (again) and have a look at whats going on. have had some issues with fuel contamination in the past, perhaps something made it past the filter

just a random thing i never got around to asking - the ports for the OMP that protrude into the carb, does anyone have the clearance between them and the venturi? mine were loose when i got the carb, i need them close enough to the venturi that they can suck the oil up, but i was wondering if there's an official distance out there somewhere? havent found anything in the books...

SOLVED

im not sure how, haha

i pulled the jets and needles, they all *looked* ok, gave them a blowout anyway

the rear fuel level was always a little bit low, and i figured that every time the car has given me trouble, its been while going up a hill. so i adjusted the float level, chucked it all back together, and she fired up like nothing was ever wrong! celebratory burnout!

thanks for the ideas guys

argh, nope not solved. the car was just lulling me into a false sense of security so it could strand my sorry ass on the side of a busy road. managed to limp it back. here's the latest;

the car starts and revs up fine out of gear. i take it onto the road (down a hill) and it goes just fine. turn into a side street and give it a bit of snot, still going fine. turn around to head back, the car is pretty much up to operating temp now, suddenly it bucks at 3000rpm and starts missing. cant hold idle. will clear up half a second later, and will behave if i keep the revs below about 3000. try and crawl it up the hill to get home, im getting alternating surges of power and misfiring, about 2 surges per second.

get it home and fire it up again, revs like nothing was ever wrong. so basically its still breaking down under load/heat?

im wanting to check my timing again, not too sure about the setup i've got here. the aftermarket pulley markings i've highlighted in yellow, contrasted with the approx. positions of the factory markings (from a 12a pulley) in red.

Attachment 672505

im a bit shaky on the timing marks? i think the leading plug should fire on TDC, the trailing at 20 ATDC, but what's that third mark for then? at the moment, my leading plug is firing on the right hand most mark, and advancing further to the right (as i guess it should) and the trailing plug is firing on the center mark.. i actually forgot to check if it's advancing :/

alternatively, i suppose it could still be that rear fuel bowl, the fuel level is sitting about 1mm below the centre of the sightglass. going up a hill could dip the fuel level below the head, and i guess accelerating could cause the fuel to surge away from the needle too :/

i live directly on a busy road, the last two times i've taken this thing out its behaved nicely, then betrayed me as soon as i get beyond walking distance to home... its getting to the point where i'm nervous to drive it