BACKFIRING AND POPPING OUT CARBS AND EXHUAST (4age)

[blair]

Car has been sitting at mechinics for ages now trying to figure out why:

it backfires after reving

and keeps popping at idle

out the carbs and out the exhuast.

(RICH PETROL SMELL)

engine: 4age rwd
carbs: twin 40mm webbers with redline linkages


all theyve replaced is bearings and headgasket
because i killed the engine somehow (turned out hg blew around the head gasket)

am 80%sure it wasnt doing this before...
if it was it was no where near to this extent (can't even drive the car cause it catches on fire)

I'm 99% POSITIVE IT CANNOT BE BECAUSE TO MUCH FUEL IS BEING FED ANYWHERE (wheres the spark come from!!)
we have put a 2psi regulator on a 7psi pump to make sure it isnt to mcuh pressure

If you advance the ignition timing to the max it sort of runs almost ok but idles ^3k = not the problem?

ive done some research on the net... every forum/article i find says it cannot be to much pressure
its either valve timing or ignition timing or both my floats are fucked?
or there is vapor and the hot barrel is igninting it or something... but that doesnt explain zorst flames so no.
only other thing that will do it is if its running lean...
which it definitely isnt? (7psi is way to much for carbs aparently)


please please please suggest thigns to try!

blair. :(

[Patto]

<div class='quotetop'>QUOTE (Blair @ Jun 18 2008, 05:53 PM) <{POST_SNAPBACK}> (index.php?act=findpost&pid=548280)</div>
Car has been sitting at mechinics for ages now trying to figure out why:

it backfires after reving

and keeps popping at idle

out the carbs and out the exhuast.

(RICH PETROL SMELL)

engine: 4age rwd
carbs: twin 40mm webbers with redline linkages


all theyve replaced is bearings and headgasket
because i killed the engine somehow (turned out hg blew around the head gasket)

am 80%sure it wasnt doing this before...
if it was it was no where near to this extent (can't even drive the car cause it catches on fire)

I'm 99% POSITIVE IT CANNOT BE BECAUSE TO MUCH FUEL IS BEING FED ANYWHERE (wheres the spark come from!!)
we have put a 2psi regulator on a 7psi pump to make sure it isnt to mcuh pressure

If you advance the ignition timing to the max it sort of runs almost ok but idles ^3k = not the problem?

ive done some research on the net... every forum/article i find says it cannot be to much pressure
its either valve timing or ignition timing or both my floats are fucked?
or there is vapor and the hot barrel is igninting it or something... but that doesnt explain zorst flames so no.
only other thing that will do it is if its running lean...
which it definitely isnt? (7psi is way to much for carbs aparently)


please please please suggest thigns to try!

blair. :([/b]


mine always popped after revving
i suggest a timing issue pre igniting fuel and backfiring out the carbs
what kind of ignition is it running ?
mine had a scorcher vacuum advance dizzy and only backfired when severely retarded

[takushi]

yeh could be spark...spark leads on the wrong cylinders

would explain why the explosion comes out the carb..

[ke kid]

Popping/backfiring out the carbie(s) generally points to a lean mixture which usually means a vacuum leak somewhere. Double check all your vac lines are either going to where theyre supposed to go or theyre blocked off. If thats not the case, check the gaskets for leaks by starting the car and pouring water over the inlet manifold/carby bases. If it starts to drop revs, then you have a gasket leak.

Good luck.

[Jonny Rochester]

It sounds like you have to check everything tune related again, back to basics. This would be my fairly complete list of things to check (on any car) in order.

1. Timing belt, get all marks lined up, check belt tension.
2. Take the spark plugs out and do a compression test.
3. Make sure piston is at the top when crank mark is at 0.
4. Make sure rotor button is pointing to No1 when crank mark is at 10. Check point or air gap in lined up also.
5. check rotation of dizzy and fireing order, 1342.
6. Crank motor and check you got spark. Check leads and put good spark plugs in.
7. Take the carbies off. Check accelerator squirting jets, open the throttles with carbie off the car, with petrol in it.
8. Check venturis are secure and not loose. Note the sizes. Also check throttle shaft is not twisted.
9. Bolt carbies on, make sure they seal on the manifold, and no air leaks anywhere. Block all vacuum hoses. Don't use silicone. Only rubber, or paper gaskets. I like ThreeBond rubber gasket glue. Cardbourd and Permatex No.3 also works.
10. A balance tube works best, but not needed.
11. Make sure all jets are screwed in and note the size
12. Start fuel pump up and check the fuel level in the carbies. May need to remove a jet holder to do this. The fuel level is critical.

The rest is selecting the right jets and doing tricks with screwdrivers. It would be way easier if you had a air/fuel ratio sensor.

[blair]

cheers for all your thoughts folks...
they are pretty much parrallel to mine :)

most of the things it could be
it bloody well shouldnt be
because the only thing changed was head gasket and bearings...

if somethings fucked then its the mechanics fault?

[gg004]

i used to have a AE86 with 4AG on 45mm webbers and it seemed to be always going out of tune. they are quite dificult at times. mine did what your desribing when the carbs went out of tune. follow the list johnny mention above and then get carbs propelry tuned.

[samc]

thats the problem with carbies^^. if you own them you have to know how to tune them because they constantly need a fine tuning, otherwise you're always going to be going to a carbie tuner.

[gg004]

exactly. thats why i ended up selling that 86 with the webbers, got sick of always working on it

[blair]

woohoo

it was the timing...

sortof

no flames yay!

[samc]

how many times did i say that lol!

[slydar]

dizzy was a tooth out ;)

[deleta]

actually what happened was, the balancer had spun on the balancer in a previous life, so we had to find the tru top dead center, and then it asked for a shit load of timing, but its still not wright, still does the big back fires out the exhaust on back off.

[blair]

:(

[slydar]

ahh yeah. happens heaps. balancers and timing gears arent that expensive. ant has a couple of the gears in stock usually, as well as some 2nd hand balancers.

[samc]

ahhh i see. shit ay

[blair]

wait huh?

meaning i need new one(s)??

lost.

[slydar]

i read deleta's post as the balancer slipped on the crank? rather than balancer, was just guessing it was a typo. as in sheered the keyway, so the balancer and/or cam gear has moved in relation to where it should be.

[blair]

not sure ay...

will get onto em

[deleta]

as in sheered the key way, but has been repaired already, but when they did the repair they did not mark tdc. will be having another crack at it today after talking to clemo, see how we go fingers crossed