Geez these carbs are giving you grief!

Fat leads are good when you have a pretty decent spark/ignition system, I'm not sure if they'll bring any good (more than standard leads) on a mild spark system.

Firstly I'd get your timing spot on, even some over adjusted rocker arms will affect your engine especially when there are other issues like poor spark or irregular spark.

Secondly I would begin to have a really good look at the second carb, if they are missing the little ball-bearings that serve as valves for the accelerator pump circuit this could contribute to a poor running engine.

It might also pay to check that the progressions holes are okay and not damaged, check the throttle valves that they are closing properly.

Sometimes when the idle mixture screws are seated too hard they will damage the hole which they regulate from meaning they'll deliver more or less fuel depending on how the damage is (if the seat is stuffed you'll need a whole new carb or body).

Check the needles of the idle mixture screws, it would pay to grab some good ones of a sigma or colt or magna (they run a downdraft Mikuni but share parts) just to try out.

Popping from the exhaust is unburnt fuel igniting outside of the cylinder/chamber, so I would be looking at the valve timing.

Popping and puffing from the carb is normally associated with a lean mixture, in this instance it's obvious this isn't the case because of the sooty plugs. You mgiht have to have a muck around with the aformentioned suggestions.

Finally check the spark plug (gaps and condition) and dizzie points (or are you running electric ign?)

I think you've got a dud carb, do you have a spare you can use?

To isolate the problem with minimal trial and error, swap the carbs over to see if the problem stays with those two back cylinders. If the problem persists on those two cylinders then you know it's probably ignition and or timing or maybe even poorly seated valves (might pay to do a compression/leak-down test too to see what's going on).

ok thanks chris ,ill pull the second carb hat off and check the ball is in there and moving

the rockers are good ,i adjusted them the day before it went to get tuned ,same goes with the timing ,its set too

wouldnt hurt to recheck !

ok progression holes are all clean ,and i checked the thottle valves when i had the carbs off last week

i wound the throttle stop screw out and then made sure it didnt touch the little arm ,so i then tilted the carb back and pushed on the throttle pump with fuel in the bowl
then i watched to see if it seeped out of the bottom of each valve evenly ,which it did

i then flipped the carby and retested it ,same result ,all good

i also scrubbed the progression holes with a tooth brush and thinners ,then i used a clean rag to get the thinners and crud off

and yes another idea was to buy brand new idle screws ,just to make sure the screws are good ,also i checked the holes and they are unmarked ,and my screws have been reprofiled to match each other

oh and

"Popping and puffing from the carb is normally associated with a lean mixture, in this instance it's obvious this isn't the case because of the sooty plugs. You mgiht have to have a muck around with the aformentioned suggestions"

i see what you mean but its only # 3 that pops ,and when i restrict the air flow it stops popping ,so i think its lean ,but i am going to try turning the pilots screw out till it stops ,otherwise it has to be another issue you mentioned

i had brand new bp5es plugs in it when i took it to get tuned ,then when i got it back tim had put bp4es plugs in ,are they hotter plugs ? or should i be running bp4es plugs ?

i still havent checked the pionts ,but ive cleaned the rotor button and the inside of the cap too

i was thinking of ringing recarb and buying an s4 carb mostly complete and building a good one out of 2

or save my pennys and buy 2 brand new s4s for $1000 then put my jets in them and start with all new carbys :D !! sounds good!


but then what if the carbs are ok and its the motor thats the problem ,will #3 pop if its low on comp ? cos if it does i should be able to put a larger pilot just to get it to stop popping !!

thanks chris ,i realy appreciate your help but i should of taken you up on your offer !!

ok so i bought a set of plug leads yesterday ,they are 8mm top gun leads but im not keeping em for long cos i realy wanted 13mm leads but they didnt have any ,so they are gonna get them in for me

when i went in and got them ,i gave them my old leads and then they gave me the new leads ,i checked 2 of them and they wee top guns
then when i got home i realised they gave me 3 top gun leads and 2 cheapo leads that were the same colour but were realy flexable and cost $3 each instead of 5 for top guns

so i took them back and the guy said ,no there all the same ,there just leads ,i then asked for them to be replced with top guns and ,he said

" its only a datsun ,it doesnt need special leads" ! wtf ,steriotyping datsuns !!!

so after a while of arguing ,i got what i paid for ,i paid for top gun leads ($5ea) and i got a couple of leads that were $3 budget leads

anyways ,im going to recheck everything tomorrow and then see if it stops popping out thexhaust and the carbs ,if it doesnt fix it im going to go with it being the motor ,there isnt anything wrong with the carbs

what ever i do it doesnt improve ,so it has to be the part im not adjusting ! ,plus if number 3 cylinder is low on comp it wont burn the same amount of fuel the other cylinders do ,so it will get sent out the exhaust and then burnt !

hoping to get it even a little better ,i can put up with abit ,but all the time at idle is just annoying !

cheers

$5 Man thats a bargan, 8mm would be well and truely up to the job. Can see the % markup with the auto stores on plug leads.

haha

for sale one set brand new plug leads

"race spec" fully race spec ,high performance leads topgun ,blue

$100 ono hehehe

and that wasnt even on account
i will probly get a price from auto one in mandurah cos i get 20% off there ,so i can get leads and stuff even cheaper there ! anyone want them let me know (sorry guys perth only )

ok so tonight i did the pionts ,cleaned them up with a pionts file then reset them to within the factory settings

put my new leads on ,runs a little better ,but then pops and spits again

could it be possible that the cam has over lap and is causing the popping ?

and will it running rich make it pop ,with everything else right ?

ok im pretty sure cylinder 3 is to blame for everything ,cos it was low on comp and that will make it have less vacume and make it harder for the fuel to be drawn in

so if i was to put rings in it ,would it maybe fix the problem ?

or could i adjust the carbys to stop the lean pops and unburnt fuel ?

heeellllllppppp ,anyone !

im thinking of drilling my main air jets out to 180-190 and then it will have more air ,so less unburnt fuel :D and then the popping at idle ,well i was going to just keep unscrewing the pilot screw till it stops popping ,then put filters on to shut any popping up abit :S just for the show :D

still need to check the tappets though ,once thats done i can confirm its either drop in comp or carbys

so far ive got 3 of the 4 Cs

Comp (on 3 cylinders haha)
Cam
Carbys


still need capacity though :(

when i get time to pick my a15 up ill have all of the Cs !

Hey Estyre,
If your donk is low on compression (particularly on one cylinder) and popping and backfiring a bit then there's half a chance you may have a burnt valve.
The best way to check if a compression problem is rings or valves is to do a "dry" and a "wet" compression test.
For the dry test, just do it as normal. For the wet test, do it straight after the dry test but put enough oil in the cylinder that it will cover the top of the piston and spill over onto the top piston ring so it creates a "seal". I dunno what the top of your pistons is like but if they're concaved then it's a fair bit of oil! If the reading is considerably higher on the wet test then you have a worn rings issue. If the compression doesn't change much then the likelihood is that your valves are gone in that cylinder.
It's worth trying in my opinion. If that fails, inject the fu#$en thing!!!

yea thanks shoota ,i have done that test

i did it and it came up from 110psi to 170psi :O so its probly got stuffed rings on that cylinder

yet the other cylinders were all at 145 -150 psi ,so theyre all pretty matched(apart from cyl #3 which is low) and the 3 good cylinders should be jetted the same ,where as the # 3 will acts differently and makes a popping note out the exhaust and inlet (of #3) at low revs :(

also today ,i found out i cant drill my main air jets out ,cos the jet drills dont go up to that size :(

im saving for an 02 sensor kit ,then i can tune it perfectly :D and ill then know if its lean ,rich or perfect !

bunnings have a drill set in the craft tools section .5 - 2.2 in increments of .2 or something,they are a bit cheap but good for correctors as they fit in a cordless chuck.are u still on the 98 gear?