carb adjustment problem

[spyghost]

Hi,

I am having a hard time finding the right adjustment for my carburetor. It is the stock carb of a 4G15A engine - variable venturi piston type carb (single jet).

please take note that i have a new set of spark plugs, air/fuel filters. distributor is in good condition, new oil, just finished right timing. i just had my carb rebuilt (cleaned). all measurements are correct. no leaks in any part, new gaskets, float bowl is correct height. all vacuum hoses are new as well.

di ko lang talaga makapa ang proper adjustment ng main jet saka a/f mixture screws.

I was able to get a good run last week, but after some time, I found my car stumbling hanggang sa mamatay makina. ang hirap iistart ulit. me-crank pero parang walang pumapasok na mixture sa cylinders. ang tunog nya e starter motor lang. parang hindi tumutuloy ang takbo. hanggang sa umandar din. at this point during idling, untiunti bumamaba ang rev na kahit WOT ako 1,500 lang ang naaabot.

another incident is while i am running (rekta na), e kakadyot ang andar. kelangan ko bombahin ang accelerator para tumaas ang rev. same case, up to 1500 lang ang WOT. pag natsambahan ng bomba, e aandar naman ng ayos ang makina.

i am worrying kasi, baka pag kasama ko ang baby ko e magkaproblema ako, kawawa naman ang bata.

i am looking at three possible things:
- lack of gas
- lack of air
- lack of a/f mixture

ano kaya itong na-experience ko na ito? nakakabaliw. i know there is a solution, kasi bago ako magbaklas e maayos naman. i just need guidance in the main jet screw and a/f mixture screw.

[youngrider]

SPARK - Ok/?

VACUMM- OK/?

CARBURETOR-OK/?

FUEL PUMP-?????

[spyghost]

SPARK - Ok/?

VACUMM- OK/?

CARBURETOR-OK/?

FUEL PUMP-?????

fuel pump is ok... i tried cranking with the hose detached. dami gas na lumalabas.

[youngrider]

Have you dismantled your carburetor, I knew someone who unknowingly lost a small 'bolitas' that somehow regulate fuel flow in his nissan sentra carburetor.

Actually yung mekaniko ang nakawala, hayun katakot-takot na problema ang resulta. Hanggang ngayon palyado pa rin, kung saang galing na bolitas ang ipinalit wala raw makitang original.

Anyway double check for spark, vacumm leaks, and carburation. This link may help you: http://www.aa1car.com/library/carburetor.htm

[spyghost]

yes, i dismantled my carburetor, but i didn't loose any part down to the smallest part.

the bulitas in my carb is actually for the accelerator pump, which functions only when you suddenly press the accelerator pedal or sudden WOT.

how can i determine if it is a vacuum leak? i also changed all the vacuum hoses. i used the replacement hoses. those 1/4" sold in auto supplies.

[reym]

Hi,

Can you simulate the hardstarting condition? If the car starts very hard then on the time it is is hard starting, disassemble the the carb or try draining it to see if there is some fuel in the carb. If there is not enough fuel in in, remove the line that is going to the carb and crank the engine again, if there is fuel, your carb's filter is clogged , if not, your fuel filter might be the culprit.

I had an intermittent carb blockage before, I solved it by 1. cleaning the tank,
replacing the filter and overhauling the carb.
turns out that a portion of the tank was chipped and is blocking the line.

[spyghost]

That's a nice idea, to pull out the carb again once I stall; however, I can't simulate it. The occurence is random.

The hard starting only occured once. I was idling, aircon on, hazard on because I was waiting.

The jerking (kadyot) happened thrice the next day. My wife and I were on our way to the grocery, when the car just jerked while running between 40-60. The second was while we were waiting for our turn to go (stoplight). The third was while I was looking for a parking slot.

Today, it didn't happen. I am really wondering what is going on inside my carb. I don't know tomorrow.

[quest_uy]

That's a nice idea, to pull out the carb again once I stall; however, I can't simulate it. The occurence is random.

The hard starting only occured once. I was idling, aircon on, hazard on because I was waiting.

The jerking (kadyot) happened thrice the next day. My wife and I were on our way to the grocery, when the car just jerked while running between 40-60. The second was while we were waiting for our turn to go (stoplight). The third was while I was looking for a parking slot.

Today, it didn't happen. I am really wondering what is going on inside my carb. I don't know tomorrow.

hmm... i'm not sure ah ako dati ganun rin.. try mo palit spark plug then check mo kung ok...

[eyshmechanic]

That's a nice idea, to pull out the carb again once I stall; however, I can't simulate it. The occurence is random.

The hard starting only occured once. I was idling, aircon on, hazard on because I was waiting.

The jerking (kadyot) happened thrice the next day. My wife and I were on our way to the grocery, when the car just jerked while running between 40-60. The second was while we were waiting for our turn to go (stoplight). The third was while I was looking for a parking slot.

Today, it didn't happen. I am really wondering what is going on inside my carb. I don't know tomorrow.

jerking is caused also of misfiring, pwedeng one of the spark plugs misfired.

[yapoy86]

one possible cause of electrical problem...

try changing your distributor cap and ROTOR... i had the same experience of intermittent problem sa nissan vannete.. parang kulang sa power at nag jerk.. yun pala basag na yung rotor causing the high voltage leak.. also have your timing checked...baka nawawala sa timing yung engine mo

[daimaoh]

kung electrical and the timing, sparkplugs & distributor cap is ok, try checking the high tension wires.

kung mababa idling, fiddle with the a/f mixture screws. taas mo yung setting ng fuel screw then timpla mo from there along with the air screw. gradually decrease it and get a feel of your "normal" idling. minsan trial & error before you get the right feel. you may have to drive it to get the feel.

recently, sinisinok din sentra ko. linis carb & sparkplugs then adjust idling lang. ayos na sya.

[spyghost]

just an update to this thread...

it seems ok na ang starting ko... i really checked on the distributor cap with a lens under a very bright light. ayun... me parang gummy residue sa loob ng conductor sa cap. hindi sya pansinin kasi ka-kulay nya yung metal. i used a small grinder to take out the gummy residue (a tool i bought from alexan during my college days :P ). to my surprise, ang laki ng difference sa startup pati takbo. onti lang ang tinanggal ko, just to expose the shniny fresh metal.

now here comes a newer problem... my car sputters at high rpm's. particularly on the 5k+ range. sometimes it does sputter when climbing to 4k rpm. i've traveled from a lean to rich mixture and the car still sputters at that range. one more thing that i notice is when the ac compressor engages, the car also jerks - mas ramdam sya at low speeds.

what else can i look for here? even though driving a high rpm is not really a practice, i can still assess that "there is something else wrong." help would be highly appreciated.