Outer Limits 4x4 Board

does any one know how to tune a carby on a 1990 sierra (1324cc) mines running really shitty wont idle properly

Might be a stupid question but have you put a tuneup kit thru it. I overhauled mine making sure to clean and blow out all drillings really well and now it runs like a dream.

To clean the carb (roughly/quickly)
1. switch spark plug leads 2 and 3
2. then start the car
3. let it cough and spluters a bit then kill the motor
4. put the leads back to norm and it might be ok

Note this is a quick fix which I have seen work heaps of times but it is a quick fix and your carb probly needs a proper clean.

SLOWLJ wrote:To clean the carb (roughly/quickly)
1. switch spark plug leads 2 and 3
2. then start the car
3. let it cough and spluters a bit then kill the motor
4. put the leads back to norm and it might be ok

Note this is a quick fix which I have seen work heaps of times but it is a quick fix and your carb probly needs a proper clean.

so what does this do exactly and how/why does it work? might help me work out if my carby needs an overhaul...

makes it backfire an blows the carby out
but it gets sucked back up again

just get some carby cleaner an run through it mine seems to idle good an that is all i use

SLOWLJ wrote:To clean the carb (roughly/quickly)
1. switch spark plug leads 2 and 3
2. then start the car
3. let it cough and spluters a bit then kill the motor
4. put the leads back to norm and it might be ok

Note this is a quick fix which I have seen work heaps of times but it is a quick fix and your carb probly needs a proper clean.

Like red zook said it backfires up through the intake but it is recommended you should only do this with wide open throttle, as it can cause damage to the carby with no where for the flame to get past the throttle plate.

that may well clean it but how do you tune it? What adjustable screws do what ? Which is fuel mixture ,which is idle screw and which is choke adjuster? and how do these effect the running of engine.

What mine is doing is : It runs ok if the revs are up a bit but when it tries to drop to normal idle it stal;ls or runs rough. Any ideas?

I would start with a good service, Plugs, leads, rotor button, dizzy cap, do the timing and get some carby cleaner (the stuff in the pressure pack that you spray in the carby whilst the engine is running) not that shit you put in the tank. Do the timing and then look at adjustments to the carby if this doesnt fix it.

Or have you already done the rest?????????

Have ya checked the vacum lines running to and from the manifold and carby, if there is a vacum leak then idle and low rev will suck and probably stall. mine was doing it today, was a loose vacum line on manifold. worth a check anyway
layto....

grey zook wrote:that may well clean it but how do you tune it? What adjustable screws do what ? Which is fuel mixture ,which is idle screw and which is choke adjuster? and how do these effect the running of engine.

What mine is doing is : It runs ok if the revs are up a bit but when it tries to drop to normal idle it stal;ls or runs rough. Any ideas?

Yeah check for vacuum leaks, easiest wayhold your hand close to the throat of the carby and spray some fuel or any other flammable additive around the manifold and base of carby, the engine will rev up slightly if you spray fuel near a leak so look closely in that vacinity for a broken hose or something.

As for tuning the mixture screw is at the base of the carby on the side closest to the rocker cover. it will most probably have an anti tampering lid on the screw if you know what your doing you can pry this off and have a bit of a fiddle. The idle speed screw is near the throttle shaft (where the throttle cable hooks on) screw it clockwise to increase throttle, scrrew it anticlockwise to decrease. But be careful these carbys are pretty tempremental and can be hard to idle correctly. Hope this helps

my carby dosent have an idle adjustment screw

and i think one time when i took it right apart to give it a clean out i put one of the spring loaded things for the choke on backwards so now when it is cold it idles at bout 300 rpm and when it warms up its at bout 650-700 rpm

but i cant be farked messin with it cos it runs bitchen'
and i dont want to stuff it up

just thought id share

grey zook wrote:that may well clean it but how do you tune it? What adjustable screws do what ? Which is fuel mixture ,which is idle screw and which is choke adjuster? and how do these effect the running of engine.

What mine is doing is : It runs ok if the revs are up a bit but when it tries to drop to normal idle it stal;ls or runs rough. Any ideas?

This was happening to my car when I first bought it, it was really irregular and would stall as soon as I clutched in with the accelerator off. I put the car in for a tuneup and was told the carby needed reconditioning. runs sweet now. cost $750 all up but I got ripped off real bad.

have been told a carby of a 1.6 vit will bolt straight on and are a much better and easier carby to tune and that they give you about 20% more power. I think i will do this and let youz know what its like.

1300 carbys are preset, no tuning is possible, just the idle and
cold idle and choke triggers are adjustable...A common problem with
1.3 carbs is dirt etc in fuel, idle jet is rather small, and blocks
up easily. Another common prob is that the auto choke plays up, they
are controlled by the temp of the rad water running through them,
and this blocks up sometimes..A quick blow through usually unblocks
them. Also if fuel pump is very old, its diaphragm can drop bits off
that get into carby. It is advisable to run a 2nd filter between
pump and carb.
The fuel tanks should be drained and cleaned if they are dirty or
rusty, that can cause blockage. Some have drain plugs, some dont.
A carby rebuild is probably best, a minor carby rebuild kit cost me
about $40, but after that, make sure rest of fuel system is clean
and functioning, or it will just block up again.
Some people rev engine hard, then back off with hand over air
intake, a bit risky to hands, but can fix temporarily, as it sux out
the junk. some people put lager jets in for idle, but I know nothing
of that?
1300 carbs are good, but only when everything is perfect, or they
play up, usually on idle..
Something I was told today, is ultra 95 octane and/or 98 octane
unleaded contains benzol which can block up smaller jets, like
bikes and maybe zooks? Am testing this theory on my bad idle, as it
only started from day I put 98oct in.
Change over reco carb is worth the effort, but at $200plus, make
sure its needed, and rest of system is clean, too. christover

only some types of 1600 carbs are convertable, not sure which ones...my belief is they only appear better, because they are usually much newer and havent had the off road dirt life as often as old sierras have...just a thought, have no evidence to back it up ...christover