Erratic idling on Sierra

[rogerramjet]

Greetings all

My 1991 1.3L Suzuki Sierra idles for long periods of time at 1500rpm and then at other times it idles at 300rpm. The is no pattern to when it revs 1500 and when it revs 300, its random. The 300rpm seems to be the actual idle set point as I have adjusted the idle set screw right out to try to reduce the revs when its going 1500rpm.

Any ideas as to the cause? I suppose it could be the choke but I don't really know how the choke works with all the carburator linkages and diaphrams. Is there a way of disabling the choke to see if that is the problem?

Thanks

Roger

[christover1]

to check choke, take top off the airbox when very cold, ie first thing in the morning, see if choke is closed... then warm it up, see if choke opens all the way.

choke is operated by water temp with radiator coolant running thru it, these can block up.

rough and changing idle can be many things, may be cruddy fuel, or time for a reco carby.

Mine don't like high octanr unleaded, or ethanol blends.

christover

[rogerramjet]

I don't think its any of those problems because it idles smoothly. It either idles smoothly at 1500rpm or smoothly at 300rpm. It might change from 1500 to 300 a couple of times in a 30 minute trip.

[christover1]

I don't think its any of those problems because it idles smoothly. It either idles smoothly at 1500rpm or smoothly at 300rpm. It might change from 1500 to 300 a couple of times in a 30 minute trip.

try http://www.zook4x4.com/ in the downloads
pix of carbs may help.
they are a fussy carby, but once sorted, they are good

[ronoor]

mine did the same drove me crazy .rebuild was the best thing ever.cheers ron

[Eff]

I don't think its any of those problems because it idles smoothly. It either idles smoothly at 1500rpm or smoothly at 300rpm. It might change from 1500 to 300 a couple of times in a 30 minute trip.

I didn't think a sierra would idle smooth @ 300rpm.

Sounds like dirt in the carbie, mine would idle perfectly one moment then idle very rough (it would even stall or get close to it at times). I got the carbie cleaned and rebuilt and havent had a problem since.......i got some power back too

Eff

[zookjedi]

when it starts the cold idle makes it idle alot faster depending on your adjust ment , i would for starters back of the cold idle screw , to do this get someone to put their foot flat to the floor on the accelerator (obviously the engine is not running) or just turn the cam with your hand and have alook under where the cable actuates the carby from the engine side , you'll see a flat head screw that rides with the actuating cam just back it out , than id start it up and see how it idles , than adjust your idle screw up to suit , making sure that your accelerater cable is not holding tension on the rotory actuator whan at idle as it should be sitting against your idle screw ,

make sure also that your accerlerator isnt sticking , i doubt it would be your choke as it would die in the ass everytime you drove it warm with the flap down restricting air flooding the engine .

[monkeyplex]

yep, 300 rpm is bloody slow, it should be around 800 at least ( dont quote me). Im surprised a little 1300 would even continue to kick over at that rate. 1500 sounds about right for a cold start, but to ensure the auto choke works properly many people press and release the throttle before a cold start. I had similar problems with a 1.6 carbie, the bastard would be rumbling all over the place on a cold morning, but now it's now problems it always goes straight to about 1500 revs then warms up to idle at 800.

[lay80n]

The idle jet in the stock asian carb is pretty small, and easy to block up. If you do find that it is blocking up, fit a secondary fuel filter between the carb and the fuel pump. This will help keep the carb clean. THe diaphram in the guel pump also has a habit of perishing , letting little chunks of rubber float into the carby.

Layto....

[Huggy]

i had the same problem with my old serria tryed all the things that have been mentioned and it didnt fix it .What it was the rod that the choke is on had worn the carby housing away and was letting air in when it shouldnt have been . I fixed by getting machined out and putting little bushes in to hold the rod