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Sierra Extremely High Idle 92 SJ70
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Author:  benckie [ Fri Jul 20, 2012 9:34 am ]
Post subject:  Sierra Extremely High Idle 92 SJ70
Hi guys i know this has been posted before and Ive been researching it on the net for a week, but Ive been getting confused about all the models and different set up and trying to find pictures of vacuum hoses and getting side tracked on the net and mine seams to behaving back wards to stock set up as in idle procedure any way here it is.

I have a 1992 Sierra SJ70 Soft Top with a stock G13BA motor, the motor has only just clicked over to 112 000 k,s and is pretty solid, its spent most of its life towed behind a bus. Ever since Ive had it about 12 months its idled high around 1200 - 1500 rpm when cold then drops when warm i thought this was strange but after researching it seams the normal for these.

A while ago its started idling even higher and getting worse, while i was away my old man gave it a service as he was using it while sorting his new car out and its is idling even higher now and not dropping back down, he said all he touched was plugs, oil and filters he is a very mechanical minded person i trust him but maybe he might of knocked a vacuum hose off and put it in the wrong location or just age got it.

Now when you start it first up in the morning it will idle at 500 - 800 rpm for a second or two then go to 1200 rpm, once it warms up a bit the idle will go to 2000 to 2400 rpm and often up to 3200 rpm screaming its head off. From the minuet you start it, its like its constantly slowly ramping up the rpm when it should be dropping, its not a good look at the traffic lights, not good for the old girl and its chewing fuel, lucky to get 180 clicks for a tank full to the brim, apart from that the motor is fine and does not skip a beat or burn oil.

I have read lots about ICS IAC and radiator coolant level, but ill be honest i don't have a clue where they are only of there function(except the radiator), i was hoping some one could point me in the right direction or be able to show my a picture, I'm hoping its just an air leak or a mixed up vacuum line as I'm not keen to swap carby's right now just spent a heap of coin on the wifes car.

What i can tell you is that i am reasonably mechanical minded have a decent amount of tools, but know nothing about these Suzuki carbs or used to running carbs with this much crap hanging off them. Now what work has been done in the last 6 months, checking manifold bolts, checking manifold for leak,s, plugs, fuel, air, oil filter change a stereo swap, new exhaust and it was on the timing light a while ago i can not remember what it was but it was with in spec and i check the coolant level often.

Being a EFI man I'm not sure what else to check on it or where to start, so I'm thinking it is a air leak on a vacuum line or the two diaphragm lines have been mixed up ? so I'm hoping you guys might have some pictures of the carby set up or be able to point me in the right direction ?

We knew the last owners but they sold it to the wreckers after there last trip on return it blew a rear right tyre and bounced the tranny in gear and locked it up so I'm not sure if he messed with any thing. I have not touched any idle or fuel mixture screws. I'm sorry for the long winded dribble just trying to give as much info as i can, but not sure what you guys will need.

Thanks for you time in advance Shane
Author:  sjzook [ Fri Jul 20, 2012 10:21 am ]
Post subject:  Re: Sierra Extremely High Idle 92 SJ70
Check all vac lines to and from carny blow them out with air
Author:  benckie [ Fri Jul 20, 2012 1:56 pm ]
Post subject:  Re: Sierra Extremely High Idle 92 SJ70
Checked all vacuum lines, some just fell apart while trying to remove them, but even replacing them made no difference. Gave the carb a good clean while still on the engine, there was a few sticky parts managed to drop a few hundred rev,s.

While i was there i noticed the choke was still 90% closed while the engine was at running temperature. I removed the carb water feed and it was blocked the tee was blocked the pipe from the tee the the top of the carb was blocked after unblocking them with wire and compressed air, i put it all back together. Now she is idling at 900 rpm and with the lights or fans on 1300 rpm and the choke is now fully opening when up to temp and it is no longer running rich.

She has never idled so well, I'm looking forward to getting more mileage out of the tank i was amazed at how a blocked water pipe on the base of the carby could affect engine performance and idle, very happy i did not have to mess with the tune as this was my first instinct.

I suggest others with the same problem check your choke and if its not working make sure your carb water pipes are not blocked as the carb needs hot water to pass through it to disengage the choke and shut the cold start valve at the base of the carb.
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