Fuel Mixture Adjustment 91 sierra 1.3L

[rogerramjet]

Hi all

I am messing around with the fuel mixture on my carby to see if I can get better fuel econony. Of course not having any equipment to do it properly makes it a bit of trial and error.

I think I have found the right screw - it is at the bottom of the craby facing the rocker cover with an anti-tamper sleeve over it. I turned it in a couple of turns (does turning it in make it leaner?) and now the motor runs a bit rough at idle and misses a little at idle and the exhaust smells funny but apart from that its running normal and not blowing any smoke. Does that mean I have made it leaner? Or could you get the same result if it was rich? Does anyone have any techniques for adjusting mixture without using the proper equipment? What can be expected if it was running really lean or really rich?

Cheers

Roger

[muppet_man67]

that is only the idle mixture screw. as far as i can tell from reading the manual suzuki carbs are not adjustable, hopefully someone will confirm this.

[JrZook]

that is only the idle mixture screw. as far as i can tell from reading the manual suzuki carbs are not adjustable, hopefully someone will confirm this.

The idle mixture screw is set from factory and is not adjustable due to the tamperproof cap over it. Once the cap is removed it can be adjusted. A way to adjust the mixture without any equiptmen is to get the engine up to operating temperature then lower the idle speed to <800rpm. This assures that only the idle fuel ciruit is used and not part of the main. To set slowly screw in (leaner) the mixture screw until the engine runs rough. Then unscrew until a smooth idle is reached. Unscrew another ~1/8th of a turn to ensure it is not running lean.

Cheers Dan

[Damo]

The only way to change the mixture is to change the size of your primary & secondary jets.

[muppet_man67]

The only way to change the mixture is to change the size of your primary & secondary jets.

thanks damo

[rogerramjet]

I am confused. There are two screws and this is what I understand them to be:

1. Idle mixture - protudes from the carby at an angle and without any tamperproof sleeve. This screw adjusts the idle mixture which in turn adjusts the idle revs.
2. Fuel mixture - protudes horizontally from the carby and has a temperproof sleeve over it and is located right at the bottom of the carby. This scew adjusts the average fuel mixture for all conditions.

Is that not correct? Some say both screws control idle settings only, some say mixture cannot be changed at all. What is correct?

[Damo]

I am confused. There are two screws and this is what I understand them to be:

1. Idle mixture - protudes from the carby at an angle and without any tamperproof sleeve. This screw adjusts the idle mixture which in turn adjusts the idle revs.

No this is to set the RPM at idle, it does not affect mixtures

2. Fuel mixture - protudes horizontally from the carby and has a temperproof sleeve over it and is located right at the bottom of the carby. This scew adjusts the average fuel mixture for all conditions.

No that is the idle mixture screw.

[lay80n]

As already said by Damo, idle mixture affecte the IDLE mixture only, to change mixture when running on primary and seconday's you need to change the jets. Is you rig running rich, or are you diagnosing the poor economy with a dart board. You need to use keep the mixture at 14.7:1 air fuel ratio. Makin it leaner will stuff ya motor (leaner mixutre reduces power and makes motor run hot). If you think you have a problem, post up what its doing and we might be able to point you in te right dirrection. Changing the jets in ya carby (if all else in ya motor is relativley standard) is pointless, and might just be covering a problem. Idle revs are controled by modulating the throttle butterfly position, where as idle mixture controls the amount of fuel per air unit that enters the manifold at idel conditions.

Layto....

[Jaffa]

Idle revs are controled by modulating the throttle butterfly position

Can someone explain this a little more for me, I have just put a 1.6 carby motor in, and it starts fine, choke opens when engine warms up, but it idles at about 2000rpm, I noticed there was an adjustment screw on the throttle linkage that was wound all the way in, so I loosened it thinking that was the prob, now it "idles" at about 3500rpm. Is this the adjustment La80n was refering to?

Any ideas?

[Jaffa]

anyone?

please help I suck at carbys

[Dozoor]

About half way down the page there is a idle adjustment zip file download
and open couple of pics and info may be of use

http://www.suzukiinfo.com/sierra/

Good luck.

Larry.

[Jaffa]

Thanks Larry,

I downloaded that, but my carby is different, mine is a mikuni carby, I looked for something similar anyways, but the one section of my carby that looks similar doesn't have the marks to line up like in those pics.

This is driving me crazy

[lay80n]

Post up some pics of your carby and draw on them showing what your are refering to. Easiest way. If you cant post pics email them to me and i might be able to help aswell as host your pics for you, but i wont be back online for a day or 2.

Layto....

[Jaffa]

Its all good now, I finally found the problem, it was just the throttle cable linkage, its a bit sticky and doesn't return fully, lubed it up a bit and now it all good.

[foolsp33d]

See my pics DID come in handy in the idle drama topic! Thanks foolspeed No worries guys, glad to have helped.. geez am i talking to myself again.. oh no!!

Also fixed my idle dramas with a reset of the throttle cable, and idle screw... OOPS.. i gotta start reading page one....

[Highway-Star]

Roger,
You say you are doing this with the aim of improving economy. It would be good if you could tell us what economy you are currently getting, and if your vehicle has any modifications. This way we could indicate if any improvement is even possible/ expected. For example: My carby 1.3 wide track, standard gearing with 27" tyres on alloys, with 2" exhaust, extractors and a 14" thermofan averages 10.5 km/L on road. Beach work with a trailer towed cuts it down to about 9 km/L, and time spent in 4WD park is similar, if not slightly better (marginly).

Anyway, that screw with the anti-tamper bit, easily removed with a dremil and small cutting disc (get someone to hold it still with some plyers whilst it gets cut.

There are other ways to improve economy, do a search, and see what you find (should be something), and not just zook specific.