Carburetor issues xp

[cupcake]

Hey guys, so i decided to mess with the sas screws because the Truck wasn't running right and now it's even worse. I have to fight the Truck just to get it to 45 mph. How do I readjust the screws back to where they were????????

[cupcake]

Also, it's a stock mikuni carburetor on a 2.0 1989 dodge ram 50 and no I'm not going to a weber anytime soon

[geezer101]

Hi cupcake, looks like you have been sabotaged by the dreaded Mikuni fiddler. I have a pic of the all alloy Mikuni/Solex carb but the screw locations are the same on the resin body Mikuni -

carcustomandprojectspares032-1.jpg
Reset you idle stop screw by winding it out until the butt end of the screw is no longer touching the linkage, then back off the fast idle screw a few turns (don't unscrew this completely as it is a biatch to put back in if you accidentally go overboard!). Now set your idle stop screw by winding the screw back in until it touches the linkage. At this point you start the engine and adjust the fast idle screw until it rpm's reach about 900 rpm. Next is the air/fuel mixture screw (the shiny brass screw in this pic - it's in the same location on the resin body carb) - while the engine is still running wind the screw in until it tries to stall out, then wind the screw back out about 1/2 to 3/4 of a turn. If it makes no difference it might be an indicator of an air leak somewhere in the carb.

Bear in mind these carbies can have a number of faults from normal wear and age like a non functioning choke assembly or the secondary vacuum actuator failing (the latter will prevent the engine from making mid to top end power), a blocked up accelerator enrichment jet or a non functioning accelerator jet pump (both of which will leave a bit of a flat spot on acceleration). If your carb hasn't been pulled down and serviced in the last 10 years it is due!

[cupcake]

Do you have a better picture?? I can hardly see the words lol

[cupcake]

Never mind, I got a clear view of it lol. Now where is the mixture screw????

[geezer101]

Hint : click on an image to make it block out the sun If you take a look at the pic I've posted up you will see a brass screw in the throttle base plate just above the "S" in the fast idle adjust text - you will find the air/fuel mixture adjust screw in the same location on your carb. I might even suggest you take the screw out completely and clean it with some cloth/paper towel and reinstall it. If you have access to an air compressor and a blow down gun, give the mixture screw hole a quick blast while the adjusting screw is out as there can also be a blockage here (can of carby cleaner is just as good if not better). While you are at it test the secondary vacuum actuator for function. If it has a split diaphragm your engine will have literally no power over 2,000 rpm. Use the search function on the site - you will find this is a really common issue but easy to fix.

[cupcake]

Ok I readjusted the carburetor and it runs a tad but better, but what is the screwbthat is right above the red arrow?????? I tried adjusting it and it did nothing

[geezer101]

The fast idle screw is located at the bottom of the primary throttle linkage (my arrow is a bit dodgy but if you look closely you will see the head of the screw in the pic) That big gnarly screw that is above the arrow is an adjuster for the auto choke linkage and won't have any impact on how the engine runs under throttle.

[cupcake]

So how do I adjust the auto choke linkage? I think that may be a significant part of my problem because this truck llves to big down

[cupcake]

My truck will try to bog down in the mornings no matter how fast I am going and it is worse when going up hill's.

[geezer101]

Have you checked the secondary actuator yet? Without a working secondary it will fall flat on it's face under load. Eliminate that as an issue and then I would start off with the basics - check your engine tune and replace anything that has reached the end of it's life if you haven't done so already - plugs, leads, distributor cap and rotor button. Once you can cross those off the list as being a possible issue I would think about a new coil pack as well (a coil with low spark will mean loss of engine power and crappy fuel economy).

Give the carb a good blasting with a can of carb cleaner inside and out and try purging it out by cupping your hands over both throats of the carb while the engine is running to starve it of air. Do it a few times but don't put your face over it while trying to purge it (just in case it decides to backfire - safety first!) This can sometimes ramp up the vacuum in the throats enough to dislodge any fine debris that may be partially blocking air bleeders and fuel jets. Make sure all the screws on the fuel bowl top cover are nice and firmly done up as well. Let us know how you progress with this and good luck!