Step 1 - you have to get a decent filter on it. No matter what filter is used; it affects the mixture. A bad restrictive filter will make it run rich, with all other settings being the same. A Good non-restrictive filter will make it run Leaner - all other settings being the same. So, getting your filter is the First step.

Step 2 - You set the Idle Mixture Screw, so that it Starts easily and stays running. Set Mixture Screw First, then adjust idle speed. May have to Play back and forth between Mixture & Speed until it is Just Right. This Idle Mixture Screw only affects Start, Idle and thru 1/4 Throttle !!!!

Step 3 - Clean Spark Plug with little wire brush and / or steel wool until it is reasonably clean. Get motor warmed up. Run it in First gear at 3/4 throttle for 3 to 4 minutes. Pull in clutch, turn ignition off (with it still rolling), put in Neutral, Coast to a stop, Get off quad, Pull Spark plug, Read Spark Plug, Looking for a Dark Toast to Very Light Charcoal Color.

Step 4 - If plug does not Read right - Unscrew 50 cent size nut on top of carb (has throttle cable going thru it). CAREFULLY, Pull throttle slide up and out of carb. Note which side of slide has the 3/16 notch on bottom outer side of slide (it will line up with Idle Speed Screw). Pull 1/8 steel ball that is attached on the end of the steel wire (throttle cable), up and out of bottom of slide and move it down the long 1/16 wide slot which is on the side of the slide, until slide is free of the throttle cable. Now, working on a Clean table (Very small pieces which can VERY easily be lost) Reach down inside the Top of the slide with needle nose pliers and remove the V shaped clip. Now the 3 long needle will come out. On the Top of the Needle are 5 small grooves with a very small E clip in one of them. Note which of the 5 grooves that the E clip is in. If Spark Plug read too Rich (too dark), you want to Lower the Needle - so move the E clip Up one groove (away from sharp end of needle). If Spark Plug read too Light (too lean), you want to Raise the Needle - so move the E clip Down one groove (toward sharp end of needle). Now, put the Needle back into the slide, put the V clip back down on top of the Needle Assembly, pull the 1/8 steel ball back up the 1/16 slot in the slide and into the bottom of the slide assembly, Insert the Slide Assembly back down into the top of the carb (MAKE SURE THAT YOU GET THE 3/16 NOTCH ON THE BOTTOM OF THE SLIDE POINTING TOWARD THE IDLE SPEED SCREW !!!!!! ) If you put it in reversed (180 degrees rotated) it will all go together; but when you go to start it the throttle will be WIDE OPEN and you WILL blow the engine before you get it shut down !!!! (As insurance - always keep your hand on the key or kill button, the first time you start it). Screw back down the 50 cent size nut on the top of the carb. Repeat Step 3.

Step 5 - IF you run out of grooves on the needle; then you will have to change the Main Jet. Either large or smaller, depending upon which grooves you ran out of on the needle

Step 6 - Tuning a carb is relatively easy - it is just VERY time consuming. Happy Carb Tuning and have a Cold One

 

H Dale, I have a carb related question. I just bought a 2006 Hi-Bird 250st used for $500. (got pics on my profile) It runs ok, but I think it has carb related problems. When you start it cold, it backfires and stalls through the carburetor into the air filter. In fact when I first got it and took off the air cleaner, it was filled with gasoline. The guy that sold it to me told me his mechanic friend has one and replaced the rubber "O" ring seal between the carb and engine and it stopped the backfiring. I did take the carb off and put a bit of silicon gasket sealant around the O-ring to seal up any leaks. It seems a bit better. It has an adjustment screw...it is nearly impossible to reach with human hands without removing the carb. I went out and bought a screwdriver with a bendable cable shaft to try to get to it. I'm going to try this weekend.
The owners manual says to get it up to operating temp and set the idle screw and then (starting with this adjustment screw out 2 full turns from all the way in) turn it slightly in or out to get the idle the fastest, then readjust the idle screw to normal idle.
Is that hard to reach adjustment screw the IDLE MIXTURE SCREW you talk about?
AND whats causing the thing to cough or backfire like that through the carburetor?
It runs pretty good, but I know it could be a lot better it I had the carb set up right.

Thanks,
Howard

 

Howard, Yes that impossible to get screw is the "idle Mixture" adjustment screw. I took a very small straight bladed screw driver and cut most of the handle off of it until it would fit in the small space. And, yes you kind have to keep going back and forth between the "idle mixture" and the "idle speed" until it starts well, idles well, and doesn't cough.
Also, to check if the "o-Ring" is leaking - take a can of WD-40, with the straw attached and spray a small amount around the mating seem that the "O-ring" seals - with the engine idling; if the RPM of the engine increases, then the "O-ring" is leaking. WD-40 contains hydrocarbon's (acts like fuel & burns) and the intake area you are talking about is under vacuum, so if the joint is leaking - it sucks the hydrocarbons right into the leak and the engine RPM increases.

 

Hey Dale, I see you are on. I went out and bought a small right angle screw driver with a ratchet action....didn't work. a small screw driver set with a flexible extention...didn't work. I was thinking of buying long hemostats to reach in and turn it. I just don't see any way to get in there. PLUS you have to do it while the engine is HOT, so you're burning your hand the whole time against the cylinder!

 

I use long needle nose pliers to make fuel screw adjustments. Its not fast but you do get about 1/16 of a turn per grip. I saw a real neat 90º screwdriver in the last motosport catalogue I got. It was made just for those annoying screws. If i wasnt so cheap I might buy one.

 

Yes, I was pondering getting a long pair of needle nose pliers. for them to work on this Hi-Bird they would have to be 12 inches or so. It just bothers me that the screw is there in plain site and I cannot get in there to move it. Maybe my hands are too big, I dunno. Things like that will bug me, I found myself looking everywhere I go to fine a tool that will make the job easier, or even possible. I thought maybe a very long pair of hemostats would work better than a long needle nose. I only get time to mess with it on the weekends, so that gives me too much time to ponder new ways to approach the problem at work.

 

Very cool tool

I thought it was more. Seems like a deal.

 

I bought this.....it looked like it would get in there flexible screw driver
only thing, I couldn't get my hand in there to hold it in the bent position.
That tool you have in that link...Is it just a long screw driver with a bent end, or do you rotate the handle and the screw driver end turns? If it did that it would be great.

 

hey, I can answer my own question. Just for the heck of it, I searched for that screw driver on eBay and found it. In the description it says that you DO rotate the handle and the end turns. Thats does make sense. Cool Tool (eBay)

 

I wouldnt recommend a sort of cool tool. [img]i/expressions/face-icon-small-wink.gif[/img]