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Post by maicohunter on May 11, 2008 8:45:34 GMT -5
Whats the deal with this screw.Im speaking of the one thats at the front of the carb [just before the intake manifold]pointing down with a plastic knob on it. The two books i have don't mention it,except that its a pilot screw and [don't mess with it] Should it be turned all the way in or out a couple turns.I ask because when i got the bike it was laying in a box with a buch of other parts.Anyone have the details on this screw. Thanks...
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Post by stevec5000 on May 11, 2008 9:28:16 GMT -5
The pilot screw is normally adjusted about 2-2 1/2 turns out for the correct mixture at idle. You can adjust it by ear for fastest idle or using a Colortune to get the correct blue color flame.
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paul
New Member
Posts: 4
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Post by paul on May 13, 2008 13:33:27 GMT -5
this is the air screw that you have described which is used for fine tuning. factory setting is 1 1/4 turns out. the pilot screw is screwed into the base inside the float chamber bowl. i thought
the same as you until i printed all the details for the sr carb from the internet. just type in yam
sr500 carb . hope this helps, paul
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Post by solo2racr on May 13, 2008 18:35:28 GMT -5
Whats the deal with this screw.Im speaking of the one thats at the front of the carb [just before the intake manifold]pointing down with a plastic knob on it. this is the air screw that you have described which is used for fine tuning. On the hundreds of bikes that I have worked on when I was doing it for a living back in the '80's, I learned quite a few things about the general layout of carbs and how they work. One thing that I have never seen change regardless of the brand or type of carb, is that if there is an idle mixture screw on it and, if it is on the air filter side of the slide, it controls air flow. If it is on the engine side of the slide, it controls fuel flow. It makes a difference because if it is air that it controls, turning it out will lean the mixture. Whereas, if it controls fuel, turning it out will richen the mixture. Either way,1/2 to 1-1/2 FULL turns would be an accepted range for the screw. Any more or less than that to get the mixture right at, and just off, idle, really needs to have the pilot jet changed. |
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Post by stevec5000 on May 13, 2008 20:04:24 GMT -5
You guys are confusing everyone talking about air screws. Stock carbs don't have air screws, just idle mixture screws. Also 1/2 to 1-1/2 out is going to be way too lean unless the pilot jet is too large.
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Post by solo2racr on May 13, 2008 21:48:34 GMT -5
You guys are confusing everyone talking about air screws. Stock carbs don't have air screws, just idle mixture screws. Also 1/2 to 1-1/2 out is going to be way too lean unless the pilot jet is too large. Your right in that it is a FUEL mixture screw. Not an AIR screw. As far as the # of turns, if it is truly a stock carb, it will have a limiter cap on it and that will keep it from getting any richer. The proper adjustment with the cap on IS full rich (all the way anti-clockwise). This is normally a bit to lean as it was there to satisfy the EPA at the time. The trick is to use a Dremel to cut the tab off that limits the screw and you can normally find the correct mixture within 1 full turn. Usually about 1/2 turn is enough. As far as the total # of turns, (1/2 to 1-1/2 VS. 2-1/2) it REALLY comes down to state of tune of the engine, wear on the engine, air filter condition, but mostly ALTITUDE. Phoenix is much lower and I'm sure requires more turns out than here in the mountains of NC. One thing that I have never seen change regardless of the brand or type of carb, is that if there is an idle mixture screw on it and, if it is on the air filter side of the slide, it controls air flow. If it is on the engine side of the slide, it controls fuel flow. I don't think this is confusing at all. Next time I'll post pictures |
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Post by mattb on May 17, 2008 2:13:25 GMT -5
This is all good to know. With the change in temperature my bike has started running really rich, so much so that it's a pain to start as it readily fouls the plug! I read the Clymer manual last night and it told me there is no adjustment screw for the fuel/air mixture, only the one (located at the hot start button) for rpm. I figured they had to be wrong, and if not, that was a plain mad design, given that the mixture simply does change depending on environment! Thanks guys, I'm glad I came across your discussion here; time to go do some tweaking.
Matt
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