Thread: High & Low on carbs
06-04-2009, 06:06 PM #1
High & Low on carbs
What are the high and low screws for on a 1995 polaris sl 750?
06-04-2009, 07:02 PM #2
- Join Date
- Jul 2007
- near Toronto, Canada
What do the carburetor adjustment screws actually adjust?
This has been covered in some other posts, but I don't have a pointer to them handy, so...
Each carburetor has small, precision holes inside that the fuel flows through before it gets sucked into the engine. The holes regulate the rate that the fuel can flow into the engine.
One of these holes is called the high speed jet. Fuel flows through this 'jet' hole when the throttle is open all the way, or nearly so.
Another of these jets is for low speed operation, when the throttle is just around idle speed, and slightly above idle speed.
Each of these jets also has a very finely tapered tip, almost like a needle tip. The adjustment screw moves this tip into the jet hole, and restricts fuel flow slightly.
The jets are normally sized so they will flow fuel just a little faster than the engine really needs it. Then the carb screws are adjusted inwards until the fuel flow is just perfect.
These screw adjustments are all measured relative to being fully turned 'in'. That means you 'tighten' the screw until it just starts to seat in the hole inside, then stop turning. Turn it too tightly, and you can damage the tapered needle or the hole.
Then you count the turns, and fractions of a turn 'out'. A typical adjustment might be 5/8 turn out, or 1 1/4 turn out.
To figure out what your current carb settings are, you would count the 1/8 turns in it takes to reach fully 'in', then wrote that number down.
06-04-2009, 08:06 PM #3
Just to clarify the adjusters a little more. The low spd adjuster changes the amount of flow through the low spd jet, because it opens or closes another passage after the jet. The high spd adjuster will add flow to the high spd circuit and not effect the flow from the main jet at all. It adds fuel independantly as its fuel comes from the fuel chamber directly and not through the main jet.
I would post the image from a .pdf file, but I don't know how, but you can find it on pg.6 of the sbn manual found > here.
06-05-2009, 08:58 AM #4
06-05-2009, 09:05 AM #5
06-05-2009, 11:43 AM #6
06-05-2009, 12:04 PM #7
06-11-2009, 10:17 PM #8
what screw is the high and what on is the low on a Polaris 750 SL?
06-11-2009, 10:26 PM #9
- Join Date
- Oct 2006
- Cleveland OH
High speed is mounted near the top with the low being close to the bottom.
Please read the manual or the Mikuni manual in the tech section.
06-14-2009, 01:03 PM #10
question on the carb adjustment, got all the specs for the carbs in the manual... but heres a dumb question which one is the front cyl or carb... the cyl facing the handlebars or facing the seat?
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