New carb- possibly a dumb question!
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Finny
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Got a new carb, jetted properly etc. was told that it was set up to run slightly rich. Does that mean I should lean it out a bit using either the mix screw ( currently 1 1/2 turns) or go down 1 on the main jet? Thanks for advice.
Mixture screw is only good for idle and how well it picks up or drops off, making it clean, once you start to open the throttle and lift the needle your on to main jet.
Leave the screw if it idles nicely and if you open the throttle quickly it doesn't try to bog down.
Changing the main jet?? Do you know what to look for if you make it too weak (although dropping 1 will have little or no effect)
If the scoot runs ok, pulls through the gears I'd leave well alone especially if it's a new top end
Rich
Leave the screw if it idles nicely and if you open the throttle quickly it doesn't try to bog down.
Changing the main jet?? Do you know what to look for if you make it too weak (although dropping 1 will have little or no effect)
If the scoot runs ok, pulls through the gears I'd leave well alone especially if it's a new top end
Rich
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Chris in Margate
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What colour is your spark plug as this is a good visual check?
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Finny
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Plug looks ok, maybe a shade darker. Pulls through gears ok and revs out fine in 2 & 3 except seems a little under powered in top gear(gp 200 gea, 47/17) hits 60 but doesn't feel it wants to give more. Thought that my less than aerodynamic bulk might have some bearing but wondered if dropping down main jet would clean it up.
Thanks
Thanks
Dropping one or even two on the main jet will not make any noticeable difference to this at all. But it MAY put the piston at risk.Finny wrote:Plug looks ok, maybe a shade darker. Pulls through gears ok and revs out fine in 2 & 3 except seems a little under powered in top gear(gp 200 gea, 47/17) hits 60 but doesn't feel it wants to give more. Thought that my less than aerodynamic bulk might have some bearing but wondered if dropping down main jet would clean it up.
Thanks
It could be the combination of gearing/exhaust/carb and 'ahem' weight that gives the feeling it's got no more to give.
Ride it and enjoy it................
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corrado
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You really need to read up on how the various components of the carb .... air screw, pilot jet, slide, needle, needle position, atomiser, main jet all work and overlap each other at various stages of throttle progression.
Then mark up your handlebar with throttle positions. Put a bit of masking tape on your light switch housing and put a mark on it, then wrap masking tape [only needs to be 1/4 inch thick] around the throttle twist and mark the stop position in line with the mark on the light switch housing, then twist the throttle to wide open position [WOT, wide open throttle] and mark that position, then mark the in between section in 1/8 graduations.
A bit like this but in reverse.
Then do plug checks at various throttle positions to check the colour of the plug at those exact points. A plug check is a photo of the plug at a split second time. To do a plug check correctly you hold the engine speed at one position and kill the ignition while instantly pulling in the clutch and coasting to a halt. The best place to do this is on roads that have lay-byes so you can kill the engine and coast into the lay-bye and safely remove the plug and check the colour.
As the above chart shows the main jet doesn't have too much influence on progression until about 3/4 throttle position, so merely changing the MJ may have little effect on the jetting. Most people I know rarely get to main jet, they'll sit at 50 mph at 1/2 to 3/4 position, which is covered mainly by atomiser and needle combination.
A carb can easily be jetted differently at various stages of progression, it's rarely just rich or lean. It can quite easily be rich, lean and back to rich again throughout the progression.
Then mark up your handlebar with throttle positions. Put a bit of masking tape on your light switch housing and put a mark on it, then wrap masking tape [only needs to be 1/4 inch thick] around the throttle twist and mark the stop position in line with the mark on the light switch housing, then twist the throttle to wide open position [WOT, wide open throttle] and mark that position, then mark the in between section in 1/8 graduations.
A bit like this but in reverse.
Then do plug checks at various throttle positions to check the colour of the plug at those exact points. A plug check is a photo of the plug at a split second time. To do a plug check correctly you hold the engine speed at one position and kill the ignition while instantly pulling in the clutch and coasting to a halt. The best place to do this is on roads that have lay-byes so you can kill the engine and coast into the lay-bye and safely remove the plug and check the colour.
As the above chart shows the main jet doesn't have too much influence on progression until about 3/4 throttle position, so merely changing the MJ may have little effect on the jetting. Most people I know rarely get to main jet, they'll sit at 50 mph at 1/2 to 3/4 position, which is covered mainly by atomiser and needle combination.
A carb can easily be jetted differently at various stages of progression, it's rarely just rich or lean. It can quite easily be rich, lean and back to rich again throughout the progression.