jet too big

[The Artist]

Ok my moped at the moment runs bad. Mixture screw is all the way in to make it run. Any less and it bogs almost immediately.

Spark plug is a nice colour when doing a plug chop at full revs.
It has a size 65 jet at the moment which I think is too small for the modified air filter and de restriction. I have bought 3 other jets 72, 77, and 82 to play with.

They will not be here till mid January because the company is being a penis.

Now I have a spare size 90 from my old bike which will fit. I was wondering if this will do any damage to my ped? Just for the next month. I knwo it means it will run richer but can I lean it out by unscrewing the mixture screw a bit, or is that just for idle.

I have heard quite a few things so I want to get this straight.

Thanks

EDIT:
I can start it easily cold but once warm I have to have full throttle for it to catch. When going along at full throttle it will stutter, I usually have it at half throttle and that is full speed if that makes sense. More throttle = less speed.

[5v3d3b0]

Not too sure about this, but I think it'll be fine apart from running a little rough and fouling your spark plug. Correct me if I'm wrong.

[The Artist]

ok i was bored so I went and did it now in the cold. Took carb off, gave good clean and stripped down etc.

Popped big jet in (90)
Went for a test, very boggy so I unscrewed mixture screw to 1 1/2 turns out. still boggy, fiddled with more and found 3 was the best. Very slow though, got to about 20-25 just. Before it was slow but not that slow.

I haven't done a plug chop yet because its too cold.

[ms51ves3]

[Ichy]

Have a quick read of this before you do anything else. You might have a bit more luck.


The pilot, controls the mixture at closed throttle, when the bike is ticking over. It can be adjusted by manipulating two parts: the air screw and the pilot jet. The air screw controls the flow of air into the circuit. Turning the air screw clockwise reduces the air flow and richens the circuit. Turning it counter clockwise increases the airflow and leans the circuit. You can therefore use the air screw to fine tune the pilot circuit. The pilot jet restricts/regulates the flow of petrol from the float bowl to the venturi. Pilot jets have a precisely machined orifice/hole running through their center which petrol passes through. Increasing the size of the pilot jet ( size of the hole ) richens the circuit by supplying more petrol; i.e. removing a 40 pilot jet and installing a 42 richens the circuit. Sometimes the mixture screw will control the fuel flow at idle. Fairly obvious if it does and it just means the screw has the opposite effect.

The jet needle – Has the greatest effect between 1/4 and 3/4 throttle. It’s attached directly to the throttle valve. As the throttle is rolled open or closed the jet needle moves through the needle jet’s bore exposing different sections of the jet needle’s profile to the needle jet’s inner bore.
Six major elements determine the jet needle’s effect on fuel delivery - the diameter of the straight section, the length of the straight section, the jet needle’s taper, the clip position, the number of tapers and the length of each tapered section. The number of tapers is normally not changed from what was supplied from the factory. Only real adjustment you can have on the needle is the clip position although not all needles allow you to move the clip. Small washers placed under the clip work just as well. I've never need to drop a needle.


The Main Jet- regulates the flow of petrol from ¾ to Wide Open Throttle. Like the pilot jet the main jet has a precisely sized hole drilled through its center. Increasing the size of the main jet ( size of the hole ) richens the circuit by supplying more gasoline; i.e. removing a 72 main jet and installing a 90 richens the circuit.



Put simply, the pilot (mixture screw) controls the fuel at zero to partially open. The Needle works for 1/4 -3/4 throttle and the main jet is full throttle. Its not this simple because of overlap but what it does mean is that the mixture screw has very little effect on the full throttle.

Usually you would tune a carb working from the top down. Main, needle then pilot.

If I was you I would put it all back to standard then do a plug chop at full throttle for a few miles. If the plug looks good then the main is fine. Next same at 1/2 to 3/4 to check the needle. Finally once its warmed up let it sit of 10 minutes on idle to check the pilot.
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https://www.metacafe.com/watch/1972097/how_to_behave_on_a_forum/

[The Artist]

Thing is I cannot ride for a long time on full throttle because it bogs and dies.

I have to keep fiddling ound with throttle on the move.

I will doa plug chop at 1/2 revs to see what the needle is like.

[adamcpi50sx08]

this is why people shouldnt derestrict bikes themselves because they always seem to forget that the jetting needs to be changed, if i were you i would take it a to bike garage or the dealer u got it from and ask they to set the mixture properly with the right jets to make it run right, but it will cost you tho
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CR 125 (OFFROADER) - DEP PIPE ETC
CPI 50 SX 2008 - NO MODS YET EXCEPT FROM A SET OF ACERBIS HANDGUARDS

[The Artist]

I know how to do it all, done it before, just want to clear up the matter which was well explained by Ichy.

I will now go and have a play around with the needle and reset mixture screw to 1 1/2 turns out.

I am not paying someone else to do something I can do easily.

And I didn't "forget" the jetting, I merely postponed the date I was getting one.

[Ichy]