Shaky jet needle?

James A. Corbally /

Well, I disassembled my carb on saturday, and managed to get it back together in working order.

One strange thing I noticed was that there was some play in the jet needle when clipped into the slider. Probably a millimetre or two at the tip, although it operates OK.

Is this normal, and if not what sort of problems would it cause?

Thanks,

James...

Re: Shaky jet needle?

Ron Brown /

James,

Normal. This allows the needle to self align in the needle jet. The down side is that it also promotes wear of the needle and jet, but that takes a while.

Ron

Re: Shaky jet needle?

James A. Corbally /

Thanks Ron, thought I had an easy fix there however :)

Basically, I've got a flat spot at just over half throttle, so I thought the carb would be a good place to start. I'm going to check out a new airbox (seal is not great in the one I have) and after that, who knows?

Regards,

James...

Re: Shaky jet needle?

Ron Brown /

James,

If you are suspicious of the needle or jet, examine them with a magnifier for signs of wear or move the needle up or down a notch.

Ron

Re: Shaky jet needle?

James A. Corbally /

I'd noticed there are four notches on the top, the current one in use being the second one up from the bottom one.

What is the effect of raising or lowering this setting? Would lowering it lean out the mixture by causing the needle to sink further in?

Regards,

James...

Re: Shaky jet needle?

Ron Brown /

James.

Exactly right. This is the mid-throttle mixture adjustment and is most effective from 1/3 to 3/4 throttle opening.

Normal proceedure is to select the correct main jet for max throttle opening by doing a high speed plug chop (the needle does not affect this), then adjust the needle up or down for mid range, then fine tune the idle mixture and speed.

Sometimes, you have to re-adjust the needle after adjusting the idle mixture if the engine stumbles just off idle.

The main jet selection is most important as you use full throttle most of the time on a ped and too small will cause overheating and/or engine siezure and too big will cause 4 cycling and fouled plugs.

Ron

Re: Shaky jet needle?

James A. Corbally /

I readjusted the needle to one notch leaner. Seems to have improved acceleration, althought there may still be some work to do.

I'm still planning on changing the air filter (will wash the foam in the meantime) and buying a new plug.

Managed to blow the fuse too. Removed the seat and disconnected the light, and the live touched the frame. Was running on tin-foil till I bought a new fuse! Gotta install a proper connector on that.

Regards,

James....

Re: Shaky jet needle?

Ron Brown /

James,

Keep tweaking, it is amazing how much difference the correct mixture makes.

Always do a plug chop after making a "leaner" adjustment to make sure you are not too lean.

Ron

Re: Shaky jet needle?

James A. Corbally /

It's weird, but even though I leaned the engine, it seems to be using fuel faster. Perhaps this is something to do with the air filters needing cleaning?

Or would there be some other cause? None comes to mind, although, given that it accelerates quicker, perhaps it's because I'm running at high speed for longer? I've also noticed that I don't tend to need to open the throttle much beyond half-way, and when I do open it more I don't get a whole lot, probably due to the bike being at full speed.

Thanks for your help BTW!

James...

Re: Shaky jet needle?

James A. Corbally /

Oh, and one more question; How do I perform a plug chop on an automatic? The only instructions I can find are for manual transmission machines.

Thanks,

James...

Re: Shaky jet needle?

Ron Brown /

James,

Same way except you can't pull the clutch. Ride at the desired speed for a few minutes then hit the kill switch before closing the throttle. The engine will still turn until you stop, but because it is not firing, the plug color will not change.

Ron

Re: Shaky jet needle?

James A. Corbally /

Gotcha. I'll be giving that a try.

It's funny how I can get full speed using only half the throttle. The other half has no effect, except for going uphill, or sometimes it gives me a burst of speed if I twist the throttle up there quickly.

Guess I should see if I can get some jets, just in case.

James...

« Go to Topic — end of thread

Want to post in this forum? We'd love to have you join the discussion, but first:

Login or Create Account