Thread: Carb caps

so whats up with the plastic caps on the carb needles? and why would i trim them?
how would i trim them? can some one post some pics?

Originally Posted by slfd721

so whats up with the plastic caps on the carb needles? and why would i trim them?
how would i trim them? can some one post some pics?

They are to limit the amount of adjustment you can make to the mixture. In some cases, they do not allow you to get a rich enough mixture. if you modify the muffler, or do other modifications, you definitely are going to want a wider range of adjustment.

They limit adjustment with plastic tabs that interfere with one another. It's a simple matter of pulling the caps, trimming off the tabs with a razor knife, and putting them back on. Some folks use a wood screw to grab at the caps for pulling. I did it for a friends saw, and made out just fine using needlenose pliers.

For some carbs, removing the caps makes adjustment difficult because the screwdriver doesn't seat well without them, and for some, they supposedly help keep the adjustment screws from backing out, so most folks put them back on after they have been trimmed.

Most saws on sale here in Ireland are fitted with these restictors which limit carb adjustment.This is to do with emmission and noise limits.The effect is to stifle saws power and rev limit from stock.As you say some are a simple matter of snipe nose pliers and pull them out .Increasingly though we are getting them with anti tamper heads to the jets.To adjust it is a matter of stripping saw and removing carb.There is usually a ring guard around jets so it is a matter of using junior hacksaw to cut slot through both jets and ring guard.This then allows adjustment when reassembled.Some saws are detuned to a rpm 1500 lower than peak.

I've seen some power equipment that brand new the mixture screws are set so lean that the motor could cook,and not enough adjustment with the limiter cap on to richen it enough.
They are installed by the factory to pass emissions standards in various countries.
They do have a good side though,to prevent untrained people from tampering with them.If the screws are set correctly to begin with.

I posted some pictures on page 3 of this thread.

much appreciated guys