Cylinder 3 misfire at low revs

[His Dudeness]

In general if you're trying to work out what jet does what you can often follow the casting in the body of the carb. Trace down from the jet to the body of the carb. There's often a raised section in the body of the carb where they've drilled to create a passageway. If you follow that it will show where the jet is going. Once you know where the jet is going you can spray some carb cleaner into the jet and watch does it come out where you are expecting it to. If it doesn't then there's a blockage somewhere

[Dynspud]

Fab stuff Dude.
Thx for all the advice and the pic & explanation of the carb.

[Whomightyoube]

Yeah it can be a right pain getting all the passages clean. The thing to remember is that you have to clean more than just the pilot fuel jet in the bowl. The idle circuit is the pilot air jet, the pilot fuel jet, the transfer ports and the mixture screw port. This diagram shows it well




At idle the butterfly valve is closed so air is drawn in through the pilot air jet (PAJ in the diagram), the air then goes to the holes in the side of the pilot fuel jet (PJ). Fuel is drawn up through the centre of the pilot fuel jet and mixes with the air from the pilot air jet. It then comes out the transfer ports just after the butterfly valve and also comes out the port at the mixture screw. So all of those passages need to be clear. If you just clean the pilot fuel jet in the bowl and don't clean the pilot air jet, transfer ports and idle screw port you can still have problems.

Can you explain your understanding of the idle circuit?


What is the function of the transfer ports?


I did some googling which indicated that the TP come into play when the TBF is just opened so if I am getting no firing when on idle on 3 it must be a blockage in the tube to the MS rather than the TP.


Also, sorry about all the questions, but what is your understanding of the Choke plunger? A choke used to be another butterfly which was closed off to choke air supply to the carburettor to enrich the mixture. One reply above says the choke is a completely separate circuit. If so where does it get the fuel from?

[His Dudeness]

When the bike is idling the throttle is closed so the butterfly valve is closed so very little fuel air mix can flow through the main opening in the centre of the carb so to keep the bike running at idle you need another path for the air fuel mix to flow through, that's the idle circuit. How the idle circuit works is air comes in the pilot air jet, flows to the holes in the side of the pilot fuel jet, at the same time fuel is drawn up through the centre of the pilot fuel jet, the air and fuel mix and the mixture comes out of the transfer ports and out of the idle mixture port. That's about as well as I can explain it in words. If that doesn't make sense have a look at the video below and if might make sense

! No longer available

You're right about the choke. Sometimes it is a second butterfly type valve that closes when you pull the choke lever and that chokes the amount of air and that make the mixture richer. But on Fazers instead of a valve that chokes air it's another fuel circuit that increases the amount of fuel rather than a plate that restricts air.