Ok. Here is the situation. My F3 has cylinder 2 dropping out at low RPMs/Throttle position. What I mean is if you are just putting through town or cruising at around 60, you are on 3 cylinders. Between 65 and 70 you can feel the cylinder kick in and smooth out. Now the same goes if you just accelerate hard. It has great power and screams like crazy. As a matter of fact it has no problem hitting 120MPH+. It also starts fine and idles well.

What I have done:

I have checked plug to and it was dry...a little cruddy, but looked ok. I switched plug 1 and 2. No change in symptoms.

My thoughts are these:

1. Carb 2 has a slow jet clogged. No fuel to the cylinder until you open the throttle enough for the mains to kick in.

2. Possible vacuum issue relating to carb 2. Hole in the diaphragm, or vacuum line clogged or pinched maybe a hole in it. My thinking is that it is having trouble building enough vacuum to pull the needle out of the main jet smoothly or consistantly. However, would this cause the problem to occur at any throttle position?

3. Can a coil wire/plug wire have intermittent problems like this?

4. Compression - again, I would think I would be seeing high end power issues...

I am going to have some time this weekend to dig into this. So I thought I would get some opinions.

Thanks in advance

 

Take those carbs off and clean them out.

Put new plugs in it while you have it apart. About $2 each from the autoparts store.

If a coil was bad you would lose 2 cylinders since these are a type of waste spark motor.
You can do a compression check if you want to make sure nothing is wrong but if you know the carb has a clogged jet its probably not needed.

If you look up IDODIRT he has alot of postings on carbs and ingnitions on our bikes and if it has something to do with either he has done it so.

 

Might try seafoam too..?

 

Ok...in case anyone is curious or if it helps anyone down the road, the problem was that the slow jet in Carb 2 was completely clogged. Blew it out with compressed air and everything is good now. Strange thing is that there was crud in the bottom of the bowl. Not sure how it got there because when I set it up for track a couple of years ago I cleaned the carbs, changed the fuel lines and put in a new filter. I even ran fuel through the lines before I hooked them up. Oh well, it is purring like a kitten now. Good to go!!

 

Thats good im glad to hear it was a simple fix