Ya know, it's interesting that we're talking about starting problems here today. Although it was not on my F3, it was on my 1994 CBR 1000F (still a CBR). I was having problems getting it to start after having sat for a long time (I'm sorry, the F3 is so much fun I hardly ride the 1000F).


To make a long story short and not as detailed, the bottom line is that you have to keep your hands off the throttle if you want the choke to work. The choke mechanism opens a passage way that allows fuel and air to bypass the throttle plate through a small opening in the top of the throttle bore. It goes up to the slide diaphram, then back down on the back side of the throttle plate. If you open the throttle, then no air is forced through this passage way and it doesn't get the rich mixture of fuel it needs to start when it's cold.

Back by the Brass throttle plate you can see a small hole near the top of the throttle bore. You can actually see a reflection of the hole in the throttle plate. The slide has been removed so you can see it.


On top of the carburetor where the slide diaphram is, you can see the groove where the diaphram gasket sits and that small extra oval shaped area where the gasket encloses 2 small holes. The dark hole is where the air is coming from behind the throttle plate, and the other hole with the brass color in it is located on the back side of the throttle plate (the brass coloring is actually the choke valve). This little passage way is where it picks up the fuel and delivers it past the throttle plate.



Here you can see the opening behind the throttle plate where the rich air fuel mixture comes out. The opening is the small hole at the top of the throttle bore.



In the bottom photo you can see the two openings where the Slow Jet and the Main Jet have been removed. The brass tube that remains (I learned) is the tube where the Choke gets its fuel from. If that tube is clogged, it's virtually impossible to get your bike to start when it's cold.

On close inspection of this tube, I could see that fuel was just sitting there, whereas the other jets were not holding any residual fuel (the one without the slot).


I used a twistie tie from a loaf of bread to poke into the opening. It was totally clogged. After a couple of minutes, I was able to work in through and clean the hole.



Afterwords, It looked like this.


You can see the small opening now. 3 out of the 4 caruretors had those openings clogged. I put the carburetors back together, and on the bike and she fired up on the 2nd try.

 

Wow man that is such great information. Thanks so much for such a great and detailed explanation. Even though our bikes are not fuel injected, its great to know what works and what doesn't for our F3s. Thanks again for the awesome research and great photos.

 

lol idodirt lives for a chance to show off his bling, aka carbs. I've seen duller chrome (nitrile gloves for carb work?)

 

You bet man... my hands have had their share of gasoline, kerosene, and other ...enes. I have to protect what I have ya know... lol.

When I was working on the bike, I was saying to myself "why isn't this thing starting", naturally frustrated. I knew in my mind that the choke system couldn't be working but I wasn't really clear on exactly how it worked. So some reading in the General Service manual as well as the F3 Shop manual I was able to see exactly how it worked and where it might be failing. I knew what and how the main jet worked and when it kicks in. I also knew about the slow jet. I always saw this other brass tube there, but never knew, a) why can't you take it out like the others (I still don't know that), and b) what's it for, what does it do, what's it's function ? It gives you a feeling of satisfaction when you know what's not happening, then determine what's supposed to happen and figure out why it's not happening. When I found those plugged ports, I knew without a doubt that it was going to work when I put it back together.

I'll probably have to do a detailed "How To" on cleaning carburetors. That's an area that probably gives people reason for pause when it comes to taking things apart and working on them. I've got 35K on my carbs and they've never been cleaned, so it'd be a good project.

 

Your attention to detail and the amount of documentation you have on these bikes never ceases to amaze, Dirt. It's really amazing. lol

 

come on over, and clean out my bike.
and i'll pay you in beer.

 

Always remember:


When you are chasing a gremlin,start with the simple stuff first.These are/were very well built bikes.Major disasters only happen when someone does something really stupid to them.