Cbr 150r Manual Pdf

[Thedore Rosa]

Irecently had the pleasure of performing a complete frame down rebuild on a 2007 CRF250R that came to me with an intolerable bog issue when the throttle was stabbed from idle or low RPM (both when riding, and on the stand). After the head was rebuilt, and the engine freshened up with a new piston and rings, the lean bog was still there. There is very little in the Honda service manual regarding the accelerator pump circuit, or leak jet, so I documented the process that I used to solve this problem, and decided to share.

In all actuality, the biggest factor that effects the duration of the squirt is the stroke length of the diaphragm. A longer stroke will mean more fuel is pumped to both the venturi and to the float bowl. If the squirt duration cannot be adjusted adequately using the leak jet to control the ratio pumped to the venturi vs the bowl, then the diaphragm stroke can be adjusted. Stroke control is built into the diaphragm, so a new longer stroke diaphragm will be needed.

Why don't we use the diaphragm as our first approach to adjusting squirt duration? The diaphragm makes big changes. It's better to step in smaller increments using different leak jets. Most times, the diaphragm that was selected from factory will be in the correct range, and you will find that simply adjusting the leak jet size will solve the problem. Also, there are many more leak jets available to tune duration than there are diaphragms.

In addition to squirt duration timing, there is also a need to control when the squirt begins. Too soon, and it will hit the back of the throttle slider valve. Too late, and the engine will be starved for fuel.

When setting the timing, I give the throttle a quick zero to 100% to zero crank while taking note of the back of the throttle plate. I then use a screwdriver to advance the accelerator pump (on this carb, turning the timing screw CW advances) until I start to see fuel hitting the back of the throttle slide plate. When this takes place, I then use an air gun to dry the back of the throttle plate, back off the timing screw a small amount, crank the throttle wide open and closed, and observe the throttle plate for signs of fuel. I repeat this process until no fuel stain is present. This ensures that when the throttle is stabbed, the squirt will start at the exact moment the throttle clears the stream of fuel.

The timing needs to be adjusted so that the squirt starts just after the throttle plate gets out of the way. This will need to be done every time the leak jet is changed. Larger leak jets retard the timing, and smaller leak jets advance the timing.

Before you start with the troubleshooting and repair steps below, use carb cleaner and an air gun to clean and blow out every jet, orifice, and passageway in the carb. In order to work correctly, the carb must be gunk free, and not worn out (eg: leaky seals). If in doubt, install a fresh carb kit to ensure everything is sealing up correctly. Here is a link to an excellent pictorial guide on how to refresh your FCR carb before you go and try to adjust a tired out old carb. The instructions are given as you click on each of the pictures. Follow in sequence.

Now that you know what's going on, and are certain that you're adjusting a carb that is in good shape, I have drawn up a flow chart to aid in troubleshooting and fixing the dreaded lean bog without having to buy expensive "fixes". (Please click on the flow chart PDF or JPG image attached).

If your bike has a severe bog issue, and you find that the flow chart is pointing you to replace the leak jet with a smaller one, I would recommend jumping by 10's. For example, if your bike has a #70 leak jet, try a #60. If the bog is present, but not severe, try jumping down in smaller increments until the bog is gone.

One other point to note: This Instructable assumes that you're working not only on a good carb with no leaks or other issues, but also that you have tuned the carb correctly prior to beginning the diagnosis flow chart. You should have the bike running well with proper pilot jet, main jet, and fuel screw settings. If the bog remains, then proceed to troubleshoot the AP circuit.

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