Joined Mar 2005
13 Posts | 0+
Rancho Cucamonga, Ca.
I just purchased a used 05 fe550e. The bike came with the Dreaded Dead Throttle Spot that occurs when the throttle is wicked open off idle.
After reading all the posts that an FCR jetting search would produce I spent several hours playing with jetting with no favorable results when I decided to check the AP (accelerator pump) for efficiency. What I found was a dribble coming out of the AP nozzle when the throttle was twisted open. I took the carb off the bike removed the float bowl so that I could check to see if the AP diaphragm was pumping fuel and also to get to the AP circuit to blow it out with compressed air. Once apart I found the AP diaphragm mechanism to be working fine so I turned my attention towards the AP nozzle. I attempted to blow air though the AP circuit and nozzle from where it would normally meet up with the other half of the circuit coming from the float bowl. At first 100 psi would barely create a stream from the AP nozzle (kind of like what an enlarged prostrate will do) then the air stopped flowing all together. I tried to spray brake cleaner through the circuit hoping that whatever plugged it would dissolve from the cleaner, I had no luck using brake cleaner to unplug the now plugged nozzle so I took the bottom half of the main carb body apart. In there I found a check valve, no doubt used to keep the fuel from draining back into the float bowl after the AP circuit had been used. This check valve looked to be a likely place for blockage to occur so I sprayed the brake cleaner through it and found it to be wide open. I then attempted to spray the brake cleaner through the remaining portion of the circuit to the AP nozzle and found the blockage to still exist at the nozzle. My experience with industrial pumping equipment has taught me that a blockage sometimes can only be dislodged by reversing the flow from the opposite end (I don’t recommend trying this for constipation). In order to accomplish this with the AP nozzle I had to remove the intake funnel to create access for a compressed air blowgun. Once I was able to blow compressed air back through the nozzle the blockage disappeared.
After I put the carb back together the AP would squirt a stream of fuel four feet with the carb at waist height (much like a human male nozzle after a six pack). With everything back together the bike ran great. The Dreaded Dead Throttle Spot was gone. With all the components within the AP mechanism, (i.e. two check valves, the rubber diaphragm, the tiny brass nozzle and all the related linkage) there is a lot to go wrong, and this component of the carb provides the quick response off idle. I believe this problem I encountered with the AP circuit on my bike may be the problem with many older bikes that have been subjected to a carb that has dried out several times between rides allowing deposits to affect the AP circuits efficiency or even make it inoperable. I believe the AP circuit is the first place the owner of an older FCR should check when encountering the Dreaded Dead Throttle Spot.
After reading all the posts that an FCR jetting search would produce I spent several hours playing with jetting with no favorable results when I decided to check the AP (accelerator pump) for efficiency. What I found was a dribble coming out of the AP nozzle when the throttle was twisted open. I took the carb off the bike removed the float bowl so that I could check to see if the AP diaphragm was pumping fuel and also to get to the AP circuit to blow it out with compressed air. Once apart I found the AP diaphragm mechanism to be working fine so I turned my attention towards the AP nozzle. I attempted to blow air though the AP circuit and nozzle from where it would normally meet up with the other half of the circuit coming from the float bowl. At first 100 psi would barely create a stream from the AP nozzle (kind of like what an enlarged prostrate will do) then the air stopped flowing all together. I tried to spray brake cleaner through the circuit hoping that whatever plugged it would dissolve from the cleaner, I had no luck using brake cleaner to unplug the now plugged nozzle so I took the bottom half of the main carb body apart. In there I found a check valve, no doubt used to keep the fuel from draining back into the float bowl after the AP circuit had been used. This check valve looked to be a likely place for blockage to occur so I sprayed the brake cleaner through it and found it to be wide open. I then attempted to spray the brake cleaner through the remaining portion of the circuit to the AP nozzle and found the blockage to still exist at the nozzle. My experience with industrial pumping equipment has taught me that a blockage sometimes can only be dislodged by reversing the flow from the opposite end (I don’t recommend trying this for constipation). In order to accomplish this with the AP nozzle I had to remove the intake funnel to create access for a compressed air blowgun. Once I was able to blow compressed air back through the nozzle the blockage disappeared.
After I put the carb back together the AP would squirt a stream of fuel four feet with the carb at waist height (much like a human male nozzle after a six pack). With everything back together the bike ran great. The Dreaded Dead Throttle Spot was gone. With all the components within the AP mechanism, (i.e. two check valves, the rubber diaphragm, the tiny brass nozzle and all the related linkage) there is a lot to go wrong, and this component of the carb provides the quick response off idle. I believe this problem I encountered with the AP circuit on my bike may be the problem with many older bikes that have been subjected to a carb that has dried out several times between rides allowing deposits to affect the AP circuits efficiency or even make it inoperable. I believe the AP circuit is the first place the owner of an older FCR should check when encountering the Dreaded Dead Throttle Spot.
