I had a VM38 YZ465 carb in a couple of weeks ago for a rebuild.
The 465 is well known for poor hot starting and general carburettor misbehaviour.
I took a close look at the air adjusting screw which was not the normal short head type, it had an extended length enabling you to adjust it with your fingers.
I'm not sure if this is standard to the model or may have been an aftermarket part.
The problem was the part of the screw the spring fits over, was about 3mm too short. This meant that when you screwed the screw in to bottom it, to then screw it out to get the adjustment, the spring was becoming coilbound and stopping the screw hitting bottom by about 3 turns.
So when you then screw it out the 1 1/2 turns or whatever to get the adjustment, it was actually out 4 1/2 turns making the pilot circuit very weak.
We machined about 3mm off the bottom of the thread which ensured the screw bottomed correctly when screwed right in.
Unfortunately, I didn't take any photos at the time but it's worth checking the screw bottoms the same with and without the spring fitted to prove it's not the spring becoming coilbound.
The 465 is well known for poor hot starting and general carburettor misbehaviour.
I took a close look at the air adjusting screw which was not the normal short head type, it had an extended length enabling you to adjust it with your fingers.
I'm not sure if this is standard to the model or may have been an aftermarket part.
The problem was the part of the screw the spring fits over, was about 3mm too short. This meant that when you screwed the screw in to bottom it, to then screw it out to get the adjustment, the spring was becoming coilbound and stopping the screw hitting bottom by about 3 turns.
So when you then screw it out the 1 1/2 turns or whatever to get the adjustment, it was actually out 4 1/2 turns making the pilot circuit very weak.
We machined about 3mm off the bottom of the thread which ensured the screw bottomed correctly when screwed right in.
Unfortunately, I didn't take any photos at the time but it's worth checking the screw bottoms the same with and without the spring fitted to prove it's not the spring becoming coilbound.
RSS Feed