03-12-15, 08:30 AM
You've changed quite a few things in one go so it'd be hard for anyone to point to exactly where the problem is. There might be a carb guru on here but in general forums are good at helping with problems that occur regularly but this is an unusual one so collective experience might not give you the exact fault here. I doubt anyone's gone through this exact problem before so you might have to do some sideways thinking to get to the bottom of it. This one needs a bit of in depth knowledge on how a carb works to pin point an exact diagnosis which I don't have, I'm not a trained mechanic but I can make a semi educated guess based on some knowledge and logic (that's my disclaimer :lol) I think you've got two options 1 play it safe and put it back to the old setup and see if it's back to normal then change one thing at a time (slow method but should work) or 2 try the cunning fox method. think about how the internals of a carb works and how the changes you're making effects it. what is the gauge actually measuring? what causes the gauge to move up and down?
Here's my Fisher Price understanding of what's happening. As I understand it the gauges measure vacuum. The engine creates a vacuum in the cylinder as the piston moves down. That vacuum passes by the intake valve and up through the intake manifold and up as far as the butterfly valve in the carbs. At idle the butterfly valves are mostly closed but they are open a small bit so that a small bit of vacuum passes by them and draws a small bit of air through the air box and that incoming air draws fuel up from the bowl through the jets and that fuel mixes with the air and get sucked into the cylinder and that lets the bike idle with a closed throttle.
When you use the gauges you're connecting them into the intake manifold and measuring vacuum in each intake manifold. If you think about it there's an almost closed chamber up to the back of the butterfly valve and it's at vacuum pressure of that cylinder. When you turn the balancing adjuster screw what you're doing is forcing a screw to push down on each individual butterfly valve's linkage and opening or closing it a small bit. By turning the balancing screw in you're pushing down on the linkage so you're opening the butterfly valve. Opening the valve causes the almost sealed intake chamber to be a little less sealed so the vacuum you're measuring on you're vacuum gauge should drop. If you turn the balancing screw out you're closing the butterfly valve and sealing the intake chamber up more so the vacuum as shown on your gauge should go up. Yours is up off the scale so that suggests that the butterfly valve is totally closed so to test that theory you could try turning the adjuster in and keep turning it in until the gauge drops. It might drop or it might not drop on the gauge depending on out far out it is. If it does drop then you've pin pointed the problem but not the cause of the problem. You shouldn't have to turn one adjuster way more than the others so you'd have to ask yourself why is that one butterfly valve out so much compared to the others?
A possible cause is that when you joined the new carb into the bank of carbs you didn't line up all the linkages correctly or maybe you left something out like a spring or a spacer. I'd take the carbs out and inspect the butterfly valves. Is the one that has the problem closed more than the others? It could be a very small difference, you might need feeler gauges to see it. Next when you open the throttle and all the butterfly valves open is there any lag with the problem one? If there is then it suggests a problem with the linkage connection to the other carbs. So check the linkages make sure they're all lined up and all the springs are in place. Have a look at the manual to be sure you've got everything in place. It can be a bit fiddly getting all the little springs to seat correctly. That's why I don't split the carbs when I clean them.
To me a problem with the linkages causing that one butterfly valve to open differently to the rest seems to be the most likely problem, that's where I'd start but there could be other cause of it. Maybe due to the internal parts that you've changed out. The sticky throttle problem should be sorted too that could be causing all the butterfly valves to be held open but that would cause an equal problem across all carbs. The tps would also effect all the carbs not just one so that's unlikely to be the problem. You're looking for something localised to that one carb
Here's my Fisher Price understanding of what's happening. As I understand it the gauges measure vacuum. The engine creates a vacuum in the cylinder as the piston moves down. That vacuum passes by the intake valve and up through the intake manifold and up as far as the butterfly valve in the carbs. At idle the butterfly valves are mostly closed but they are open a small bit so that a small bit of vacuum passes by them and draws a small bit of air through the air box and that incoming air draws fuel up from the bowl through the jets and that fuel mixes with the air and get sucked into the cylinder and that lets the bike idle with a closed throttle.
When you use the gauges you're connecting them into the intake manifold and measuring vacuum in each intake manifold. If you think about it there's an almost closed chamber up to the back of the butterfly valve and it's at vacuum pressure of that cylinder. When you turn the balancing adjuster screw what you're doing is forcing a screw to push down on each individual butterfly valve's linkage and opening or closing it a small bit. By turning the balancing screw in you're pushing down on the linkage so you're opening the butterfly valve. Opening the valve causes the almost sealed intake chamber to be a little less sealed so the vacuum you're measuring on you're vacuum gauge should drop. If you turn the balancing screw out you're closing the butterfly valve and sealing the intake chamber up more so the vacuum as shown on your gauge should go up. Yours is up off the scale so that suggests that the butterfly valve is totally closed so to test that theory you could try turning the adjuster in and keep turning it in until the gauge drops. It might drop or it might not drop on the gauge depending on out far out it is. If it does drop then you've pin pointed the problem but not the cause of the problem. You shouldn't have to turn one adjuster way more than the others so you'd have to ask yourself why is that one butterfly valve out so much compared to the others?
A possible cause is that when you joined the new carb into the bank of carbs you didn't line up all the linkages correctly or maybe you left something out like a spring or a spacer. I'd take the carbs out and inspect the butterfly valves. Is the one that has the problem closed more than the others? It could be a very small difference, you might need feeler gauges to see it. Next when you open the throttle and all the butterfly valves open is there any lag with the problem one? If there is then it suggests a problem with the linkage connection to the other carbs. So check the linkages make sure they're all lined up and all the springs are in place. Have a look at the manual to be sure you've got everything in place. It can be a bit fiddly getting all the little springs to seat correctly. That's why I don't split the carbs when I clean them.
To me a problem with the linkages causing that one butterfly valve to open differently to the rest seems to be the most likely problem, that's where I'd start but there could be other cause of it. Maybe due to the internal parts that you've changed out. The sticky throttle problem should be sorted too that could be causing all the butterfly valves to be held open but that would cause an equal problem across all carbs. The tps would also effect all the carbs not just one so that's unlikely to be the problem. You're looking for something localised to that one carb