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Yamaha T50TLRC, 2004

C

CL sailor

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I just cleaned out the four carbs. on my motor, as i had idle problems -they were pretty clean. Cleaned all jets and bodies individually with carb. cleaner and finished with compressed air. After assembly, started up and to my surprise, the motor only runs at 3-4K rpm! I can't get it to run lower or even idle. Butterfly valves are closed and individual idle adjustments remain as they were and checked throttle linkage. Very strange. Before I remove the carb. unit again, any suggestions?
 
Sometimes Carburetors run on the rich side. A air leak at the base gasket would suck air and lean it out and RPM would increase. Some thing to check GOOD LUCK
 
flabob1 said:
Sometimes Carburetors run on the rich side. A air leak at the base gasket would suck air and lean it out and RPM would increase. Some thing to check GOOD LUCK
Click to expand...

Thanks for your suggestion.

I took off the carb. bank and checked "o" rings seals, doesn't seem to be the problem. I have to take apart the carbs. again to install the Viton "o" rings onto the main nozzle caps as I used rubber ones to test my rebuild. But, even a small air leak should not enable the motor to go to 4K rpm with the butterflys completely closed. 4K rpm needs a lot of air!
 
Didn't notice that you said 4K, We could rule out a air leak.
You didn't say if you advance the throttle if the rpms increase normal. Also that the throttle moves smoothly forward and aft. So I have to assume that it did. I would first say that your linkage ( cable ) is out of adjustment.
When at Idle you are supplying fuel by the float system inside of the carb. Think of it as a toilet bowl and how it works. If the float goes down you get more water in your bowl. In the carb when the float goes down fuel fills the chamber and shuts off when the float come up . When you start the engine at Idle the engine sucks the fuel and lifts the valve open and fuel from the float is sucked out. When you advance the throttle to high RPM a different valve ( jet )come into play and dumps fuel along with the fuel from the float chamber.
So if your linkage is correct what would increase your RPM and not let you reduce them. You have four carbs , what's command to four of them. It's possible you have a float sinking in the bowl or a valve seat bad of one carb and letting fuel out. That would increase the RPM. But 4K , It might ?. You still should be able to reduce the throttle and than it would be running rich and run rough. I worked on large A/C engines , Car engines and all float carb's work about the same. If this is a carb problem its a good one and I would like to know. Good luck.
 
flabob1 said:
Didn't notice that you said 4K, We could rule out a air leak.
You didn't say if you advance the throttle if the rpms increase normal. Also that the throttle moves smoothly forward and aft. So I have to assume that it did. I would first say that your linkage ( cable ) is out of adjustment.
When at Idle you are supplying fuel by the float system inside of the carb. Think of it as a toilet bowl and how it works. If the float goes down you get more water in your bowl. In the carb when the float goes down fuel fills the chamber and shuts off when the float come up . When you start the engine at Idle the engine sucks the fuel and lifts the valve open and fuel from the float is sucked out. When you advance the throttle to high RPM a different valve ( jet )come into play and dumps fuel along with the fuel from the float chamber.
So if your linkage is correct what would increase your RPM and not let you reduce them. You have four carbs , what's command to four of them. It's possible you have a float sinking in the bowl or a valve seat bad of one carb and letting fuel out. That would increase the RPM. But 4K , It might ?. You still should be able to reduce the throttle and than it would be running rich and run rough. I worked on large A/C engines , Car engines and all float carb's work about the same. If this is a carb problem its a good one and I would like to know. Good luck.
Click to expand...

Thanks for your suggestions. I have rebuild a number of auto engines, including carbs. and even the old Rochester fuel injection systems so I am very familiar with fuel systems, but this one has me stumped. I disconnected the throttle and even applied pressure on the four carb linkage - which I checked to see if all butterflys were closing, they were - yet the dam thing still ran at 3-4K!!! Most problems I have read about concern poor idle, no start, or no high rpm speed, etc. If the floats were off, or the float needle was leaking, that would cause poor idle, or no idle at all. As I mentioned before, I have to get the correct O rings (Yamaha calls them "washers") for the caps to the main jets. When I do and - again - take apart these carbs, I'll check everything again and see if this still happens and let you know results, probably end of next week. Thanks, again.
 
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