TB90BC Bushcutter-Help

B

Boyde

Member
I give up, I need help. I have been working on my Troy-built TB90BC Bushcutter. It is old, but still use to work. It will run on choke. Idles great and runs great for about 30 seconds, then just dies. I have cleaned the Zama C1Q-P18A carburator in my ultra sonic cleaner over night. (Before this it would not start). New sparkplug, new diaphragm, new gasket, try with gas cap off. It will run on choke forever. It reves up real clean, idles at a good rpm. Then just dies. I am going to try to attach a video and two still pics.
Please help.vedio of TB90BC
 

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Mark H_NO said:
Have you checked the fuel pickup and fuel lines? It sure seems like it's not getting enough fuel.
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Thanks, I did put a new fuel filter on it, no change. I have not replaced the fuel line, yet. I have been thinking the same (I just went for a long walk, when I do my best thinking). The lines do not appear to be cracked or split. However, the primer pump does seem to be drawing air, not consistent solid gas.
 
I would replace the fuel lines. The primer can draw from the carb to the tank. That can end up pumping more air than you'd expect. If it starts well, I'd assume the prime system is working. Where was the filter you replaced? Was it in the tank? Check on what Rivets said too.
 
Rivets said:
I’ve attached a Zara service bulletin which may be of some help. ,if I had it in front of me, I would try adjusting the high speed mixture to give it more fuel. Also, are you sure you installed the diaphragm and gasket in the correct order. Service manual should. https://www.zamacorp.com/wp-content/uploads/2024/09/Disassembly-Servicing.pdf
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Thank you. I am going to try replacing the primer pump. In my mind, I am thinking it is not holding the pressure, the bulb will not get hard. The check valve is not closing (I think). At this point I am not sure of anything.
 
Mark H_NO said:
I would replace the fuel lines. The primer can draw from the carb to the tank. That can end up pumping more air than you'd expect. If it starts well, I'd assume the prime system is working. Where was the filter you replaced? Was it in the tank? Check on what Rivets said too.
Click to expand...
Thank you . The filter was in the tank. The primer is suppose to draw (pull) gas from the tank through the carburator, and back to the tank. The current primer bulb does not get hard. I suspect that might be an issue.
 
I replaced the primer. Did not help. Seems to prime better, but the machine still dies. I tried pressing on the primer before it dies, pulling more gas into the carburetor. Did not help, still died.
I need some more of your thoughts, please.
 
I changed all the fuel lines and the primer. No change, still dies.

I am going try adjusting the high speed adjuster. I think I need a special tool to do that. I am attaching a pic of the top of the carburetor. The choke is the bigger white thingy. The other thingy (the white and red thing) will be the adjustments. Any tips as to how to adjust that?
 

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