# Ford 8N RPM Fluctuates (video)



## KristofMI (Jul 7, 2021)

My first tractor ever. Bought it for our newly acquired land. Problem I have with it , that I didn't noticed when I bought it, is the RPM's are going up and down. Checked everything "under hood" and found a crack in the manifold. New one on the way. Will it cause the problem? Or it's more related to carburetor? Hopefully nothing major. 
Below you can see the crack. When tractor is running I can feel hot air escaping from it. 










And here is a video of the tractor running.


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## SidecarFlip (Mar 25, 2021)

Could be the manifold but sounds like the carb needs a good cleanout and rebuilding.


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## KristofMI (Jul 7, 2021)

SidecarFlip said:


> Could be the manifold but sounds like the carb needs a good cleanout and rebuilding.


I can rebuild a carburetor no problem. Only thing I worry about and at the same time suck at is adjusting it. Are there any easy instructions on how to do it? I ordered a shop manual for 8N and it's on the way. Hopefully it will provide on how to do it.


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## Gomarshoif (Jul 30, 2021)

Could be a combination of things. I would start with the obvious. The exhaust manifold and intake are one unit. If the crack extends through both, then you have a vacuum leak as well as pumping exhaust back into the intake. This will definitely cause a surging and rough running issue. As far as carb adjustment, a bench setting of idle screw just contacting the plate then in three full turns will get you to 800 rpm. Place both mixture screws all the way in then back out one turn. Once started adjust the idle to 400 rpm. This will usually get you close to where you need to be and usable.


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## KristofMI (Jul 7, 2021)

Gomarshoif said:


> Could be a combination of things. I would start with the obvious. The exhaust manifold and intake are one unit. If the crack extends through both, then you have a vacuum leak as well as pumping exhaust back into the intake. This will definitely cause a surging and rough running issue. As far as carb adjustment, a bench setting of idle screw just contacting the plate then in three full turns will get you to 800 rpm. Place both mixture screws all the way in then back out one turn. Once started adjust the idle to 400 rpm. This will usually get you close to where you need to be and usable.


I replaced the manifold and adjusted the carb and here is how it sounds now. I don't think it is right. I ordered carb rebuild kit and will clean everything in ultrasonic cleaner (even the new parts just in case) and put everything together. As you can see on the video if I move my throttle below half way it will die. What might cause that?


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