Carb adjustment

Bens n's

Member
I have a Zenith carb on my early 8n. I have been through it a couple of times and have sprayed through and cleaned every jet and orifice. My tank has been cleaned and dipped and the screens were cleaned at that time...maybe a year ago. I get a good flow of fuel through the carb.

Problem: No power under a load

The upper carb screw only works if it's all the way in. If I adjust it out any, it will die at lower idle. When all the way in, it idles fine. The main jet screw doesn't seem to make much difference. All the way in will kill it and so will several turns out. It runs the same from a half turn out up to 2 or 3 turns.

It seems to run fine just driving around, but when mowing it will die if I don't constantly stop and rev up the brush hog.

General stuff done to the tractor:

new distributor, points,
new plugs and wires
converted to 12 volt
all new wiring
new exhaust/intake manifold
new governor
cleaned and dipped tank...cleaned screens

the plug wires are in the correct sequence.

ps. it does appear to still have a manifold leak in spite of my best efforts with thermosteel
 
ps. it does appear to still have a manifold leak in spite of my best efforts with thermosteel.
It sounds to me, you know what the problem is.. time to have the manifold milled flat..
 

It had these symptoms even before the leak manifested again.

It's a new manifold. I was told the block must be pitted. It was around certain cylinders, but not all that bad. The termosteel that I purchased sucked really bad. It was chunky and hard to work with. It never smoothed out even after being compressed behind the manifold and wax paper. Was thinking to identify a better product and try again........but Im not convinced this is the primary issue with the power loss.
 
Ben,Several guys here have had problems with new after market manifolds hitting on the side covers and not sealing up to the block.You might want to check your manifold in that area.I have used high temp red RTV to seal up block imperfections and has lasted for years.Or copper high temp RTV sealer,even JB weld would work also.Maybe the Termosteel that you purchased was old and lumpy I don't know about it as I have never used Termosteel.
 
Have you tried firing it up then spraying some Starter Fluid around that manifold?
If the engine RPMs go up you have an intake leak and most likely your problem.
Might keep your Extinguisher handy just in case. But if it did catch fire if would flash and go out quick.
 
I appreciate all of the comments everyone!

I'll have to pull it apart and mess with it again. It did, however, have an intake leak prior to replacing the manifold (which was cracked) the first time. It looks like it's leaking in a different spot now though.

I'll see if I can carve out some time to hit it again and keep you posted.
 

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