Henry, I'm not familiar with the exhaust and intake manifolds on a 9N. I'm sure that some of the other guys on this forum are and will provide correction if my opinion is wrong. So, for what it's worth, here goes. The exhaust manifold should not be sucking air since it is exhaust, not intake. If it is leaking, it should be blowing exhaust gas out. Although this is not a good thing, it should not interfere with the operation of your engine, and certainly should not be causing backfires or misses. Backfiring and missing are indications that you are not getting spark at the spark plugs at the right time in the engine cycle. I think that your most productive plan of action would be to go over your ignition system. If you have not serviced the ignition system within the past year or so, I think that you should start by replacing the points, condenser, rotor, distributor cap, and spark plugs. If the spark plug wires haven't been replaced within the last couple of years, it would be a good investment to replace those too. Make sure that you get plug wires that for your tractor, not just generic plug wires. You should have honest to goodness copper wires, not carbon wires. And finally, when you're sure that the components of the ignition system are good, you should check and adjust the timing. I'd be very surprised if this doesn't fix your problem. If you are certain about the ignition system, but still have a problem, let us know, and we can go a little deeper in problem determination. Good luck, Tom
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