8N - Interesting trouble shooting question

I've been meaning to go over tractor and do major tune up; looks like the time is now. Motor was rebuilt less than 150 hours ago, compression fine, etc.

I would note that the exhaust pipe (new approximately 4 years ago and still plated in most parts) burned through on the seam just below the manifold. I'm guessing this is unrelated to non-starting problem, but I am a newbie.

I went through tune up, gave it new copper wires, cap, rotor, .... etc. Got it back together today and have bright white blue sparkies.

When I replaced plugs I noted that #1 looked normal light tan, #2 lighter tan, #3 almost white, #4 like new white.

Has new screen in tank and tank was drained when screen installed, fuel bowl clean. Carb screens were clean. Fuel runs out of bottom of carb when the drain plug pulled.

Gave it a shot of ether in the carb and not even a pop.

I'm guessing it has a bad manifold. Just happen to have a replacement from Just 8N ready to go.

Any predictions before I pull manifold? I've been squirting the 4 bolts with Silikroil for over a week. Here's hoping!

It's too windy and cold to go fishing or oystering, so may as well cut firewood and get the 8N straight!

Many thanks.

The throat of the old carb was bright and clean; I wonder what is going on. Gas poured out the drain hole when I removed it, so the float must have been letting gas into the carb. Guess I'll find out when I rebuild/clean this one. It had not been on the tractor very long.

I plan on going over the linkage tomorrow. However, I'm first going to squirt some WD-40 around the intake to see if the rpms jump.

As I was look at the manifold bolts I noticed that the end bolts were larger than the middle two. Is this normal? It look like the middle two were 5/8 and the end two 11/16.

I'll update in a new post to let folks know how it turned out.

Again, thanks for the help.

If I were working on this machine, I would say it's an ignition problem. Why, Because you momentarily solved any possible fuel problems with the ether. Ether is a great way to find out if your problem is fuel or ignition. Since it didn't pop on ether, It would seem to be an ignition problem. I know you checked it all out, but I'd go back over it again. Regards, Rich

If the compression is low enough, even starting fluid won't get you going.

hth

Mountainman...CA

Thanks,

Bill 41 9N88110

Salmoneye

Since #3 and #4 share a common intake port, I suspect you have a poor gasket seal right at that port. It takes more than a hairline crack or minor leak to cause a "no start" problem this bad. The problem should be readily visible once you remove the manifold.

If everything looks good, you can make a pressure test jig for the N manifold fairly easily. Get some steel plates of any convenient thickness sufficient to cover the intake ports. You can use one long plate to cover both, or even a really long one to cover the exhaust ports as well. Get some gasket paper sufficient to cover the ports over (don't have to open up the port opening, just seal them). Either drill some holes in the plates where the normal bolts go, or use C-clamps or welder's Vise-Grips to clamp the metal plates and gasket material and thereby block the intake ports.

You can make up a similar plate for the carb flange. Drill a hole in it sufficient for the rubber tip of an air gun.

Immerse the whole works in a tub of water, pressurize the intake system through the hole in the carb flange plate, and see if there are any extraneous bubbles (especially due to hidden cracks through to the exhaust side).

I did this to prove conclusively that my leaned-out idle problems were NOT being caused by vacuum leaks from the intake manifold. They weren't.

If your problems happen only when the tractor gets hot, there is a slight possibility that you have a crack or bad gasket seal that opens only when the manifold gets hot. The pressure test I suggest might not find problems of that class. But my problem (and yours) exhibit themselves even when cold.

Forgive me if I am wrong or misunderstanding, but wouldn't your test only tell you if there was an external crack/vacuum leak?...These manifolds have been known to crack internally between the intake and exhaust sides...Worst when cold and can completely go away when hot due to the metal expansion and sealing of the crack...

Has been mentioned here more than a few times in the last few years...

Just a thought...

I was picturing a plate across the entire manifold to engine mating surface...

Told ya I was mistaken ;-)

Excellent idea, by the way!

Salmoneye

Good luck.