INT.424 "pops" through intake

[jinman]

The only thing I can add to what others have said is you might try running the tractor in the dark. Bad spark plug wires or a bad distributor cap sometimes are easy to see at night.

 

[LAD1DER]

ok, put new plug wires on (replacing set that was less than a year old) and they have a copper core. no change in problem.
switched #1 and #3 plug wire on distributor, and tractor ran rough, but, the pop through intake went away.
I have a new cap and Autolite plugs to put in next. Currently, the cap is less than a year old, and I do have Champion plugs in it.
I'm trying to do as much to rule out the ignition system before pulling the valve cover.

Thanks for the suggestions so far, and I'll keep you posted.

 

[bones1]

While at idle, take a crisp dollar bill, you can use a fifty if you got it like that, and hold it flat by one end up to the exhaust pipe.If you have a bad intake valve it will suck the bill like a vacuum to the exhaust pipe.
Poping back through the carburetor is usually intake valve if not found to be electrical.

 

[LAD1DER]

I'll ask my wife if I can borrow a dollar and try that.

 

[LAD1DER]

Well, it sucked the dollar into the exhaust pipe. I guess the valve cover is coming off next. Stay tuned............

 

[IH3444]

Check valve adjustment.

 

[RichNJKubota]

Do a leakdown test on all the cylinders. You can make a setup yourself. Take an old spark plug. Bore it out and braze a fitting onto it so you can connect an air line for air compressor. For each cylinder - put at TDC - firing position - and pressurize with about 30-40psi. Hold crank if needed to keep engine from turning. Listen to where the air is coming out. Intake valve? Exhaust valve? Rings?
When you said the compression check showed it was close to the others - that did not sound good to me. Variations of a max of 10% may be OK.

Rich
NJ

 

[scott_vt]

Check valve adjustment.

I agree totally !!!

 

[slowrev]

If any of the valve clearances are extremely loose, check for bent pushrod.
Ben

 

[bones1]

Remember the old vacuum guage in the bottom of your toolbox?It can be a very good tool for finding problems.At idling speed, a good engine at sea level should show a steady vacuum reading between 14" and 22" HG. A quick opening and closing of the throttle should cause vacuum to drop below 5" then rebound to 23" or more. With the engine idling, continued fluctuation of 1 to 2 inches may indicate an ignition problem. Check the spark plugs, spark plug gap, primary ignition circuit, high tension cables, distributor cap or ignition coil. Fluctuations of 3 to 4 inches may be sticking valves. Vacuum readings at idle much lower than normal can indicate leakage through intake manifold gaskets, manifold-to-carburetor gaskets, cracked intake. Low readings could also be very late valve timing or worn piston rings. If the leak Is between two cylinders, the drop will be much greater. You can determine the location of the leak by compression tests. I believe since the dollar bill was sucked in, with a vacuum guage you will find the problem.