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706 backfire

T

Tvertiz

Member
I have a 706 with a gas engine and it is backfiring on the number 5 cylinder, it is coming through the carbourator. Cap is good and fireing order is correct according to the block and what is stamped on the cap. When I unplug #5 cylinder it stops. I have switched around the wires and used different wires but keeping the fireing order the same with the same result. Could this be a carbourator issue and what should I do to fix it. Any guidance would be appreciated

Thanks Tom
 
I know it is backfiring only on that cylinder because when I unplug cylinder the popping sound coming out of the carb goes away. It only happens on this cylinder.
 
It is not carburetor. Better check your valve train for bent push rod, rocker arm or just backed off adjuster.
 
Like Pete23 said, there is something wrong with the exhaust valve on the cyl, either the push rod is way bent, or the rocker arm is broke, pull the valve cover and check.
 
check that plug for fouling. Have a W4 that misses on one cylinder change the plug its good again for a while. I think it needs to get in for valve job (at the minimum) to fix it.
 
I would suggest that you check the compression on the engine. I bet you have a burnt exhaust valve in cylinder #5
 
Backfire through the carburetor should indicate a burned intake valve.
Remove the spark plug from the suspect cylinder, bring the piston up on compression and blow compressed air into spark plug hole. Have someone listen at the carburetor (air intake hose removed) for escaping air.
Buy a leak-down tester and learn how to use it. Great diagnosis tool.
 
I cannot hear your tractor from here but this is what I will tell you from your explanation. A burned or leaking exhaust valve will rap in the exhaust. A leaking intake valve will mess up the intake to all cylinders and can cause popping back in carburetor. A bent push rod or anything that prevents the exhaust valve from opening fully will cause a pop back into carburetor. How it works is on the compression stroke it build pressure in cylinder but because exhaust does not open when it should the compression in cylinder is then released back into the intake side when intake valve opens. This happed a lot on the 400 series diesel engines when they were first released due to a poor rocker arm that would fail and not open one of the EXHAUST valves. A compression test would confirm leaking valve or better yet a cylinder leak down test. You can usually hear a valve leakage problem by reving engine wide open, shut switch off and listen to intake and exhaust while engine is coasting to a stop. You can also hear compression loss by grounding coil wire and cranking engine listening for unevenness in speed.
 
You can overhaul the carburetor, replace all the ignition components and then when it still isn't any better you can follow Pete's advice and get the problem fixed.
 
Looks like I need to pull the valve cover and get a little more serious with this problem, I thought I was gonna have some time to work on this when I posted this originally but looks like it is gonna be a couple of days before I get to it, two kids and Christmas coming does not leave a lot of time for wrenching on a project tractor. Thanks for the great advice and I will defiantly update when I find the problem.
 
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