Vanguard 18 HP plug issue

[DaveL]

I have a Max II with a Vanguard 18 HP engine that the plugs have been fouling after only a few minutes of running. I have rebuilt the carburetor, new air cleaner, tried different plugs, and checked the shear pin on the flywheel. Any ideas on what to check next?

Dave

[Eldon]

I would check engine compression(Don't know the specs on the 18 hp.) take both plugs out and take reading with throttle held wide open.record that reading,then put a spoonful of oil down the plug hole and immediately take another reading again with throttle held open as you roll over to get a reading.Then see how the compression compares to the specs.If the readings are not in spec. without the oil then it is ring or valve trouble.If the reading improves to spec with the oil,then problem is rings,if it doesn't improve to spec with the oil problem is valves.Before going to this trouble check the plugs for a healthy spark if it a weak orange spark.....trouble is coil. but the probable cause is coil.........then next could be head gasket,

[DaveL]

Thanks Eldon I will give that a try!
Will be picking up a compression gauge today.

Dave

[Robinhood02]

is there no smoke coming from the exhaust ?? fouling after only a few minutes would suggest to me that there must be a pile of smoke comming out, if the smoke is blue it is burning oil, ( if it mainly smokes while under load or heavy throttle it is likely rings ,if it smokes mainly while idling or decelerating or going down hill it is likely valve seals ), if the smoke is black it is an excessive fuel problem (probably float level or choke ), are both your plugs fouling the same ?? if so is it greasy black or is it dry black powdery ?

[Roger S]

My armchair guess is like Robinhood's, they're gas fouled, but I can't see them from here unless you hold them up to the monitor If gas fouled, could be carb or coils, which might be the diode wire between the coils and not the coils themselves.

You will have to back the valve clearance way off if you're trying to use a compression gauge due to the compression release holding the exhaust valve off it's seat on part of the compression stroke. But really, if it's black sooty smoke instead of blue, it's a fuel or ignition misfire issue.

If it is blowing clouds of blue smoke, could be the crankcase breather/oil seperator is broken. Of course, overfilling the crankcase will have the same symtoms, but I won't assume you overlooked that. We've all seen a max or argo tilted over far on it's right side, blowing blue smoke like a bug fogger. It's too much for the internal baffle and crankcase to handle.

[DaveL]

Thanks guys this thing has been driving me crazy!
Here is what I have so far- no smoke runs great with fresh plugs or plugs I have cleaned, idles smooth good response on throttle. Oil level is good breather tube is intact and both plugs seem to carbon up at the same rate. The carbon is dry not wet and spark looks good, blue not orange. When turning the engine by hand the compression seems to be good on both cylinders. Have not checked the diode wire between the coils yet. I have never had this problem before with any small engine and I sure expected to have some type of smoke from the exhaust if I am fouling the plugs. I have only seen smoke when first starting the engine and that only lasts for a few seconds. When it starts to run rough and looses power I know I only have a little while before it will just quit running.

When I bought the machine the carburetor was gummed up from setting for several years, the engine would surge and not run with out the chock pulled out, after much cleaning and a rebuild kit it ran good. Shortly after that it started backfiring and I discovered the plugs to be fouled and have had issues with fouled plugs ever since. I would get anywhere from 1 hour of run time to 15 minutes. The engine had RC12YC plugs in and that is what I was putting into it when changing, I up graded to the RC14YC and, after talking to a Briggs tech, installed new air cleaner element after that change I ran about 12 hours without a problem. Now it is back to fouling the plugs every 15 minutes. I have not installed new plugs but have been cleaning the fouled plugs using a torch and burning off the carbon.

I plan right now to check the diode wire and put it back together with new plugs and see how long it runs this time.

Thanks for all the help and if you have any more ideas feel free to reply even if you think its obvious.