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Garden Tractors Discussion Forum

18HP Vanguard fouling plugs

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Magilla

08-04-2004 05:02:46




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I have an Encore ZTR mower with an 18hp Briggs Vanguard motor. It is 5 years old, but only has about 300 hrs on it. It has started fouling plugs this year. It will run about 15 hrs before starting to run rough and blow black smoke out the exhaust, at which time I have to replace the plugs, then it runs fine for a while. I switched to full synthetic motor oil last year, could this be causing the problem?

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Jerrie

08-05-2004 20:40:58




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-04-2004 05:02:46  
One thing the Briggs tech told me quite some time ago is to never oil the prefilter on an OHV briggs and stratton engine it will always make them run too rich. The fuel system is a lot more touchy than the old L-head engines. Jerrie



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tuke2

08-05-2004 17:13:27




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-04-2004 05:02:46  
I'd check the timing and points setting. Does it ever make any kind of rattling noise that would indicate a valve problem?



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txblu

08-05-2004 07:48:42




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-04-2004 05:02:46  
I had a BS V twin once that used a nylon float /valve/interconnect, rather than a rubber/metal valve, brass interconnect and brass or plastic float.

Over time, the nylon weakened and allowed the bowl to overfill which resulted in fouled plugs; dry (damp) sooty, very black.

5 years would put you in the right area as to time/fatigue, and manufacturing engines with the nylon float. I would think that current engines are better equipped in this area..... .least I hope so. I returned it to the dealer for a Kohler powered mower and have no more problems.

Synthetic oil is the right answer as far as oil is concerned.

Mark

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sammy the RED

08-04-2004 23:59:48




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-04-2004 05:02:46  
Are you running your mower WOT ?



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JT

08-04-2004 07:14:00




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-04-2004 05:02:46  
if it is fuel fouling the plugs, you more than likely have a carb problem. Synthetic oil should have nothing to do with it, unless you are running a real light multi-vis oil, then it might cause the problem, is it probable, no.
When was the last time you replaced the air filter??? Do you run a pre-celaner?? Did you oil it?? if you did oil it and got too much oil in the foam, that could be the problem. One other thing to check, if this has a choke control seperate from the throttle, make sure the choke is being fully opened, it you have a cable that is stickiy or slipped, it can leave choke on partially and also cause this problem.

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TheRealRon

08-04-2004 05:17:45




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-04-2004 05:02:46  
The oil has nothing to do with it.

"Fouling" means nothing. Put new plugs in it, run it an hour or two and then read the plugs. If they are OIL fouled then you have a ring problem. If they are GAS fouled then you have an ignition problem... in this case, the engine would also experience some "missing".



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Magilla

08-04-2004 06:16:26




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 Re: 18HP Vanguard fouling plugs in reply to TheRealRon, 08-04-2004 05:17:45  
How do you tell the difference between gas fouled and oil fouled? The plugs after 15 or so hours are black and have like carbon deposits on them that feel kind of chalky, but do not feel oily.



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TheRealRon

08-04-2004 06:56:10




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-04-2004 06:16:26  
What you described is gas fouling but it could be the result of the plugs being oil fouled over time.

So, do what i suggested earlier and then read the plugs.



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Magilla

08-05-2004 09:41:25




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 Re: 18HP Vanguard fouling plugs in reply to TheRealRon, 08-04-2004 06:56:10  
Did as Ron suggested, plugs are black after an hour and it sounds like it is missing, especially at lower rpms. A little more info, I always run at WOT, it has a new air filter and battery. Where do I go from here?



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Magilla

08-05-2004 09:49:26




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-05-2004 09:41:25  
One more thing, it acted similar to this earlier in the year when the battery was dying. I would charge the battery and it would run good, then about 30 minutes later it would start to cough and run badly. When the battery finally died completely, I replaced and it seemed to take care of the problem. This makes me think maybe it is an ignition problem. What can go bad on an electronic ignition motor, the coil, plug wires, coil wire? Does this thing even have a coil? If so where is it? Thanks

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txblu

08-05-2004 09:58:40




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-05-2004 09:49:26  
Read my post at the top of the post.

Battery should not have any thing to do with ignition in a (most) air cooled engines of current design.

They use a magneto which is a coil of wire with a magnet (imbedded in the flywheel) which passes by the coil generating the spark. They don't even use ignition points any more (some). Battery is not part of the ckt...think of the old hand crank tractors..they had magneto's (more sophistocated but none the less, self contained spark generators).

Engine is stopped by grounding a tap on the coil which shorts out the coil and the plug voltage disappears, hence engine stops. Ground is applied via the stop position on the ign switch; or maybe an interlock via seat or pto.

Go after the carb first. Your problem doesn't sound magneto related.

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Magilla

08-06-2004 12:17:54




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 Re: 18HP Vanguard fouling plugs in reply to txblu, 08-05-2004 09:58:40  
What can I do to check out the carb, other than taking it apart and looking for obvious stuff?



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txblu

08-08-2004 09:00:57




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-06-2004 12:17:54  
Pay particular attention to the float and fuel sealing device (normally a steel needle valve with/without black rubber insert to do the sealing). As I recall this was all in one molded piece in the BS V engine. If it's bad, the sealing point would be scored (a scratch would do it) or if you turned the carb upside down, the float would not be parallel to the carb housing; the end that the float's on would be bent towards the housing. That's how it fails. Material fatigue of the nylon and it can't resist the fuel pressure against it and yields which keeps it from pushing the shut off valve into the fuel line to the bowl and stopping the flow of gas.

Mark

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Magilla

08-09-2004 08:53:38




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 Re: 18HP Vanguard fouling plugs in reply to txblu, 08-08-2004 09:00:57  
The carburetor has a wire coming out the bottom of what appears to be a nut. Is this what I remove to check out the float and seat?



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txblu

08-11-2004 08:54:59




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 Re: 18HP Vanguard fouling plugs in reply to Magilla, 08-09-2004 08:53:38  
That sounds like a fuel shut off valve which holds the bowl on. Yes. Some engines only have the nut (screw) holding the bowl on; no shut off valve.

Mark



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