Jump to content

fouled plug


mishmosh
 Share

Recommended Posts

so my wonderfully reliable, mkIV engined herald, has an little quirk.  If I work on it on tickover  ( eg, when its Moted ) The no 3 plug (counting  from front)  fouls up. I then have to remove it and clean all the thick black crud ,off. All others are spot on.  Its running an standard  head ( and has been for twenty two yrs, no additives used ) so guess that may be the problem. I do around 1500 miles a yr. Thoughts ? Not lifted the head so havent checked rings.

Link to comment
Share on other sites

mishmosh.

 

That sounds like a rogue plug not operating within its correct heat range (i.e. burning off correctly) OR the HT lead to that plug is starting to break down by not delivering sufficient spark.

 

I would swap that plug with another known good one or better still swap it (after cleaning it up and checking the gap) with one of the others already in the head; do the swap between plug 1 and the dodgy plug 3 - that provides a bit of space between the plugs & cylinders.  

 

If the "new" plug goes dirty and the "dodgy plug" stays clean then you can safely say there is a problem with cylinder 3 - be it top or end problem. If the "dodgy" plug goes dirty at cylinder 1 then the plug must be at fault.

 

Once you have established which of the above applies, then you can take it from there.

 

As Clive states, it will be worth doing a compression test at any rate but I would do that after the plug swap; when you may have gleaned more information accordingly.

 

Best wishes.

 

Richard.

Link to comment
Share on other sites

Went on a weekend away to lake vyrnwy. Clocked up 250 miles of quite varied motoring up some big hills. Performed well. This weekend I intend to check the plugs. I have noted an increased need to use full choke this year. The choke sticks if it's pulled on full.

Link to comment
Share on other sites

Create an account or sign in to comment

You need to be a member in order to leave a comment

Create an account

Sign up for a new account in our community. It's easy!

Register a new account

Sign in

Already have an account? Sign in here.

Sign In Now
 Share

×
×
  • Create New...