Plugs & ports cleanliness

[Sea Rider]

Does somebody have a tech answer on why you will find more carbon buildups on lower plugs and exhaust ports that on upper ones, specially on 2 cylinder engines that runs at 3/4 to wot most of the time ?

Happy Boating

 

[Frank Acampora]

Re: Plugs & ports cleanliness

It is for the same reason that typically only one piston melts when the engine is run lean.

Depending upon engine and manifold design, One cylinder will always run just a bit richer than the other. If you set the carb for best idle and most efficient running, one cylinder will be lean and depending upon setting, it will eventually or immediately suffer damage.

 

[Sea Rider]

Re: Plugs & ports cleanliness

It is for the same reason that typically only one piston melts when the engine is run lean.

Depending upon engine and manifold design, One cylinder will always run just a bit richer than the other. If you set the carb for best idle and most efficient running, one cylinder will be lean and depending upon setting, it will eventually or immediately suffer damage.

If that's so on 2 cylinder single carb engines, would it make any good for the engine to clean, gap & rotate plugs at each maintenance interval, let's say every 50 worked hours, than letting them in same postion untill they are replaced by new ones at 100 worked hours ?

Happy Boating

 

[Frank Acampora]

Re: Plugs & ports cleanliness

If you are going to clean and gap the plugs, it doesn't make any difference into which cylinder you replace them.

 

[Chris1956]

Re: Plugs & ports cleanliness

I always thought the lower cylinder pairs on my inline six ran a bit richer than the upper cylinders. That is cylinder 2,4 and 6 shared a carb and reed block with cylinders 1,3 and 5 (3 carb motor), and the even cylinders seemed to run richer. Also carbs 2 and 3 ran a bit richer than carb 1. I always thought it was gravity giving the lower carbs a bit more fuel pressure, and the even (lower) carbs burning any fuel that dripped down from the upper carb.