Surface Gap Spark plugs
 

Hi guys, I am looking for some guidance regarding replacement plugs for my 1980 200Hp Mercury outboard. I wanted to have a couple of spare plugs on board and purchased NGK BU8H surface gap plugs in error. Will these plugs work on my old merc? Theoretically, they look like they would be less likely to get gummed up. Curious whether the group has any experience with this plug design.

Thanks, Duke

I wouldn't if it was mine. Surface gap plugs are good if you're running it flat out for long periods of time, but for mixxed use with some idling they tend to foul out easy. Whenever an engine called for a surface gap or an electrode style, I always used an electrode style.

Thanks Fermanator, I appreciate your input. Standard plugs it is.

Duke

I m guessing with a 80 model, you don’t have oil injection, so the gapped plugs would be my choice,also. Make sure you check the gap before installing, have found a few almost closed from banging around, i guess.

I completely agree that given the choice go with the gapped ones. but look up your engine specs though. Some engine manufacturers specified surface gap plugs instead of gapped plugs. I always go with what the engine maker calls for. :head:

I do as well, but sometimes they reccomended both styles, one was for general use, and the other for sustaned high rpm runs. Omc used to do this with the ql77jc4 gapped plug for general use, or the ql7iyc which had an extended electrode for sustained high rpm use. They worked great if you were running 5K+, but idlefor 5 minutes trolling and they were all fouled. Put ql77jc4's in and no more fouling.

Or how the early 80's cross flow omc outboards origanally used surface gap plugs, but omc changed there reccomendation in the 90's due to fuel changes, and now they call for a gapped ql77jc4 unless it's on a performance boat in which case you can still run the surface gap plugs to minimize detonation.

Yep. Completely agree. That's why I said "given the choice go with the gapped". I've had more than one set of surface gapped plugs foul up on me.

First of all, thank you all for your help. There is a wealth of practical experience with the folks on this website. I had an opportunity to get to the boat this weekend. As it turns out, the old plugs are surface gap NGK BU8H. That is also the plug that is listed for my outboard (1980 Mercury 200 HP) on the Mercury 2016 US Accessories Guide...Mercury part number 33-13686Q. So, that is what I purchased today.

The engine runs well at cruising speeds, but idles rough and stalls. Hopefully a fouled plug is the cause (?). I will find out in the next week or two.

Thanks Duke