Surface gap versus standard sparkplugs

[tacx]

Hi All,
The plugs in my 1970 9.8 hp 110 mercury are NGK BUHW-2. These are the surface gap type plugs. I believe thats what they are called. After doing some research some have said that these plugs are not the best for good idle? And that if a good idle is wanted that a standard plug should be used? Can anyone expand on that. My motor runs great at top end but the idle is crappy? That said, if a standard plug can be used, does anyone know what plug to try?
Thanks
Tom

 

[Alumarine]

If the motor calls for surface gap plugs that is what will work best with the motor.
Your idle problem could be a carb adjustment.

 

[jimmbo]

Some engine did spec both surface gap and a regular style plug, with direction that the regular plug 'may' work better in prolonged idle situations. When the Surface Gap plugs were introduced in the mid 60s the claim was these ultra cold plugs prevented detonation, and the Electronic/CD ignitions could reliably fire these plugs even if they were fouled.

iboats has this Champion listed for your engine gap@0.040
http://ww2.iboats.com/mall/partfind...gd_poid=173506&gd_row=31&session_id=417117675

 

[merc850]

You have to be careful because some piston designs come very close to the plug and may hit it, also figuring out the heat range may cost you a lot in test plugs.

 

[tacx]

After more research I understand the piston comes very close to the plug. And, this was done to help keep the plug clean by burning off any carbon accumulation. Anyway, looks like I will stick with the surface gap plugs.
Tom

 

[merc850]

Run your motor in the lake in gear until it's warm then slow it down to idle speed and turn the low speed adjustment screw slowly out until it runs poorly; then turn it the opposite way until it runs smoothly. The gas oil ratio is 50:1.

 

[merc850]

A little history on surface gap plugs

 

[roscoe]

Maybe just switching to the Champion L78V surface gap plug, from the NGK, will give you an improvement.




[h=2]Replacement spark plugs for NGK BUHW-2:[/h]

AC Delco	V40FFK
Autolite	2872
Bosch	W4AC
Bosch	WEA
Champion	L78V

Brand Model

 

[jimmbo]

I always liked the AC Delco plugs the best, at least on our old Evinrudes and Johnsons

 

[tacx]

UPDATE, I took my engine to an old timer who was a outboard mechanic for many years. As mentioned in another thread, someone installed after market coils in my engine. So the surface gap plugs, that mercury recommends, did not play well with the after market coils. The old timer changed the plugs to standard plugs which are Champion QL77JC4 and the engine started first pull and runs like a top both low and high speeds.
Tom

 

[roscoe]

great !