Will hotter spark plug prevent fouling?

[brc1981]

I have a Mariner 9.9 682C and have problems with it fouling the plugs when am idling for long periods of time. The lake I frequent is idle only so the motor typically only gets to hit idle speeds. I have make sure my fuel mixture is correct and last spring I rebuilt the carb, but the problem still persists. It calls for a NGK B7HS-10 plug but was thinking if I could find a hotter plug it might prevent the fouling. Is this something I should try, if so what plug? If not what else should I look at?

Thanks.

 

[matt9923]

Re: Will hotter spark plug prevent fouling?

Yes i would get a hotter plug and gap it bigger so it burns more exes fuel.
That should help. Are you saying you cant go over idle cause of speed restriction on the lake? You should get a small motor maybe?
Also try adjusting the low speed so it doesn't foul.
Matt

 

[brc1981]

Re: Will hotter spark plug prevent fouling?

Yes, the lake is restricted to idle speeds only. I do have a trolling motor, but the lake is large my battery wouldn't laster longer than a 1/2 day of fishing. I have been toying with the idea of finding a smaller 5HP outboard.

 

[cr2k]

Re: Will hotter spark plug prevent fouling?

Plugs could help, but be careful if you go too hot and run it somewhere else at higher throttle you could burn the pistons. Hot when idling you should change/check the impeller. Should be changed every 2 years if you use boat or not. Also once they overheat there is a small plastic grommet that goes under the powerhead to the water tube that will melt and deform restricting water flow.

Also DO NOT USE cheap oil. Use GOOD TC-2W oil. I know it cost up to $25/gal but it will save big bucks down the raod.

 

[Silvertip]

Re: Will hotter spark plug prevent fouling?

Go to the NGK web site and pull up the marine spark plug application chart. Look up the plug number you currently have. It will indicate its heat range. Pick the next hotter plug. Make darned sure you pick a plug that has the same number except for the heat range. You cannot stick a long reach plug for example into an engine that takes a short reach plug. And just so you know, just because you buy a smaller engine does not mean you solve the fouling problem. That 5 HP engine must run at idle also so it will likely foul plugs as well. Before you mess with plugs, you might consider running the fuel mixture with less oil than the 50:1 rate. The engine should live just fine on say 60:1 or even 70:1 as long as it never gets above idle. Another thing to try is a full synthetic oil. Less smoke, cleaner burning, and better for the engine and the environment.

 

[matt9923]

Re: Will hotter spark plug prevent fouling?

Get like a 2hp of eBay fro $150. Then you can open that up and it will be like idle.
Matt

 

[brc1981]

Re: Will hotter spark plug prevent fouling?

My mariner calls for NGK B7HS-10 plugs. Once I get back out on the lake the plan is to try to stick with the specified plugs, but if the fouling isses start again I'm going to swap in some B8HS-10 plugs. If I go elsewhere that isn't restricted to idle speeds only I'll swap the B7HS-10 plugs back in.

I'm also going to look into the synthetic oil, but I've never seen it around here.