spark plug question?

[spete]

Yamaha 115 owners manual/Clymer indicate .035 - .039 for the NGK BR8HS-10 specified for the motor. <br /><br />Had mechanic checking out a rough idle and he indicated the the plugs were gapped too close and he gapped out to .045 - stated that the "-10" after the "HS" meant to add .010 to the gap. Just wondering why the spec wouldn't just be the gap with the .010 already added? Also, it did seem to make my motor idle better/no sputtering - is there anything wrong with running a wider gap on the plugs if it is actually wider than manufacturers spec?<br /><br />Thanks for your advice.

 

[zzzzz]

Re: spark plug question?

according to my NGK catalog,the "-10" means that the plugs are factory gapped to .040,"-11" means .044,etc...no matter what,i always check gap-don't rely on factory gap.

 

[spete]

Re: spark plug question?

So, should I gap plugs at .035-.039 as specified or should I go with plug manufacturer?<br /><br />And, is the wider gap (.045) I'm currently set at right now going to hurt anything?<br /><br />Thanks ...

 

[ob]

Re: spark plug question?

spete,If your engine runs best where they are set now I'd leave them there.It won't hurt a thing and your probably getting a more complete burn is why it idles better.

 

[spete]

Re: spark plug question?

Yes, it's running much better and I'd rather just keep the set-up i have - just wanted to make sure it wasn't affecting timing/burning too hot/etc. <br /><br />Thx OB

 

[BillP]

Re: spark plug question?

Strange, usually a too wide (not too close) gap shows first as rough idle. Anyway, I'd personally go with the mfgs specs. Just for the heck of it you may want to check Yamaha tech bulletins to see if they have changed the gap specs.<br /><br />Wait a minute, you said Clymer manual...do not depend on Clymer for absolute accuracy. Many folks who have used lots of Clymer manuals will tell you they generalize and make mistakes. I use them as a last resort. Double check the gap with your Yammy manual.

 

[spete]

Re: spark plug question?

Clymer & Yammy manual both indicate .035 - .039 ... I don't know how .005 or .006 added gap could make that much of a difference but it seems to have fixed the rough idle so I guess I'll stick with it

 

[fridays]

Re: spark plug question?

A wider gap actually makes your engine run a little leaner. If in your case it runs better at idle that simply means that your idle mixture is a little too rich. Go back to the standard spark plug gap and lean out your idle mix screws about 1/4 turn. The results should be about the same smoothing out your idle and you won't run the risk of the motor running lean and burning a piston at high speed.

 

[spete]

Re: spark plug question?

Fridays - looks like there's a pilot screw on the carb and an idle speed screw on the carb linkage. Idle speed is just idle speed - not idle mix correct? <br /><br />Is this pilot screw what I use to adjust the idle mix? Looks like the two barrel is set up differently than the smaller 90 hp/single barrel with no indication of an idle mixture screw on the carb diagram. Book indicates 3/8 to 7/8 turns out on the pilot screw ... Is this what I adjust? Do these things work themsleves out of adjustment over time?

 

[ICEMAN]

Re: spark plug question?

Hi, I hate to add controversy (spelling?) to a statement, but how does a difference in gap make a motor run leaner? I don't see where it would change the fuel to air ratio, I could understand it changing the timing of the spark by a milisecond, which could could have a very small possibility to be enough to cause pre-ignition, but not make it run leaner.

 

[spete]

Re: spark plug question?

That's a good question, now I'm really not sure about the wider gap on the plugs/downside. I'm guessing that the wider spark burns/helps ignite more fuel - creates a longer burn and perhaps a leaner/hotter combustion??? I'm guessing ...

 

[Boatist]

Re: spark plug question?

Spete<br />The spark plug gap will not make a motor run leaner or richer. Fuel misture is set by the carb and if it running good I would leave it alone.<br /><br />Increasing the spark plug gap will have some effects. Making the gap wider will require a higher voltage to fire the plug. If you pulled the plug and grounded it you would find spark will jump a very wide gap but in the motor it is under high pressure so takes more voltage to jump the same size gap. I do not see what year your engine is and do not know what type spark system you have. The way the plug fires is voltage builds until high enough to jump the gap of the pulg. With a wider gap needs more voltage so voltage will build up much higher before plug fires. In a old point and condenser system normaly will not hurt it, but even here voltage builds to a higher level so coil and plug wire will have to be in good shape so as not to short out. In some newer systems with power pack to high a voltage could cause power pack to fail. <br /><br />I would set to your normal factory setting. I bet it will not effect your motor. A difference of .005 probably not enough difference to hurt engine but I bet has no effect on preformance either.<br /><br />Dealer may have changed plugs or set idle or timing to fix your engine.<br />Let us know what you do and if has any effect.

 

[spete]

Re: spark plug question?

good information to know - thanks boatist. My motor is a 98 Yamaha 115 with oil inject. Just looking over the electrical diagram there are two charge coils, two pulser coils, a lighting coil, ignition coil, CDI unit and rectifyer/regulator. I don' t see how .005 could make any difference in correcting a rough idle but for whatever reason is has. I am planning to pull the plugs and recheck the gap just to see where mechanic actually put the gap? I know that the NGK plugs have a conical washer on them that crushes down - they only recommend tightening 1/4 turn after hand tight. Will i need to replace the plugs if I pull them or do they sell replacement washers?

 

[Boatist]

Re: spark plug question?

Spete<br />You can reuse plugs just do not over tighten when you put back in. I check, clean, and gap plugs all the time then put back in. My plugs have same washer. I put my hand right on top of the ratchet shaft and tighten snug only, do not use the handle. Note how tight they are when you take them out. Many people over tighten plugs. Even finger tight if put plug wire on where it pulls in a direction that will tighten plug it will be fine. You manual should have a torque setting.

 

[spete]

Re: spark plug question?

Thanks Boatist - will try and use the old ones. I think i checked and re-tightened a previous set of plugs too tightly and I started getting a bit of seepage from around the plug, just wasn't sure about those washers on the NGK plugs.