quiestion on spark plugs

antonio88

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May 23, 2013
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So i took my boat to the lake last week is 1995 90 hp force motor, i couldn't get it to plane the rpms were les than 2500 at wot so i went back home i clean the carburators, replaced the fuel linea and a new filter and i check my spark plugs with my multimeter for continuity form one end of the spark plug to the other end and i dnt have continuity i checked other spark plug from my mercury and i have continuity is that normal for my spark plugs on my froce no continuity?
 

ondarvr

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It depends on the exact locations on each end that you checked, but just replace them either way.
 

Jiggz

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Do you have the BUHW plugs? When was the last time you replaced them? If it's been more than a couple of years, I say replace them. As for continuity checks, are both plugs in question identical? If not then no logical comparison can be made. Now, to compare apples to apples, with those three plugs are they all reading the same? If yes, then maybe that's just how they are. But the final test is to do a spark check using an in-line spark tester.
 

Frank Acampora

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The question is: What plugs are you using? That engine should be happy with Champion L76V or NGK BUHW. Some automotive type plugs do have an air gap internally and will show 0 continuity on a multimeter.

With that much lack of performance the spark plugs could be a problem but as Jerry said, check compression ratio and check for spark on all cylinders.
 

gm280

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I have to agree with Frank above. Some spark plugs used a little spark gap internally to make for a hotter spark once they fired over the gap. So some plugs will have no resistance. If you are comparing equal plug against the same and some have resistance and others don't, change them all. JMHO!
 

antonio88

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May 23, 2013
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well for some reason the existing spark plugs on my motor are BUHX i was reading the manual and the specs aks for the ones yall saying BUHW there is any difference
 

antonio88

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and since im here how can i know what type of electronic ignition do i have prestolite or thunderbolt
 

Frank Acampora

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1995 will have the Mercury Thunderbolt ignition. It will also have a Mercury lower unit and water pump. It may have the Mercury square fuel pump--I forget though

There is very little difference between BUHX and BUHW. One is very slightly cooler than the other, but not enough to cause problems. If you look and compare, there is little visible difference.

Just for a little schooling: Spark plugs are rated by how much combustion heat they retain. Surface gap plugs like the BUHW or others are dead cool. This is because Force outboards run a bit hot. The shell of the plug completely covers the porcelain insulator. Thus, very little of the insulator is exposed to combustion heat and there is a very short path for heat to sink through the head. This prevents the center electrode from overheating and causing pre-ignition

Bent electrode plugs have much more of the insulator exposed to combustion heat and the cooling path is much longer. Thus the center electrode runs much hotter.
 

antonio88

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May 23, 2013
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i did the compression test and i have 120 on all 3 cyl, and my spark is nice and blue, 1/4 to 3/8 jumping gap
 

oldboat1

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1/4 to 3/8 inch would be pretty weak for your CD system -- if a maximum spark. I like to use a tester to see what the maximum is for a system. If a spark will travel a half inch using a tester, I figure the system will fire a .030 gapped plug with no difficulty.

btw, I use a continuity tester for the supply of NOS Champion plugs I use on my '50s motors. I did a continuity test earlier this year as a last resort -- was unable to figure out why I was seeing good spark with a tester, but the plug was not firing. Turns out there was corrosion at the terminal nut on the top -- cleaned it up and restored continuity (and firing). Having found a "bad" plug in my supply, I guess I'm on the lookout for it now. I never routinely checked flywheel magnets either, until I had a bad one earlier this year -- another last resort idea.

(Check the magnets.)
 
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