What kills spark plugs?

[maginoodle]

Hi all, i havent come across this problem before.

I have an old forklift that has a mitsubishi engine. It has a points type dizzy.
A couple of months ago it started running rough and when i went to check for spark i had none on number 3 and 4 plugs. There was spark at the lead but both those plugs were dead.
I replaced them and everything was good.

The other day it started running rough again so i checked and both plugs again and they were both dead.

I have never had plugs that were totally dead before, i have had them with very weak spark but not zero spark.

So what causes them to die?
This time i replaced them with second hand plugs cause until i find the problem i dont want to keep buying new plugs.
I dont know what plug they are supposed to have in them i just replaced what was in there when i bought it.

Any help/ideas appreciated.

Cheers Shane

[DevilDRake]

If you tell me the brand, year, and what type of engine it is I can check it up at work.

[maginoodle]

If you tell me the brand, year, and what type of engine it is I can check it up at work.

Hi its a mitsubishi fork 1972 model fg25.

Cheers Shane

[Darren_L]

what did the plugs look like when you removed them ?
were they fouled with oil, carbon, sooty ?

if the engine is overfuelling it can foul up the plugs and eventually stuff them. Also make sure the plug gap is correct for that engine.
I know when the carbs were out of balance on my bike, I used to kill plugs all the time from overfuelling. Without warning, it would just start misfiring on one cylinder. Once I balanced the carbs, didn't kills plugs anymore.

[VT-565]

If the insulation cracks down inside the plug it will spark straight to earth.
General plug condition would be a good indicator

[VR38]

Prolonged idling will foul a plug, if this is the case then maybe switch to a hotter plug.
Read the colour of the plug and compare it to a google search...

[strgas]

lean mixtures will also over work the plugs , giving the plugs a higher resistance reading too a point where the spark will not go thru the plug but thru the plug boot or the easiest path to earth .

[Tree cutter]

I have heard of plugs failing when they get coolant on them from a blown head gasket.
Does the inlet manifold sit level when looking from front to back? Most carby engines will get a puddle of fuel sitting below the carby at times and if the manifold is not level the fuel will run down to one end causing the cylinders to run rich at that end. The forklift could have a sagged engine mount or the wrong tyres fitted which could let the manifold sit lower at one end.

[DevilDRake]

Hi its a mitsubishi fork 1972 model fg25.

Cheers Shane

Sorry, I haven't been back at my original work for a few weeks, i'll check it up for you tomorrow, i wrote it down.

[maginoodle]

Hi all, another pair has died in 3 and 4 again. They were bpr6es plugs, just put some bpr6ef's in them.The only difference i could see from a quick look is the socket size you need to get them in and out.
I have plenty of those around so i wont run out any time soon. But i would like to find out whats killing them.

Cheers Shane

[ari666]

ok so: Traditional Spark Plug, 14mm Thread Size, 19mm (3/4") Reach, 13/16" (20.6mm) Hex Size, Gasket Seat, Resistor, Solid Terminal Nut, JIS Height, Projected Tip, .035" (0.9mm) Gap, Heat Range 6

what do the tips look like after they 'die' also i dont suppose you have checked the condition of the rotor button and dizzy cap? intermittant misfiring from crappy caps can cause them to foul really quickly.

spark plugs are pretty tough little f'kers. unless you have your heat range waaaay too low or too high they dont really go worng much. dont suppose you can post a pic of what the end of the plug looks like?

[Andrew426]

You sure its not corrosion on the end of the lead? I have had that problem before. A corroded boot has caused a misfire, putting a new plug in it has cleaned/scraped enough crap off it to get it running right again, but the corrosion then spread back onto the plug and the misfire came back a few weeks later.

[STEEV888]

Hi all, another pair has died in 3 and 4 again. They were bpr6es plugs, just put some bpr6ef's in them.
Cheers Shane

bpr6es is honda lawn mower plugs...