Spark Plug Gap for HP500?
 

Does anyone know what the gap should be for 1999 HP500 carb engines? I just bought Denso Iridium plugs and want to get this right.

Thanks!

.035

Thanks LaVita.

No problem.

Should've asked yesterday!

I figured they came pre-gapped. I was talking to I'CE today and he asked me what the gap was supposed to be - got me thinking. It turns out they were all at 0.35 already.

Now I have new plugs, wires, distributor caps and rotors. Looking for lost RPMs.

thunderbolt IV and V found spec. @ .040 and sterndrives.com has spec @ .030 what gives ?

The merc flame arrestors have .035 stamped right on them

Doesn't hurt to check.

I have a question I just run the mr43 delco plugs what's the selling point with the iridium plugs do they not foul or just last longer

if these are the very fine wire spark plugs U are not suppose to change the gap on these plugs. Mercruiser had a SB on these many years ago to not change the gap because it can cause a engine miss.

The reason for the engine miss is - U are off centering the tip from the electrode and R taking a chance of bending the fine wire.

Also I have worked on Small block carb motors that they changed the spark plug gap to the lower spec gap for that app using the fine wire Iridium plugs.

The engine had a slight miss - plug change and non fine wire at the correct gap fixed the problems. The double platium tip portion of the plugs was off centered from the lower re gap. FYI