Do I really need to use a surface gap plug?

[etd66ss]

All the plug charts I can find on the net are telling me my Evinrude 150849S uses either Champion UL77V or NGK BUHX.

Will the crossflow pistions hit the electrodes if I use QL77JC4's?

 

[boobie]

Re: Do I really need to use a surface gap plug?

I don't have the charts in front of me, but I know there were certain mtrs of your era that required surface gap plugs due to the reason you mentioned. QL16v was another option. It was a little hotter plug than the 77's.

 

[etd66ss]

Re: Do I really need to use a surface gap plug?

I don't have the charts in front of me, but I know there were certain mtrs of your era that required surface gap plugs due to the reason you mentioned. QL16v was another option. It was a little hotter plug than the 77's.

I got the motor running tonight with electrode plugs, didn't see that they were getting hit by the pistons...

 

[Daviet]

Re: Do I really need to use a surface gap plug?

You can always use a small screw driver to measure the distance from the piston to the cylinder head with the piston on TDC.

 

[boobie]

Re: Do I really need to use a surface gap plug?

The true test would be to take it out and run the hell out of it and see what happens.

 

[oldrudedude]

Re: Do I really need to use a surface gap plug?

The factory manual for my 1971 50hp suggests using surface gap plugs but the surface gap only well if you do a lot of high RPM driving. I use regular electrode plugs in it and find it idles better and the plugs don't foul as easily.

 

[fucawi]

Re: Do I really need to use a surface gap plug?

If you use standard plugs with a CDI you risk Pre ignition as the spark engergy is 10 x that of a standard plug and this can over heat the centre electrode .If you must run wire electrodes run a cold plug and if all is well dont change from the brand spec you are using

 

[Dhadley]

Re: Do I really need to use a surface gap plug?

First, never run NGK plugs in that motor. With todays fuel the Champion QL77JC4 plug is just fine.

 

[Sprky]

Re: Do I really need to use a surface gap plug?

First, never run NGK plugs in that motor. With todays fuel the Champion QL77JC4 plug is just fine.

Please explain?

Fucawi................Almost every motor built within the last 30 years is powered by a capacitive discharge ignition. Plenty run standard electrode plugs, why would OMC call for regular electrode plugs in their other motors if this were the case?

You can run the ql77jc4's or the ql77cc's or b9hs10 down to the 7's if you have problems with fowling. Some of the head castings will allow even you to run the projected tip ql78yc's.

I have found that the NGK BU8H seems to work the best and are as cheap as the champions, cost wise.

Old rude got it right........surface gap for wfo running, regular electrode will run a little better if you do a lot of idling.

 

[Haffiman]

Re: Do I really need to use a surface gap plug?

First, never run NGK plugs in that motor. With todays fuel the Champion QL77JC4 plug is just fine.

No danger of running NGK plugs in Evinrude/Johnson as long as you stay away from anything marked 'R'!!!
Use the 'Q' marked Champion, or non-'R' NGK. However with a 'normal' plug in those engines, you run a risk of burning pistons if driving hard. If you have problems with idling and the UL77 plugs, go for the QL16V and be sure your cooling system and thermostats are fresh!!

 

[Dhadley]

Re: Do I really need to use a surface gap plug?

The carb'd OMC motors are calibrated around the Champion plug heat ranges. Just like the Merc and Yamaha fuel delivery systems are calibrated for NGK plugs. Some OMC motors are more tolerent to heat range differences but some are very sensative.