to lean??

[fs5]

i'm currently running .056 jets in my 55 merc .the weather is starting to cool down a bit over here.i don't want to run my motor to lean and risk damaging it.
could i get away with running 98ron fuel instead of the usual 89 ron i run it on.
i took a couple pics of the plugs,i eased off from about 6200 and shut it down.
the plugs were running around 59 F (15c)air temp,the coldest i run it at is about 40 F (5c) cool dry air.
thanks.

[Fastjeff57]

I've seen plugs running 10 % ethanol gas come out ligther than that.

My late buddy ran 100 % methanol in his SB Chevy drag car. The plugs were always stark white, but the air/ fuel mixture was spot on.

Jeff

[zul8tr]

Sure you could run the 98 but do you need it?

The RON is only 1/2 of the octane rating. What is the MON of the fuel so the average will be known which is what is stated on the pumps?

I assume that your 55 (what year?) is a stocker that has relatively low compression. These engines run fine on Mid Range 89 = (RON + MON) / 2, as stated on the pump. I prefer no E fuel if you can get it.

Your plug color generally looks OK to me, but color can be missleading. All plugs should read alike and their are color differences in the three. What advance are you set at? Have you looked at the piston crown thru the plug hole for any evidence of aluminum pocking? Any evidence of aluminum frags down in the crotch of the plug or on the slectrode? There are other items to plug reading besides color. I have a Champion Hi Performance, Racing, Heat Range and Tuning Guide that goes into the details of plug reading and other items and I could PDF you the plug reading parts of it if you want it.

[Mark75H]

I don't see any evidence of loose aluminum. I would not use any higher rated fuel.

[zul8tr]

I don't see any evidence of loose aluminum. I would not use any higher rated fuel.

I don't either by the photos but I take to the magnifier with plugs in hand when viewing them.

[Mark75H]

I have to use a magnifier and a flashlight, even in daytime

[zul8tr]

I admit the magnifier power goes up with age :eek: and a flashlight helps!

[fs5]

thanks for your replies,the plugs are a tad lighter in real life.
the motor is pretty much stock,the timing is set @ 25* so its 23* @ 5000rpm+.
the motor came with .058 jets in it from the factory.
the plugs are all slightly different in colour,#1 is the leanest #2 runs a bit fatter and #3 is the richest.