2.7 head pre install / cyls 5&6 lean burn ????

[Tightrig 12]

23 Eliminator Daytona, twin johnson v6
Last run of year boat ran 75 at 6200rpm
Jetting is stock 62D 1-4 / 65D 5&6
Removed head to prep for 2.7 heads install
Both motors cylinders 1-4 show burn on piston
5&6 piston look new. Did spark check, all cyl are firing.
Not sure what to think of this....to me, they appear to be lean but I had not over heat warnings or any other signs. Boat ran good. any input would be helpful.

[bullet20vee]

I can tell you from recent experience that you are flirting with disaster. If you keep running like that, you're gonna have melted pistons and a bunch of aluminum on the cylinder walls. Jet it way up and come down to where it looks good. If you are putting the 2.7 heads on, you need to be upwards of 72's

[Tightrig 12]

Thanks Bullet
I purchased 64D's for 1-4
And
67D's for 5&6..... this was before I saw this.
I'm thinking 64's will be fine since upper 4 are showing good burn on piston

[bullet20vee]

Check back and see what Racer said on the other thread. You're gonna bump the compression up a lot with those heads. You wanna go rich and adjust down from there. I still have those other jets if you need them.

[Tightrig 12]

What sizes do you have

[Tightrig 12]

From info I gathered....im not gutting the air box so going only 2 sizes up....obviously more on bottom 2 after seeing pistons

[bullet20vee]

I have 2 #62, 2 #67, 1 #69, 6 #75, and maybe more if I do some digging.

[racer]

Lower ones are rich washing the carbon

[Tightrig 12]

Thanks Racer...see PM

[Tightrig 12]

Bullet
I'm on the fence for sizes right now after seeing lower cyl.
Once I make a decision I can see if you have any I need.
Thanks again
Bart

[bullet20vee]

Just curious Racer, how can you tell it's rich and not lean? Mine looked like that and was lean, melting the piston. Thank you for sharing your knowledge with us and thanks for all of your advice in the past. :cheers:

[racer]

65D with all the air box parts including baffle is generally rich, also the top 2 in the photo are slightly rich. IMO 3 sizes above stock is more than needed for bottom cylinders unless the engine has another issue like timing out of spec. If it were so lean that no color is on the piston or head it would already show signs of melting over the exhaust port. A good photo of the ground strap on the plug to see where the heat is will confirm.

[Tightrig 12]

Thanks for input Racer...good info
There seems to be no other issues...cylinders and pistons 5&6 both motors look good, no signs of excess heat.
I ran this boat hard for 3 days speeds of 60 to 75 before pulling heads. I'm guessing, but if it was lean...i would have had a problem within those 3 days.
In your opinion, after seeing these photos, would I be good running stock jets, as is now(62 upper 65 lower )
With 2.7 heads
Or
Recommend 2 sizes up as we discussed before (64 & 67)
Stock air box
Thanks, Bart

[racer]

Per what I mentioned via pm a few months ago.

[Tightrig 12]

Thanks Racer....appreciated as always
B
See PM