imq707s

Well I decided to just get a K&N flame arrestor instead of messing with my stock one. The boat gained about 200 rpm's , but now I've got another problem. Before when I would made a high speed WOT run and then stop and check the plugs, they would have the perfect light brown color. After I put the K&N on , I wanted to do the same think, well I did and the plugs are bone white with just a high of tan color to them. I guess all the extra air that the motor is sucking in made it run a little lean. Is it OK to have the plugs white with just a hint of tan, or should they be a solid light brown? If I need to richen up the carb a little (4160 Holley 750 vac. secondary) how do I do it since I have no secondary jets? I don't want to go up a size on the primary jets, that will affect the mixture at cruiseing speeds? Do I need to buy one of those aftermarket secondary metering blocks (the same that comes with the double pumpers) with jets in it for my 4160?
If I got one of those secondary metering block with jets, what jet should I put in there to start testing with? I was thinking somewhere between 74 and 82's? What do you think? Thanks


21' Scarab w/350 chevy, stock thru transome exhaust, and alpha I

puder

ncie boat looks very similar to mine just a few feet shorter

ww.puder.com/scarab

Griff

imq, the color of the plugs sounds ok. When I dial in my secondaries at WOT, I look at the heat line on the spark plug electrode. You should be able to see a light, but distinct line somewhere on the tip of the electrode. Ideally it should be right at the bend in the electrode. If the heat line is close to the tip then its lean. My plugs are nearly all white after a 2 minute WOT run, but the heat line is right at the bend.
As far as the carb, you may be able to richen it up a little by changing the secondary spring, but will probably need to add a metering block with jets to do much.

Griff

As far as jets, I would start with some that are about 5 sizes larger than the primaries.