Carb jet size

[Longhorn21]

I have a 87 supra comp ts6m with a 351 ford windsor. I have a 4160 marine carb, can anybody tell me what size jets they have in their carbs. I called the Holley tech support today and gave them the list# on my carb and they told me I should be using 74 size jets, but I have 65 size jets in their now. To you more experience boater's does that sound right. Why would my jet size be 9 sizes to little. I would like to know what everybody has out their so I can compare. Thanks

[Longhorn21]

Oh I forgot it's a 4 barrel single pumper with 600 cfm

[warek1814]

Pull your spark plugs and look at the color. If they are white it is lean and you need to go up on jet size. If the plugs are black it is to rich and you need to go down on jet size. You want the plugs to have a tan/light brown color. If I had to guess I would say a 70 or 72 on that motor. Your pulgs will tell you what you need to do though.

[Longhorn21]

They are not white they are black, but my engine is surging at low rpm's which makes me believe my jets are too little. My black spark plugs could be because my engine has been flooding lately.

[warek1814]

The best time to check the plugs is on the water. Run the boat at about 2,500 rpm and then hammer down on it to about 4,000 -4,500 then shut it down. Don't let it idle. Pull a plug real quick and check it. The plug will be hot so break it loose with a rachet and then slide a piece of 3/8 vaccum line over the end of the plug. That will keep you from having to touch a hot plug. Engine needs to be at temp when this is done. Check the air fuel screws on the side of the meetering plate. With motor idling screw them in until motor starts to die. Then back them out until motor is at it's highest idle.