Holley Carb Jet Size?

I've got a 4 barrel Hollley Carb on a 351 PCM. I brought it from sea level and haven't changed the jets. I've heard mixed reivews about doing it, the local lakes are around 6,500 ft above sea level. Anyways since I recently pulled my carb apart and have an idea about what's going on, I've been thinkin about rejetting it. She's running great, but definatly not as strong as sea level- I know you lose hp when you got higher.

So I guess the qustion is what size is the stock jet and what would be the recomended change?

your jets will be marked with a two digit number. probably 66. you can drop a size, but the mains only come in at 2500-3000 rpm or so after the power valve starts to close.

what do your plugs look like now?

You will definetely need to re-tune the carb. Ask the local boat shop or boat mechanic what they put in.

It's not hard, but carburetor gas leaks are definitely a big concern in a boat as it will explode if you do something really stupid. Here is how to test if you have the right size jets. Clean all plugs or put new ones in. Put the boat in and warm it up. Take off and run the boat under heavy load with weight, etc for one day or session or whatever. Pull a plug. If it is white, you are lean, you need bigger primary jets. If it is brownish or even very light brownish, leave it alone. If it is black, get your carb and/or engine looked at or replaced.

(Message edited by cyclonecj on July 03, 2004)

If this is a mystery to you, do as Peter suggests and get it looked at by a competent mechanic. Good car guy is better than a crappy boat guy in this case.

I would say leave it alone. Carbs work on a pressure differential. They are better at self adjusting to altitude than you would think. Pro stock drag racers don't even change jet sizes when they go to Denver, they may make a suttle air bleed change but thats it. This is not to say your boat will run as good up there, there is still less air. I am just saying that carbs do a good job of correcting for it. An EFI engine will not run as good up there either. Any change you might make would not make it run like at sea level and probably not be worth your effort unless you are like me and like messing with that stuff. If I did anything for altitude it would be a prop change.