Hello,
I picked up a used holley 600 carb(1850-2 0645) to put on a mild built 351w . After playing with it I took it to someone. He could not get it leaned out enough. He told me to check the # on the jets. I took it apart and the heads on the jets were marred telling me someone else had their hands in the pot. The number on them are both 64. What size should I go down to. Someone also told me go to a boat dealer and get a marine kit and this would stop my holley from flooding halfway up a steep climb with my 4x4. Any help would be appreciated. Rich

 

The general rule is to change two jet # sizes at a time example would be from 64 to 62 but if it is running way to rich then you may want to drop more sizes the color of your spark plug electrode is a good indicator of how rich or lean you are running

 

I don't know if you are describing the problem correctly. 64 is a very standard front (primary) jet size. If those are too big, you might have poor gas mileage, but I don't think you would notice anything else.

Or is it too rich at idle and low speed? Holley carbs have a power valve closed by vaccume. Todays fuels and age harden the diaphragm, and when they sit off an engine, take a set and are now stuck open, flooding the engine with fuel all the time. Buy a new one, and screw it in the metering plate. They are calibrated for different idle vaccume levels, depending on cam and transmission. You will need help to get the right one for your truck.

 

there could be a couple of problems, one could be the power valve. it is located in the metering block behind the rear fuel bowl. holley's are known for blowing these at the littlest of backfires.holley makes a power valve replacement block-off for the minimal cost of it it would be worth replacing for future occurences. the second could be jet size, yes 64's are usually standard on 600's and 650's but your valve size and head work could demand smaler jets, the best is to buy a holley jet kit and start with 61's and test and tune from there. each motor is different so look for throttle response and idle.

 

well thats great you bought the holley carb they are very good carbs. you just need to know how to set them.your 64 jets are fine you dont need to remove them. first you need to make sure your power valve is the correct size for your engine get a vacuum reading from your engine lets say its 10 inches at idle and in gear then subtract 1.5 from your reading 8.5 is then the size you need. next inspect everything blow out anyholes you can see with carb cleaner.you have two air bleed holes that need to be clean at the top of your carb.(oh dont buy a power valve block plate you have to increase your jet size about 8 to 10 numbers bigger and your truck will idle rich)next when your carb is all together and sealed up start your truck and set your float to just the fuel drips out the sight hole. after that your truck should be warmed up. with it in gear and a vacuum gauge at hand hooked up to your intake source adjust your idle as low as it goes (your choke should be fully opened or removed if you dont need it) without stalling then turn your idle mixture screws in or out until the high vacuum reading go back and forth you should be fairly close to the same amount of turns on each side after you have achieved your highest vacuum reading then set your idle to your choice. and you dont need to go buy a marine kit for it just hook up a hose from front vent back to the back vent , make a small hole at the crest of the hose for ventilation(make sure your air claener lid is about 1/2 inch from it or the air intake charge can pull fuel out of the hose) that will keep fuel out of the carb on step grades.