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" Live Laterally "
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Discussion Starter · #1 ·
i just bought a boat from Cali and I am in CO. I am at 6500-8000 ft. I have a demon carb on a bbc and need to know if, how, where to change the jets so I can run it up here. Please let me know and thank you in advance.
 

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First off, If? Yes. You have less air up there and you are going to be noticably rich. How and where, jets, primary and secondary screwed into metering blocks found once you remove float bowls. Pull a bottom screw with a can under it to catch the fuel. Barry Grant makes a nice tool for this. Remove float bowls, you'll see the jets on the bottom of the metering blocks. They will be numbered 77, 84, something to that effect. You need to know what you have before you buy anything. I would start by dropping down 1 or 2 numbers at a time, primary and secondary evenly. Boat should start picking up performance and rpm as you close in on the optimum A/F ratio. You might ask this question in the on the dyno section, there are some very knowledgable people in there, and there is a formula for predicting jet changes based on elevation/ air density, I just don't know what it is. At minimum you need to know what jets are currently in your carb. Good luck, and don't tell anyone I was in here, the V-drive section got boring! F1~:D
 

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" Live Laterally "
Joined
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4,536 Posts
Discussion Starter · #4 ·
First off, If? Yes. You have less air up there and you are going to be noticably rich. How and where, jets, primary and secondary screwed into metering blocks found once you remove float bowls. Pull a bottom screw with a can under it to catch the fuel. Barry Grant makes a nice tool for this. Remove float bowls, you'll see the jets on the bottom of the metering blocks. They will be numbered 77, 84, something to that effect. You need to know what you have before you buy anything. I would start by dropping down 1 or 2 numbers at a time, primary and secondary evenly. Boat should start picking up performance and rpm as you close in on the optimum A/F ratio. You might ask this question in the on the dyno section, there are some very knowledgable people in there, and there is a formula for predicting jet changes based on elevation/ air density, I just don't know what it is. At minimum you need to know what jets are currently in your carb. Good luck, and don't tell anyone I was in here, the V-drive section got boring! F1~:D
THank I will do so. :)hand
Very good.
I wasn't here either.
LOL
hil:) NICE!
 

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Well so much for the Dyno section guys helping you out. They can be a funny bunch to put it mildly. I think you might be scaring them with the "where to change jets" part. Here's what I want you to do. Get yourself a copy of Demons book on their carbs. It's out there, I've seen it. Read it cover to cover, and you'll know their carbs forward and backward. Pull your spark plugs out of your motor, buy new ones, put them in. Nothing fancy, same things you took out, or their equal in Autolite. Take it to your local lake and run it as is, do not change a thing at first. Who's to say it was ever jetted right in California. Maybe it was lean to begin with. Take it out and run it. If it's rich it's gonna tell you. Your gonna smell the excess gas, it might smoke a little, and your new plugs will turn black and wet. Then take my first advice. Do that and I'll try and check in on you once in a while for more help. Chow, F1~:)
 

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I live in New Mexico and boat at 5000 ft. You can lean an out of box carb about 4 to 6 steps. I run a 482cid with solid roller with mid .650 lift and 245 duration, big port dart iron heads a Team G with an 850 holley. I run 82 jets squared without power valves. Also you can bump your timing to aronnd 38 to 40 degrees. Hope this might help. good luck.
 

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Every motor and application is different, and going lean out of the box will melt down some peoples engines. Example my combo with an out of the box Holley 1050 had to go up over 10 jet sizes to get to where it was happy. It was way lean as delivered for my application. Your motor will tell you what it wants, you need to learn how to speak it's language. F1~
 
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