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Discussion Starter #1
Ok, I just pulled off my holley bowls, to rebuild the thing. What shize jest should i put in? It is a 650 DP Dfeed. The jets in it now were 61. and which jets flows more gas a 60 or a 61? Just need to know if bigger # equals more gas. thanks
 

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The larger the number (on the jet), the more fuel it flows.
Why are you assuming you need to go bigger? What has drawn you to this conclusion?
 

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Discussion Starter #3
i just can to this conclusion because you allways hear of people doing jet changes. Are these (60,61 jet sizes) just about ok for my st up?
I have a 289 flat top pistons, Windsor Jr. heads, .512 lift cam 228 duration. Roller rockers, t-5 in my 1966 mustang.
 

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Sounds like it may be lean to me. I had to go from 68 to 74 on the primary side to cure a lean stumble off idle.
 

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Fx, it sounds like you have had the same identical problem I have with my 4777-6. Mine would stumble coming off the line at anything less than around 3000 rpms. I tried all kinds of shooters, pump cams, 50 cc pumps and no amount of pump shot would fix it. I finally just started jetting it up 1 front and 1 back until the stumble went away. I'm up to 74 front and 79 back with a 6 1/2 front power valve. The 74's are big and will charc up the plugs a little easing it around in the pits but thats what it wants coming out of the hole to prevent the stumbles. I think the problem is caused by leaving the line with the power valve shut and it takes a moment for it to pop open at the line. I tried to run with no power valve but it was so rich it constantly blacked my plugs and I didn't like it at all that way. I would actually like to be able to switch the power valve open at the line and just run it manually, LOL. That would allow a smaller primary jet for the cruise around stuff at the track and keep the plugs cleaner.
 

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On a 650 holley double pumper,the stock jet sizes are 67 primarys and 76 secondarys.If you had a 61 primary,that's too small.Holley says, stay to a 10 jet size split from front to back if possible.Nomore than that.Soo, I would put in the STOCK jet sizes and go from there!!! I found with a really hot motor,72 or 74 jet sizes front and 80's on the rear!
 
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