Jet sizes?
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Jet sizes?

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    Default Jet sizes?

    Regarding my Holley 850dp carb. I am currently running 82 primary and 80 secondary jets with 6.5 powervalves. If I screw the mixture screws in all the way it picks up rpm and likes it. Does this mean I should jet down a couple sizes? the funny thing is after a WOT shutdown the plugs look perfect with the mixture screws out 1.5 turns.. What's going on here?

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    gn7
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    idle mixture screws have virtually nothing to do with your jet sizes. if the motor likes the screws turn all the way it means either your float is too high or your idle bleeds to to be enlarged, but if you don't know what your doing here then just leave them screwed in however far the motor likes. are the power valves in the primaries only? why are your primary jets larger than than the secondaries? 82's plus a power valve? this is way backwards



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    Quote Originally Posted by gn7 View Post
    idle mixture screws have virtually nothing to do with your jet sizes. if the motor likes the screws turn all the way it means either your float is too high or your idle bleeds to to be enlarged, but if you don't know what your doing here then just leave them screwed in however far the motor likes. are the power valves in the primaries only? why are your primary jets larger than than the secondaries? 82's plus a power valve? this is way backwards
    I looked up what the carb came with stock and it said 6.5 pv's on the primary and secondary and 80 jets primary and 78 jets secondary... I didn't have those jets so I jetted up a bit. The floats are dead on (fuel to the bottom of the sight plug).

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    gn7
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    if you have power valves on the pri & sec then that not nearly as weird as I first thought, I don't usually run PV on the sec side. More like 72 with a pv on the pri side and 80's & no PV on the sec. But none of this effects your idle. Is this a single or dual carb on a tunnel ram?



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    As gn7 said, idle and WOT mixtures are totally separate animals, don't try to connect them.

    I run a more "conventional" setup that gn7 is used to seeing in a holley, 67pri, 77sec, and a 6.5" power valve in the primary only. Kind of odd to see dual pv's is all.

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    Quote Originally Posted by SmokinLowriderSS View Post
    As gn7 said, idle and WOT mixtures are totally separate animals, don't try to connect them.

    I run a more "conventional" setup that gn7 is used to seeing in a holley, 67pri, 77sec, and a 6.5" power valve in the primary only. Kind of odd to see dual pv's is all.
    Is there an advantage to blocking one pv off? I guess I'm alright considering it does great at speed. there are some other minor things such as one accelerator pump coming in late but thats no big deal.

    GN, it's a single carb deal.

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    Quote Originally Posted by gn7 View Post
    idle mixture screws have virtually nothing to do with your jet sizes. if the motor likes the screws turn all the way it means either your float is too high or your idle bleeds to to be enlarged, but if you don't know what your doing here then just leave them screwed in however far the motor likes. are the power valves in the primaries only? why are your primary jets larger than than the secondaries? 82's plus a power valve? this is way backwards


    So if I turn the mixture screws all the way in and it wants to keep gaining RPM then I should be lowering the float levels?

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    gn7
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    also is this pri idle only or four corner. you want to rethink your whole jetting and PV set up. Dump the sec. PV and run the sec 7to10 larger than the pri.
    72/w PV and 80 sec is safe and then jet down from there. Don't know your combo so it's hard to tell, just basing it off what your running now



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    Quote Originally Posted by gn7 View Post
    also is this pri idle only or four corner. you want to rethink your whole jetting and PV set up. Dump the sec. PV and run the sec 7to10 larger than the pri.
    72/w PV and 80 sec is safe and then jet down from there. Don't know your combo so it's hard to tell, just basing it off what your running now
    4 corner idle. Its a 461 12:1 single carb jet. What is the reason for dumping one PV? So to give that a try Ill plug the sec PV and run a 80 and 72 on the Primary with a 65 PV and go out and do the kamakaze WOT shutdown and see how the plugs look? I'll do it if there is a reason why it's better

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    if the jetting seems ok then leave it. it has ZERO effect on your idle. NO do not lower your float level, only mentioned it because it can effect the idle, I run my pri at the bottom of the hole and the sec a little higher but the bottom is OK. More than likely you will have to run the screws turned in because of the 4 corner. these carbs were built for engine with pretty lumpy cams and a bad cab signal. If the cams is moderate then it pulls to much fuel at an idle. Just run them turned in and worry about it.



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    Quote Originally Posted by gn7 View Post
    if the jetting seems ok then leave it. it has ZERO effect on your idle. NO do not lower your float level, only mentioned it because it can effect the idle, I run my pri at the bottom of the hole and the sec a little higher but the bottom is OK. More than likely you will have to run the screws turned in because of the 4 corner. these carbs were built for engine with pretty lumpy cams and a bad cab signal. If the cams is moderate then it pulls to much fuel at an idle. Just run them turned in and worry about it.
    So what I gather is the config you listed with one PV and the way I have it now will have the same results, just two ways of doing it?

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    Default another thought...

    Check to see if you're exposing the transfer slots under the butterflys. You may have to open your throttle too far to get tnough idle signal, exposing the transfer slots and causing a too-rich idle condition. PV's will not effect idle.
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