Jet size for 850dp
Thread Starter
Burning Brakes
Joined: Aug 2001
Posts: 1,002
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From: Bay City MI.
Jet size for 850dp
Going to put the Holley 850dp, 4 corner idle on my car this week, was wondering if the jets are the right size. Its got 80 in the primary and 80 in the secondary. I have been running 74 and 80 in my 780 vac carb, seems to like the extra fuel, but runs out of top end at about 5500 plus. My plugs are tan in color now with the old carb. By the way if someone wants the 780 let me know, $125 plus shipping!
Racer
Joined: Aug 2001
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Re: Jet size for 850dp (467-Ratman)
Dont know about Holley, but my SpeedDemon 850 came with 80/85 . It was too rich for my set up, so i went with an Edelbrock 800 single pumper - its ideal now. I like the secondary air valve on it. , and changing metering rods are a breeze without draining the fuel from the carb.
Safety Car
Joined: Aug 2000
Posts: 3,909
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From: Clymer PA
Re: Jet size for 850dp (467-Ratman)
Tom:
I'm running a Holley 850 Double Pumper with 4 corner idle circuit also. I ran it for a while with the stock jetting....it was pretty rich. Curtis helped me out with my jetting. I'm running a Holley Strip Dominator single plane intake. The jetting that i am currently using is:
Primary: 76 Jets w/ 6.5 Power Valve
Secondary: 80 Jets w/ Power Valve Blocked Off
Just by changing from the Torker II Intake and stock 850DP jetting to Strip Dominator and new jetting I picked up .5 and 3MPH in the 1/4 mile.
Hope I helped.
I'm running a Holley 850 Double Pumper with 4 corner idle circuit also. I ran it for a while with the stock jetting....it was pretty rich. Curtis helped me out with my jetting. I'm running a Holley Strip Dominator single plane intake. The jetting that i am currently using is:
Primary: 76 Jets w/ 6.5 Power Valve
Secondary: 80 Jets w/ Power Valve Blocked Off
Just by changing from the Torker II Intake and stock 850DP jetting to Strip Dominator and new jetting I picked up .5 and 3MPH in the 1/4 mile.
Hope I helped.
Melting Slicks
Joined: Apr 2000
Posts: 3,286
Likes: 8
From: San Jose California
Re: Jet size for 850dp (467-Ratman)
80's on my L88 made for a 14:1 A/F mixture when running open headers; but, with minimal back pressure with the uncapped baffles, the A/F dropped to about 12:1. Perhaps 75-76's would be better with the baffles.
If I was racing on a road course I would probably want my A/F closer to 13:1 for engine safety. 14.5:1 would be pretty ideal for street, so a little leaner for the primaries, a bit richer for the secondaries.
Chuck
p.s. I run power 6.5 power valves front and back. If you don't run a power valve in the rear, you must richen the secondary jets to make up for this. I think I recall that you need to richen the jets 6-8 numbers if you don't use a power valve.
[Modified by Chuck Harmon, 10:21 PM 9/9/2002]
If I was racing on a road course I would probably want my A/F closer to 13:1 for engine safety. 14.5:1 would be pretty ideal for street, so a little leaner for the primaries, a bit richer for the secondaries.
Chuck
p.s. I run power 6.5 power valves front and back. If you don't run a power valve in the rear, you must richen the secondary jets to make up for this. I think I recall that you need to richen the jets 6-8 numbers if you don't use a power valve.
[Modified by Chuck Harmon, 10:21 PM 9/9/2002]
Thread Starter
Burning Brakes
Joined: Aug 2001
Posts: 1,002
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From: Bay City MI.
Re: Jet size for 850dp (bence13_33)
Thanks for the info, sounds like 80's are too big for the primary setup. I will give it a try with a set of 76's, still should be an improvement from my 73 size in the 780.
Race Director
Joined: Nov 2000
Posts: 11,872
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From: Waterloo ontario Canada
Re: Jet size for 850dp (467-Ratman)
I run a pair of 850 double pumpers 4 corner idle and I am back to the 80's all around. I started dropping the primary jetting and used a Edelbrock air fuel meter to help. I find the idle circuit way too rich on these carbs. Leaning out the jetting is just a bandaid for the poor rich idle circuit. Once I leaned out the idle circuits the stock 80 jets run lean. My plugs are white and my air fuel gage shows around 14.5-15 to one under light cruising. I also believe strongly in power valves. I drill 1/8th holes in the throttle plates, all 8 and put .015 wires in all the idle circuits. I also run my power valves very close to the idle in gear vacuum value to get the power valves to open without pushing the car too hard. This drops my ratio back to 13-1 for passing, hill climbing etc.
I get 12 mpg around town with this 2 4 setup.
I get 12 mpg around town with this 2 4 setup.
Thread Starter
Burning Brakes
Joined: Aug 2001
Posts: 1,002
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From: Bay City MI.
Re: Jet size for 850dp (norvalwilhelm)
I hope that the 850 will give me a better idle than my 780vs. We drilled holes in the primary throttle plates to even out the idle, before I had to have the idle screws turned out about 4 or 5 turns. Now they are about 2 turns out. With the 4 corner how many turns out for the screws? My plugs in my existing setup are showing tan color.
Race Director
Joined: Mar 2001
Posts: 11,322
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From: Living in the Hartland
Re: Jet size for 850dp (467-Ratman)
I hope that the 850 will give me a better idle than my 780vs. We drilled holes in the primary throttle plates to even out the idle, before I had to have the idle screws turned out about 4 or 5 turns. Now they are about 2 turns out. With the 4 corner how many turns out for the screws? My plugs in my existing setup are showing tan color.
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Thread Starter
Burning Brakes
Joined: Aug 2001
Posts: 1,002
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From: Bay City MI.
Re: Jet size for 850dp (norvalwilhelm)
Dumb question, but how and where in the idle circut does the wire go? My friend who built the engine was the one who suggested to drill the throttle plates. He said that it would help the idle and before that it was starting to pull fuel from the jets at idle ? In any event I have to back the screws out now or it just dies. The motor really spits , sounds a little like a boat at idle! Maybe I should change the name on the back of the car from Corvette to Chris Craft!!
Safety Car
Joined: Sep 2000
Posts: 4,679
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From: Charles Town WV
Re: Jet size for 850dp (467-Ratman)
On this same subject, I think my engine is running WAY too lean (diesling after shutoff, running *EXTREMELY* hot etc). I just pulled the fuel bowl off and discovered I have 71's for primary jets. This is in an 850 DP on my 468. The headers got so hot they made the rag joint start smoking and the Z-bar squirted grease out of it's zirk fitting.
Should I bump these puppies up to 76 as well?
Thanks
Should I bump these puppies up to 76 as well?
Thanks
Thread Starter
Burning Brakes
Joined: Aug 2001
Posts: 1,002
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From: Bay City MI.
Re: Jet size for 850dp (Steve Straus)
Steve, We just put the 850dp on the motor on Friday, it has 80 jets for both. We reset the timming and I can say the motor is running awesome! I wish that I had bought the 850 earlier in the year. Seems like my 467 really likes the extra fuel, does not seem to rich?
Safety Car
Joined: Sep 2000
Posts: 4,679
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From: Charles Town WV
Re: Jet size for 850dp (467-Ratman)
Steve, We just put the 850dp on the motor on Friday, it has 80 jets for both. We reset the timming and I can say the motor is running awesome! I wish that I had bought the 850 earlier in the year. Seems like my 467 really likes the extra fuel, does not seem to rich?
Safety Car
Joined: Sep 2000
Posts: 4,679
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From: Charles Town WV
Re: Jet size for 850dp (71,454,4spd)
I would say do something Steve, thats freakin hot. :eek: What was your engine temp?
[Modified by Steve Straus, 9:53 PM 9/22/2002]
Melting Slicks
Joined: Apr 2000
Posts: 3,286
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From: San Jose California
Re: Jet size for 850dp (Steve Straus)
.
Steve,
The first 6 inches of my primary pipes were glowing red at idle when viewed in the dark. This problem went away when I re-timed the cam to straight up specs instead of 4 degrees advanced. The coolant temperature didn't seem to matter either way. The point of the exhaust valve opening seemed to make a bigger difference than I would have expected.
Chuck
That's the thing, the engine temp didn't get much over 200 which isn't all bad considering the car was idling for a while. It's the freakin exhaust that's getting hot, which is why I think it's the mixture giving me problems.
The first 6 inches of my primary pipes were glowing red at idle when viewed in the dark. This problem went away when I re-timed the cam to straight up specs instead of 4 degrees advanced. The coolant temperature didn't seem to matter either way. The point of the exhaust valve opening seemed to make a bigger difference than I would have expected.
Chuck
Safety Car
Joined: Sep 2000
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From: Charles Town WV
Re: Jet size for 850dp (Chuck Harmon)
[QUOTE
The first 6 inches of my primary pipes were glowing red at idle when viewed in the dark. This problem went away when I re-timed the cam to straight up specs instead of 4 degrees advanced. The coolant temperature didn't seem to matter either way. The point of the exhaust valve opening seemed to make a bigger difference than I would have expected.
Chuck[/QUOTE]
You retarded the timing at the distributor? or did you have the cam degreed at the sprocket? What were straight up specs? I know they're different for my engine, I'm just trying to establish a baseline.
I'm sure the fact that my jet size is so small is a large factor of the heat as well.
--
Steve
The first 6 inches of my primary pipes were glowing red at idle when viewed in the dark. This problem went away when I re-timed the cam to straight up specs instead of 4 degrees advanced. The coolant temperature didn't seem to matter either way. The point of the exhaust valve opening seemed to make a bigger difference than I would have expected.
Chuck[/QUOTE]
You retarded the timing at the distributor? or did you have the cam degreed at the sprocket? What were straight up specs? I know they're different for my engine, I'm just trying to establish a baseline.
I'm sure the fact that my jet size is so small is a large factor of the heat as well.
--
Steve
