750 Holley Jets?
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Senior User
Joined: Jan 2012
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From: Antelope, California
750 Holley Jets?
Bought a 750 holley, vacuum 2ndary, i have it on my 390, bored 30 over, 9.4:1 compression, and it has #72 jets in it now. It is running super rich, all my right bank spark plugs are black. I had #67 jets in my 600 and it ran about 13.6:1 stoch. Good for a performance engine. I dont have the money to run over to the dyno and get this thing tuned again, so im curious what jets i should run if anyone knows or what you are using with good results. Thanks!
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From: Antelope, California
you have it jetted with 2 different jets? are you supposed to do that?
Lead Driver
Joined: Aug 2003
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From: **** hole San Jose ca.
Jetting depends on if your running headers with large exh. pipes, Hot coil or high energy ignition system & altitude. Most 600 cfm Holley's come with #.66-67 I've come across with these jets. Now if you have a weak or bad plug wires it will cause plug fouling also. Plus what cam your running. I'd drop 3 sizes and do a plug reading but clean your plugs first or driver it 30 or 40 miles at 65mph. I may have some extre holley jets #70 69,67, But will have to look in my stock plie box of jets.. Are you using a vacuum meter when adjusting your air/fuel mixture idle ?? This maybe your problem also..
orich
orich
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Senior User
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From: Antelope, California
Jetting depends on if your running headers with large exh. pipes, Hot coil or high energy ignition system & altitude. Most 600 cfm Holley's come with #.66-67 I've come across with these jets. Now if you have a weak or bad plug wires it will cause plug fouling also. Plus what cam your running. I'd drop 3 sizes and do a plug reading but clean your plugs first or driver it 30 or 40 miles at 65mph. I may have some extre holley jets #70 69,67, But will have to look in my stock plie box of jets.. Are you using a vacuum meter when adjusting your air/fuel mixture idle ?? This maybe your problem also..
orich
orich
Holley 600's come with #65 Jets. Everything on my engine is brand new, less than 2000 miles. I cant use a vacuum gauge due to crappy vacuum readings because of my cam. I put 69's in it the other day, it runs lean and falls on its face at 1100-1900rpms now unless i really step on it. Im going to put the 70's back in it that it came with and try that. I dont have any 71's and the stock 3310 #72's were too rich. But i also had to re-adjust both float bowls as they were spewing fuel out of the sight plug holes when i puled the plugs. so maybe the 72's will work now.. idk.
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From: Antelope, California
The 3310 is a 750cfm vacuum secondary. Correct me if im wrong but those only have a block in the back and a primary metering block in the front with only 2 jets. at least mine does because i had it all apart less than a week ago. If you have a double pumper, it will have 4 jets, 2 in both metering blocks, one in the front and one in the back.. that number behind the dash makes that much difference? Mine is a 3310-4
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From: Antelope, California
ok so i did some research because i was curious. The 3310-1 has 72's in the front and 76's in the back. they are old so they came with 2 blocks. The newer 2,3 and 4 all have 134-21 metering plates and are part number 4160's. The -1 is a 4150. Also, the -1 is a 780cfm not a 750.
http://1970mgr.org/_HolleyCarbs.htm - more info here
http://1970mgr.org/_HolleyCarbs.htm - more info here
Lead Driver
Joined: Aug 2003
Posts: 7,592
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From: **** hole San Jose ca.
I have a 3310-4.
Holley 600's come with #65 Jets. Everything on my engine is brand new, less than 2000 miles. I cant use a vacuum gauge due to crappy vacuum readings because of my cam. I put 69's in it the other day, it runs lean and falls on its face at 1100-1900rpms now unless i really step on it. Im going to put the 70's back in it that it came with and try that. I dont have any 71's and the stock 3310 #72's were too rich. But i also had to re-adjust both float bowls as they were spewing fuel out of the sight plug holes when i puled the plugs. so maybe the 72's will work now.. idk.
Holley 600's come with #65 Jets. Everything on my engine is brand new, less than 2000 miles. I cant use a vacuum gauge due to crappy vacuum readings because of my cam. I put 69's in it the other day, it runs lean and falls on its face at 1100-1900rpms now unless i really step on it. Im going to put the 70's back in it that it came with and try that. I dont have any 71's and the stock 3310 #72's were too rich. But i also had to re-adjust both float bowls as they were spewing fuel out of the sight plug holes when i puled the plugs. so maybe the 72's will work now.. idk.
Fleet Mechanic
Joined: May 2001
Posts: 1,396
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From: Cupertino
You are running on the primaries 99% of the time. The secondaries only come in when you romp it.
Read the plugs. They tell you all. As above, make sure the wiring is intact and check around the site for plug heat range for your motor, cam, carburetion.
My experience is that you tune the primaries for daily driving and go fat on the secondaries.
Read the plugs. They tell you all. As above, make sure the wiring is intact and check around the site for plug heat range for your motor, cam, carburetion.
My experience is that you tune the primaries for daily driving and go fat on the secondaries.
Lead Driver
Joined: Aug 2003
Posts: 7,592
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From: **** hole San Jose ca.
Have you removed the air/fuel adjustment jets and make sure someone has not over tighten it an damaged it? SWITCH these jets and see it it makes a difference. If you can close these by screwing them in all the way and it keeps running then you have a bad power valve or leaking or screwed up something . Engine should stall out as you cut off the idle circuit fuel..
orich
orich
Thread Starter
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Senior User
Joined: Jan 2012
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From: Antelope, California
You are running on the primaries 99% of the time. The secondaries only come in when you romp it.
Read the plugs. They tell you all. As above, make sure the wiring is intact and check around the site for plug heat range for your motor, cam, carburetion.
My experience is that you tune the primaries for daily driving and go fat on the secondaries.
Read the plugs. They tell you all. As above, make sure the wiring is intact and check around the site for plug heat range for your motor, cam, carburetion.
My experience is that you tune the primaries for daily driving and go fat on the secondaries.
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Senior User
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From: Antelope, California
You say it ran lean only because it feel on it's face. You may just only need to change your the pump shot squirters or shooter size up and smaller main jets. You did not say if your using a 50cc or 30cc-pump. Even the pump cams play a big part in dialing in the carb with flat spots. Also not having any play in the pump arm you'll have a low end flat spot as you may know by now. You main thing to not to foul the plugs Then dial the carb in. This all takes try and error of test driving then the fine tuning. Some times you can't have your cake and eat it to=. Building a race motor wild cam and use it as a street machine. Plugs load up and foul ez. Been there done that 47 yrs ago..orich
Have you removed the air/fuel adjustment jets and may sure someone has not over tighten it a damaged it? SWITCH these jets and see it it makes a difference. If you can close these by screwing them in all the way and it keeps running then you have a bad power valve or leaking or screwed up. Engine should stall out as you cut off the idle circuit fuel..
Lead Driver
Joined: Aug 2003
Posts: 7,592
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From: **** hole San Jose ca.
I'm just running a 600 cfm #68 jets with .031 pump shooter added a 50cc acc pump with matching pump cam Brown. on a 390 bored 0.30 with 428 crank & mild porting polished port runner heads. HEI dizzy ign system and Sanderson shorty coated tube headers 2.5 pipe with 2009 mustang mufflers. And a Comp Cam H.E 267 at sea-Level.. Jetting was to over come any flat spots with a good plug color..my 2cents orich