what jet sizes - The 1947 - Present Chevrolet & GMC Truck Message Board Network

justin4260 · 02-28-2015, 11:01 PM

I've got a 350 sbc care engine with a 600 cfm 4 barrel holley. my jets are 65 primary not sure yet secondary. i need to change the but not sure what to. anybody know or do i just have to try different sizes till i get it how i want it?

71 super · 02-28-2015, 11:29 PM

The secondary's are controlled via a metering plate unless it has been converted and the plate is the equilivent of 72 jets if I remember correctly. What makes you think it needs to be re- jetted? The reason for asking is the carb is very close as it sits for a stock- I assume - 350. I have a 650 on stock bore stock headed improved cam motor with 66 in front and 72 in rear and runs like a top. 8 degrees advance, th350 dual exhaust with stock exhaust manifolds and knock off dual plane rpm intake. What type of Vaccum is it pulling? Have you checked the power valve to make sure it is the right one. Have you set the mixture with vacuum guage? Adust mixture screws to highest vac reading and should be good to go.

justin4260 · 02-28-2015, 11:36 PM

well the reason I think i need to change them is i just put this new holley on from a q-jet and when i am driving and i give it throttle it will hesitate and then go. I've adjusted the air fuel mixture screw to get the most vacuum but no matter how much i adjust it my vacuum is not changing. i believe my idle is set too high. the reason my idle is set too high is because when its set normally and i put it in gear it dies. when i set the idle to high and put it in gear it runs fine and idles fine. i think the jets are too small and not delivering enough fuel unless you set the idle high, also the reason for the hesitation and the go. the 350 i have in it has been bored by the previous owners brother and the guy didn't know how much...so I'm not sure about the bore size.

71 super · 03-01-2015, 12:15 AM

Check for vacuum leaks first. Take some carb cleaner and spray around base etc. and see if engine rpm increases. If you have leak, the mixture screws and idle will not be right. Sounds like the idle is set too high and you are into the intermediate circuit in carb. Check for leaks then we can go from there. But too high of an idle is not sign of need for jet increase and other symptoms point towards a vac/ air leak

GASoline71 · 03-01-2015, 12:30 AM

You have a vacuum leak is what it sounds like. Make sure your timing is spot on as well. Also if a Holley stumbles when you push on the gas it needs more pump shot. If it's a stock Holley 1850 (600cfm) it will have a metering plate (not adjustable with jets) in the secondary. Unless it has had a metering "block" (4150 style) installed in the secondary, then you will be able to rejet the rear.

Are you using the stock cast iron manifold with an adapter? If so... you more than likely have a vacuum leak. Also try bumping your timing up to about 12 to 14 degrees at idle.

Gary

Steve Cole · 03-01-2015, 10:47 AM

Subscribed. My Edlebrock 1405 carb is doing the same thing and I have tried all three accelator pump settings.

justin4260 · 03-02-2015, 06:13 PM

I'm using the stock intake manifold and an adapter plate to go from a quadrajunk to a holley. i have to set the idle really high in neutral to keep it running in gear. haven't driven it like that haven't had time. how can i tell if i have a vacuum leak around the adapter plate? and how do i fix it?

justin4260 · 03-02-2015, 09:04 PM

im also getting about 8-10 mercury inches of vacuum I'm park and i couldn't keep it running to check in drive. so yeah probably vacuum leak. how cn this be fixed?

geezer#99 · 03-02-2015, 09:45 PM

Quote:

Originally Posted by justin4260

im also getting about 8-10 mercury inches of vacuum I'm park and i couldn't keep it running to check in drive. so yeah probably vacuum leak. how cn this be fixed?

Put some timing in it!
As much initial timing as possible and still start hot easily.
Low vac reading doesn't always mean a leak.

justin4260 · 03-02-2015, 09:46 PM

I'm new to car engines I've done motorcycle timing but never on a car. how do i do that?

geezer#99 · 03-02-2015, 10:00 PM

Quote:

Originally Posted by justin4260

I'm new to car engines I've done motorcycle timing but never on a car. how do i do that?

Do a google search.
Here's one of many including youtube vids on 'how to set the timing on a sbc 350'.

http://www.ehow.com/how_6369972_set-...350-motor.html

justin4260 · 03-02-2015, 10:24 PM

the timing was fine before i put the new carb on as far as i know it was running and driving fine. do you need to change it because of the new carb? the q-jet before the holley had a big vacuum leak in the choke it had the vacuum choke and it was torn. so maybe the po adjusted the timing to offset the vacuum leak?

02-28-2015, 11:01 PM	#1
justin4260 Registered User Join Date: Feb 2015 Location: houston texas Posts: 206	what jet sizes I've got a 350 sbc care engine with a 600 cfm 4 barrel holley. my jets are 65 primary not sure yet secondary. i need to change the but not sure what to. anybody know or do i just have to try different sizes till i get it how i want it?

02-28-2015, 11:29 PM	#2
71 super Registered User Join Date: Sep 2005 Location: Canton North carolina Posts: 3,079	Re: what jet sizes The secondary's are controlled via a metering plate unless it has been converted and the plate is the equilivent of 72 jets if I remember correctly. What makes you think it needs to be re- jetted? The reason for asking is the carb is very close as it sits for a stock- I assume - 350. I have a 650 on stock bore stock headed improved cam motor with 66 in front and 72 in rear and runs like a top. 8 degrees advance, th350 dual exhaust with stock exhaust manifolds and knock off dual plane rpm intake. What type of Vaccum is it pulling? Have you checked the power valve to make sure it is the right one. Have you set the mixture with vacuum guage? Adust mixture screws to highest vac reading and should be good to go. __________________ 67 blue step side- bb 68 gold and white swb cst anniversary 68 custom swb hot rod Ls swap 69 swb cst 6 cylinder/ overdrive 69 black/black cst bb swb 70 orange and white cst Canada built truck swb bb 71 black and white super swb bb 71 red and white super swb 72 green and white super swb 4x4 62 nova wagon 400 series Ls swapped 68 Camaro 327/4 speed- 1 owner, original paint 66 Volkswagen bettle 69 auto stick Volkswagen Beetle

02-28-2015, 11:36 PM	#3
justin4260 Registered User Join Date: Feb 2015 Location: houston texas Posts: 206	Re: what jet sizes well the reason I think i need to change them is i just put this new holley on from a q-jet and when i am driving and i give it throttle it will hesitate and then go. I've adjusted the air fuel mixture screw to get the most vacuum but no matter how much i adjust it my vacuum is not changing. i believe my idle is set too high. the reason my idle is set too high is because when its set normally and i put it in gear it dies. when i set the idle to high and put it in gear it runs fine and idles fine. i think the jets are too small and not delivering enough fuel unless you set the idle high, also the reason for the hesitation and the go. the 350 i have in it has been bored by the previous owners brother and the guy didn't know how much...so I'm not sure about the bore size.

03-01-2015, 12:15 AM	#4
71 super Registered User Join Date: Sep 2005 Location: Canton North carolina Posts: 3,079	Re: what jet sizes Check for vacuum leaks first. Take some carb cleaner and spray around base etc. and see if engine rpm increases. If you have leak, the mixture screws and idle will not be right. Sounds like the idle is set too high and you are into the intermediate circuit in carb. Check for leaks then we can go from there. But too high of an idle is not sign of need for jet increase and other symptoms point towards a vac/ air leak __________________ 67 blue step side- bb 68 gold and white swb cst anniversary 68 custom swb hot rod Ls swap 69 swb cst 6 cylinder/ overdrive 69 black/black cst bb swb 70 orange and white cst Canada built truck swb bb 71 black and white super swb bb 71 red and white super swb 72 green and white super swb 4x4 62 nova wagon 400 series Ls swapped 68 Camaro 327/4 speed- 1 owner, original paint 66 Volkswagen bettle 69 auto stick Volkswagen Beetle

03-01-2015, 10:47 AM	#6
Steve Cole Registered User Join Date: May 2012 Location: Faith,NC Posts: 1,626	Re: what jet sizes Subscribed. My Edlebrock 1405 carb is doing the same thing and I have tried all three accelator pump settings.

03-02-2015, 06:13 PM	#7
justin4260 Registered User Join Date: Feb 2015 Location: houston texas Posts: 206	Re: what jet sizes I'm using the stock intake manifold and an adapter plate to go from a quadrajunk to a holley. i have to set the idle really high in neutral to keep it running in gear. haven't driven it like that haven't had time. how can i tell if i have a vacuum leak around the adapter plate? and how do i fix it?

03-02-2015, 09:04 PM	#8
justin4260 Registered User Join Date: Feb 2015 Location: houston texas Posts: 206	Re: what jet sizes im also getting about 8-10 mercury inches of vacuum I'm park and i couldn't keep it running to check in drive. so yeah probably vacuum leak. how cn this be fixed?

03-02-2015, 09:46 PM	#10
justin4260 Registered User Join Date: Feb 2015 Location: houston texas Posts: 206	Re: what jet sizes I'm new to car engines I've done motorcycle timing but never on a car. how do i do that?

03-02-2015, 10:24 PM	#12
justin4260 Registered User Join Date: Feb 2015 Location: houston texas Posts: 206	Re: what jet sizes the timing was fine before i put the new carb on as far as i know it was running and driving fine. do you need to change it because of the new carb? the q-jet before the holley had a big vacuum leak in the choke it had the vacuum choke and it was torn. so maybe the po adjusted the timing to offset the vacuum leak?



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