stumbling II
Thread Starter
|
Senior User
Joined: Jan 2004
Posts: 166
Likes: 0
From: Masontown, WV
stumbling II
Maple, I didn’t want to steal your thread so I started my own. My problem is nearly the same just different carbs. I rebuilt my 400 about a year ago and it ran great. A “RV” cam and headers are the only mods. I kept the stock 2150 carb and it was fine until it blew a power valve or something and started flooding. Ran fine at all rpm but wouldn’t idle.
So, I picked up a edelbrock 400 with egr( not using the egr) on ebay and bought a new holley 600 cfm with a vacuum secondary and put them on yesterday. Idled perfect, and as long as I stayed in the primaries ran perfect. When I opened it up to the point of the secondaries coming in it stumbled, opened a little more, backfired out the exhaust. I thought I might need to advance the timing so I did and the backfiring went away but still stumbles and now it also stumbles when under no load and the throttle is just off idle.
I think I might try cooler plugs. BTW I pulled all the plugs before I adjusted the timing and they looked good, light brown, all 8 of them. The guy at the parts store told me that the carb would be too big for my engine and would need to be jetted down. I didn’t think over jetting would cause the problems I am having.
Thanks,
Gregg
So, I picked up a edelbrock 400 with egr( not using the egr) on ebay and bought a new holley 600 cfm with a vacuum secondary and put them on yesterday. Idled perfect, and as long as I stayed in the primaries ran perfect. When I opened it up to the point of the secondaries coming in it stumbled, opened a little more, backfired out the exhaust. I thought I might need to advance the timing so I did and the backfiring went away but still stumbles and now it also stumbles when under no load and the throttle is just off idle.
I think I might try cooler plugs. BTW I pulled all the plugs before I adjusted the timing and they looked good, light brown, all 8 of them. The guy at the parts store told me that the carb would be too big for my engine and would need to be jetted down. I didn’t think over jetting would cause the problems I am having.
Thanks,
Gregg
Posting Guru
Joined: Dec 2002
Posts: 2,003
Likes: 2
From: chicago burbs
from http://www.mortec.com/carbtip1.htm , there is a lot more there about setting up a holley if you have another issue after this one is resolved.
"There are a number of ways to tune the moment when the vacuum secondaries open on a Holley four barrel carb. The vacuum secondaries are controlled by a diaphram and a color coded spring. Holley makes a number of different springs with different tension on the springs. You can change the springs and change the opening moment. The color coded springs run from light tension to heavy:
White - Lightest
Yellow (Short Spring)
Yellow
Purple
Plain (Steel grey)
Brown
Black - Heaviest
If there is a bog or hesitation when the secondaries open, the spring tension is too light, go to the next heavier spring. Holley offers a kit (PN-20-13) which contains one each of the above color springs. When you change springs you'll note that the stock cover over the spring and diaphram is not all that easy to get to. Holley makes a special cover (PN-20-59) that makes spring changes quick. Finally, Holley also makes a completely adjustable thumbscrew operated diaphram cover (PN-20-99). This cover limits the travel of the diaphram and therefore limits how far the secondary throttle plate can open. It makes secondary throttle opening adjustable."
"There are a number of ways to tune the moment when the vacuum secondaries open on a Holley four barrel carb. The vacuum secondaries are controlled by a diaphram and a color coded spring. Holley makes a number of different springs with different tension on the springs. You can change the springs and change the opening moment. The color coded springs run from light tension to heavy:
White - Lightest
Yellow (Short Spring)
Yellow
Purple
Plain (Steel grey)
Brown
Black - Heaviest
If there is a bog or hesitation when the secondaries open, the spring tension is too light, go to the next heavier spring. Holley offers a kit (PN-20-13) which contains one each of the above color springs. When you change springs you'll note that the stock cover over the spring and diaphram is not all that easy to get to. Holley makes a special cover (PN-20-59) that makes spring changes quick. Finally, Holley also makes a completely adjustable thumbscrew operated diaphram cover (PN-20-99). This cover limits the travel of the diaphram and therefore limits how far the secondary throttle plate can open. It makes secondary throttle opening adjustable."
Posting Legend
Joined: Sep 2001
Posts: 30,255
Likes: 37
If you do not have access to any instruments. It is possible to get an idea of whether the primaries or secondaries on a carb are running too rich or too lean by using a small ~3x6" sheet of metal. If you start closing off whichever side of the carb you are running on slowly with the sheet of metal it will enrich the mixture. If the vehicle starts to run better then the circuit was too lean. If it starts to run worse then it is either OK or too rich.
Be very careful when working on a running engine. Keep a fire extinguisher and a hose handy. Watch your ventilation. Running outside is best in case a fire starts. Water will not put out a liquid fuel fire and will spread it but it can extinguish other materials that are ignited.
Be very careful when working on a running engine. Keep a fire extinguisher and a hose handy. Watch your ventilation. Running outside is best in case a fire starts. Water will not put out a liquid fuel fire and will spread it but it can extinguish other materials that are ignited.
Last edited by Torque1st; Mar 6, 2006 at 08:13 AM.
Thread Starter
|
Senior User
Joined: Jan 2004
Posts: 166
Likes: 0
From: Masontown, WV
I thought I would give an update. After hooking up the fuel pressure and vacuum gauge I found a steady 7psi at any position, and vac 16" in gear. With the vacuum gauge in the cab I was able to see a lot. I ran 10 mile passes staying out of the power valve setting of 6.5" and checked the plugs and found it as running lean. I started rejetting. The factory jetting was 64 it’s at 69 now and the plugs are nice and brown. BTW, what I thought was brown earlier was white. I also had to richen the idle to cure the off idle stumble. Now, no backfiring and very smooth power. Not even in the secondaries. Next, I'm doing the secondaries. My carb has a secondary plate so I ordered a conversion kit so I can use regular jets. Thanks for all the help.
Thread
Thread Starter
Forum
Replies
Last Post
crazyeddie
Fuel Injection, Carburetion & Fuel System
9
Aug 5, 2010 09:35 PM
Hellbore
FE & FT Big Block V8 (332, 352, 360, 390, 406, 410, 427, 428)
10
May 24, 2006 10:31 PM
DarkWolf40
FE & FT Big Block V8 (332, 352, 360, 390, 406, 410, 427, 428)
7
Jan 2, 2006 09:15 PM
