Carb problem at start up.
Thread Starter
Race Director
Joined: Jan 2002
Posts: 11,615
Likes: 350
From: No Where USA
Carb problem at start up.
The car has a brand new ZZ502 4 speed. I put a 850 double pumper on it. Carb is also brand new. It ran fine for awhile but now when I leave it overnight it starts right up but then the car stalls and seems to be loaded up. After I drive it for awhile it seems to clear up. I haven't pulled any plugs yet to see if they are gas fouled before start up. The floats are adjusted so the level is right at the bottom of the sight glass. It also had the same problem with the float level higher. The air/mixture screws are turned out about 2 turns. The timing is set at the 10 degrees before top dead center that the instructions call for. The vacuum advance is not hooked up, also what the instructions called for. The only thing I haven't adjusted yet was the accelerator pump. The car also has a Holley mechanical fuel pump. I haven't pulled the carb yet to take anything apart to check. Just looking for some ideas right now.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
I take it, this is either a Holley or a QF. It must have the electric choke? Do you know how to set it and the high idle cam?
I wonder why Vac Adv is not recommended on a 502? I would think it'll run better with Vac Adv.
On the acc pump adjustment, there are videos on YouTube. Very simple to do. Just need a couple wrenches and a 0.015 feeler gauge.
I wonder why Vac Adv is not recommended on a 502? I would think it'll run better with Vac Adv.
On the acc pump adjustment, there are videos on YouTube. Very simple to do. Just need a couple wrenches and a 0.015 feeler gauge.
Last edited by HeadsU.P.; Sep 18, 2018 at 07:17 PM.
Thread Starter
Race Director
Joined: Jan 2002
Posts: 11,615
Likes: 350
From: No Where USA
I take it, this is either a Holley or a QF. It must have the electric choke? Do you know how to set it and the high idle cam?
I wonder why Vac Adv is not recommended on a 502? I would think it'll run better with Vac Adv.
On the acc pump adjustment, there are videos on YouTube. Very simple to do. Just need a couple wrenches and a 0.015 feeler gauge.
I wonder why Vac Adv is not recommended on a 502? I would think it'll run better with Vac Adv.
On the acc pump adjustment, there are videos on YouTube. Very simple to do. Just need a couple wrenches and a 0.015 feeler gauge.
The carb is an 850 Holley double pumper. There is no choke or choke horn on it. I know how to make all the proper adjustments. I am just looking on some ideas of where to start. It's a brand new carb, less than 10 miles on it and it shouldn't be doing this.
Le Mans Master
Joined: Aug 2017
Posts: 8,336
Likes: 2,810
From: Cool Northern Michigan
That engine is not a avg daily driver. I think you want it to act just like a 2018, V6, fuel injected, computer controlled mill. Not going to happen.
Just let it warm up a bit. That 850 DP is a gusher and it will take some getting used to.
Just let it warm up a bit. That 850 DP is a gusher and it will take some getting used to.
Thread Starter
Race Director
Joined: Jan 2002
Posts: 11,615
Likes: 350
From: No Where USA
I appreciate your response here. But there is obviously something wrong with the carb. It didn't do this 2 weeks ago. It started right up and ran smooth. I have been around Holley carbs for a long time and never had a new carb act this way. The 850 is a gusher? How about the 1150 I have on the 540 in My 67 GTO race car, that must really be a gusher. When it started to happen I made some additional adjustments. I realize the motor I have and that it will not idle like a 2018 car. If I want a car that acts like that I will get into my 2018 Nissan.
Last edited by 540 vette; Sep 18, 2018 at 08:55 PM.
Racer
Joined: Sep 2011
Posts: 414
Likes: 55
From: Humboldt county Ca
I don't know much about these things but I've sometimes had idle problems helped by pulling the air/fuel screws, shooting some carb cleaner down them and blowing some compressed air through them. You've probably been down that road before though.
Sorry, wish I knew enough to help.
Sorry, wish I knew enough to help.
Melting Slicks
Joined: May 2002
Posts: 2,717
Likes: 121
From: Sulphur LA
St. Jude Donor '05-'06,'11,'13-'14,'16,'18,'19,'24, '25
the mixture will continue to get richer as the engine warms up, so it may not be loading up it may be lean to start with then getting rich enough as the engine warms to keep the engine running.
I would try a couple things, try opening the idle mixture screws some more and see if it gets better, at 2 turns out you may not be able to make it any richer than it is so at this point you may try putting a small strand of wire in each of the low speed air jets to make it richer (just a trial).
If this doesn't change things to the good you may need to take it apart and look for foreign objects (trash).
It would be a good idea to make sure the transition slots are set correctly as they will do the same as you describe.
with a carb that has no choke usually if the mixture is set for a warm engine they will be very lean at start up and will require some peddle to keep them running until warm.
Neal
I would try a couple things, try opening the idle mixture screws some more and see if it gets better, at 2 turns out you may not be able to make it any richer than it is so at this point you may try putting a small strand of wire in each of the low speed air jets to make it richer (just a trial).
If this doesn't change things to the good you may need to take it apart and look for foreign objects (trash).
It would be a good idea to make sure the transition slots are set correctly as they will do the same as you describe.
with a carb that has no choke usually if the mixture is set for a warm engine they will be very lean at start up and will require some peddle to keep them running until warm.
Neal
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