Edelbrock Carb Questions
10-11-2015, 02:06 PM
#1
Race Director
Thread Starter
Edelbrock Carb Questions
Not my Corvette but a lot of owners run Carter and Edelbrock carburetors. Hopefully someone with some experience with these carbs can answer a couple questions.
On my GTX I rebuilt the #1412 800 cfm carb earlier in the year and it was running really well until recently when it developed an off-idle stumble. I pulled the carb off this morning to look it over and when I worked the throttle I got nothing from the accelerator pump squirters. I pulled the top and looked at the plunger and all that was there was the plastic tan holder and shaft and no plunger seal. First thought was crud, how did I forget that in the rebuild and then I realized it had been running good until recently. When I pulled out the spring and looked in the bottom of the well, the blue rubber/neoprene/? umbrella cup was lodged down in the very bottom. Pulled it out stuck it back on the plunger and under the 4 fingers and it's running like a champ again.
Anyone had a problem with these AP cups coming off the plunger before? Is there a better accelerator pump umbrella seal to use?
Also, all the instructions say to set the accelerator plunger with the idle speed screw backed out, to where the top of the shaft is 13/32 inch above the top of the carb top. That's about where mine would be if I put the rod in the middle hole but the Edelbrock instructions call for the rod to be in the top hole on the #1412 - which would result in maximum stroke for big engines. That puts the top of the shaft way above 13/32 inch on mine. Can anybody think of a reason I should bend the rod link to lower the plunger to this dimension? It seems all it would do is possibly shorter overall plunger travel.
Possibly there is some connection with the seal coming off and this high setting???
Thanks
On my GTX I rebuilt the #1412 800 cfm carb earlier in the year and it was running really well until recently when it developed an off-idle stumble. I pulled the carb off this morning to look it over and when I worked the throttle I got nothing from the accelerator pump squirters. I pulled the top and looked at the plunger and all that was there was the plastic tan holder and shaft and no plunger seal. First thought was crud, how did I forget that in the rebuild and then I realized it had been running good until recently. When I pulled out the spring and looked in the bottom of the well, the blue rubber/neoprene/? umbrella cup was lodged down in the very bottom. Pulled it out stuck it back on the plunger and under the 4 fingers and it's running like a champ again.
Anyone had a problem with these AP cups coming off the plunger before? Is there a better accelerator pump umbrella seal to use?
Also, all the instructions say to set the accelerator plunger with the idle speed screw backed out, to where the top of the shaft is 13/32 inch above the top of the carb top. That's about where mine would be if I put the rod in the middle hole but the Edelbrock instructions call for the rod to be in the top hole on the #1412 - which would result in maximum stroke for big engines. That puts the top of the shaft way above 13/32 inch on mine. Can anybody think of a reason I should bend the rod link to lower the plunger to this dimension? It seems all it would do is possibly shorter overall plunger travel.
Possibly there is some connection with the seal coming off and this high setting???
Thanks
10-12-2015, 07:14 AM
#2
Race Director
Thread Starter
I posted here because I seem to remember that awhile back someone discussed an issue with a Carter accelerator pump and there was mention of different types of pump seals that could be used - problem is it may have been Frankie and he's apparently not responding any longer. I guess I will try to scroll back over his old posts and see if I can find something.
10-12-2015, 10:36 AM
#3
I posted here because I seem to remember that awhile back someone discussed an issue with a Carter accelerator pump and there was mention of different types of pump seals that could be used - problem is it may have been Frankie and he's apparently not responding any longer. I guess I will try to scroll back over his old posts and see if I can find something.
10-12-2015, 11:23 AM
#4
Racer
It is more than likely that the pump cup fell off due to the gasoline having a high content of ethanol, heat will also cause the ethanol to be more active. for every 10 degree C. increase in heat it doubles the rate of ethanol related problems. if this is a one time problem you may have got a tank of fuel with a higher than normal ethanol content.
the blue pump cups are generally the best depending on who made the pump cup but the Edelbrock red cups are OK.
I hope this helps Henry @ olescarb
the blue pump cups are generally the best depending on who made the pump cup but the Edelbrock red cups are OK.
I hope this helps Henry @ olescarb
10-12-2015, 12:30 PM
#5
Race Director
Thread Starter
Ughh - high ethanol - I guess that's quite possible and the cup did apparently come loose this summer. Hopefully it was a freak thing and it will hang in there from now on.
Henry - do you think the high accelerator pump setting is an issue or should I lower it to Edelbrock's specs? I bought the carb used and rebuilt it and I don't remember which hole it was in at the time - although Edelbrock says it should be in the top hole for this model. It may have been tinkered with because the primary jets in it were not stock.
Thanks
Henry - do you think the high accelerator pump setting is an issue or should I lower it to Edelbrock's specs? I bought the carb used and rebuilt it and I don't remember which hole it was in at the time - although Edelbrock says it should be in the top hole for this model. It may have been tinkered with because the primary jets in it were not stock.
Thanks
10-12-2015, 01:34 PM
#6
Racer
[QUOTE=DansYellow66;1590678281]Ughh - high ethanol - I guess that's quite possible and the cup did apparently come loose this summer. Hopefully it was a freak thing and it will hang in there from now on.
Ethanol is mixed with the gasoline by a process that the gas companies refer to as stop light blending where the tanker starting and stopping mixes it with the gas but you can see parts of the tanker load that has 2% ethanol while other portions could be in the 20 % range.
Henry - do you think the high accelerator pump setting is an issue or should I lower it to Edelbrock's specs? I bought the carb used and rebuilt it and I don't remember which hole it was in at the time - although Edelbrock says it should be in the top hole for this model. It may have been tinkered with because the primary jets in it were not stock.
The pump system and jetting may have been changed to cover a lean off-idle problem that is common on the 750 and 800 cfm Edelbrock carbs. I avoid rebuilding or tuning on the 750 and 800 cfm Edelbrock carbs because we have seen too many that have a lean off-idle issue that would take hours of work to cure to make me happy with the a/f mixture curve. but the adjustment should not have caused the pump cup to fall off, that was most likely cause by the fuel.
I hope this helps Henry @ oles
Ethanol is mixed with the gasoline by a process that the gas companies refer to as stop light blending where the tanker starting and stopping mixes it with the gas but you can see parts of the tanker load that has 2% ethanol while other portions could be in the 20 % range.
Henry - do you think the high accelerator pump setting is an issue or should I lower it to Edelbrock's specs? I bought the carb used and rebuilt it and I don't remember which hole it was in at the time - although Edelbrock says it should be in the top hole for this model. It may have been tinkered with because the primary jets in it were not stock.
The pump system and jetting may have been changed to cover a lean off-idle problem that is common on the 750 and 800 cfm Edelbrock carbs. I avoid rebuilding or tuning on the 750 and 800 cfm Edelbrock carbs because we have seen too many that have a lean off-idle issue that would take hours of work to cure to make me happy with the a/f mixture curve. but the adjustment should not have caused the pump cup to fall off, that was most likely cause by the fuel.
I hope this helps Henry @ oles
10-12-2015, 07:19 PM
#7
Race Director
Thread Starter
Thanks Henry.
10-29-2015, 07:52 PM
#8
Race Director
Thread Starter
Edelbrock carb accelerator pump problem
Still having a bog with my AFB style Edelbrock carb. But fixed now - I think.
After pulling the carburetor apart again I started studying the accelerator pump system. The pump well fills from a long slot in the side of it that opens to the primary side float bowl. It extends down over an inch from the gasket line. After measuring it and the pump rod/umbrella seal and the set height of the rod above the carb top plate, I realized that even with the rod in the top hole, the plunger seal was still resting several 32' of an inch below the slot and therefor no fuel could enter the well.
I thought the last rebuild kit I installed might have included the wrong accelerator pump (too long) so I ordered a new one specific to the carb and although it has a red umbrella seal instead of a blue one it was the same length - so no help.
The only option left was to bend the accelerator pump link further so that the pump rod could rest higher than specified. Even resting at full height, without the pump link installed, the seal was only about 2/32 inch above the bottom of the fill slot. So, I could only pre-load the accelerator pump about 1/32 inch and be sure that the side slot would fill the well at closed throttle. This was considerably above the Edelbrock specifications. This is also a function of how far open the primary throttle plate is opened by the idle speed screw since the link is connected to it.
I ended up having to put almost a 90 degree bend in the accelerator pump rod link in order to shorten it enough to get the height where it appeared the umbrella seal needed to rest for proper operation. I ended up with the 1/32 inch preload and from the best I could measure with calipers, the slot in the side is uncovered about 1/32 inch at closed throttle so the well can fill from the bowl. After buttoning it back up I took it for a short drive and it seems to be functioning well now - no off-throttle stumble.
This is a 1412 model Edelbrock which is an 800 cfm carb and I think it's a bit of an odd ball model. I suspect the main body is cast with a shorter slot in the well in order to increase the capacity of the accelerator pump circuit. The Edelbrock specifications do call for the height of the pump to be set 2/32 inch higher than other, smaller cfm models (18/32 inch). But I had to exceed this setting by another 3/32 inch to ensure function.
Anyway - if anyone is running a Carter or Edelbrock carburetor and having problems with bogging off the line, this is something to look into.
After pulling the carburetor apart again I started studying the accelerator pump system. The pump well fills from a long slot in the side of it that opens to the primary side float bowl. It extends down over an inch from the gasket line. After measuring it and the pump rod/umbrella seal and the set height of the rod above the carb top plate, I realized that even with the rod in the top hole, the plunger seal was still resting several 32' of an inch below the slot and therefor no fuel could enter the well.
I thought the last rebuild kit I installed might have included the wrong accelerator pump (too long) so I ordered a new one specific to the carb and although it has a red umbrella seal instead of a blue one it was the same length - so no help.
The only option left was to bend the accelerator pump link further so that the pump rod could rest higher than specified. Even resting at full height, without the pump link installed, the seal was only about 2/32 inch above the bottom of the fill slot. So, I could only pre-load the accelerator pump about 1/32 inch and be sure that the side slot would fill the well at closed throttle. This was considerably above the Edelbrock specifications. This is also a function of how far open the primary throttle plate is opened by the idle speed screw since the link is connected to it.
I ended up having to put almost a 90 degree bend in the accelerator pump rod link in order to shorten it enough to get the height where it appeared the umbrella seal needed to rest for proper operation. I ended up with the 1/32 inch preload and from the best I could measure with calipers, the slot in the side is uncovered about 1/32 inch at closed throttle so the well can fill from the bowl. After buttoning it back up I took it for a short drive and it seems to be functioning well now - no off-throttle stumble.
This is a 1412 model Edelbrock which is an 800 cfm carb and I think it's a bit of an odd ball model. I suspect the main body is cast with a shorter slot in the well in order to increase the capacity of the accelerator pump circuit. The Edelbrock specifications do call for the height of the pump to be set 2/32 inch higher than other, smaller cfm models (18/32 inch). But I had to exceed this setting by another 3/32 inch to ensure function.
Anyway - if anyone is running a Carter or Edelbrock carburetor and having problems with bogging off the line, this is something to look into.