Carb tweaking question
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Mountain Pass
Joined: Oct 2004
Posts: 119
Likes: 5
From: SW Washington State
Carb tweaking question
1978 f250 4x4 w/ 428. Headers, 3" exhaust, Performer manifold, and Edelbrock 1406 600 cfm carb
Question: Runs damn good, but when I really get on it, and the secondaries kick in, it bogs a bit... like it's getting too much gas. (And it doesn't keep accelerating like it should) It is running rich by the smell at at idle, though it's smooth. (It pops just a bit when decelerating downhill) I'm thinking of turning up the air a bit. Is this the right thing to do?
Thanks
Question: Runs damn good, but when I really get on it, and the secondaries kick in, it bogs a bit... like it's getting too much gas. (And it doesn't keep accelerating like it should) It is running rich by the smell at at idle, though it's smooth. (It pops just a bit when decelerating downhill) I'm thinking of turning up the air a bit. Is this the right thing to do?
Thanks
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
Doesn't these carbs have the "AIR" controlled flap on the secondaries?? My old 500 Carters did?? They kinda made it like a vac. secondary carb by using weighted flaps to ease the fuel on.
I start with idle mix screws 1 1/2 turns out, then slowly adjust in til motor starts to stumble, then back out 1/4 turn. Do both so that they are basically the same turns out.
I've never had a motor backfire while decelling. Don't know if that is a rich or lean condition. Excess fuel in the cylinders could be the culprit? If it was lean, I guess it would pop up thru carb, not exhaust.
I start with idle mix screws 1 1/2 turns out, then slowly adjust in til motor starts to stumble, then back out 1/4 turn. Do both so that they are basically the same turns out.
I've never had a motor backfire while decelling. Don't know if that is a rich or lean condition. Excess fuel in the cylinders could be the culprit? If it was lean, I guess it would pop up thru carb, not exhaust.
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Mountain Pass
Joined: Oct 2004
Posts: 119
Likes: 5
From: SW Washington State
I got the problem solved.... it was the timing. Also hooked up the vacuum advance (couldn't get it to work right before due to electrical problems making it impossible to get the timing right in the first place) Then it was just a matter of setting the idle fuel mix, and the beast is beastly again!
Keep your fingers crossed on Thursday. I will have a 3000 lb camper on the truck, and will be towing a 3500 lb trailer..... Right up a mountain! *grin*
Keep your fingers crossed on Thursday. I will have a 3000 lb camper on the truck, and will be towing a 3500 lb trailer..... Right up a mountain! *grin*
Lead Driver
Joined: Jan 2003
Posts: 9,893
Likes: 12
From: Ohio
The air pulls past the plates, trying to OPEN the secondaries. The weights are there to help slow it down. Grinding the weight off thus lets the sec. open quicker. Just like a Holley and the different springs for sec opening...but with Ebok..there is no going back!! Unless you solder metal back on?
BTW, glad you got it figured out natira121.....have fun on the camping trip!
BTW, glad you got it figured out natira121.....have fun on the camping trip!
Posting Guru
Joined: Jul 2003
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From: Eureka, Ca.
Originally Posted by Freightrain
The air pulls past the plates, trying to OPEN the secondaries. The weights are there to help slow it down. Grinding the weight off thus lets the sec. open quicker. Just like a Holley and the different springs for sec opening...but with Ebok..there is no going back!! Unless you solder metal back on?
BTW, glad you got it figured out natira121.....have fun on the camping trip!
BTW, glad you got it figured out natira121.....have fun on the camping trip!
Post Fiend
Joined: Mar 2004
Posts: 6,056
Likes: 8
From: Union, Washington
The throttle plates move as mechanical, just like the Quadrajet. The air valve prevents the air flow and fuel flow until the engine needs it. Just like vacuum secondaries do the same job differently.
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Posting Guru
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Lead Driver
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From: Ohio
Yup, Bear. It gives you both worlds. Mech actuation, but then the air flap regulates the total flow by engine vacuum.
You can take the flap out of the carb, just remove lid and slip it out. This will give you total mechanical. But you will then most likely feel the bog. Since it has only ONE squirter...it will be real lean until it starts to pull fuel.
If you notice ALL Holley mech carbs are DOUBLE pumpers. Giving the additional squirt in the rear to help fill in the lag. Holley made a conversion kit years back that had a special squirter that had tubes that went to rear holes to make a vacuum carb a double pumper. It also had a gear set that mounted on side of carb to convert to mech linkage. Buddy ran one of these years back on race car...it worked!
You can take the flap out of the carb, just remove lid and slip it out. This will give you total mechanical. But you will then most likely feel the bog. Since it has only ONE squirter...it will be real lean until it starts to pull fuel.
If you notice ALL Holley mech carbs are DOUBLE pumpers. Giving the additional squirt in the rear to help fill in the lag. Holley made a conversion kit years back that had a special squirter that had tubes that went to rear holes to make a vacuum carb a double pumper. It also had a gear set that mounted on side of carb to convert to mech linkage. Buddy ran one of these years back on race car...it worked!
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