Carb Fine Tuning

[1strodeo]

Your vacuum gauge is past tense. A new one should only cost you about 15 bucks. So get one..

Again, the vacuum gauge was brand new and has been sent back for a replacement.

1/2 turn of the idle mix screws did not help, in fact the only difference I noticed was a couple small backfires/pops when going from 1st to 2nd gear. I'll pull the carb tomorrow and check the transfer slot. thanks guys

 

[blubuckaroo]

1strodeo, I'd still try the next stiffer metering rod step-up spring.

 

[jckkys]

The step up springs are as follows;3"Hg (blue), 4"Hg (yellow), 5"Hg (orange), 7"Hg(pink), and 8"Hg(plain). If any engine produces less than 8"Hg barely off idle, it has serious problems. 1strodeo stated that his Bronco "drives great accelerates great" so it's a safe bet that his engine has a lot more than 8"Hg when running "at very light throttle". There are no stiffer springs than the plain or 8"Hg. The metering rods provide high load enrichment. An incorrect spring would have been a problem for driving and accelerating. 1strodeo says these were great so there's no reason to change them. The lean serge off idle never involves the metering rods or step up springs. The fact that he doesn't have an accurate vacuum gauge isn't a problem in diagnosing his off idle lean serge. A good idle mixture can be easily achieved by simply finding the smoothest idle. He has no complaints about his idle. There is no reason to get into ignition issues. If there is an ignition miss it would have occurred during acceleration. That didn't happen, as 1strodeo says his acceleration is great. I look forward to hearing what the tech people at Edelbrock have to say. I want to add that Edelbrock has an owners manual that is included with new Performer AFBs. It tells you how to use the calibration kit. If you don't have one, they are down loadable on their sight.

 

[Skytrooper15]

The step up springs are as follows;3"Hg (blue), 4"Hg (yellow), 5"Hg (orange), 7"Hg(pink), and 8"Hg(plain). If any engine produces less than 8"Hg barely off idle, it has serious problems. 1strodeo stated that his Bronco "drives great accelerates great" so it's a safe bet that his engine has a lot more than 8"Hg when running "at very light throttle". There are no stiffer springs than the plain or 8"Hg. The metering rods provide high load enrichment. An incorrect spring would have been a problem for driving and accelerating. 1strodeo says these were great so there's no reason to change them. The lean serge off idle never involves the metering rods or step up springs. The fact that he doesn't have an accurate vacuum gauge isn't a problem in diagnosing his off idle lean serge. A good idle mixture can be easily achieved by simply finding the smoothest idle. He has no complaints about his idle. There is no reason to get into ignition issues. If there is an ignition miss it would have occurred during acceleration. That didn't happen, as 1strodeo says his acceleration is great. I look forward to hearing what the tech people at Edelbrock have to say. I want to add that Edelbrock has an owners manual that is included with new Performer AFBs. It tells you how to use the calibration kit. If you don't have one, they are down loadable on their sight.

You need to go back and read his first post where it says that when he lightly touches the gas,just very lightly I think that qualifies as an off idle stumble which is most often caused by plugs or timing.

 

[jckkys]

Where do I find any reference for that. It defies logic and experience. With no reliable reference or explanation, I can't believe it. You had to get this from somewhere or some one. Who or where? The normal definition of an off idle stumble applies to a situation where the accelerator/throttle is moving from closed to open, not a throttle that is held in a position barely open. The former is usually an accelerator pump issue. Neither is an ignition issue.

 

[1strodeo]

Hey jckkys can you help me relate the diagram to the picture please?

My guess is the two lowest (in relation to when the carb is mounted, not the pic) 'dot' ports are for the mixture screws, the two vertical slots are the transfer slots and the two horizontal ports, 1 below and one above the throttle plates, are .....I don't know %) thanks

 

[1strodeo]

actually the higher horizontal port (farthest left port in pic) is dead even with the throttle plate at idle

 

[rmk57]

The round ports are for ported vacuum. With the throttle closed you shouldn't be able to see them. I'm more of a Holley guy so I could be wrong.;D

Looks like I am wrong. the round ports are idle discharge ports.

 

[blubuckaroo]

Lots of Hmm here.
I'd still try stiffer step-up springs.

 

[jckkys]

You're correct. The round holes are for the idle mixture. If you remove the idle mixture screws you'll be able to see through them. The vertical slots ARE the transition slots. With the throttle closed to where you have set your curb idle speed, you should be able to see the bottom edge of those slots. The horizontal slot below the throttle plate is manifold vacuum, just like any port in the intake manifold. The horizontal slot above the throttles plate is the ported vacuum source to the vacuum advance can on the distributor. Sorry rmk57, Holleys and AFBs are different in this respect.
If the throttle starts to open without exposing the bottom of the transition slot, there will more air but no more fuel resulting in an off idle lean condition or what you describe as skips and lurches. It's hard to believe a defect this big in a new Performer/AFB. I believe a vacuum leak could be introducing more air. The idle mixture screws can be opened enough to compensate for the leak at idle, but when the throttle starts to open, the additional air is no longer compensated for and the engine "stumbles".
I'm glad to see you have the owner's manual. It will help with all aspects of tuning an AFB.

 

[1strodeo]

Looks like I am wrong. the round ports are idle discharge ports.

Yeah but as soon as you said 'vacuum ports' I knew exactly what the upper and lower horizontal ports were duhhhrrrr so thanks for that ;D

Lots of Hmm here.
I'd still try stiffer step-up springs.

Yes the whole point of the gauge was to know which springs to use as it says use springs rated at half the vacuum reading OR the stiffest springs, I need to check-see if the ones I put in were the stiffest. I don't think they were but sounds like they are doing the job, but like you said it's an easy swap and it may improve some aspect of performance which I think is adequate. I'm thinking the stiffest should be obvious without knowing the colors. %)

With the throttle closed to where you have set your curb idle speed, you should be able to see the bottom edge of those slots. The horizontal slot below the throttle plate is manifold vacuum, just like any port in the intake manifold.

If the throttle starts to open without exposing the bottom of the transition slot, there will more air but no more fuel resulting in an off idle lean condition or what you describe as skips and lurches. It's hard to believe a defect this big in a new Performer/AFB. I believe a vacuum leak could be introducing more air. The idle mixture screws can be opened enough to compensate for the leak at idle, but when the throttle starts to open, the additional air is no longer compensated for and the engine "stumbles".

I REALLY appreciate you breaking this down for me, you'd touched on a vacuum leak earlier but I didn't really get it. Now I do. I've had a limited understanding of carbs for some 30 years now but it's great to start to really understand them. Only wish I'd gotten a pic with the throttle closed, I do know that the transition slots were visible under the plates when closed.

I cleaned all six ports out with a wire and carb spray, reinstalled and same result. I did not pull the top of the carb off though. Sounds like I may need to start looking for a vacuum leak. Thanks again to all.

 

[blubuckaroo]

Yes the whole point of the gauge was to know which springs to use as it says use springs rated at half the vacuum reading OR the stiffest springs, I need to check-see if the ones I put in were the stiffest. I don't think they were but sounds like they are doing the job, but like you said it's an easy swap and it may improve some aspect of performance which I think is adequate. I'm thinking the stiffest should be obvious without knowing the colors. %)

I wouldn't use the stiffest spring unless it's needed. If you do, the enrichment will happen way too soon and the exhaust will probably be really smelly while cruising.
Your 1406 came with yellow step-up springs. Why not try going to the orange springs to see what happens?

 

[Skytrooper15]

Where do I find any reference for that. It defies logic and experience. With no reliable reference or explanation, I can't believe it. You had to get this from somewhere or some one. Who or where? The normal definition of an off idle stumble applies to a situation where the accelerator/throttle is moving from closed to open, not a throttle that is held in a position barely open. The former is usually an accelerator pump issue. Neither is an ignition issue.

You need to go back to school if you ever went and while you are there get some manners.Did you read the first post that he made?You talked yourself in a circle again on this.What is an off idle stumble?It's when you barely touch the gas pedal..You know OFF Idle coming off of the idle circuit in the carburetor and pressing the gas...Where do you get your info?Out of an old Ford shop manual with missing pages?

 

[1strodeo]

I cleaned all six ports out with a wire and carb spray, reinstalled and same result. I did not pull the top of the carb off though. Sounds like I may need to start looking for a vacuum leak. Thanks again to all.

Well I STAND CORRECTED when I went to look for vacuum leaks yesterday, I saw that I had left the ported vacuum hose unhooked from the carb the day before %) in other words I found a vacuum leak lol

Hooked it back up and went for a drive, I'd say 95% of the light throttle skipping was GONE, like only enough that a car guy would notice, so I think that did the trick. HOWEVER I ran out of gas later on in my joyride, as I often do because my gauge doesn't work, threw in my one-gallon-reserve and trotted straight home because I had dinner in the oven. Going through the neighborhood with minimum throttle as I always do - once in 2nd gear that is - it starts skipping again!!! So either more crap got lodged in the transfer slot or it just didn't like having a gallon of gas in the tank. More to come.....

I wouldn't use the stiffest spring unless it's needed. If you do, the enrichment will happen way too soon and the exhaust will probably be really smelly while cruising.
Your 1406 came with yellow step-up springs. Why not try going to the orange springs to see what happens?

Yes the "OR the stiffest spring" suggestion from Edelbrock was only IF you have no vacuum gauge...which I don't at the moment, so thanks for the tip, now just gotta ask my son which one is Orange

 

[dholder]

I can't see the color on most of my springs either. Go online to summit, I think, and they show a picture of each spring. If you compare lengths and tightness of coils, you can figure out which spring is which, without being able to see the color.

 

[blubuckaroo]

The spring color fades away when they've been used.
The Edelbrock carb manual has a section in the back to log the jet size, metering rod size, and step up spring color.
Best to log it or you won't know what's in there.

 

[m_m70]

my 1403 came with the orange springs. Change out to pink and cleared up my stumble. You have the springs and they're really, really easy to change so might at least play with them and see if it gets better or worst.....

I spent a good part of a day changing jets, rods and springs and when it finally got happy it's was so worth it!

Just my 2 cents...……..