carbs bog!!!

[saltshaker]

car bogs off line ( 2x4 mr intake...450's mech carbs)....timming 16 int 36 total
haven't changed the power valves ...came with 8.5's and has 12 to 14 inchs of vacum at idle.
Jon

[jhv48]

Does it bog just applying the throttle lightly off idle?

Or are you flooring it?

[saltshaker]

stepping on it lightly....

[Jerry Clayton]

progressive linkage???
Carbs facing backwards???

Jetting and pump/nozzle sizes??

[saltshaker]

stock 450's....#58 jets, 8.5 power valves, #31 squiters, progressive linkage and they are backwards
Jon

[Gunner]

I just went through the full process of getting my car to stop a light bog off the line. Many things were suggested (thread is here in the FE Talk forum, "Accelerator Pump tuning"). In the end, careful idle tuning plus a more aggressive accelerator pump cam did it. A change from 15+21 timing to 18+18 timing didn't hurt, may have helped.

Jets and power valves have almost nothing to do with an off-idle bog. The relatively cheap and simple progression is:

• Bigger accelerator pump squirter - go up two sizes, twice, to see if it helps;
• More initial timing - go to an 18* stop and 18-20* initial;
• More aggressive accel pump cam - I went from pink to blue and it made more diff than anything else;
• Make sure the idle is set correctly. In my case, my "perfect" tune using vacuum was too lean and I opened everything up another quarter turn for noticeable improvements.

In the end your power valves may be too high - the rule is idle vacuum / 2 + 0.5, use nearest next-higher value. For 14 inches, that would be 7.5, so you're a little sluggish on the added fuel... but that only applies under heavy load and a lot more throttle than normal off the line launches.

I'd bet 37 or 41 squirters will show some improvement, given that it's such a small primary carb. 37 squirters and an orange or blue cam, and I bet you're most of the way there. The timing change will help, too... FE's love advance.

[saltshaker]

thanks...did a little research on the FORDFE forum...I have #60 jets and 6.5 power valves ...will get some larger sqiuters,some where in the 38 range and change the cams....let you know how it goes. as for timing, if I go to 18 or 20 int I'll have 38 or 40 total and with ported iron heads and 10.5 comp not sure about 93 oct gas
Jon

[Gunner]

I don't know much about jets in multi-carb setups, but 60 sounds about right for a 450 - you'd have to use the usual plug check for lean or rich, or a F/A meter, to adjust them sensibly. A 6.5 power valve is probably close enough - I'd guess it might come in a little early and rich, not a problem except in tweaking for max power. Also a problem for final tuning, though, not off-idle performance. If you're seeing reasonable performance once you're past idle and no strong lean/rich indicators, I'd worry about jets and the PV later.

I think you'll find a squirter size increase and cam change will help a lot. Try that, and making sure your idle settings are optimal, before you mess with anything else.

If you have an MSD distributor, it's pretty trivial to change out the max advance stop for the 18* one (largest in the standard set). Then you can run 18-20* initial with no problems. Even with iron heads, FEs just love a lot of advance - LOTS more than SBF or most other engines.

[saltshaker]

thanks again...dizzy is a points style ford unit recurved with a pertronix 2 in it...orginaly set with 14 int and 20 advance by 2600rpm
not sure how to change that!
Jon

[Jerry Clayton]

you have listed two different sets of jets/ pv ratings--what do you have???

Disconnect the seconary carb, and see if this bog is just on the primary carb---

Are the carbs stock 427 carbs?? you listed mech---- do they use seconary metering plates instead of jets??? any pics of your setup???

On the ford dist--the advance is under the breaker plate and has 2 differnt notches for amount of advance--usually about 3 or 4 degrees differance.

[Jerry Clayton]

Also---do your primaary float bowls have the ball check valve for the accerator pump???

[saltshaker]

today I went to start the car and it wouldn't stop poping out the exhaust...bad plug...changed it and the car started to run realy nice. worked on adjusting screws in metering plates( now about 3 turns out) and ran even better. pulled all the plugs (bf22 auto lites) and they are all black. reinstalled and changed timing to 18 int and squiter to 37 on front carb......nice. ? Now if I could get my plugs tp look better at idle..
any suggestions?
thanks again Jon

[Tom Kirkham]

I would not even think about tuning up a carb with out a wide band O2 sensor. I use the AFX, others use the LM-1 or LM-2. The LM series sensors data log and this is a very nice feature to have. The wide band O2 sensors will save you a ton of time. It also might save your engine. We have found that the most important circuit to get right is the transition circuit (idle to main jets). This is where most of the driving on the street is done. This requires some drilling and tapping in the metering blocks. This circuit needs to be right before you worry too much about the accelerator pumps.

[Tom Kirkham]

Salt Shaker assuming everything else is correct (real big assumption with dual fours), your idle circuit is too lean. The idle circuit is correct when the idle screws are about only a turn and a half out. How do you have the butterflies set in the carb? Does the butterfly square off the transition slot? How far open are the secondaries?

To get more advance in your distributor, file the slot, if you want less then you will need to have the slot welded up a little bit.

[jhv48]

Wouldn't three turns out be too rich?

[Gunner]

It sounds like you need to start with a full baseline on the carbs. Disconnect the secondary carb and adjust the primary first. There are any number of good threads and reference sites that will take you through the basics. It starts by setting the butterflies, then tweaking the idle mixture for the smoothest, fastest idle with the butterflies as closed as they can get. For most carbs, this is between 3/4 of a turn and 1-1/2 turns out. A vacuum gauge can help you find the point of max idle vacuum, which for some engines is optimum; as I painfully learned recently, another quarter turn or so rich from that point can work wonders.

Trying to keep diddling a carb that has more than one setting wrong can be very frustrating. Take it down to the base starting point and work as if it's a new carb.

Given that you don't have a very easily adjustable distributor, leave the timing alone for now. Get the carbs set up correctly first.

[Tom Kirkham]

Originally Posted by jhv48

Wouldn't three turns out be too rich?

If you must adjust the idle screws that far rich it means the idle circuit is too lean. This could be due to a vacuum leak, a dirt in the idle circuit, a throttle blade opened too far, too big of hole drilled in the throttle butterfly, etc.

If the throttle blade is opened too far at idle you will be out of the transition slot...

Check out Innovate Motorsports web site and forum:
http://www.innovatemotorsports.com/f...isplay.php?f=7

[elmariachi]

One thing is for sure and maybe you know this, but messing with more than any one of these above (timing, idle screws, jets, butterfly position etc.) at a time is a recipe for failure. If you don't have access to AFR equipment, a spirited 10 mile highway run on a brand new set of plugs will tell quite a bit.

Here are a few good reads:

http://www.aedperformance.com/Tuning%20Tips.htm

http://www.bob2000.com/carb.htm

http://www.tuningmadeeasy.com/tuning...uretor-part-1/

[cdnus]

Tom,
Perhaps when you have a little time, could you please post more info on how to alter with expected results the transition circuit.
A few photos would be greatly appreciated also, for the carb challenged.

Craig

[elmariachi]

See pic below. I have a big cam and very little vacuum at idle, so I needed to open up the butterflies on my Demon 750 using the idle position screws just to get it to idle. But then that introduced a stumble/bog. So I had to then install larger idle air bleeds to further emulsify the idle mixture. That in turn allowed me to crack open the butterflies/transition slots a bit more to get it to idle (without stumbling.) I know, clear as mud.