[Formula jg]

In case anyone would to continue to follow journey I started another thread in the electrical section to help determine potential distributor issues that may be contributing to the stutter and stumble problems.

Here us a direct link:

http://forums.maxperformanceinc.com/...d.php?t=834056

[Formula jg]

Update.
Resolved the stumble/bog issue with a distributor cap replacement (a couple of the coil screws were stripped in the cap, go figure). After that I decided to replace the 30yr coil and pickup coil.

Now back to the carb, although there is no noticeable stumble when stabbing the throttle there still is a huge lean spike showing up on the data logger. I tested larger squirters and added 50cc accel. pump but no change. Also plugged the secondary PV and up the jets to 86, no impact to the major lean spike with this either.

Went through the carb several times and all is good and clean, I don't know what else to test or check, any ideas are welcome.

[Kenth]

Originally Posted by Formula jg

It all looks and feels intact.

Center cam is upside down.
You'll need to turn it over.
Also, do you have the original springs?

[Formula jg]

Kenth, ok I will flip the center cam and as for the springs they are not the originals. I do have several different sets of springs I can sort through.

Timing when riad tested yesterday was as follows:
Initial 13-14
Mech 23
Total 36-37 all in @ 2000rpm
Manifold Vac Adv 7* starting at 7”hg

I rest timing but not road tested yet as follows:
Initial 10-11
Mech 23
Total 33-34 all in @ 2000rpm
Manifold Vac Adv 7* starting at 7”hg

As for the carb can someone confirm the dry float setting is 0.4” for a BG Mighty Demon?

[Scott65]

Does your Demon have sight glasses for the float level? I always used them for final determination, middle to slightly above. As for your spike on the data logger, you could conceivably get a spike from going way rich momentarily. If it runs good, and the plugs look good, I wouldn't let a momentary spike ruin my day. Lots of things are in play, like the location of the sensor, the fact that its reading all 4 cylinders on a bank together(likely, you didn't specifically say how you're monitoring afr) etc. When you're happy with the ignition, try backing down on the squirter, in small increments, or cam position, or go back to the 30cc pump, it's possible your seeing the fuel "dump" at wide open "put out" the sensor momentarily.

[Formula jg]

Scott65, it’s a bad lean spike not a rich spike and there is a stumble that occurs at that moment. I’m close to resolving the timing issues and once that’s good will reset float then move on to HSAB testing.

Kenth, I flipped the center cam and had to reset timing several times. The detonation is gone and these are the current settings:

Initial 17
Mech 17
Switched to ported Vac Adv. 7* starting @ 6”
Total 34 all in @ 3300rpm

I have several springs sets and will try to get it all in somewhere between 2600-3000.

Also found this in my tool box drawer that holds all my distributor spare parts but not sure what it does. Looks like it’s suppose to lay on top of the weights and under the springs or am I way off?

[Scott65]

Originally Posted by Formula jg

Update.
Resolved the stumble/bog issue with a distributor cap replacement (a couple of the coil screws were stripped in the cap, go figure). After that I decided to replace the 30yr coil and pickup coil.

Now back to the carb, although there is no noticeable stumble when stabbing the throttle there still is a huge lean spike showing up on the data logger. I tested larger squirters and added 50cc accel. pump but no change. Also plugged the secondary PV and up the jets to 86, no impact to the major lean spike with this either.

Went through the carb several times and all is good and clean, I don't know what else to test or check, any ideas are welcome.

You said the stumble/bog was resolved. We all try to help with the info you provide... Trends are to be given more weight than "spikes". And a slug of fuel will confuse an O2 sensor.

[Formula jg]

The stumble has reared it’s ugly head again, it was gone for a day or two, what can I say I started celebrating too soon.

[Formula jg]

Update
I'll start with the bad news, after replacing everything spark related from spark plugs all the way back to pickup coil this issue is still present. Now it wasn't all bad because there were somethings that actually needed replacing and except for the terrible studder/stumble when stabbing the throttle it actually runs a little stronger now.

Good news is after swaping out the 850MD for a 750SD with vac secondaries the studder is gone which means the problem is in the 850 and I can refocus my attention back on to that carb.

I have confirmed the following:
Fuel pressure is good,
Needle & seat is clean,
Power valves functioning properly and removing sec. PV did not help,
No debris in the IAB or HSAB,
Both accelerator pumps react instantly and larger squirters did not help,
Float levels within spec,
There is probably a few other things I checked or tested but ultimately the problem is still there.

I'm open to any and all recommendations.

[Formula jg]

I know this thread is getting old however I would like to update it in hopes of getting some more advise.

Quick recap the problem occurs when I stab the throttle while cruising and no fuel gets to the engine causing a huge stumble, so bad that if I keep the throttle pinned it will kill the engine.

Distributor is ruled out as the problem.

Fuel pump is ruled out as the problem.

All individual carb componets are clean and functioning properly.

What I found was the stumble only occurs when cruising under 2200rpm. so I'm thinking the issue is related to the transition circuit but I'm not sure where to go from here. The following pics show the pri. and sec. transfer slot relationship to the closed plates. Pic with closed plate is primary side and pic with the black pencil line represents the bottom side of the sec. plate when its closed.

Are these set correctly?

["QUICK-SILVER"]

What happens if you take it up to 2,200 rpm's in low gear and kick it?

Clay

[Skip Fix]

On Holley/Demons the idle circuit is involved sometimes up into the 3000 rpm range. I had a lean off idle bog I swapped pump cams squirters until I put the AFR on it with the idle in gear. Being in gear lugged it down and it was lean at idle vs the AFR in P/N idle. Fattened the idle up and bog was gone.

[shaker455]

Originally Posted by Formula jg

I know this thread is getting old however I would like to update it in hopes of getting some more advise.

Quick recap the problem occurs when I stab the throttle while cruising and no fuel gets to the engine causing a huge stumble, so bad that if I keep the throttle pinned it will kill the engine.

Distributor is ruled out as the problem.

Fuel pump is ruled out as the problem.

All individual carb componets are clean and functioning properly.

What I found was the stumble only occurs when cruising under 2200rpm. so I'm thinking the issue is related to the transition circuit but I'm not sure where to go from here. The following pics show the pri. and sec. transfer slot relationship to the closed plates. Pic with closed plate is primary side and pic with the black pencil line represents the bottom side of the sec. plate when its closed.

Are these set correctly?

So John when rear plates are closed no transfer slot exposed?

[Formula jg]

Quick-Silver, any gear over 2200rpm it takes off like bat out of hell.

Shaker, yes rear plate closed and transfer slot is completely covered. If I crack the rear plates (with TS still covered) it idles to high.

[Tom Vaught]

When you have the Primary blades set properly and the secondary blades are closed, what is your adjustment on the Idle-Eze circuit?

Tom V.

[Formula jg]

Skip, in P/N AFR is 12.6 and in D it’s 13.0

[Formula jg]

Tom, Idle-eze is fully closed.

[shaker455]

Originally Posted by Formula jg

Quick-Silver, any gear over 2200rpm it takes off like bat out of hell.

Shaker, yes rear plate closed and transfer slot is completely covered. If I crack the rear plates (with TS still covered) it idles to high.

When you do have the back blades open and Idles too high have you ever checked your timing to see if it's moved from your set initial?
What is your initial and @ what RPM it start to advance?

In some cases I have extended the T-slot to accommodate blade position

[Skip Fix]

Originally Posted by Formula jg

Tom, Idle-eze is fully closed.

Mine went from 12s to 15 in gear.

[Formula jg]

Shaker, I have not checked if timing jumps with the sec. blades cracked open but the current setting is 12 initial which starts to advance at approx. 1200rpm.

The pri. T-slot was elongated several years ago when I was setting up this carb because it had multiple issues out of the box including the lack of pri. T-slot exposure with closed blades.

Will extending the sec. T-slots below the closed blade have any negative impact to other circuits?

Also, what is the purpose of those weep holes next to the T-slot?

I should mention that I also reset and centered all 4 plates within there holes. That said is it normal if the plates do not completely seal around their individual holes (a little bit of light passes through sort of like a lunar eclipse)?