Lean MisFire

[Mercmarc]

Good Morning All,

Great reading today and thank you Charlie Ny for your questions, thoughts and jumping in on this.

Answers to posted questions:

12 volt negative ground system. Gramps

Direct linkage on the carbs, not progressive. Charlie

I ordered 4.5 PV's and 52 jets from a recommended supplier who modifies the PV to clear the bowls. I read about him on the HAMB regarding 94 jets and PV's. Charlie

Non stock cam (274 lift and duration) on intake and exhaust according to Mike Herman of H&H. Mike recommended 5 degrees advance initial with a total of 24 degrees advance for this cam. Tinker

The electronic failures were, first distributor had a cut wire from the vacuum plate moving back and forth, the wire loop was not secured adequately. Second distributor failure was a bad PC board in the base the distributor. Their solution to the wire loop was to silicone it to the housing reducing the size of the flex loop. Tinker

Test drive today with fresh plugs and a new HEI distributor with a 45K output coil. Also to collect actual driving condition vacuum gauge readings for determining the best suited power valve. Hopefully.

PS yes I will have a gauge reader, note taker. I get to drive my car :-)

Respectfully

Marc

[tubman]

I hope your "recommended supplier" was not Charlie Price at "Vintage Speed". He has a reputation of supplying re-drilled jets and jets with the size stamp ground off. Oh yeah, most of the jets he sends out are used.

[Mercmarc]

Hello Again, 11/2/2021

Todays adventures continue, A test drive once again with fresh Autolites 216's a vacuum gauge and note pad.

Main jets are 52, power valves are 4.5
Warm idle vacuum 16 to 17 inches

Round one
First gear, light throttle, on level ground vacuum drops to around 10 in, slight to heavy bucking.
2nd gear, light throttle, 10 to 12 inches and 1400 rpm and the bucking continues up 2000 rpm.
3rd gear, light throttle 12 to 15 inches 2000 rpm and still feel bucking.

Round two
1st gear, moderate acceleration, 5in vacuum, pulls hard, no bucking until vacuum increases to about 9 to 10 inches vacuum.
2nd and 3 gear same results, pulls hard when at 5 inches vacuum until around 8 to 10 inches and the bucking begins.

Round three
Brief full on load, first , second and third, 0 vacuum runs well and pulls hard until vacuum increase to above 10 in, then the bucking begins.

I am of the opinion that if I plug the power valves while only using size 52 jets, the engine will not get enough fuel to pull as hard as it does. 5 inches of vacuum and less and the engine does not miss a lick.

Going to reach out to Charlie Ny and discuss his distributor options.

Many thanks

I will continue with updates until resolved.

Respectfully

Marc

[chuck stevens]

Marc, What kind of fuel are you running? If it is the watered down methanol that is so popular you will have a hard time getting any engine with a carb to run smooth. I increased my main jets from 50 to 55, this helped but MPG went south-10-12. As an experiment try a tank full of the recreation, (alcohol free), fuel. seems to be a lot better ,but over $4.00/ gal. it should be. It has a plus side-cold start up no choke.

[Mercmarc]

Hello Chuck,

Great question, one I should have addressed earlier,

I am running Chevron premium, 93 octane with 8 OZ of Lucas ethanol treatment to combat any affects of ethanol and 8 OZ of Marvel Mystery oil per tank, 16 gallon tank

[Mercmarc]

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I have rejected these 94's from 49 all the way to 62, in concert with 4.5 power valves, condition gets better but does not go away. I reinstalled the 52's and test drove again yesterday with very poor results at a light throttle condition. Heavy footed and she runs strong. I am in touch with Charlie Ny regarding a modified distributor using a Petronics (spelling?) system.

[Mercmarc]

rejetted Darn auto correct, its a helpful curse

[flatjack9]

Originally Posted by Mercmarc

I have rejected these 94's from 49 all the way to 62, in concert with 4.5 power valves, condition gets better but does not go away. I reinstalled the 52's and test drove again yesterday with very poor results at a light throttle condition. Heavy footed and she runs strong. I am in touch with Charlie Ny regarding a modified distributor using a Petronics (spelling?) system.

Forget the Pertronics and use one of Charlies distributors with vacuum advance. That is all I use on my rebuilds.

[tubman]

I second the use of a conventional points in the distributor. Aftermarket electronic ignitions can too often be troublesome.

[Ol' Ron]

52's are a little rich! Gramps

[Mercmarc]

Hello Flatjack9, tubman and Gramps

I have been in touch with Charlie and he is the one suggesting I use the Petronics in the distributors he builds. Charlie asked me to purchase a Petronics system kit from Napa and have it shipped to him for his build.

Now I am more confused, is there more than one Charlie doing chevy distributors for Ford flatheads?

If I should be using points and condenser, why can’t I use the ford distributor I am using now that starts easy, and runs well under load.

I still have not figured out the carburetors lean condition that is causing the off idle to 1500 rpm stumble. I am not blowing black smoke, the plugs are still brownish.

When I hold the gas pedal steady and at any RPM just past idle and up to about 1500 the engine runs rough, when I restrict the carbs with my hands the engine smooths out, the vacuum increases. This condition is not as bad when using jets drillers to 58 while using 4.5 power valves. Plugging the power valves will only contribute to running too lean under load correct?

Marc

[Crankster]

Originally Posted by flatjack9

Engines used to run with full vacuum at idle. As emissions laws came in to effect, vacuum was changed to ported to help lower emissions.

Some engines did. Some didn't. Ford always used ported didn't they? All the OEMs basically changed to ported though, when federal emissions laws were enacted, to reduce NOX. Retarded ignition timing, late valve timing, compression reduction. A real goat roundup.

They did make a concession and used a temperature solenoid to revert to manifold vacuum after it overheated, which wasn't uncommon because ... the ignition timing was retarded. LOL! (Never mind that the engine is now probably roached).

[Charlie ny]

Marc,
What I suggested is if you want to use Pertronix I request you purchase
it so it is in your name for warranty purposes. I reluctantly will build one of my distributors with Pert at the customers request but prefer by a WIDE margin points
and condenser.
I am Charlie ny the other Charlie I seem to recall resides in Florida. A long
time ago during the Shelly days I real quick added ny to my name to differentiate
he and me.
I reread Marc's posts and think maybe the Ford Load a Matic is back in the motor. In a private email to me Marc made mention of a CRISP stumble rather than
a gasp. Until assured otherwise and from time with Load a Matics I think the crisp
stumble could be from the hot wire beneath the breaker plate shorting out. It's not uncommon ,if the insulation is compromised, that as the breaker plate advances the

uninsulated wire can contact the body of the distributor.
Load a Matic distributor are ok with one carb and a stock cam. Adding carbs and a cam reduces engine vacuum making the all vac operated Load a Matic ineffective.
The Chevy/8BA distributor has a great mechanical advance feature and
is easily recurved. Addiitional vac adv is available as well.
Wish I lived in Roseville.
Charlie ny

[Mercmarc]

Hello Charlie ny,

Lets use the KISS principle here. LOL

I checked the wire on the Ford Load-a -Matic distributor, no shorting via Ohm meter and after running with a disconnected advance, same driving condition. I replaced the 52 jets with 49 as suggested and the driving condition was worse.

I believe I am fighting a lean carburetor condition in the Dennis Carpenter model 94 carbs. When I run larger jets the condition gets better but does not go away completely, and my spark plugs remain brownish. I have run jets drilled to 58 with better results in these carbs but still not a smooth drive under light throttle and a sustained speed wether its 10 mph or 20 or 30 mph. Once I am holding steady the bucking begins. The smaller the jets the worse the bucking/stumbling.

This all said. I want to purchase a points and condenser Chevy/8BA distributor from you Charlie ny that is set up for the 1950 239 flathead flathead with dual carbs. No Petronics for me please. :-)

Sincerely

Marc

[chuck stevens]

Marc, You are on the right track with changing the main metering jets. But the fuel with 10 percent alcohol will always be troublesome with a carb. If you can get a tank full of pure gasoline just as an experiment.
Oh there are more than one Charlie, Charlie NY is a great guy for carbs and distributors. Old point ignition or petronics probably won't act much different if the fuel isn't up to old standards. High test isn't necessary, dont know about the additives.
Chuck.

[Gene1949]

Your 11-01-2021, 08:59 PM post describes a classic [low] float level problem.
Kinda sounds like a problem when you transition from idle (uncovering the transition port). Running the float level at it's max (or maybe even a little beyond) MIGHT give you a positive result.
Just my $.02/shot in the dark

it's already been said;
Lose the load'o'matic distributer and get a [good] functioning GM type.
The old Mallorys were created for multi-carb and 4 barrel use back in the day.
How it makes spark really doesn't matter as long as it's functioning well and a mechanical curve designed for a flatty AND the vacuum can using manifold vacuum. THEN we can chase the carb issue..

Don't give up, there is enough brain power in the Ford Barn to solve your problem.

[Gene1949]

One other thing; an old axiom..
multiple carbs exacerbates [INCREASES] carb problems by the coefficient [number] of carburetors used.

On a more serious note;
you are decreasing the airflow divided by the number of carbs used. That is why I believe uncovering your transition port (starting main jet fuel flow) AND float level is related to your lean misfire.

[robib]

There are three circuits in a carburetor. Idle, transition and main jet. From what you are describing, the circuit involved is the transition circuit. Had a similar situation, only mine was running rich. Added more air to the transition and my problem was fixed. You need to add more fuel to the transition circuit "only" or possibly "less" air. I am not familiar with 94s, so I can't tell how either more fuel or less air can be accomplished. Someone here should know.

[Mercmarc]

Good morning chuck stevens, Gene1949 and robib

Hello Chuck,

The Lucas additive is to address any residual alcohol in the fuel, and the chevron high test was to use a fuel with a minimal alcohol content. The Marvel Mystery oil was recommended to help offset any ill affects of California fuel on rubber parts, hoses, gaskets and the like.

I am working with Charlie ny on a distributor as we speak.

Hello Gene1949,

Thank you for your suggestion on float level. I raised the top of the float to with in an 1/8 of and inch of the carb top. No change. Great information on the multiplier for troubles.

I have asked Charlie to build a distributor with points and condenser and I will ask for the vacuum can version.

Hello robib

I understand and concur about the 3 circuits in the carb and I have the same issue of not knowing the best way too increase fuel or reduce the air in the transition circuit. My gut feeling is to increase the size of the venturi metering rods. Then I should be able to scale back the main jet size to the more common 49 to 52 sizes that have been suggested.

I believe a possible problem lies in the emission criteria for california. A bigger main jet is less affective if the venturi metering rods are restricted to much.

When my vacuum drops enough to open the power valves the engine performs great.
I have installed jets from 49 to 62 in small increments with improvements along the way but not correcting the actual problem. With such a large increase in the jet sizes and only a moderate change in drivability I feel the new carbs are flawed.

I have several ford script model 94’s but the venturi parts did not want to interchange with the new carb bowls and frankly the ford script bowls were in pretty bad shape. I was hoping to swap the venturi bowls using an earlier type venturi system and see if that corrected the problem.

As I mentioned earlier, even with such a large increase in the jets and I could not get enough fuel to soot up the plugs I believe the main jets are not the only trouble with these new carbs.

I will install Charlie ny’s distributor and begin from there on the air fuel troubles.

Just another note, I have run two electronic GM distributors from Total Street Performance on this engine and carb combination with no change in drivability.

Respectfully

Marc

[Crankster]

Not to put too fine a point on it, but there are at least four carburetor circuits. You guys left out the power enrichment. Five actually, if counting the float circuit.

Now admittedly I know next to nothing about running multiple carburetors. I bet it's multiple expensive, and it sounds like it's multiple pain in the &@$$. Isn't tuning just a single carburetor punishment enough??

It would be interesting to use a wideband AFR meter, these make carburetor tuning a whole lot less guess and by golly. Plug reading alone is difficult with modern gasoline. It's just as important as it ever was but it's tricky. You should post a clear pic or two head on and close up. What I noticed using a wideband is major changes in AFR numbers don't necessarily make major changes in plug color.

What elevation are you running at? A steady 17 Hg on a mechanics vacuum gauge is "good" and indeed is "in the green" on the dial, but it might be up to 3" or 4" low depending. That's a lot. There is a correction factor applied of about 1" for every 1000' ASL. It's kind of a judgment call. What I mean by that is one would have to know what a particular engine is capable of for engine manifold vacuum. Camshaft selection and installation affects this in a big way, as does the base ignition timing setting.

Virtually any stock or stock-ish engine should pull 19" to 21" at sea level with ignition timing set to factory spec. What I'm getting at is if your particular engine "should" be pulling 20", but it's only pulling 17", find out why and remedy that and it should go a long way with the unpleasantness.