Lean MisFire

[Mercmarc]

Hello All,

Has anyone run across a lean mis fire under light throttle condition with new model 94's from Dennis Carpenter? Jet sizes from 49 to 62 and power valves from 5.5 to 4.5.

Background:

New 1950 239 built by Mike of H&H with the 94's on it. Ran well on the engine stand. Driving under light throttle just off idle to 1500 RPM it bucks, lean on the throttle and the bucking stops.
Parked in the garage you can raise the rpm and choke the carbs slightly and the engine speeds up slightly, even with the jets at 59.

Idles well, runs well under moderate to heavy throttle, plugs are still brownish.

Many thanks for any input, solid wires, HEI and point distributors, autolite plugs have been used with no change.

Respectfully

Marc

[koates]

Connect a test vacuum gauge to your intake manifold and check the readings against the test chart. That is an approved way of diagnosing problems. Regards, Kevin.

[Bill OH]

I had a pair of Hollys on a 239 back in the day and I experienced a flat spot in the transition from idle to mains. You might try opening up the idle mixture to see if that helps. I had vacuum leaks between the bowl and the base and with other problems I switched to 97s, which I also have on a 221 running stock mains and #71 pvs. Runs very well!!!

[Mercmarc]

Many thanks Gents,

I will do the vacuum test today and go from there. I was hoping to avoid going to the 97's because of cost and the fact that I just spent 1K on the two 94's. If that turns out to be the problem, then so be it. I will keep you posted.

Thanks again

Marc

[flatjack9]

94's are generally jetted with 49 - 51 main jets depending on your altitude. Under the conditions you describe, the idle system is still contributing. Might try opening the idle screws a bit.

[51 MERC-CT]

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Would be interesting to see what an AFR meter has to say about the condition.

[Ol' Ron]

What distributor do you have? I like the 94's better than the 97;s
Gramps

[Mercmarc]

I am running the original ford distributor with the vacuum advance. New Taylor solid wires, new coil with a new ballast resistor. New plugs that are Autolite 216.

I have run two electronic HEI distributors from different suppliers with the same results. ( still stumbles off idle up to 1500 RPM). Both versions failed within 50 miles of each other for different reasons. One had a cut wire by the advance plate moving, the other one failed because of a failed electronic board. That is why I am running the old original distributor with new points and condenser and the shaft is tight with no point variation while running a dwell meter. Condition is the same regardless of the vacuum advance connected or not. Ventury vacuum from one carb.

[Mercmarc]

one distributor was made by TSP pro series ready to run HEI with an adjustable vacuum advance old style GM cap using

[Tinker]

I shouldn't add, but I believe on a duel carb step up you want 3.5 pv's making it 7 all in vacuum dump. When you hit the throttle the vacuum drops.


Just an oldtimey thought. Idle good and revs in the garage, underload bucks. Sticky valves or condenser. New motor tight guides.

[flatjack9]

The stock distributor will not advance properly with 2 - 2's. You are probably running quite retarded. You need a Charlie N Y converted distributor with manifold vacuum advance.

[Tinker]

Not familiar fully with HEI, but wouldn't that require spiral wound plug wires, even with points? Interesting setup.

[Mercmarc]

Thank you's to everyone who has weighed in so far.

The results of todays efforts are this.
17 in of vacuum at idle. 4 degrees advance from the pointer on the crank pulley.
No vacuum at idle from the carb as noted above.
The engine idles well, throttles up well in the garage when revved.
The condition I am trying to solve is from just off idle to approximately 1500 RPM the engine stumbles.
While holding the pedal steady and the RPM around 1300 the engine runs lean. I can choke the carbs down and the vacuum increases to near 20 inches and the engine smooths out. Remove my hands from the carbs and it begins stumbling again all while holding the foot feed steady (second person) :-).

I am running 52 main jets with 4.5 PV. I took the carbs completely apart today which are new from Dennis Carpenter, looking for an obstruction in the venturies of any sort. None found, only a throttle plate issue that I resolved. No change in performance or the issue that I am addressing.

This engine was built by Mike at H&H with these carbs on it. On the stand it ran well, once it was in the car this condition became evident. I have 175 miles on car and engine at this point. I have tried multiple distributors, both HEI and points with no change in the condition. I have tried jets from 49 to 62 with no significant change except for a better rev at the richer condition. The plugs remain brownish and at idle I get 1 inch of vacuum variation while at 17 inches plus or minus 1/2 inch. I don't know what cam Mike installed other than to say it is the same as he runs and he was certain I would be very happy with it. (no help I know) Editorial humor:-). H&H are great people.

Tomorrow I will drive the car again with the vacuum gauge attached to the manifold port and see what driving reading I get. More to follow

Again thank you to all

Sincerely

Marc

[Mercmarc]

I have had no issues with the solid wires that I purchased through Summit and I was told that the Taylor wires would work well with the HEI setup. I wish the HEI distributors held up.

I will check in with Charlie NY to see what he needs from me.

[Tinker]

It's really a cross over electronic and point dizzy. So I have no idea on wires. Solid for points, spiral for electronic ignitions. I like the 97's too so.


Think Flatjack makes a great point on duel 94 carbs and where you pull vacuum from. CharlieNy is a good cat.


I like your idea of running a vacuum gauge in the cab also. I run them full time on my basic 36.

[Mercmarc]

Thank you Tinker, I just received a replacement (warranty) for the HEI system that failed on the electronic portion. I may give it one more try while working with Charlie Ny. I will try running the manifold vacuum to the advance on the electronic version just to see what affect it has overall. The vacuum advance begins pulling at 8 in vacuum but can be tightened up to begin moving closer to 13 in. Either way, at 17 in vacuum at idle it will be full on until leaning hard on the pedal. May not be a bad thing. Still have the centrifugal also. Light springs max out at around 3000 RPM if I remember but I will check the data sheet to be certain. If I recall correctly late 60's SBC used to run full advance at idle.

More to work through.

More updates to follow.

Respectfully

Marc

[Tinker]

Flathead runs idle 18-21 vacuum. 19-20 normal idle.

But with blowers and multicarbs it changes, lowers.

Beyond me, best of luck!

Not sure I know much about sbcs, but I'm not sure they run full advance at idle rpm's.

Just because a motor preforms on a stand or in the garage, Doesn't mean that it will do the same thing when you put load on it.

If you are smoking the electronics, it might not be vacuum.

Interesting to see how it goes for you.


.

[Ol' Ron]

Is this a 6 or 12v system? Charley can make a points style dist for 6v. You just can't use a stock dist for 2 carbs.
Gramps.

[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.

[Charlie ny]

Merc,
Per chance are you running progressive linkage ? Best to run direct linkage,
progressive 2x2 can be a tuning headache with 94's. I will suggest running one carb

at a time... use a carb block off plate if you have one, set the mixture screws for the
smoothest idle and set idle speed at 500. Square that carb and go for a ride....ditto
all for the other carb.
4.5 PV's might be to high in/hg. If your PV's have the rectangular outlets
and big soft gaskets take heed, they are not correct for 94's even if they came in the kit's you purchased.

The vac operated power circuit on 94's can be a pain with multi carbs especially when a non stock cam is introduced. Thru the years on 2x2 setups I plug the PV's and run 52 jets.

The Chevy conversion distributor is a simple upgrade. Once installed the rate of adv and total can be changed without removal from the motor, pretty cool.
Charlie ny
[email protected]

All this is my opinion only...I absolutely respect alternative ideas and opinions

[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.

[Mercmarc]

Hello Crankster,

Good point on all the carb circuits. Lets not ignore the choke circuit. I get choked up about that one. Just keeping it light. :-)

Unfortunately I do not have access to a Wideband and yes that would take some of the guess work out of AFR numbers.

Elevation of Roseville Ca is 161 ft above sea level.

Camshaft is a 274 lift and duration.

I will install Charlie ny distributor when it arrives and keep everyone posted on the electrical side of things. Then turn to the carb questions once again. Solve or eliminate one thing at time. As mentioned before, I have run two electronic distributors and one ford load a matic with absolutely no change in driving performance on this engine.

With the engine being new from H&H I am not going to second guess Mikes work. Under load the engine runs strong, and the engine idles with a slight attitude per Mikes original set up with these carbs. The lean misfire surfaced once the engine was in the car and driveable.

Please stay tuned

Respectfully

Marc

[Crankster]

Originally Posted by Mercmarc

Good point on all the carb circuits. Lets not ignore the choke circuit. I get choked up about that one.

I'm gonna throttle you for that one!

Unfortunately I do not have access to a Wideband

Sure you do, they are "only" ~ $150 - a fraction of the cost, a fraction!, percentage wise, in any case of your investment in the engine & carbs I betcha. You're being Thrifty! Spouses as you are no doubt aware, are especially appreciative of this line of reasoning A lot of guys these days swear they won't mess with a carburetor without an AFR meter, at least for any serious work.

Elevation of Roseville Ca is 161 ft above sea level. Camshaft is a 274 lift and duration. With the engine being new from H&H I am not going to second guess Mikes work. Under load the engine runs strong .. lean misfire surfaced once the engine was in the car and driveable.

Well we're not asking you to second guess Mike, no sir. But there is at least a possible issue with the average manifold vacuum for whatever reason. Carburetors in general are extremely dependent on having the correct vacuum signal through them. And any problems are always going to surface when installed. This is especially true at idle or just off idle & the transition circuit where a lot of driving is done. 17" Hg might in fact be excellent with that particular cam, I don't know. The AFR meters allow one to tailor each individual carburetor circuit with confidence, I'd recommend one even when you get this particular tuning defect remedied.

[Bill OH]

Some thoughts: How about plugging the windshield wiper port on the intake or has the connection for the vacuum gauge accomplished this? Does your intake have defects in the exhaust heat cross over? You can remedy that with core plugs in the block cross over ports within the block. Your manifold new or used? If all of the foregoing proves satisfactory and Charlie’s GM distributor does not correct the problem, which I hope it does, then pull the carbs and have them rebuilt by Charley NY or install Stromberg 48s with 48 jets and perhaps lean the power valve and send the existing carbs back to the vendor. Holleys are not top rung for me. I have used 48 carbs and they performed very well. You have the displacement and cam to take advantage of 48s. Another thought: Use a bored out Merc manifold mounting a Rochester 2GC!!! Your call!!!

[Mercmarc]

Hello Crankster and Bill OH,

That was a good one Crankster, :-)

I took the plunge and ordered an Autometer analog face AFR meter along with a SS tail pipe clamp for holding the O2 sensor. Let the fun begin when the tools arrive.

I apologize for my poor choice of words regarding second guessing Mikes work.

I was really just trying to express my complete confidence in Mikes work and therefore invest alll our efforts in the ancillary items.

I am very grateful for the continued dialog with everyone while working through this mystery.


Hello Bill OH,

Yes the vacuum port is currently occupied by a vacuum gauge. (Wipers are now electric)
The manifold is a new aluminum one with no name on it.
I am using one inch aluminum risers below the carbs. No difference when removed, they have been reinstalled.

Mike of H&H recommends Strombergs for his engines, but I am not certain which series he is selling 48’s or 97’s. He did say he would rejett the carbs with 48 jets if I ordered some from him.

I am partial to the look of the dual carbs, but the 2GC carb is certainly an option.

I have invested a bit of time and effort redoing the throttle linkage and associated mounts for these 94’s after my wife requested AC and a heater. But If I cannot make them work then Strombergs it will be.

Respectfully

Marc

[Mercmarc]

Hello All,

Update on lean misfire (stumble) just off idle (850 to 1500 rpm)

Final solution:
GM distributor from Charlie ny, works great.
52 Main jets for the new Dennis Carpenter model 94's
7.5 power valves
Rich idle mixture screw settings

Car is very drivable from a dead stop on a slight incline and all through the gears with no stumble and no excessive clutch slipping or RPM revving.

Realtime AFR readings from each tail pipe to follow in the near future.

Many thanks to all for everyones interest and input.

Respectfully

Marc

[tubman]

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Thanks for getting back to us with the results. It's always good to know what works (and sometimes, what doesn't). It figuratively "ties a bow on the package".

[Mercmarc]

:-)

YEAH Ford Barn

[Crankster]

The old mechanic saying went "90% of the carburetor problems are ignition related."