Lean MisFire

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
 
Mercmarc said:
Good point on all the carb circuits. Lets not ignore the choke circuit. I get choked up about that one.
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I'm gonna throttle you for that one!

Unfortunately I do not have access to a Wideband
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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.
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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.
 
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!!!
 
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
 
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
 
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".
 
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