View Single Post
Old 09-18-2012, 09:03 AM   #1
Robert Dip
Senior Member
 
Robert Dip's Avatar
 
Join Date: Feb 2011
Location: Candiac, Qc.
Posts: 483
Default Souped-up flathead problem solved

Long read, but maybe worth it
Last year I wrote in on poor performance and 5 mpg dilemma. This engine is on my ’39 Coupe, ole 50’s Hot Rod with the original Navarro heads and dual carb intake, 97s and tube headers. Before I acquired it, it was put in ‘running condition’ after being taken out of storage in the mid 60s. After a better going over on brakes & tires, etc, I realized that the gas mileage was very poor and that the engine was not pulling as it should. Oil pressure was good, motor ran cool ( thru a 40s truck rad ) but the plugs were black with soot…..terrible rich on fuel. Not going through all of the minute details, all was changed. Plugs, wires, distributor, carbs re-built with .043 jets, pressure regulator, and on and on. Still was not happy, it just did not run the way it should. Maybe the cam was shot, but after close inspection with the intake off, clean engine, Johnson adjustable lifters….maybe not a problem there. Ole Navarro heads would probably have to come off…but dreaded the idea of removing a set of aluminum that have been there for most probably 60 years….heads frozen on the studs came to mind with all of the horror stories leading to total head destruction upon the removable process.
With the hood opened, engine running and discussing all of my problems with a buddy, I just by chance leaned over the engine and pulled of the two Helmet design air cleaners. Now, here comes the shock…the revs picked up by a few hundred rpm!!!!! The light bulb just lit, and I stood there without motion….just trying to realize what had happened. I revved up the engine and slight backfires followed, now that is strange. Drove back the car to my shop, and tried to figure out the situation.
First…the paper filters in the air cleaners were way too restricted.
Second…take a look at this Helmut design cover, and the air intake is very small, about 3/16” air gap around the base.
Third….the timing was now off to compensate for the rich mixture
Forth….the jet size, reduced to .043 became too lean, as the plugs burned white instead of blacky soot.
All of these problems because of bad design air filter covers ( yes, they are the coolest looking and had them on for every test run originally performed ) and cheap Asia import paper design filters…just bought 2 new ones from Speedway….I’ll put them in my trophy room & mark….’Remember this…do NOT use’
How can anything this stupid thing have eluded me for over one year! Don’t believe me….just read in Tex Smith’s book on this VERY PROBLEM. The section on carburetors clearly states this very exact problem.
Fifth….still stubborn on have the Helmut air cleaners, I drilled holes in the base ( see photos ) and forget the inner filters, it would just cover up the hoes just drilled. By the way, I had to drill these holes, because, even without the filter element, the 3/16” air cap entry was still too restrictive….believe me…my tests proved this.
Six…..remember the reduced .043 jets that seemed so important…..joined my trophy room stash of non-used parts. Last year, I bought a set of 97 carb re-building kits from Speedway, and regretted this junky purchase. The supplied .045 jets actually miked in at close to .047, what garbage….but wait, I know have them in the carbs…..seemed to be the perfect size for my setup…..why, you say….again in Tex’s book, it clearly states…two carbs now give you MORE air, and less gas suction from the jets….may have to open up the jets. 100% CORRECT for me. I’m learning….takes a while, but one day at a time.
I am now running the engine without filtering elements….but don’t give a damn. Engine is going like gang busters…yea, had to install a tach to see where the revs were at, it even pulls off generator pulleys and I feel the clutch slipping in high gear under full throttle. As they say….More Power….more problems……but better ones.
Better check those air cleaners…..I acquired enough gray hairs with this. Robert
Attached Images
File Type: jpg 044a.jpg (56.0 KB, 94 views)
File Type: jpg 002a - Copy.jpg (160.3 KB, 87 views)
File Type: jpg 003a - Copy.jpg (137.4 KB, 89 views)
Robert Dip is offline   Reply With Quote