Flat-head six cylinder engine in an airport tug: troubleshooting
December 2010
Manolet Ramos wrote from an airport in Manila, Philippines: "We use a Chrysler Flathead Six engine in one of our tugs - the small trucks that pull planes. The engine works fine for a few minutes after start up but misfires when it warms up. What could be the problem?"
The Chrysler Flathead Six was made from 1929 to 1960 for cars, until 1968 in trucks, and possibly until around 1972 in industrial applications (it is possible that production ceased earlier and the company continued to sell from inventory). It was the last surviving engine to have the imprint of Carl Breer, Fred Zeder, and Owen Skelton, the "three musketeers."
The engine tag showed it was model 30-1449-1, serial number E (for "Export"?) 0803 44. The engine had Champion H10C spark plugs. Forum members made many suggestions.
68RT wrote: "Check with your local forklift dealer; the industrial 30 engine was common in them. The sales literature only says 14mm, resistor type spark plugs."
Manolet replaced the spark plugs, but the engine still ran rich, with black soot on the plugs after just one minute of idle. He replied that the mechanic wanted to adjusted the jet, which required opening the top of the carburetor. "The carb seems to have two adjustments. An screw near the base that, I believe, adjusts the amount of air flowing into the carb, and an idle adjustment screw on the other side."
68RT replied: "The only adjustment inside most Carter carburetors is the float level adjustment; one screw adjusts the idle speed air/fuel mixture and the other does the idle speed. You may have other issues inside, like the main jet having come loose.
"A cold engine will run rich because the choke will be on for a while, unless it is a manual choke or you have overridden the spring-applied choke. Unleaded fuel will give a more more sooty look than the older leaded fuel. I agree that you probably are too rich. ... Most of the flathead 6 engines were timed at a low idle with a pointer located in a hole at the rear of the engine that reveals a steel ball embedded into the flywheel. You matched them up and that is it."
ImperialCrown:
dana44 added:
ImperialCrown responded:
Don Crider added: "The exhaust headers take the heat from directly below the carb, which is part of the warming up that was part of the original design. Without that, you will need a richer mixture when cold to make the engine run smoothly causing some of your over-richness."
68RT added: "The simple thing is to look down the throat at idle and see if any gas is coming out the main jet which empties into the center of the venturi. If the float is high, you will have dribble coming out the hole and that will overwhelm the idle screw. The rare (but once in a while) thing is the low speed jet air bleed hole is plugged and instead of just air being pulled through at idle, it will siphon fuel though that jet. The nice thing about a Carter is that you can actually follow the circuits start to finish easily."
dana44 added that there was another way to see if the engine is running too large a jet, if no air-fuel sniffer is available: "[With the idle screw,] at 1.5 turns you are very close or right at optimum, plus or minus one quarter turn; as long as the needle itself is in good condition and is able to regulate the fuel bleed below the butterfly correctly, then all the way in without a change indicates the jet(s) is (are) too large, always checked at idle, so a smaller jet is in order if the air bleeds are not plugged and there are no vacuum leaks. "
Chrysler Flathead Six page
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December 2010
Manolet Ramos wrote from an airport in Manila, Philippines: "We use a Chrysler Flathead Six engine in one of our tugs - the small trucks that pull planes. The engine works fine for a few minutes after start up but misfires when it warms up. What could be the problem?"
The Chrysler Flathead Six was made from 1929 to 1960 for cars, until 1968 in trucks, and possibly until around 1972 in industrial applications (it is possible that production ceased earlier and the company continued to sell from inventory). It was the last surviving engine to have the imprint of Carl Breer, Fred Zeder, and Owen Skelton, the "three musketeers."
The engine tag showed it was model 30-1449-1, serial number E (for "Export"?) 0803 44. The engine had Champion H10C spark plugs. Forum members made many suggestions.
68RT wrote: "Check with your local forklift dealer; the industrial 30 engine was common in them. The sales literature only says 14mm, resistor type spark plugs."
Manolet replaced the spark plugs, but the engine still ran rich, with black soot on the plugs after just one minute of idle. He replied that the mechanic wanted to adjusted the jet, which required opening the top of the carburetor. "The carb seems to have two adjustments. An screw near the base that, I believe, adjusts the amount of air flowing into the carb, and an idle adjustment screw on the other side."
68RT replied: "The only adjustment inside most Carter carburetors is the float level adjustment; one screw adjusts the idle speed air/fuel mixture and the other does the idle speed. You may have other issues inside, like the main jet having come loose.
"A cold engine will run rich because the choke will be on for a while, unless it is a manual choke or you have overridden the spring-applied choke. Unleaded fuel will give a more more sooty look than the older leaded fuel. I agree that you probably are too rich. ... Most of the flathead 6 engines were timed at a low idle with a pointer located in a hole at the rear of the engine that reveals a steel ball embedded into the flywheel. You matched them up and that is it."
ImperialCrown:
dana44 added:
Manolet responded:
ImperialCrown responded:
Manolet noted that the carburetor is a Carter YF 4371S, which was also used on 1967 Chevy six-cylinder trucks. dana44 added:
(The firing order was correct.)
Don Crider added: "The exhaust headers take the heat from directly below the carb, which is part of the warming up that was part of the original design. Without that, you will need a richer mixture when cold to make the engine run smoothly causing some of your over-richness."
68RT added: "The simple thing is to look down the throat at idle and see if any gas is coming out the main jet which empties into the center of the venturi. If the float is high, you will have dribble coming out the hole and that will overwhelm the idle screw. The rare (but once in a while) thing is the low speed jet air bleed hole is plugged and instead of just air being pulled through at idle, it will siphon fuel though that jet. The nice thing about a Carter is that you can actually follow the circuits start to finish easily."
dana44 added that there was another way to see if the engine is running too large a jet, if no air-fuel sniffer is available: "[With the idle screw,] at 1.5 turns you are very close or right at optimum, plus or minus one quarter turn; as long as the needle itself is in good condition and is able to regulate the fuel bleed below the butterfly correctly, then all the way in without a change indicates the jet(s) is (are) too large, always checked at idle, so a smaller jet is in order if the air bleeds are not plugged and there are no vacuum leaks. "
Chrysler Flathead Six page
Home •
Engines •
Reviews •
Chrysler 1904-2018 •
Upcoming •
Trucks •
Cars
Spread the word via <!--Tweet or--> Facebook!
We make no guarantees regarding validity or accuracy of information, predictions, or advice - .
Copyright © VerticalScope Inc. All rights reserved. Dodge, Jeep, Chrysler, Ram, and Mopar are trademarks of Fiat Chrysler Automobiles.