I have a 49 Desoto Custom flat 6 Carter BB carb. I am trying to get it running right, and am haveing problems with it dying (from starvation) when it gets hot and not wanting to start unless I wait awhile. At Idle their is an occasional light miss. To keep it happy at Idle it seems like It wants to run just alittle to rich. It has good compression Heres some backround on what I've done to it. I bought it not running. Got it started and found a miss in the 6th cylinder. I lapped the valves and installed a new gaskets (Head, manifold, etc.) I replaced the condensor, plugs, and vacum advance. I sucked up some bad gas from the tank (first time with a barn find) Cleaned the carb, purged the lines and replaced the back halves, Cleaned the tank. I also had to make a float for the carb. The solder was disintegrating. The second question is about the gear selector. I cannot feel a differnce between high and low range and I think I'm only getting into low range. Am I suposed to be able to feel the difference in gears like a normal shifter? Can someone explain the Shift linkage to me and how it is spossed to feel when ya move the selectore? It has a Fluid Drive with OD and it does shift like it's supposed to (let off the throttle and hear a clunk) I know it's a long post especialy for a first post but I am stumped? Thanks
First of all it's not a flat 6, it's a flathead 6. Corvairs, Porsches and Subarus have flat 6s. Your car has a flathead 6. Calling it a flat 6 stamps you as a newb. Hope this is clear. I don't know why but this bugs the piss out of me. On your car the gearshift is like a 3 on the tree with low gear position missing. From neutral the positions are, Reverse gear, toward you and up Low range, straight up High range, straight down. The linkage gets gummed up if the car sits a long time. A little oil here and there will help. Other than that, it's just like a 3 speed column shift manual trans. There is a definite difference between high and low range, as much as between second and fourth in a four speed. Could be your shift linkage is on the fritz. Can you slide under the car and watch it work, or look under the hood, while someone shifts the gears? Make sure both levers on the trans are going all the way forward and back. You may need to fix some sloppy joints. If you need to adjust the linkage let me know, it is not hard to do, I can give you the directions from the factory repair manual. On the carburetor thing. Do you have the heat shield between the fuel pump and exhaust manifold? This is a piece of tin about 4" wide and a foot long, bent into an L shape that goes above the fuel pump. Sometimes they get lost over the years but you have to have it especially with today's lousy gas. Could also check the fuel feed. Disconnect the fuel line at the carb, stick it in a can or 2 liter pop bottle and turn the key. If fuel flow is inadequate you could have a plugged up filter. Chryslers had a big fine screen filter inside the gas tank that is impossible to remove or service. You could also have a slight vacuum leak around the carb base or manifold gasket. If you spray these areas with WD40 while the car is running and it speeds up it indicates a leak. You might check the plug wires and go over the ignition and carburetor again. The engine should idle down to 450 and purr like a big cat if everything is right.
If it's running poorly after warming up you might take another look at the valve lash adjustments. A few thousandths too tight can let the engine start and run OK cold but cause issues after everything's up to operating temperature. The heat causes thing to expand just enough that the lash goes away and it holds the valves just slightly open. After warming up, when it starts missing and just before it dies do you maybe hear a slight "popping" out the exhaust or up thru the carburetor? After the engine cools down the lash comes back, the valves seat properly and it will start back up again.
Definitely. 2 big thumbs up for that. Usually when I run into one of those I just click the red X and move on. Don't even bother reading the question never mind answering. Another thing I can't figure out is why they never make this mistake with a Ford. I have never seen even the greenest newbie refer to a Ford flat 8 or Model A flat 4.
Good point especially if he did not adjust the valves after lapping them. Lapping or grinding will close up the valve adjustment. One would assume he would know this and adjust the valves without being told but you never know.
Thanks for the info and yes I am a NEWB. Pretty proud of it I'll soak up all the info ya throw at me. Yes the valve lash was adjusted when I did the lapping but it never hurts to recheck. I just checked for leaks and yes the carb is leaking at the manifold gasket. It only happens after running for around 10 minutes. I'll fix this first. Also the Heat shield for the fuel pump is missing. I'll make one and get it on there. I also poked my head under the car and had my buddy move the shifter. I traced all the linkage from the shifter to the levers and everything moves and does not seem to be binding. The upper lever doesnt seem to be moveing all the way forward though. If you could post the adjustment instructions I would be very gratefull. Thanks for the help with my Flathead Six.
These instructions are for the manual trans from a Chrysler dealer's manual for 1949 - 52 models. Your trans should be about the same. Gear Shifter Control Rod. This is the rod that goes to the upper lever on the transmission. It is the control that has the bell crank in the middle. Loosen the stud nut on the upper lever, on the lower end of the steering column. Make certain that the transmission gears are in the neutral position and the column shifter is set at the horizontal position. Tighten the lock bolt. Gear Selector Rod. This rod goes from the column shifter to the lower lever on the transmission. Make certain the gears in the transmission are in neutral position. Loosen the lock nut at the bottom of the steering column. Tighten nut until all play is removed from rod, then back off 1/2 turn for clearance. Tighten lock nut.
Did you know the valves are supposed to be adjusted HOT with the engine RUNNING? This is not as nutty as it seems. You have to go for a drive then jack up the right front wheel and remove it and remove the access plate behind the wheel to get at the valve chamber. With the covers off and the engine idling you can check the clearance with a feeler gauge, and adjust any that are off. Or shut off the engine then do the adjustments. The engine idles down so slow this is not a difficult job. And because the lifters are solid not hydraulic they do not throw oil around like an OHV engine. .008 intake .010 exhaust Do not over tighten the carb bolts you could warp the carb base. Someone may already have done this. If you check the base with a straight edge and it is warped you can file it flat and put in a new gasket. Lock washers are a good idea. For some reason carb and manifold bolts on old sixes tend to work loose.
I got home and did a few more squirts with carb cleaner and pinpointed the leaks at the manifold gasket and the throttle shaft. I tore the carb off and I decked all the mating surfaces (there was some warpage) and made new gaskets. The throttle shaft is fine but the holes are worn. Any suggestions on how to fix this? Thanks for the info on the trans and valve lash. I'll set them both straight ones the carb is taken care of.
Worn throttle shaft, don't worry about it unless it is real bad. It will cause a slight vacuum leak but when you adjust the idle mixture it will be OK. About the only way to fix it is to ream out the holes with a special pilot reamer that goes all the way through and install an oversize shaft. This is part of a carb rebuild. In other words if it is real bad you have the carb rebuilt.
It's funny that you picked 450 RPM for the idle speed. Years ago a friend's sister had a '50 Dodge pick up that she was trying to get running and I got enlisted to help out. We got it to fire up and run but after warming up it acted just like Animal's DeSoto and stalled out. Wouldn't start again till it cooled back down. After a hot compression test she pulled the head and we found, oddly enough, a slightly burned intake valve and a couple exhaust valves didn't look too good either. She replaced them and lapped the seats and put the head back on. Then I got the dubious honor of setting the valve lash, hot and running. We'd gotten some advice from a trusted source to maybe set the lash like .002" looser than stock specs to possibly avoid things getting too tight when the engine got hot. I started out setting things to specs (.008/.010 I guess) and was amazed that it ran as quietly as something with hydraulic lifters. And after a bit of fiddling with the idle mixture and speed I remember looking at the tach and being surprised that it would indeed idle at exactly 450 RPM and pull a good steady vacuum. Before we buttoned it up though I reset the lash a couple thousandths looser. It was just slightly noisier but hardly noticeable with the side cover reinstalled. And I think we ended up setting the idle to a slightly more stable 500 RPM or so. It idled smooth as silk and you could barely hear or feel it running at idle. She had a lot of other work to do on that old pick up but I don't think we ever had to turn a wrench on the engine again.
450 RPM is the factory spec. If it idles much faster than that the transmission won't shift correctly. If the motor is in good shape it will idle down slower than that. Solid lifters are as quiet as hydraulics or quieter and they stay that way for the life of the engine if adjusted once in a while. Hydraulics have more to do with saving time on the assembly line and in the service shop than with making the engine run better.
Wonder if you could knurl the throttle shaft, then size as needed for a better fit. Knurling might help, though you would have the knurled grooves to allow vacuum to escape. But I doubt it would take much knurling to bring it to size of hole.
Please don't refer to your transmission as fluid drive or OD, it is neither, It is an M-6 semi automatic transmission powered through a fluid drive intermediat assembly. They are seperate and distinct. The semi auto is a dual range two speed unit, low range is only food for about 25 mph, so if you can drive faster you are selecting the dual gear of the high range. Low range is usually oly good for pullig buildings off thier foundations, or driving through quicksand, and occasionall descending steep grades while towing an airstream of something. Check out the repair section of the Imperial Club website, they have several sections on the care and feeding of the M6 semi automatic. They were the same whether in the Chrysler, Desoto or Dodge. Check your float level, I have found they like to set to allow just a bit less gas inthe chamber than stock for todays gas formulas. Hot start problems are many times traced to fuel perculation causing a flooded condition. this occurs as gas in the bowl expands in the hot engine compartment, overflows, and results in a Puddle of raw gas in the intake. When this happens, try holding the throttle at WIDE open before crankig the starter. If this helps, then lower your float about a 32nd or 2 from the current setting.
There MUST be some clearance or the shaft won't turn. Design tolerance was 0.004~0.006 inch. Our experience is that an additional 0.003 will still be fully acceptable. You can measure this with a dial indicator. If tolerance exceeds 0.010 inch, the proper method of repair would be to have a machine shop install bronze bushings in the throttle body. While this is a precision task, any good machine shop should have the tools to do the work. Bushings are readily available, but the installation does require some knowledge of the procedure. Call if you need instruction. When we have bushed these carbs in the past, we generally set the final clearance at 0.0055 inch. We tried the factory 0.004, but occasionally ran into this tolerance being too tight. An oversize throttle shaft will disturb the airflow, plus is more expensive to acquire or fabricate than installing bushings. If necessary, before installing the bushings, you might check the identification number on the carb and look for a replacement. Jon.
"Please don't refer to your transmission as fluid drive or OD, it is neither, It is an M-6 semi automatic transmission powered through a fluid drive intermediat assembly." If you want to be technical Chrysler called it a Hydraulically Operated Transmission. I can show you the original owner's manual for my 51 DeSoto. The factory supplied shop manual calls it a Simplimatic hydraulically operated transmission. I refer to it as a Fluid Drive transmission because that is its common name and one that appears on the trunk lid name plate. There is enough confusion about these transmissions (and Fluid Drive units).
Prestomatic, Gyromatic, tip toe, what ever, the transmission is the transmission and the fluid drive is seperate and distinct despite the marketing trim. a 49 dodge says fluid drive on the bumper regardless of whether its has a three speed standard transmission or a Gyro-matic bolted behind it. It will say Gyro-matic on the dashboard and maybe on the trunk when so equipped. Lots of confusion out there. lets just use the M-6 engineering term rather than the marketing appilations. http://www.allpar.com/mopar/m6.html
I'd be curious about your float, you said you made one? they are kinda precise things. #1 is that solder don't 'disintregrate' - do you still have your original float? if yes, then clean it up and test it in a bowl of hot water to see if it is airtite. After verifying i'd reinstall it as per the guy above suggestions with allowance for modern fuel.
The M6 transmission is only one model. They used at least 2 others with Fluid Drive and that does not count brand names. I prefer to use the factory approved nomenclature which is hydraulically operated transmission. But when answering questions it helps to use terms the questioner understands.
M4, M5, and M6. 48 and newer are all M6, by what ever name they are called by the assembly brand. Some poeple called then under drive and over drive, but since they were all 1 to1 final drive, in high range, that is a marketing, shadetree, grease monkey term, and is incorrect.
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