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No power at 50mph and sooty plugs

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Since rebuilding my distributor recently I picked up a new issue. My 49 Windsor now bogs down at 50-55 mph and won't go any faster; it takes just a couple of miles to foul the plugs (black and sooty). I had a couple plugs wires mixed and did get a backfire after the rebuild, so that has to have something to do with my issue. I just took the carb back off and cleaned everything I could get to, leaving only the main vent tube as I don't have the special tool, and installed new plugs. It took it just two miles down the road and the plugs were black and sooty while the car still chugs at 50-55.

It's obviously running way too rich, so I turned the idle mixture screw until seated and the car doesn't idle down whatsoever. Could this really be a result of the clogged main vent tube? Carb was rebuilt a year ago using a rebuild kit and ran fine up until the distributor rebuild.

Edited by Chrysler49

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Welcome. You say that you turned the idle set screw and seated it. It should not be tight but adjusted until the engine is idling at its smoothest. That is why there is a spring on it. A vacuum gauge works well to achieve this. Turn the screw in or out until the vacuum reading is at the highest steady reading. As far as the bogging down goes, are you sure that the ignition timing is set correctly and your choke is fully open? Do you notice black smoke behind you when this is occurring?  Another thing to check out is the exhaust manifold heat riser to be sure that is not stuck in the closed position. Where you said that the car ran fine before, it does rather seem that the problem lies with the distributor or timing. Good luck to you.

John R

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If you have a B&B carb you might want to check to see if the step up circuit and components are functioning properly. If the step up piston is stuck in the up position or not getting vacuum then it would cause the rich mixture.

 

Hope this helps, Jeff

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I seated the mixture screw just in an attempt to lean the mixture out as much as possible. The car should have started stalling and died, but didn't. I'm thinking my timing may be off, but would That explain the extremely rich mixture? Honest question, as I'm not overly familiar with timing. I did invest in a light though, but haven't used it yet.

There is black smoke now, and there wasn't before. I actually just replaced the spring on the heat riser this morning as it was broken, but it hasn't made any difference.

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The mixture screw is for setting idle mixture. It should have no effect at speed. If your mixture is off at speed then I'd look at things like the main jet.

 

But since this symptom seems to have occurred when you rebuilt the distributor I'd keep in mind the old adage that 90% of carburetor problems are electrical and go back and review the distributor.

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A few years ago I did a tune up and forgot to use the extra leaf springs on the breaker points.  Car ran idled and ran fine up to about 50mph.  I guess the lack of spring tension on the moveable arm on the points caused the points to not close at higher rpm--sounds a little similar

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If my timing were off enough would that explain the very rich fuel/air mixture? And shouldn't the car have died when completely seating the idle mixture screw?

The more pressure in the cylinder the higher voltage the spark has to be to ignite the mixture. If your spark is weak for some reason (poor coil saturation due to problems with dwell maybe, maybe other things) then the mixture in the cylinder may not be burning fully which might look like a rich mixture.

 

On my Plymouth and on all the cars I used to have with a old fashioned carburetor, yes, the engine will/would die if you tried to idle it with the idle mixture screw all the way in. But if the mixture screw tip or the seat have been damaged, as they often are by someone cranking the screw down, then all bets are off on that too.

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Don't forget the other side of the fuel air ratio.  Rich means too much gas or not enough air.  If your air cleaner is blocked or your choke is not opening fully it will result in an over rich mix.  Check to assure your throttle plate is closing completely. If it doesn;t close the idle circuit will never come into play.  Id the vacuum path to the step up valve free and providing vacuum signal?  Other wise it will be in the open position all the time and that results in having two jets providing gas when only the main jet is supposed to be.  The other item to check is your float level, if it is ot set correctly the bloat bowl will over flow putting raw gas into the carb without regard to any jets being opened or closed.  An remember that old saying. 90% of carburetor problems are ignition related and 90% of ignition problems are caused by the fuel system.

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We may have a winner. Took the distributor back off and compared the pics I took before rebuilding and now. There are two leaf springs on the old points, and only one now. I threw out the old points, but for $8 I can swing another set. Hopefully this is the primary cause of my issue, but I'm still not entirely convinced it's why even at idle the car is excessively rich.

In regards to my air flow, I did soak the air cleaner in kerosene and changed the oil, so that shouldn't be an issue.

Edited by Chrysler49

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The mixture screw allows the air and fuel mixture to come past the throttle plates when they are closed. That's why they only affect the engine at idle. If turning the mixture screw has no effect then most likely your throttle plates are not closing all the way. Usually this is the idle speed adjustment screw increasing the idle because the engine will not idle with the throttle plates closed. Most times that can be caused by ignition problems or vacuum leaks.

Edited by Lloyd

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If the old oil bath air filter is the issue then why not just go to a paper modern air filter?  If you are just using the car as a driver and taking to local shows then set it up for a modern oilles air filter. 

 

I feel that the modern paper air filters work just as well as the old oil bath filters and with out the mess.

 

remember when these car were built we had a lot of dirt roads and gravel roads that were being used. Now that we have paved roads and really very little dirt or gravel roads except for maybe a driveway inthe country or an occasioanly trip into an area that still might have a dirt road we basically have 99% paved roads.

Even if you cannot conver the existing unit to a paper filter then go look for an after market unit and then install that on the car and then when you go to a show then putthe old oil bath back on the car to maek it period correct.

 

Hope that all the issue was the spring and possibly the extra kero that was in the old mesh air filter.

 

Rich HArtung

Desoto1939@aol.com

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If the old oil bath air filter is the issue then why not just go to a paper modern air filter?  If you are just using the car as a driver and taking to local shows then set it up for a modern oilles air filter. 

 

I feel that the modern paper air filters work just as well as the old oil bath filters and with out the mess.

 

remember when these car were built we had a lot of dirt roads and gravel roads that were being used. Now that we have paved roads and really very little dirt or gravel roads except for maybe a driveway inthe country or an occasioanly trip into an area that still might have a dirt road we basically have 99% paved roads.

Even if you cannot conver the existing unit to a paper filter then go look for an after market unit and then install that on the car and then when you go to a show then putthe old oil bath back on the car to maek it period correct.

 

Hope that all the issue was the spring and possibly the extra kero that was in the old mesh air filter.

 

Rich HArtung

Desoto1939@aol.com

Sorry Rich, but some of us have to travel about half the time on dirt roads- at the least about five miles for me before I get to pavement!

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Sorry Rich, but some of us have to travel about half the time on dirt roads- at the least about five miles for me before I get to pavement!

 

Like I said in my reply I know that here are still dirt roads that some of us have to use. So in your case could you convert to the use of K&N modern filter that is washable and you spay on  their special oil that helps caputure the dust?  That might work for you. I know these are not cheap filters but in your case with the dusty roads this might protect the engine with all of the dust.  Just a thought.

 

My reply was more pointed to the Chrylser 49 owner that was having issues with the plugs fouling as a possible solution to his problem.  But thanks for your input.  Just trying to help another owner.

 

Rich

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And listen to those who pointed out that the idle circuit has nothing to do with the main circuit...the main being what the car is running on a somewhere just above a fast idle.

ken.

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I actually have run the car a little bit without the air cleaner, and it didn't make any difference. I ended up picking up a new Set of points at the auto-parts store today, but haven't gotten around to installing them yet. I'm actually pretty confident that the lack of the second recoil spring could be the cause of my bogging down and fouled plugs.

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That second spring being there can depend on the brand of points.  If memory serves me correct, Echlin had the double springs.

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vacuum gauge. look into a simple vacuum gauge & what it can do for you. it will help you with many questions on engine performance & trouble shooting.

if your engine is in idle circuit it should die when idle screw is screwed in all the way.aka vacuum leak?  also don't play with multiple things if it ran ok before distributor repair its probably in the distributor. but a vacuum gauge is a good idea to help anytime.

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