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Cold start problem Weber conversion?


Mike c

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Hi

 

I’m new to this so bear with me. 

I have a 49 Plymouth with the flat head straight six in it. I’m having trouble starting from cold unless I pour some fuel down the carb. So Dose any one know if a Weber 34 inch carb be ok to go on it as I’m worried it would be under fueling the engine? 

 

Thanks mike

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Most likely your problem is ethanol enriched gasoline as it evaporates much faster than non enriched fuel. Suggest you install an electric fuel pump near the gas tank and power it up with a push and hold button. Then simply push the button before attempting to start the engine until the electric pump reaches pressure and stops pumping. By doing so your carburetor should be full and your engine should fire off.

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I have an electric fuel pump on it already but dosent make any difference was thinking a Weber as the spray fuel down the manifold when you pump the throttle pedal and the  original on is on a vacuum pull through of that makes  sense. So I’m abit stuck as I don’t want to put the that Weber on if it’s going to under fuel the car

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my first question is if the Sissons choke is operational and second do you know how to energize the choke to operate properly when starting the vehicle.  If the solenoid is good and closing the butterfly of the choke when starting.  Many make the mistake of holding the gas pedal down, this will not allow the choke mechanism to lock the butterfly and step up the idle.  When starting, the choke solenoid is energized when the starter is turning, you push the accelerator down 1/3 droning cranking and while engine is turning you release the accelerator, this is what lock the choke plate and sets the high idle adjust against its cam.

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so what are the tune up and stats/specs of your engine, recent good tune with great spark when cold (cold starts take high amperage that can starve the ignition) and what is the compression of your engine, are you really sucking and compressing at the proper rate to ensure that the choke circuit will benefit from the velocity of the air through your air horn and you have the compression needed for proper combustion?  An engine with a bad carb and other good tune and engine stats good will fire immediately with a bit of fuel poured into the carb.  Verify these and report your findings.

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The car is a 49 Plymouth Special Deluxe with a flat head straight six with a 12v conversion done . My thoughts are that if i put a carb on it that pumps fuel when I pump the throttle pedal it will start better as the carb that’s on it now will only put fuel in the when it’s turning over. 

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When I push the throttle on my stock 52 the mechanical accelerator pump squirts gas right away.  I think that Plymouthy is on target here.  Make sure everything is up to spec. It took me a long time to get my Sission choke to work correctly.

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I have seen some carbs squirt fuel down the manifold when the throttle is pumped so was thinking that would help start it. So was asking if anyone has modified a different carb to go on the manifold and what make? 

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your carb has that very feature, and if this is not working then I can assume you have not even tried to rebuild or investigate the operation or physical aspects of the carb and its features for proper operation.  However, even without this functioning, you should never need 20 minutes of pouring fuel into the carb to get an engine to start as this pouring action is the very same result you would achieve with the accel pump.  Sounds more like poor tune and compression.  

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As stated above, check the accelerator pump.  There is a soft plug on the inner side just below the carb top. Remove it and run a welding tip cleaner or very thin wire through it.

This often solves the problem.

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Have you visually verified that there is fuel in the carburetor before you try to start your engine?  Have you observed fuel or no fuel when you work the accelerator pump?  It may be as simple as replacing the acc. pump

leather piece which don't tolerate ethanol well.  Is your choke butterfly closing to its proper cold start position. Why do you think the weber will under fuel the engine?  What was the weber designed for?

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I assume you started this thread seeking advice. There has been a lot of it, all good, given by members who really know these cars and their flathead engines. You need to heed it! Putting a carb on the car that was not designed for it will likely lead to other complications. I would only use the Weber carburetor if you exchange the Land Rover engine into the car as well. Not really a realistic option.

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So you want to put a carb from a 2/2.5 liter 4 cylinder on a 3.3 liter 6 cylinder?  Might start better, might not, might flow enough, might not, maybe you can richen the main jets enough maybe you can't.  Is it a single barrel or one of those progressive linkage two barrels?  Does it have a manual choke, electric choke or one of those hot water chokes?  Can you bolt it to the manifold or do you need an adapter.  Does the carb need an internal manifold vacuum signal for the step up circuit if so is it supported by the manifold/adapter?  Can you utilize stock throttle linkage or do you need to bodge something that might work or might not? Does it provide a ported vacuum signal for your vacuum advance?  Just askin'!

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4 hours ago, Mike c said:

I have an electric fuel pump on it already but dosent make any difference was thinking a Weber as the spray fuel down the manifold when you pump the throttle pedal and the  original on is on a vacuum pull through of that makes  sense. So I’m abit stuck as I don’t want to put the that Weber on if it’s going to under fuel the car

 

Are you saying your original carb is not squirting gas down the carb.  If not your accel pump is dried out and not working.

 

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Mike C, your engine should start and run fine if everything is properly set up and adjusted correctly. As Don C pointed out about the ethanol fuel now used and it's evaporating after a spell, my two '67 Plymouth Fury's take a little time to start if if haven't used them for two or three days, but never 20 minutes. I don't have an electric fuel pump on either car. If I had your car, I would perform the test listed on this thread and get everything in order. Swapping for a different designed carburetor would not be something I would try. My opinion and good luck to you.

John R

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