Running Rough A

T

TradModelA

Member
Hello I have an all original Tudor with a zenith- 2 carb, the issue is engine runs like it's rich all the time but the inside adjustment is all the way lean (to the right or clockwise) it makes the engine shake and spudder when not under load. Under load is ok, only seems to run good when you turn the gas tank valve off and right before it runs out of gas it idles up and runs smoothly. What could this be? Thanks
 
Have you done/tried everything else ? Like the ignition system and the low mixture adjustment ?
 
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Thanks, i haven't got into the ignition yet. I did however, replace the spark plugs cause they were dirty. I Just picked up this car, dont know too much about what's been done and not. Thanks for the help.
 
You have already noted it's running rich and shown it by turning off the gas and seeing it smooth out when it runs low on gas, so I'd take the carb apart and clean it. Check that the needle and seat close all the way and check the hight of the float. Use compressed air to blow out all the passages.

If you have an air filter, remove it first and try the car.
 
when you go through the carb put in a set of flow tested jets from renners corner very important as this can cause it. also make sure the trhrottle shaft is tight in the bore. if not its easy to install an oversize....
here is the link
http://www.rennerscorner.com/carburetor.html

renners float level tool is also good quality compared to all the vendors

use this site for refrence when going through the carb
http://www.modela.org

go through all your basic settings first timing, points, plugs before proceeding.
 
Renners sells a quality kit..as does.most of the vendors .. Since ur getting the jets combine shipping
I use the viton tip float valve with great success , others use the old style valves it gets debative so we all go with what works for us. Lol
 
Not sure what the "internal adjustment " is, but the idle mixture screw richens the mix if turned clockwise and leans the mix turned counter clockwise. Check out MODLE A CARB basics. Its good. Good luck.
 
Sometimes they only need a good cleaning, float level set properly, & make SURE all jets are screwed in TIGHT. Buy that little float level tube & the special wrench for tightening the jets. Zenith carbs are oh so SIMPLE.
Bill W.
 
Sorry for the late response here , I spoke to the previous owner about the issue and he said the carb was newly rebuilt, however the motor , which had sat for many years and developed a stuck valve during that time. He unstuck the valve but said that often times they will run rough afterwards. He suggested I run Marvel Mystery oil to further loosen it up- is this stuff bogus? Now this makes me rethink my rich smelling exhaust , etc.
 
Hi , in your original post you said the engine ran best after shutting the gas petcock off so it sounds like it is running rich. What is the "inside" adjustment you speak of? The external idle mixture screw on Zenith card richens the mix when turned in, or clockwise. Your float might be set high or the needle and or seat not working. MMO is sometimes debated on this site. I'd do a compression test to see if you do have a hung valve, but run it again and then starve it for fuel and see if it runs better. That should point you in the direction of your problem. Good luck
 
Sorry Vic, the inside adjustment I learned is called the GAV or lean /rich adjustment on the choke rod.

So can an engine have a sorta stuck valve, or a sticky valve ,one that does open and close just not like it should? Thanks.
 
A compression test will indicate if the problem might be a stuck valve/sticky valve. MMO does work and might help with unsticking a valve. If it runs good right before it stalls from no fuel, look at the MODEL A Carb basics at the home page. Long distance diagnostics are difficult. Clean the carb and set the float level per the site, try some Seafoam in the fuel.
 
Mine ran rich that caused a terrible exhaust smell and plug fouling until I installed the flow tested jets from Renners. The best money I could have spent.
 
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