Runs rough

Mlloyd

Mlloyd

Junior Member
Last spring my1930 roadster started right up and ran well. Things happened that prevented driving it until now. Sounds terrible like it is running on two cylinders, however when I shorted the plugs with a screwdriver there is spark and a noticeable change on the sound. The plugs are new. I drained the tank, cleaned screen and sediment bowl. I've dismantled and cleaned the carburetor several times. Replaced the manifold gasket, and am stumped. There is black smoke coming from the tailpipe but it runs so poorly I can't get any adjustment done on the carb. Any thoughts?
 
Running rich enough to generate black smoke?...I'd be looking for a stuck open needle and seat in the carb or a float with a hole in it.
 
Almost sounds like you are one cylinder off on distributor cap with the screwdriver test. Engine gets enough spark to fire but not enough to run right, hence unburnt gas (black smoke).
 
look at plugs to see which cyls are not firing. put a thumb over the hole and run the starter see if you have compression on dead cyl. if you do take some sand paper and clean up plug posts and bands. simple stuff first. black means your taking in a lot of gas that your not burning. you shouldn't have to change settings you haven't changed. you can look at the valves and run the starter to see if they move a stationary valve should be easy to spot.
 
First:

Make or think of a list of exactly what you touched or worked with since your Model A last ran with no problems:

If carburetor problems, and in looking at:

"I've dismantled and cleaned the carburetor several times."

Do you have a carburetor fuel level gauge, (Part No. 14680 in Bratton's on line catalog) to test to see if your bowl has too high a level of gasoline.

A. Maybe carburetor flat metal bowl tab is not be adjusted properly;

B. Bratton's Part #14300 series float valve could possibly be leaking gas in lieu of shutting off the supply of fuel when float rises.

C. Try placing carburetor float in a pan of boiling water .... if small air bubbles observed exiting bowl, bowl is leaking, not fully floating, and allowing too much gas in carburetor fuel bowl.

It always will be something so simple .... keep in touch.
 
A compression test shows 55lbs on each cylinder. Am I correct assuming that this indicates there is not a stuck valve?
 
I would say its a carburetor problem. If you have a spare carb or can borrow one I would swap the carb out. It happened to me and I replaced the carb and it runs fine now.
 
Rev it to about 1000 RPM and turn off the fuel tap and see if it comes clean for about 10 seconds before it runs out of gas.
 
FWIW: Sometimes we all become obsessed with technicalities, precision, and whatnot & often ignore some of the most simple items that are overlooked.

"If" this engine ran and stumbled along with too much gas, (i.e., too rich a fuel mixture), and "if" you now have black foul plugs which are loaded with carbon, later substituting a perfect carburetor and a perfect distributor will not allow this engine to run smoothly & properly without first cleaning these plugs "if" loaded with carbon.
 
It kinda sorta seems like a carburetor issue to me. Good compression and spark tend to lean toward fuel issues.

What does 'cleaned' the carburetor mean ? I don't mean anything by that, I'd just like to know what that means to you. Was the carb soaked ? Passages sprayed out and air blown thru them to make sure they are clear? Was float checked for leaks and proper height ? Is there the infamous 'dimple' in the float arm that may be causing the float to hang ?

The easy way to check is to use a known good carburetor if you have access to one. But, these don't take very long to go thru.
 
pooch said:
Rev it to about 1000 RPM and turn off the fuel tap and see if it comes clean for about 10 seconds before it runs out of gas.
Click to expand...

Good easy quick test for a rich running cab, and this is what I would do first. :)

Don't touch anything to do with ignition yet.
 
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