Runs rough
 

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?

Re: Runs rough
 

I would suspect stale gas or stuck valves. Did you have stabilizer in the gas?

Re: Runs rough
 

Not this summer. Old gas was drained and replaced with fresh.

Re: Runs rough
 

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.

Re: Runs rough
 

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).

Re: Runs rough
 

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.

Re: Runs rough
 

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.

Re: Runs rough
 

Point gap and cleanliness should be checked.

Re: Runs rough
 

Is #4 spark jumping through the Dist Body, to #3 connector strap?
Bill W.

Re: Runs rough
 

A compression test shows 55lbs on each cylinder. Am I correct assuming that this indicates there is not a stuck valve?

Re: Runs rough
 

yes it passes the comp test. a stuck valve will show 0 compression.

Re: Runs rough
 

Re: Runs rough
 

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.

Re: Runs rough
 

Is your GAV set proper? Close down all the way and open 1/2 turn.

Re: Runs rough
 

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.

Re: Runs rough
 

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.

Re: Runs rough
 

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.