Carburetor issue, advice.

Great Lakes Greg

Great Lakes Greg

Well-known member
New engine being run in for the first time with a Zenith carb a couple of days ago. Start up went well, high idle until 20 minutes in, then it stalled. I went out tonight, re-torqued the head nuts and tried again. The engine started right away and idled like it did the first time. It didn't last. Like the first time, it started to run rough about 20 minutes into it, and would have stalled, but I nursed it along with the choke. It runs with the choke 90% closed, which sounds like a vacuum leak to me. I figured once it is getting hot, the manifolds might start moving a bit and opening up somewhere. I sprayed starter fluid around the intake ports, where it should have sped the engine up. Nothing. I put a spare Zenith carb on and it runs like it should as long as I want. Slow idle, revving, whatever.
What could be happening inside the first carb to make it fail at the same time?
The carb and intake manifold are cold to the touch as it is running, so I don't think it is vapor lock. Where would you suggest I start?
 
Greg,
Long shot, but gas line might be in too far or strainer partially plugged restricting fuel flow to carb. Also, the shut off valve might not open fully and gas is not being replenished as fast as it is getting used up.

Jerry
 
Check your idle jet-The idling circuit is 90% independent of the rest of the carb but when it fails it throws the whole carb out of kilter. no gasket on idle jet! and tight.May be just dirty.as above check for clean and tight jets. Manifold crack at the bend back side where it connects to muffler? Vacuum wiper?
 
Great Lakes Greg said:
I put a spare Zenith carb on and it runs like it should as long as I want. Slow idle, revving, whatever.
What could be happening inside the first carb to make it fail at the same time?
The carb and intake manifold are cold to the touch as it is running, so I don't think it is vapor lock. Where would you suggest I start?
Click to expand...

Has to be in the carb
 
New engine ....... maybe a new "inexperienced" engine re-builder?

We always think we already heard of everything while reading Model A Forum or any mechanical forum questions; however, for a wild, twice in a lifetime experience guess ............

If it is not a carburetor problem, if not the manifold leaking, not clogged fuel passage conditions; but, when "hot" it runs with "choke" at 90%, one (1) in a trillion possibilities seen before may be too little clearance provided between valves & valve tappets when the engine is cold.

Then, when engine gets hot, valves get hot and expand in length where valves cease to seat ....... hence, loss of vacuum in combustion chamber, loss of fuel in combustion chamber where it resembles a fuel starvation manifold vacuum leak problem.

Learned years ago through years of conducting mechanical maintenance instructions, "anything" is possible when one is in the process of "learning" to become a mechanic ......be kind, have patience ...... we all started from scratch ...... and it is usually difficult for doctors in New York to diagnose unseen patients in Tahiti.
 
Sometimes the float in the carburetor can hang up in the bowl allowing only slight fuel flow. It's hard to tell if assembling right side up. Turn upside down when assembling and you can tell better. Good luck! Ron W
 
I'm thinking valves too tight.If it seems to be happening at the same time each time,it points to something expanding as it gets warm.It comes from somebody setting things too close to the minimum trying to eliminate noise as much as possible.I've done it,more than once,trying to get rid of the valve noise.I like to hear it,but some seem the think there should be zero noise from the valves.I did one for somebody that would run almost exactly one hour,then just lose power.He actually had to be shown that his car would not run silently.
 
Please.................reread his orig post. He swapped carbs and everything "hunky dory". It's something in the orig carb that's not right.
Paul in CT
 
Great Lakes Greg said:
New engine being run in for the first time with a Zenith carb a couple of days ago. Start up went well, high idle until 20 minutes in, then it stalled.

Nothing. I put a spare Zenith carb on and it runs like it should as long as I want. Slow idle, revving, whatever.

Where would you suggest I start?
Click to expand...

Call Berts to get one of his rebuilds.
 
Know this is not the reason for this post, but very interesting info about the valves. My coupe makes noise like mentioned. So, when the weather gets better, better adjust the valves. Thank you for the info.
 
Hi Fred,

You are welcome ..... I wrote this with the intention as "if" this ever happens ...... (only runs well for only 20 minutes) ....... and as noted above ....... "if" it is not the carburetor.

Just one (1) opinion based on an actual Long Model A story in 1959, experienced 57 years ago:

Bought a Model A engine for $35.00, but block was cracked ..... asked professional cast-iron welder to weld it ...... he took my engine & stopped at a bar where his friend gave him a newly rebuilt block ..... like the "rebuilt engine" mentioned above in Post No. 1.

Re-built engine had cylinders re-bored to 0.060, all new pistons, rings, & all new Babbitt were provided, except this engine owner wanted to provide the new valves ..... new valves provided, but with no clearance on some valves ....... all (4) exhaust valves were burned and leaking ....... owner got disgusted, removed newly re-built engine, re-installed same old engine & blamed the re-builder for a lousy job.

In my Model A, I brought burned valves to local Ford dealer who re-ground all (8) .... after looking at my Model A he only charged me (50) cents. Used this engine for 36 years. Changed detergent oil religiously every 500 miles, used Bardal (sp?) top cylinder lubricant religiously, (4 ounce can per 10 gallons), at every re-fill, air filter was a compressed Bronze Metal Brillo Pad soaked in oil and cleaned in Kerosene every week ....... still have this engine with same Babbitt and same rings.

Rest of story: In 1996, 37 years later, extracted this engine with spotless oil pan and interior and brought this engine to a 90 year old Model A engine rebuilder for evaluation ..... (he was well known by Mr. Walt Bratton) ...... he recognized his method of his cutting grooves in Babbitt and asked me where did I get this engine ..... he knew the former owner and he had rebuilt this engine ...... he told me to keep the same pistons, rings, and Babbitt "as is" ..... and that people never realize the value of filtering air and providing fresh oil often.

Opinions based on past experiences of others can help some people .... sometimes.

Maybe title of story: No valve clearance can sometimes mean a Free Re-built Engine.
 
Thanks H.L. for the story. Sometimes experience rather than assuming something may work, might be a better way to go.

So I think when the weather gets better and I get off my lazy winter blues, I will have to get out there and adjust those valves.
 
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