Atomic Four puzzler: Stalls out after 60 seconds

[gary randall]

Forumites:

My '65 A-4 (Tartan 27) has been stalling out like clockwork, 40-60 seconds after putting it into forward. It started having this problem late last year. It starts up fine after it stalls and it runs fine at an idle for as long as I want it to.



In trying to fix the problem, I have:

-- Pumped out the gas tank and put in 10 gallons of fresh gas. Took out approximately 2 cups of water in the process.
-- Checked the gas tank vent by running the engine without the gas cap on. Runs fine both at idle and during the 40-60 second interval while in gear.
-- Replaced the gas filter/water separator.
-- Installed a new electric fuel pump.
-- Made sure pump was working by disconnecting outlet hose and seeing gas flow into container.
-- Replaced the inline fuel filter.
-- Disassembled and cleaned the carburetor, checking the jets, float valve and needle valve.
-- Replaced the oil pressure sensor.
-- Checked the compression: 90+ in each cylinder.
-- Replaced the spark plugs.
–– Replaced the points, condenser and distributor cap.
-- Checked to make sure that the distributor wires are installed in the correct order.
-- Miscellaneous info: Coil temp: 116 degrees F., oil pressure about 38 psi, cruising, running temp: about 140.

This may or may not be relevant: When I idle down to a very low RPM, it backfires and stalls out. I can keep this from happening by maintaining a slightly higher RPM than I would like. This was not a problem before I did all the work listed above, so I'm thinking it is a timing issue unrelated to the larger problem.

Also, after I performed aforementioned work, it sometimes stalls out when I put it into gear unless I carefully increase the RPM as I shift into gear. It does not stall out when I put it into gear before starting it up.


Any ideas on what to do next would be greatly appreciated.

Thanks, Gary Randall

[Al Schober]

Gary,
Don't know if it's your problem, but I'll give you something else to check.. your centrifugal advance. It could be non-functional because of corrosion or mis-assembly, or it could just have a broken spring. In either case, you wouldn't be getting the proper change in firing time between idle and cruise. If you have a timing light, it should be easy to see if the timing angle changes from idle to higher RPM. There should definitely be more advance at higher RPM.

[hanleyclifford]

I am interested in what you are showing for dwell; and what is your point gap setting?

[romantic comedy]

At the top of your post, you say it stalls when you put it in gear. At the bottom, you say you can start it in gear, What happens then? Does the engine run in gear?

Does it rev up at all? in gear? in neutral?

Is the prop fouled? Stuffing box too tight?

The spitting sounds like a lean condition. Is the idle mixture screw adjusted correctly? Possible air leak?

[Mo]

Hi Gary,
Check everything the guys have said. I looked at a boat last year that had almost identical symptoms your's has. I checked compression with my thumb and they all pushed my thumb off indicating all was good. I see you have numbers for your compression so you must have used a gauge.

Here's what I did with that boat.
-removed and cleaned carb...no change, but slightly better when rich...during this time he purchased a new carb that he didn't need.
-adjusted reversing gear...no change.
-went through all ignition components and timing....no change.
-dove on prop to ensure it was clear...he even removed 13 inch martock and put on 12 inch 3 blade...no change.

Problem WAS stuck valves: Head was removed, valves cleaned and reseated.

That engine idled wonderful and rpms would come up when not in gear...as soon as load was put on the engine it didn't have it. The problem with my initial diagnosis was that I took the thumb guess on compression as absolute confirmation...it wasn't.

PS: I helped out a guy last week with a Tartan 27. He rebuild his engine two winters ago due to valves...he had a bad exhaust system that was allowing water in on top...FWIW you might want to look at your exhaust set up as well. I realize you did valves a while back but if the cause is not sorted it will recur.

[Sony2000]

Running the engine in the dark, see if there is any blue sparking between the spark plug leads or from a lead to the block.
Afterwards you could even spray a little water on the leads to encourage the spark to jump off the lead.

[tenders]

Partially blocked exhaust? Enough throughput when the engine isn't trying very hard, but once it starts to labor it can't expel enough to keep the cycle going.

[tenders]

(duplicate post)

[ndutton]

Just a thought . . . .

There are a few symptoms that indicate a particular problem area simply by the time it takes them to manifest. An example is the shut down after around 45 minutes of running, engine will restart but only after a 20 -30 minute waiting period. By the timing alone the coil is suspect and also whatever may have done it in.

One of your symptoms is such an indicator, the 40-60 second time before shut down. Coincidentally it's the same amount of run time you'll get at fast idle when there's no fuel pump function. Extrapolating that a little, if your fuel system were delivering fuel but at an insufficient rate AND you're burning more fuel under load than at idle, the timing could very possibly be the same.

Therefore my guess based on the symptom timing alone is a fuel delivery issue.

[gary randall]

A game plan and a quirky thought

Forumites,

Thanks for your input. I haven't had so much fun since taking power mechanics in 1968. How I miss it, now.

Later today I'll be checking the centrifugal advance mechanism as well as point gap. (I'll also be ordering a dwell meter. Recommendations, Hanley?)

I did at one point check the stuffing box and it did not seem to be too tight. The prop shaft was difficult to move by hand, mostly because of space restrictions, but I could move it with pliers.

I'm thinking that with 90+ compression, the valves are working OK. Is this a bad assumption?

I rebuilt the exhaust system last year and logged a good 50 to 75 miles on it with no problems, so I'm assuming that it is not the culprit. But I will be taking another look at it later this week if things persist.

Finally, I had this thought after ndutton's post:

I have a bag of miscellaneous carburetor parts.
I noticed yesterday that there are two types of float valve seats with different size inlet holes. Today I noticed that Moyer sells two differently sized float valves, one for late model, one for early model.
If I installed an early model seat in my late model carb, could that be the culprit?

I got the unlabeled bag of parts a few years ago from a retired Atomic Four parts guy, and – now that I've given it some thought – they may not even be A-4 parts!

Thanks for all of your replies.

Gary

[hanleyclifford]

The most important number in the distributor is dwell. Because our distributor cam lobes are so worn it is necessary to reduce gap well below specification to get the dwell up to spec. The old .018" to.020" spec for point gap is no longer relevant. This why I eventually went to EI where dwell is fixed (and high; but that is another story)

[gary randall]

Which dwell meter?

Anybody have any thoughts on which dwell meter?
I have never used one before, but Hanley's comment about the distributor lobes getting worn down makes a lot of sense.
I'm sure these models represent the low end, but they fall within my budget.
Or is it a case of six of one, half dozen of the other.....

[67c&ccorv]

Forumites,

Thanks for your input. I haven't had so much fun since taking power mechanics in 1968. How I miss it, now.

Later today I'll be checking the centrifugal advance mechanism as well as point gap. (I'll also be ordering a dwell meter. Recommendations, Hanley?)

I did at one point check the stuffing box and it did not seem to be too tight. The prop shaft was difficult to move by hand, mostly because of space restrictions, but I could move it with pliers.

I'm thinking that with 90+ compression, the valves are working OK. Is this a bad assumption?

I rebuilt the exhaust system last year and logged a good 50 to 75 miles on it with no problems, so I'm assuming that it is not the culprit. But I will be taking another look at it later this week if things persist.

Finally, I had this thought after ndutton's post:

I have a bag of miscellaneous carburetor parts.
I noticed yesterday that there are two types of float valve seats with different size inlet holes. Today I noticed that Moyer sells two differently sized float valves, one for late model, one for early model.
If I installed an early model seat in my late model carb, could that be the culprit?

I got the unlabeled bag of parts a few years ago from a retired Atomic Four parts guy, and – now that I've given it some thought – they may not even be A-4 parts!

Thanks for all of your replies.

Gary

Yep...I would pull that carb and check.

[hanleyclifford]

Either of those meters would do fine. I have one of each.