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Don't run well when warmed up


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randdleavitt
Novice

Sep 13, 2022, 10:52 AM

Post #1 of 20 (408 views)
Don't run well when warmed up Sign In

Hi there. I am working on a 1952 Pontiac Chieftain with the original straight 8 flathead motor. The odometer reads 53590 but judging from the road dirt buildup on the chassis I think it may have been around. The problem is - it runs and starts super when cold, but when it gets warmed up it will not rev up. It gets a little RPM and then just sputters and won't rev any further. It still will start and idle great. Sounding like carburation, I had the carb rebuilt without any change and even sent the carb back twice for rechecks. The second time back, he enlarged the jets and reset the float level higher. I have rebuilt the fuel pump, replaced the points, condenser, and rotor. Drained the fuel tank and put in fresh gasoline because the car had set for 2 years before I got it. The vacuum at the distributor isn't great but is in the green on the gauge. I have run out of ideas. Thanks for any help. randdleavitt


Hammer Time
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Sep 13, 2022, 11:04 AM

Post #2 of 20 (401 views)
Re: Don't run well when warmed up Sign In

My first suspicion would be wear in the distributor.

If you have a dwell meter, watch the dwell when you rev the engine up and see if it changes dramatically.

Also try it with the vacuum disconnected and plugged.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



randdleavitt
Novice

Sep 13, 2022, 11:17 AM

Post #3 of 20 (393 views)
Re: Don't run well when warmed up Sign In


In Reply To
I did the check with the dwell meter and the reading did not change at all when I revved the engine.



Hammer Time
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Sep 13, 2022, 11:21 AM

Post #4 of 20 (389 views)
Re: Don't run well when warmed up Sign In

What was the dwell reading and did you trying it both with vacuum connected and disconnected?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



randdleavitt
Novice

Sep 13, 2022, 11:41 AM

Post #5 of 20 (384 views)
Re: Don't run well when warmed up Sign In


In Reply To
Dwell angle is 22 degrees with or without vacuum. The dwell meter reading does not change as I rev the engine up in either case.


Tom Greenleaf
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Sep 13, 2022, 11:42 AM

Post #6 of 20 (384 views)
Re: Don't run well when warmed up Sign In

Just notes: Dwell changes when if shaft of distributor is worn for an 8 if more than 5* it's borderline.

Oh no - making jets larger, raising the float wasn't a good idea.

I plain don't know all set ups some you can see how high it floats, top off carbs. Gas today has to weigh less a factor perhaps this was a leaded fuel engine and no Ethanol.

IDK, if you have an exhaust gas analyzer check that or the "not running well" it's probably choking on fuel despite pre smog anything still wants a mix about 14.5 to one air to fuel ratio ALL the time is nice not cold allowed to be rich.

Richer isn't more power, leaner isn't more efficient any gasoline engine want just right all the time as much as possible.

Miles: It's so old "been" around is tough to know for sure will say second round the #s will lose lining up well like might see part of a sinking first digit or second also?

Dirt doesn't tell alone a thing OMG think how old it is where it might have been stored, how used, lots more dirt roads and so on.

Sorry if you said back then lifter idea was called tappets may have covers on side to check if to spec.

Real octane of today isn't as good either as even lower rated (a conversion now) see if compression is even or actually too high - it's before me but recall owners taking head off to scrape of carbon build up - a lot if low use was a routine so was period CLEANING yuk off of spark plugs would cake up too,

Tom



Hammer Time
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Sep 13, 2022, 11:59 AM

Post #7 of 20 (378 views)
Re: Don't run well when warmed up Sign In

I would expect a 8 cylinder to be around 30 degrees. Are you sure the points are set correctly?



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



randdleavitt
Novice

Sep 13, 2022, 12:19 PM

Post #8 of 20 (373 views)
Re: Don't run well when warmed up Sign In


In Reply To
The shop manual specification is 21 - 30 degrees, but perhaps 22 degrees would work OK on a new tight motor. 22 is perhaps too low for this old chief. The odometer numbers don't line up straight so probably gone around once. I will reset the points to as close to 30 degrees as I can get. I also appreciate the idea of checking the compression for pressure variations and the condition of the spark plugs as well. Thank you. Will do later.


Tom Greenleaf
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Sep 13, 2022, 12:48 PM

Post #9 of 20 (365 views)
Re: Don't run well when warmed up Sign In

I'm not going to have exact spec MORE used just feeler gauges. When revved up # should nudge higher as I recall - don't quote me on that one but a little one way or the other - normally.

You can set most points with a dwell meter just while it's cranking then check again running. The screws were usually made to turn offset like a cam nudge it one way of the other.

Try it! Higher dwell also advances timing - OMG this is old for me. As bumper to 8 lobe point cam wears dwell goes higher.

Note on finding NO VACUUM? Where do hoses go on the carb? Lower is actual manifold vacuum if middle port is speed of air created a vacuum - a venturi thing.

So, revved up or if you can give it some load and still nothing they leak or don't get what was intended. Rubber of diaphragms may be leaking newer they do a little on purpose.

Use a hand pistol type vacuum pump test that they hold even if off engine if made to come apart vs crimped you can seal some leaky ones - say so I won't carry on, on how,

Tom



randdleavitt
Novice

Sep 16, 2022, 9:11 AM

Post #10 of 20 (311 views)
Re: Don't run well when warmed up Sign In


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Hi there again. Still trying to make this Pontiac run as good hot as it does cold. I have done some further testing on the car to provide more details on what I am up against. I replaced the points, condenser, and rotor and reset the dwell angle. I now have 28 degrees without vacuum and 26 degree with vacuum. I did a compression test (dry) and got a range of 95 - 110 psi. I put a timing light on it and the timing is good and the vacuum advance does advance the timing when cracking the throttle. I did also replace the spark plugs just because I could. The vacuum at the distributor, idling is at 3 inches of vacuum and climbs to 20 - 22 inches of vacuum when revved up. Still it starts and runs like it should until the temp gauge get near running temperature. ???


Hammer Time
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Sep 16, 2022, 9:31 AM

Post #11 of 20 (305 views)
Re: Don't run well when warmed up Sign In

Nothing is making sense about this. These old engines are far easier to keep running good when hot rather than cold.

I know you said something about enlarging jets earlier. That would be the opposite of what a warm engine would need. The fact that it runs good cold would indicate it's getting sufficient fuel. Do you have a different carb you could try?

Make sure there isn't a restricted fuel supply making starve for fuel after running a while.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Sep 16, 2022, 9:33 AM)


randdleavitt
Novice

Sep 16, 2022, 9:59 AM

Post #12 of 20 (299 views)
Re: Don't run well when warmed up Sign In


In Reply To
I don't have another carb available. The issues with it running badly were identical before and after the jet enlargement. I'm not sure how much he opened it but, but it wasn't a lot This car was supposedly running until he was out in it and it started running bad. he got it home, parked it in the garage and let it sit for a couple of years.


Hammer Time
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Sep 16, 2022, 10:03 AM

Post #13 of 20 (296 views)
Re: Don't run well when warmed up Sign In

I would try getting a 5 gallon can of gas and use a rubber hose to connect it to the fuel pump and see if it will run better.

If any of the rear fuel lines are rusted the fuel pump will suck air instead of fuel after a while.

If you don't already have one I would install a clear fuel filter before the carb so you can monitor the fuel supply.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



Tom Greenleaf
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Sep 16, 2022, 4:31 PM

Post #14 of 20 (279 views)
Re: Don't run well when warmed up Sign In

Bear with me, just back from a 300 mile run! OK - when dwell or gap for points gives you a range usually chose the lowest as bumper wears the point get closer.
I doubt this is the fussy part at all.

Fuel must be too rich if running well cold. IDK no emission controls normal exhaust odor would be so. Your nose and guess - does it smell rich? NO DON'T EXPOSE YOUSELF TO THAT LONG JUST A QUICK PASS BY TAILPIPE PARTLY UNBURNED FUEL WOULD BE OFFENSIVELY STINKY.

If you suspect sucking air from rusted line it probably would leak some there also with engine off.

Fuel filter clear AFTER a pump AYOR vs metal if many plastic got too hot or near something hot is at least adding risk, but done all the time.

Buy quality as best you can either way.

Basics - line off outlet of mechanical fuel pump see how fast it can fill a pint/quart of fuel should be plenty - pressure ranges were usually 4-6 PSI. Other is some fuel pumps were vacuum pumps also on top? Yes it pumps - idea is pump is moving anyway use top as a mechanical vacuum pump not the intake manifold steadier supply for more vacuum motors used include some wiper motors - other thing depends on what features it has.

Messing with carb? No sure if original idea or if (had to be) replaced just gaskets, needle valve floats would be hollow brass if a leak they would splash fuel inside if so those get weighed is tell-tale if too heavy.

Is this a manual choke or automatic one? IDK as both were probably used some made manual on automatic chokes as they failed common to run just a cable instead.

1952 - lots of changes thru a decade - anything rubber was inferior then isn't OE now it couldn't last that long so is newer some hose if around is marked might be tel-tale or say year made on it assorted things.

Jets again. IDK , bet could be a hardware store item (good drill make your own?) put back to OE you don't generally do that and make things better? Tom



randdleavitt
Novice

Sep 20, 2022, 11:32 AM

Post #15 of 20 (241 views)
Re: Don't run well when warmed up Sign In


In Reply To
Back again, more things to check. The exhaust smells like normal old car exhaust and no blackness to it. The engine runs really well without the gallop of one running too rich. I did add an inline metal filter so I could make sure no grr was coming through the line and it continues to be full and clear. The vacuum line to the windshield wipers had been re-routed to use manifold vacuum, probably because the fuel pump was messed up, but after rebuilding the pump, I changed it back so the wipers are now using fuel pump vacuum. The choke is the original automatic and it works surprisingly well. I have it adjusted so it is wide open when the engine is warmed up. I checked the fuel pump output and it is pumping out a good amount of fuel. Would fill a water glass in several seconds.

I might be able to say that I believe it is running a bit better. I seems to have a dead spot at a particular RPM where it runs bad and rejects the idea of revving any further, but if I crack the throttle and the accelerator pump cycles a couple of times, it will rev up above the dead spot. I think this is some progress. I let the engine warm up and spritzed water at the intake manifold all over to check for vac leaks. I prefer to use carb-clean for this test but didn't really want to burn the car to the ground. Heard no indication of a leak.

An old mechanic up the street said they used to have trouble with the old flathead motors because they had no upper cylinder lubrication except for the lead in the gas. He thought maybe because the car had been sitting, the valve guides may have been tight and unlubricated making the valves a bit sluggish closing when hot and at higher RPM's . He said to add some two-cycle motor oil additive to the gas and it might help. I did and a change isn't jumping out at me but, maybe it is running a bit better and will eventually work out of it. Watcha think ??


Tom Greenleaf
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Sep 20, 2022, 11:50 AM

Post #16 of 20 (238 views)
Re: Don't run well when warmed up Sign In

Notes again only:
Lead in gas was to increase octane rating did nothing but foul plugs or help valve - an old lie.

> Flatheads still sold for equipment, air cooled usually.

Dump that ancient fuel as Hammer said, direct to fuel pump. This era may have a drain plug in gas tank - just look?

Rust in a carb just BTW in in there will mostly come out with a pencil type magnet!

The muddy rust if seen has to go, rusted fuel lines you see outside inside it what matters IDK if brass or what like newer ones,

Tom



Tom Greenleaf
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Sep 20, 2022, 12:04 PM

Post #17 of 20 (233 views)
Re: Don't run well when warmed up Sign In

New post in case already read. OMG, forgot, gas cap must be vented there or will make a vacuum in tank fuel pump fights with - hear me?

It sat a while rubber products if not branded once Neoprene (Dupont) or with markings only last a couple years HELLO 1952!

Tom



Hammer Time
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Sep 20, 2022, 12:12 PM

Post #18 of 20 (228 views)
Re: Don't run well when warmed up Sign In

This is why I suggested running this thing directly from a 5 gallon can of gas. This will bypass everything from the fuel pump back.



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We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.



(This post was edited by Hammer Time on Sep 20, 2022, 12:12 PM)


Tom Greenleaf
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Sep 20, 2022, 12:32 PM

Post #19 of 20 (220 views)
Re: Don't run well when warmed up Sign In

YES, YES, YES. That I've done (don't tell anyone) just gravity from a gas can w helper holding it on the roof! Other problem - that car needed a fuel pump - emergency I needed it at my shop! T



Hammer Time
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Sep 20, 2022, 12:35 PM

Post #20 of 20 (218 views)
Re: Don't run well when warmed up Sign In

He doesn't necessarily have to drive the car around. Just run it for a while. He should be able to tell if it's running differently or not.



~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

We offer help in answering questions, clarifying things or giving advice but we are not a substitute for an on-site inspection by a professional.







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