Starts great cold. Not so much when hot.

[Skidplate]

Hey all. Just completed the Dual Carb setup and fixed a lot of the issues recommended by all those who piped in to assist... thanks to everyone who helped. So now for the tweaking of the minor issues.

A few things: a number of people have confirmed that they too have Hot Start issues. Starts fine cold but you have to choke it and hold it to the floor and any other list of combinations when it's hot. And when it does start, I have to basically blow everything out for a few seconds to get it smooth again.  If there were any really common solutions, I didn't see them posted. For the sake of Full Disclosure, I'm still running the original plugs that came in it and they are not a number that I recognize. I only know that they are a HOT config so I'm going to try something a little colder and see if that helps.
That's the first continuing problem. The second one is for some reason it will come to an idle just fine when I'm stopping straight but tends to want to die when I am slowing down and turning. And I even suspect it's more prevalent when turning right than left. Is that weird or what? Installed an electric fuel pump so not likely starving for fuel and even if it was, the carb bowl has more than enough to supply a second or two on its own. Any thoughts would be appreciated. Cheers 

[carbking]

Try this:

 

DIFFICULT HOT STARTS

 

Jon

[JFranklin]

Ethonol gas makes my vintage cars start poorly when hot.

[Skidplate]

Not running ethanol so that isn't it. Actually read about the foot pedal technique but kinda forgot it. I'll try to remember but I REALLY have my doubts. Positive... Think Positive. 😣numi numi numi.

[EmTee]

2 hours ago, Skidplate said:

Not running ethanol so that isn't it.

No, not ethanol, but modern fuel is still more volatile than gasoline was 20, 50 or 80 years ago.  When I shut my '38 off after a drive I can raise the hood, put my ear next to the carb and literally hear the fuel boiling in the float bowl.

[nat]

     If it starts okay cold but  not when hot it sounds like too much fuel.  Are the carb floats leak free and at the correct height?  Are the automatic chokes open all the way when the engine is warm?

     These old engines love fuel when cold but often need a foot to the floor to start when warm.

Nat

[Bloo]

27 minutes ago, EmTee said:

No, not ethanol, but modern fuel is still more volatile than gasoline was 20, 50 or 80 years ago.  When I shut my '38 off after a drive I can raise the hood, put my ear next to the carb and literally hear the fuel boiling in the float bowl.

 

That was a problem in the mid 30s, too. 36 Pontiacs have an "anti-percolation valve". If adjusted absolutely right, it prevents the fuel from winding up in the intake manifold, but the fuel still boils. I think by 1938 Carter (who made my Pontiac carburetor) had gone to some other way of dealing with percolation. Not sure about other brands of carburetor.

 

Was it still Marvel carburetors on Buick in 1938? Mid 30s Buicks have an automatic fuel drain on the bottom of the intake manifold. Flooding from percolation is probably not the only reason for that, but I'll bet it's one of the reasons.

 

[carbking]

1 hour ago, Bloo said:

 

That was a problem in the mid 30s, too. 36 Pontiacs have an "anti-percolation valve". If adjusted absolutely right, it prevents the fuel from winding up in the intake manifold, but the fuel still boils. I think by 1938 Carter (who made my Pontiac carburetor) had gone to some other way of dealing with percolation. Not sure about other brands of carburetor.

 

Was it still Marvel carburetors on Buick in 1938? Mid 30s Buicks have an automatic fuel drain on the bottom of the intake manifold. Flooding from percolation is probably not the only reason for that, but I'll bet it's one of the reasons.

 

Anti-percolater valves were still standard on many Carters in the mid-1950's. It doesn't prevent fuel from ending up in the intake, but it does reduce the amount.

 

Jon

[Skidplate]

So let's just assume that there is an amount of percolating going on with a hot engine and too let's assume that that is causing fuel to be deposited into the intake while it is setting there not running. Let's also assume that as it stands, the only way to start the car when hot is with full choke and the pedal fully depressed. ( For now we'll disregard the suggestion that there is a technique that if done correctly will start the car every time, no fuss, no muss... which I am eager to try in the very near future) Wouldn't that suggest that whatever fuel has already been dumped down the intake due to percolating has basically had no effect on whether it will start or not? As in, adding more fuel to too much fuel (due to percolation) doesn't really suggest that the preexisting percolated fuel is the problem. Damn, can I use percolat* in a sentence any more times? Because if that were the case, then it would seem that giving it no gas and either using the choke or not would most certainly start the car. And NO I'm really NOT trying to be difficult. Therefore is it even remotely possible that a colder plug, having been able to cool sufficiently more in that length of time because it is, wait for it, colder... could that even remotely be a fix to this problem?

[Bloo]

19 minutes ago, Skidplate said:

Therefore is it even remotely possible that a colder plug, having been able to cool sufficiently more in that length of time because it is, wait for it, colder... could that even remotely be a fix to this problem?

No. That's not how you select a plug. Heat range will only make a difference for starting in the most minimal roundabout way, and in that case hot would be better.

 

Fresh *clean* gapped plugs, either new or used but with the center electrodes filed flat so there are nice sharp edges like a new plug can help with starting quite a lot. In your case, I think more troubleshooting is needed.

 

[EmTee]

11 hours ago, Bloo said:

Mid 30s Buicks have an automatic fuel drain on the bottom of the intake manifold.

Yes, my '38 has one.  The carburetor is a Stromberg (AAV).

 

Edited April 5, 2023 by EmTee (see edit history)

[EmTee]

8 hours ago, Skidplate said:

Let's also assume that as it stands, the only way to start the car when hot is with full choke and the pedal fully depressed.

This seems to support the theory that fuel is being deposited into the intake manifold.  The full-choke part seems counterintuitive, but I wonder whether that is because the float bowl is initially low due to loss of the fuel that was dumped into the manifold.  I recall that you stated that you installed heat shields under the carbs, correct?  I wonder whether the carbs you have include any anti-percolation features...

[carbking]

8 hours ago, Skidplate said:

Let's also assume that as it stands, the only way to start the car when hot is with full choke and the pedal fully depressed. 

NO! - NOT FULL CHOKE! NO CHOKE!

 

When the volatility of fuel was MUCH less, the technique of holding the footfeed to the floor (called "unloading") when starting the engine worked pretty well. With the volatility of modern fuel, this technique no longer works as well as it once did, as fuel will continue to flow as long as the THROTTLE PLATES, not the choke plate, are open. The linkage was adjusted so this procedure would open, at least slightly, the choke plate.

 

Jon

[nat]

     If you have suppression ignition wires get rid of them and switch to FM radio.

[Skidplate]

Ok, we'll, two steps forward and one step back. Pulled the top of the previously leaky front carb and adjusted the float down just a bit. Put in the new plugs. Yes they're probably too cold but they're new at least and that's worth something. Enough for today and it's a little late so we'll test drive tomorrow. This morning I hit the new wizbang high torque starter and it started right up... no surprise. Went down the road a ways, maybe quite a ways. Stopped and checked everything for leaks or just anything. All looked good. Did the "don't touch the gas" technique and it started right up. That's new. Ok, that's a good sign. Took off again and went even further down the road then up the interstate. Might've ran a little above its limit. Got up over 70mph in a stock 248 coupe. Pretty happy with that. Got off and onto a quiet side road and checked everything again. Seemed to be ok. Looked for any fuel flowing out of the side of the carb... nothing. Checked around with my laser pointer heat gun. Carbs were pretty cool and the heat shield was kinda hot but not bad. Didn't check the oil but it was full before I left. Drove another 10 miles and that's when things kinda crapped. Driving through a little downtown it kinda started loosing power so I pulled into an abandoned parking lot just in time for it to die. Tried to restart. Nothing. No barely give it gas, no pump then hold to the floor, no pull the choke with full throttle... nothing. Looked everything over. No fuel leaking anywhere. That's good. Everything dry. That's good. Checked the oil just for grins. A quart low. What the...? So I figured what the hell. Let it cool off a bit and walk down and find a parts store. I bought a quart and brought it back and put it in. Maybe an hour to cool down. Tried to start it and after all kinds of gyrations with gas and choke and still trying to look really cool in my shiny vintage coupe... it finally started. Drove it back home and all seemed ok again. So the only thing I can figure, it doesn't really suck oil unless I really put my foot in it. And when I do, maybe I'm adding just enough heat to cause a vapor lock? The oil never got below the low line so I'm not thinking anything actually overheated. I'm going to reroute my fuel line maybe a little further from the front of the engine. Oh, and I pulled the plugs when I got home and they probably are a little too cold. I figure they'll fowl pretty quick. Anyway. 2 steps forward is with something. Cheers.

Edited April 7, 2023 by Skidplate (see edit history)

[Bloo]

Miles per GALLON of oil chart from a 1936 Pontiac shop manual. What was considered normal in the prewar era might shock you. There was nothing particularly unusual about this. Postwar overhauls with modern piston rings, or better yet modern pistons and rings did much better.

 

Take a good close look.....

 

[nat]

Skidplate,  Check or replace the condenser to rule it out.  

[EmTee]

Hmmm...  Maybe the oil consumption rate of my '38 isn't that far off after all...  I think 10W-30 would be lower viscosity than SAE 20.

[nat]

As for the hard starting, rule out the coil and condenser.  Both have fooled me more than once.

[nat]

     Is the exhaust manifold heat control functioning?  Mine isn't....,Yet.

   The manual says:

    Heat control shafts must operate free.  Valves stuck in closed position may cause overheating, warped manifolds, blown gaskets and hard staring when hot.

    Valves stuck open may cause poor carburetor operation due to lack of manifold heat.

Edited April 7, 2023 by nat
Foreceps at birth (see edit history)

[Skidplate]

The coil is new but the condenser Is not. Good idea.

Heat control valves are good... enough. They tend to stick open more than closed but they seem to work OK.

good to see the oil consumption chart.

I had the heads redone during the restoration but not the bottom end. I pulled all the pans and covers and cleaned everything out as much as possible. Repainted everything. Had the rocker arm shaft coated with something that I can't remember from the powder coat people. Supposed to have added an extra amount of slick. Had the water pump rebuilt just for extra luck. Also used plastigauge to check and then reshim the main bearings. Did everything I could think of short of pulling the crank, cam and pistons. Put it all back together and have been running Rotella T6 along with Magic Mystery Oil and changing the oil filter almost every 100 miles until everything finally started running pretty clean. This whole thing has been a cross your fingers kinda rebuild. So all in all I'm not complaining. Anything that will still run (seemingly pretty well) after 80 some years can't be too bad. Now it's just working out the bugs.

 I found that the best starting procedure is, don't touch the gas but just pull the choke out about 1/3 ways and tap the starter. Starts pretty good that way until it gets really warmed up. Then not so much. 
So Nat you mentioned Ignition Wires. Are you talking about the Plug Wires or the wire from the coil to distributor? Either way I can't imagine how they would cause such an extreme reaction unless they were just ridiculously faulty and then I'd expect them to be bad when cold too. But maybe not.

On another note; has anyone determined what a reasonable Air/Fuel mixture these old engines require? I've been tweaking my jets to give me something between 11 & 15. Haven't really gotten any feel for what works best yet. All I can guess is go by engine performance and spark plug burn pattern and don't let it get too lean.

[EmTee]

8 hours ago, Skidplate said:

I've been tweaking my jets to give me something between 11 & 15.

Just be aware that even with dual carburetors, the fuel distribution to end cylinders on these straight-8 engines is a challenge.  You do not want to optimize the average F/A ratio and have cylinders 1 & 8 run too lean.  The best gauge for assessing the required jetting is looking at the spark plugs.  If they look sandy colored/tan and fairly uniform across cylinders you should be OK.  Too white means that cylinder is running leaner.

 

[edinmass]

Install a fuel pressure guage just in front of the carburetor. When it’s hot and no starting check pressure, and check the accelerator pumps to see if they are dumping fuel. Poking around guessing is getting you nowhere. Rule out fuel. Do you have an electric fuel pump to purge the system? 
 

Checking spark when it’s hot and not starting is easy. Just bring along someone to crank it for you.

 

If the car runs and drives fine without any issues and it’s just a hard start condition when hot indicates a fuel issue.  Also, how long does it sit before the problem occurs. Two minutes? Ten minutes? Half an hour? Sure sounds like a hot soak issue to me from what you are describing. 
 

For strange fuel supply problems I use a 12 gallon boat fuel tank with an electric pump and its own battery. It completely bypasses the cars fuel system by hooking a line directly to the carb. It’s a quick and easy way to determine if you have fuel supply problems or a host soak.

[EmTee]

7 minutes ago, edinmass said:

Just bring along someone to crank it for you.

Or throw one of these in the car:

 

[nat]

8 hours ago, Skidplate said:

So Nat you mentioned Ignition Wires.

     I was referring to the plug wires.  That's not your problem, I just hate suppression wires.  

     Looking at all the plugs will tell you how each cylinder is burning.  The color inside the tailpipe is a good indicator of the average mixture.

[Skidplate]

I just replaced the condenser but haven't driven it yet. TBD if that helps.  After getting carbs leveled and adjusting the floats to match the level I've been getting this nagging carb overflow issue that hops from one carb to the other and back. I thought it was the float settings for quite awhile but am coming to the realization it's most likely the new design (Grose) needle valves that came with the new carbs. Oh they look really great and on paper are a great improvement. Turns out (or at least I'm suspecting) this is the heart of my overflow problem. Seems the little ball that stops the fuel also is so tight clearanced that any amount of impurities blocks the seal and continues pushing fuel out of the throttle pump rod hole. I kinda proved it out when I pulled the inlet banjo assembly (just back from the needle valve) off the then leaking carb (as I mentioned, fix one and the other starts) and blew air through it and it stopped leaking for a while. So anyway, I tracked down two new old style needle valve assemblies and will install those once they come in. Wish me luck. Cheers

Oh, and thanks for the note about the end cylinders and their burn issues. I have been checking them ALL as a final but do tend to look at the easiest one's to get at (the middle two or three) during initial tweaking. 

Edited April 16, 2023 by Skidplate (see edit history)

[carbking]

1 hour ago, Skidplate said:

After getting carbs leveled and adjusting the floats to match the level I've been getting this nagging carb overflow issue that hops from one carb to the other and back. I thought it was the float settings for quite awhile but am coming to the realization it's most likely the new design (Grose) needle valves that came with the new carbs.

Think I read in a different thread where you opted for the English copies of the Ford version of the Stromberg EE-1 carbs.

 

The original Stromberg type EE-1 carbs took a maximum fuel pressure of 3 psi; I doubt this was improved on in the copies, as the float pin placement is the issue.

 

As far as the "gross-jets" are concerned; we bought out LOTS of carb shops, parts dealers, etc. over the years. Every single gross-jet we acquired was immediately relegated to the scrap brass bin.

 

You might place a pressure gauge at the carburetors to see what type pressure you are getting from your electric pump.

 

You mentioned acquiring new old stock fuel valves. Stromberg number is P-20287 (0.098). Some of the aftermarket valves, due to the popularity of these carbs for racing, had orifices of 0.113. These will flood at the standard 3 psi under less than WOT conditions.

 

Jon

Edited April 16, 2023 by carbking (see edit history)

[nat]

     The weight of the float, (when the top is inverted), should seal the needle and seat perfectly.  The specified PSI, (3?), is ideal but not so critical if the needle and seat make a positive seal.

[Skidplate]

So I would say that I've gotten everything about a good as it's going to get. The carbs are level. The old style needle valves work great and don't stick open every five miles and blow fuel out of the top of the carb. The floats are adjusted just below where the fuel wants to percolate out the side. I can still hear it bubble just a little after shutoff but it's apparently just low enough to not overflow. I went back and adjusted my valves again  after a good run down and back to the next exit. That also helped a little. It still doesn't start as well hot but just a little pedal while starting and it fires right up. I have O2 sensors on each of my exhaust ports and a switch to feed a single O2 gauge under the hood. So between those 2 readings front to back and checking my plugs after a quick run to the state line (round trip about 100 miles), I've been able to adjust the variable jets to get the carbs pretty well tuned. And because of the jets (and I know some don't like them) but because of those with the intake manifold splitting which side of the carbs effect which particular cylinders, it's allowed me to get ALL the cylinders to burn pretty much evenly. And I'll reiterate, these issues probably aren't near as problematic at sea level, but at 6000', having some extra adjustment is sweet.
There's only one little quirk that I just can't put my finger on. About half the time when I'm everything but stopped and turn sharp to the right (it doesn't do it turning left), it dies. Any other condition, it comes to a stop or not and the idle stays spot on. Only sharp right and only about half the time. What's with that?

Edited May 7, 2023 by Skidplate (see edit history)

[nat]

     Foot to the floor for hot starting is often what works best even if that's not what activates the solenoid.

     Try taking three left turns....About half the time.

[Skidplate]

Nope. Just a little gas works great. As for the right turns, I'm thinking it only had so many in it and I've used them all up. 😂

[mcdarrunt]

On my 37 Special with a 52 263 I tried everything I could think of to stop fuel percolation during a hot shut down. Run gas line completely away from exhaust, set float at minimum height, had fuel pressure at 2#, and even installed a ball valve at the float bowl that could be manually turned off. Still had to grind for at least ten seconds and always a big cloud of black smoke. Finally modified an Olds V8 HEI to fit Buick block and gapped plugs at 0.060. Did NOT cure perk problem but arc welder hot spark fires engine in about three seconds. The big HEI unit means no plug wire tin shield and is ugly so Ben Bruce had HEI guts put in a factory distributor and the module mounted of the firewall---works good and looks good.

 

 

[Skidplate]

Yep, between the high torque starter and HEI distributor the stock 248 really does do a lot better. When it's cold I literally just tap the starter and it fires right up. When it's hot I hold it for maybe a full second or two with just a little gas and again...starts right up. I've also found that if I run it at not much over 3000rpm (or less) it uses hardly any oil. 3500rpm on and it drinks a quart per tank. And as for the perc* problem, it still does just a little but the float level adjustment seemed to correct it more than anything else. Granted, it seems like the last thing we do is always the primary fix, even if the the five previous steps we took were also substantial improvements.
Did a couple 100 mile loops this week and last and all did really well, but I didn't deviate much in elevation change. As soon as it stops raining here in Colorado in a day or two it'll be time for 5k to 9k elevations and hopefully a good 200 mile day. There's a 1000 mile rally coming up in August that we're signed up for and I intend for Baloo to run  it with NOOO problems. 🤞

Edited May 11, 2023 by Skidplate (see edit history)