Discussing Heat & Fuel Related Issues

[keithb7]

My mind continues to crave more education about these old flatheads.

 

 I hear different conflicting opinions about vapor lock. Also fuel boiling in the carb. I’m not convinced I believe understand all that I am hearing from so many didfernt internet sources. I do believe and respect very many members here. 

Some folks run the stock mechanical fuel pump system and claim they have never experienced hard, or no start systems when the engine is hot. Especially when its a hot sunny day out. 
 

Some of us do experience this phenomena. Even with a fuel pump heat shield and a carb base heat shield in place, I’m prone to suffering from hard starts when hot. However it seems intermittent. A sprung toggle switch hooked up to a back-up electric fuel pump has saved my bacon a couple times lately.  

So I am left asking myself, why? Especially intermittently, why does this happen? Others have zero problems. 
 

A pic of my carb is seen below. There obviously is a ton of heat very near, from the exhaust manifold. Heat travels up. Right into the carb. By design this really makes for great fuel atomization. I’ve measured temps of 150F on the fuel bowl surface with my laser thermometer.
 

After the big hill home today, ambient air about the high 70’s today. 30 mph 3rd gear. Low RPM chug up the hill. All the torque she’s got.  She’s good ‘n warm when I get in the drive way. Its not overheated yet. 
 

People talk about the fuel boiling in the carb. I assume some of it evaporates when a hot engine is shut off. Car parked. The accelerator pump linkage is not sealed. Gasses can escape here I guess.  Then I assume the fuel level drops in the bowl.  Empty? I’m skeptical. (Would sure be cool to have a clear bowl) So is this low fuel in the bowl creating  hard or no starting?  I assume if the fuel is evaporating from the bowl, it is likely also vaporizing in the fuel lines? Double whammy happening? Mechanical pump can’t push fuel? Can’t fill bowl? Engine won’t start?

 

Like a shot of nitrous, a flip of the sprung electric fuel pump switch seems to save you in this example. An electric pump will push vapor through it.  
 

I’m again scratching my head wondering if I may be missing some parts?  How are some others never experiencing hard starting? Many of us assume its due to vapor lock  maybe its not?

 

Perhaps we need to move the carb accelerator pump linkage from the winter position to the summer position? On the winter setting are we overfueling when we start the hot summer engine? Maybe. Perhaps we are flooding our engine and blaming vapor lock?

 

Below here are my pics. Carb and fuel pump heat shield. Am I missing anything here on my ‘38 Ply?

 

Are some people adding concoctions to their fuel to prevent vapor lock? I’ve heard a little diesel helps.  Kerosene too, and some other questionable fluids. 
 

I’m not even sure I suffer from vapor lock. I’m starting to question the idea. Flooding it?  Hmmm.  Maybe. 

 

So many questions. Sorry. Pick any  questions you’d like to address please. Your comments and experience is appreciated.  As always, thank you in advance. 

[keithb7]

I forgot to mention one more thing. When in the driveway after the hot hill home I pulled the air filter off today. I looked  down the venturi with a flashlight and cycled the throttle linkage.  The squirt from the accelerator pump is weak and not a nice consistent stream. An hour later, same scenario, nice full jet like stream of raw gas from the accelerator pump. 
 

Seems odd to me. Too hot in the bowl? Gas is low and evaporating? Seems plausible. 

[Dodgeb4ya]

And you have the stubby BBS carb on there..I assume the phenolic insulator is below the aluminum heat shield?

[keithb7]

Unsure Dodgeb4.  This is how is came into my hands. Here is a side shot. Am I missing this phenolic insulator you speak of?

 

 

[Sniper]

I don't have an issue hot starting, even in 100+ degree days.  But it's a 51 Plymouth so the engine bay is different.  Might be lack of air flow in the fuel line area.

 

If you take you side covers off does it do it as well?

 

I also see you have a lot more hose from the carb to the pump than I do.  Mine is hard line to the pump, no hose.  I think I would, at the least, replumb with hard line and route it as far away from heat as is possible and I would route it so that it makes the 90 degree turn from the carb bowl while it is still above the heat shield. 

Edited May 10, 2020 by Sniper
added pic

[Dodgeb4ya]

21 minutes ago, keithb7 said:

Unsure Dodgeb4.  This is how is came into my hands. Here is a side shot. Am I missing this phenolic insulator you speak of?

 

 

There is no heat insulator..there should be.

That's a 1954 and later carb...a good Carter carb.

I ran one for years with no issues...had the heat shield and insulator. 

[keithb7]

Hmm. I guess I’ll try and round one up. 
thanks @Dodgeb4ya . The engine is a 1954 Canadian Dodge 228 ci model. So the carb is appropriate. 
 

@Sniper I am still experimenting with  my electric fuel pump placement. Also I am still sorta field testing my rebuilt mechanical fuel pump. It gave me troubles early on but I think now they are all sorted out. Its been reliable now since I slobbered JB Weld on the fulcrum pin ends. I will proceed to plumb the fuel system with hard lines. That’s a good plan. 
 

Am I right to assume that hard fuel lines dissipate heat better than fuel hose?

 

I just set the accelerator pump linkage over to summer stroke. I’m wondering what, if any difference that’ll make? We’ll see. 

[keithb7]

@Sniper I’ve been running all spring with the inner lower fender cover off the right side. Took it off to clean sludge out of the valve area. I have not re-installed  it yet. You can see right through to my wheel here from the engine bay. 
 

I plan to to get in there again and check the valve set eventually. I am just addicted to driving it. So I tend to procrastinate jobs that may put the car down for longer than a few hours.  Valves? Yes you’re right it doesn’t  take more than a few hours...Too many other priorities! 
 

 

Edited May 10, 2020 by keithb7

[Sniper]

Yes, it is my understanding that the rubber hose holds heat more so than the hard line. 

 

As a last gasp effort, one could plumb a return line back to the tank and use either a bypass regulator or a small orifice in the return line to control  the return to the tank, this will tend to keep the fuel constantly flowing and lessen heat soak or vapor lock issues.  I would T it in right at the input to the fuel bowl if I went that route. 

[keithb7]

@Sniper Wouldn't that extra loop back to the tank only prevent vapour lock while driving? While the is engine running?  I tend to believe vapor lock conditions are prime when you shut off a hot engine, on a hot day. You  head into a store. Or maybe fill up at the gas station. The engine is off. The stagnant fuel in the lines vaporizes at that point. Then the darn thing won't start until everything has cooled down.

[keithb7]

Something like this I assume @Dodgeb4ya?

https://www.dashman.net/product.html?id=264

[Dodgeb4ya]

That's it.

[Worden18]

Keith, my heat shield is a 3 layered aluminum plate.  I sometimes wonder if it's just more surface area that becomes hot and helps boil the gas in the bowl since it's so close to the carburetor.  The only thing saving me from the car not starting after that "magic" (or un-magic) 5-10 shut off fuel percolation/hard starting issue is the fact that I hold the accelerator to the floor and just let her crank.  It's never not started when I've done that.  I remember you saying that didn't work for you.  Maybe the hard fuel line and the fat gasket are the ticket.  Those are two things I don't have that I'm absolutely going to update.  One other thing that I believe really helps my car start is the pertronix 40,000v coil.  I'm interested in seeing how much better my car will start now that it's timed correctly.  It pops off nicely but I didn't try it after a 5-10 minute shut-off.

[keithb7]

I just took momma out for a sunset ice creme cruise. Came back up the hill. Engine good'n hot.  Pulled into the garage. Shut the car off and 5 seconds later I flashed it back up. Instantly. No problem. Then I shut the car off and came in the house for 10 mins. I wanted to let everything bake in the engine compartment. Went back out....Crank, crank crank. No start.  I began assisted priming with the electric fuel pump. Still cranked for a bit and no start. Finally I held the electric pump on, then mashed the gas pedal to the floor and it started. It would seem that changing my accelerator pump linkage rod over to the summer setting had zero effect.

 

This confirms that the fuel issue happens when the hot engine is shut off, and the radiating heat bakes everything. This is why, as the ambient temps heat up these days,  I am reluctant to shut off the engine to grab ice creme, when we are out for a cruise.  While driving, I am have zero issues. I am going to get a phenolic spacer. It makes sense and will prevent direct heat transfer from the manifolds to the carb. 

 

In a different post last week I mentioned the engine bucking, coming up the hill under full load. Dropping the float level seemed to address that. No more bucking. Yet then I developed a 1 second flat spot in the carb when accelerating from idle. Weird thing is that flat spot totally vanished after the new exhaust system was installed. Maybe it's doing a better job scavenging the cylinders? Maybe...

 

I still prefer driving these old cars compared to a new one. My wife says I'm weird. The new cars sit. They are boring to me.

Edited May 10, 2020 by keithb7

[Sniper]

Vapor lock refers to the gasoline turning to vapor in the fuel delivery system while the engine is running.  Obviously the pump cannot pump vapor and once the bowl empties you stop running.  Heat soak is what happens after you shut the engine off, it essentially boils the gas out of the carb and lines.

 

One other thing to look at, is your exhaust flapper working properly?  If it's stuck closed then your intake is getting heated all the time by the exhaust and this may be the issue, your new exhaust comment lends me to think that is something to consider. 

[keithb7]

@Sniper, thats a brilliant suggestion. The  exhaust flapper valve does indeed need repairs. I had forgotten about that. It is on my long to-do list. I incorrectly assumed it would effect a cold , engine taking longer to warm up. I had not thought about it directing too much heat to the intake when not required.  That would definitely help bake the carb. 
 

I love these a-ha moments. All of a sudden things become clear.
 

Between the phenolic spacer dodgeb4ya mentioned, and fixing exhaust flapper valve I’m optimistic.  Thank you. I’m on it. 
 

 

Edited May 10, 2020 by keithb7

[DJK]

Has anyone installed insulating sleeve to the fuel lines?

[MackTheFinger]

Looks like Sniper had the right idea.

 

I had one vehicle that gave me problems with heat soak and sometimes vapor lock, too. It was a heavily modified big-block V-8 in a small engine bay. I had installed a large metal inline fuel filter just in front of the cylinder head. Removed the filter, re-routed the fuel line as far away from the engine as possible and the problem went away.

[Sam Buchanan]

1 hour ago, MackTheFinger said:

Looks like Sniper had the right idea.

 

I had one vehicle that gave me problems with heat soak and sometimes vapor lock, too. It was a heavily modified big-block V-8 in a small engine bay. I had installed a large metal inline fuel filter just in front of the cylinder head. Removed the filter, re-routed the fuel line as far away from the engine as possible and the problem went away.

 

Heat shields in my P15 for the carb and metal filter...note the carb shield doesn't touch the carb:

 

 

 

[RobertKB]

14 hours ago, Sniper said:

I also see you have a lot more hose from the carb to the pump than I do.  Mine is hard line to the pump, no hose.  I think I would, at the least, replumb with hard line and route it as far away from heat as is possible and I would route it so that it makes the 90 degree turn from the carb bowl while it is still above the heat shield. 

 

Line should be steel all the way from the pump to the carb. I am willing to bet this is part of your problem. I run steel lines that way on all three of my old mopars. I have a heat shield above each fuel pump but do not have any heat shield below the carb. Never a problem starting.

 

Any flexible hose should only be between the frame and the fuel pump. It is worth checking that hose as well as when they get old they tend to collapse when hot or when the engine is pulling hard.  

[greg g]

In the pic with the wrenches there is no shield between the exhaust manifold and the fuel pump.  Also not mentioned yet is the condition of the heat riser.  If the spring is broken it will allow the riser to feed exhaust flow to the chamber under the carb.   If it moves rotate it as far as it will go clockwise and secure it there with some mechanics wire.

[Sniper]

the picture with the wrenches is my 51.  I don't have an issue with heat soak, vapor lock or hard starting when it's hot out and 100+ degree days are very common here, last Tuesday it was 104 on my thermometer.  The OP's 38 is different enough from my 51 in the engine compartment that might make my experience somewhat moot.  I used to own a 38 way back in the 90's but my memory is foggy on the details anymore.   I don;t need a heat shield and I do make a habit of checking the flapper's operation whenever I am under hood and its not heated up, not going to burn my hand for that, lol.  In fact I was working on my EFI swap earlier today and I checked it, which brought up a question I'll ask in a new thread as it is at best tangentially related, sort of.

[Dodgeb4ya]

I used to find the aluminum heat shields under the shorter  BBS carbs all the time in the older junk yard hunting days.

I had a couple sets of those I'd saved... don't know where they are today though.

[plymouthcranbrook]

Although I have not seen any issues with either viper lock or heat soak on my 52 with all stock fuel set up I wonder what if anything might change when I install the Langdon carb setup.  2 bbl is on a adapter that raises the carb a couple of inches it looks like.  I have a mechanical pump and no assist from an electric pump. 

[keithb7]

Dug into my used parts today and took apart a set of manifolds to get a good look at the flapper valve. Grasp a better understanding.  Then I wired my ‘38 flapper valve closed. I Went for a drive. Warmish day here. Sun beating down.
 

I indeed suffered fuel starvation while pulling 2 different long hill climbs today. Back up electric pump saved me both times. When I got home I shut off the key and let heat soak take over. 15 mins later...No start.  I am comfortable now and have mastered the fuel boil start procedure.  Electric pump engaged. Mash the throttle and hold it down and crank. Then it’ll start.  I’m somewhat happy I can deal with this interim. 
 

I’ll proceed to get a phenolic spacer. All metal fuel lines. Maybe wrap them in  some type of heat wrap insulation too. We’ll see. Also will fix the exhaust flapper set up. 
We shall overcome!....Hopefully.