Hard to start after warm. Fires up when floored.

[Buckeye]

12 hours ago, Mucci said:

Is item 3 the fuel return valve? Is there a way to check if this is working properly?

Yes. What year is your car? you have picture on engine bay?

See jimk first reply in this post regarding how to test Fuel Return Valve

 

 

[TobyB]

16 hours ago, Mucci said:

So now I'm hearing two opposite theories. Either the engine is flooding after a short ride or the bowl reserve is evaporating.

 

What's the best way to diagnose which one it is?

 

I probably cranked it over 60 times on my last errand run with zero sign of starting. Then tried the floor-it technique and it fired right up. I would think that much cranking would refill a dried up bowl no? I also only left the car for about 10min.

Since flooring it starts it,

it's flooding. 

 

Fuel will evaporate from a hot carb, but in reasonable climates (i.e., NOT Sacramento in the summer) it takes a lot longer than

10 minutes for the bowl to dry out.  On my car, it was usually a few days, at least.

 

I had one carb that did this, and I stuck it on the shelf for diagnosis... and then they demo'ed the building, so maybe it's

floating in the Sound, now.  But there's an easy check to spot gross flooding-

 

get it nice and warm, then park it in your driveway.  Pull the air cleaner... and watch.  You'll want a flashlight, (not a match)

and maybe something to read.  What you're looking for is fuel puddling in the plenum of the manifold.  If the vapor pressure

of the fuel's overwhelming the float, you'll see it dribbling out of the venturi boosters (the things in the middle of the bore)

or down the wall of the carb where the booster meets it.

 

Another test is to get it to not start- do the 60 crank thing- and then pull the plugs.  If it's flooding, they'll

be wet with fuel.

 

It's worth fixing, as some of the liquid fuel gets into your oil every time it happens, and it washes the oil film

off the cylinder walls and piston skirts.

 

t

[Mucci]

4 hours ago, Buckeye said:

Yes. What year is your car? you have picture on engine bay?

See jimk first reply in this post regarding how to test Fuel Return Valve

 

 

 

Ok sounds easy enough. Unfortunately this isn't really helping diagnose the original problem. I'm trying to think of a way to test what the actual issue issue without just replacing things piece by piece until something works. 

 

My car is a '75. I've removed the emissions said but the return valve is still there.  

 

I wonder if running a wideband 02 on a carbed motor would shed some light on what's going on at cranking. 

Edited March 23, 2020 by Mucci

[Mucci]

6 minutes ago, TobyB said:

Since flooring it starts it,

it's flooding. 

 

Fuel will evaporate from a hot carb, but in reasonable climates (i.e., NOT Sacramento in the summer) it takes a lot longer than

10 minutes for the bowl to dry out.  On my car, it was usually a few days, at least.

 

I had one carb that did this, and I stuck it on the shelf for diagnosis... and then they demo'ed the building, so maybe it's

floating in the Sound, now.  But there's an easy check to spot gross flooding-

 

get it nice and warm, then park it in your driveway.  Pull the air cleaner... and watch.  You'll want a flashlight, (not a match)

and maybe something to read.  What you're looking for is fuel puddling in the plenum of the manifold.  If the vapor pressure

of the fuel's overwhelming the float, you'll see it dribbling out of the venturi boosters (the things in the middle of the bore)

or down the wall of the carb where the booster meets it.

 

Another test is to get it to not start- do the 60 crank thing- and then pull the plugs.  If it's flooding, they'll

be wet with fuel.

 

It's worth fixing, as some of the liquid fuel gets into your oil every time it happens, and it washes the oil film

off the cylinder walls and piston skirts.

 

t

 

Good ideas Toby!

[zinz]

I've been quietly watching this thread. Toby describes the problem succinctly.

 

Having battled this in central Texas for many years, and with the advent of ethanol-laced fuel, the problem is paramount any time the ambient temps go above 85 F.  Long cranking and pedal at WOT using the Weber 32/36.  

 

I've tried many things, mostly to no avail.  You must use a phenolic spacer under the carb, but that only helps a little.  JimK told me of a guy who installed a small fan under the hood that pointed at the carb. It was set up to run after the car was shut off... it was either timed, or had a thermo-switch to shut it off. (I wonder if you were running the stock air cleaner thru the snorkel, if you could run a small fan to duct cool air to the carb after shutdown?) 

 

The problem as Toby describes, is that the carb sinks a lot of heat and the fuel "boils" out into the manifold... causing a flooding symptom.  Not good...

 

If you can buy non-ethanol fuel, try that and see if you get any relief.  

 

Perhaps someone can devise a better heat sink, carb spacer... an aluminum one with lots of cooling fins?

 

Ed

 

 

[Mucci]

25 minutes ago, zinz said:

I've been quietly watching this thread. Toby describes the problem succinctly.

 

Having battled this in central Texas for many years, and with the advent of ethanol-laced fuel, the problem is paramount any time the ambient temps go above 85 F.  Long cranking and pedal at WOT using the Weber 32/36.  

 

I've tried many things, mostly to no avail.  You must use a phenolic spacer under the carb, but that only helps a little.  JimK told me of a guy who installed a small fan under the hood that pointed at the carb. It was set up to run after the car was shut off... it was either timed, or had a thermo-switch to shut it off. (I wonder if you were running the stock air cleaner thru the snorkel, if you could run a small fan to duct cool air to the carb after shutdown?) 

 

The problem as Toby describes, is that the carb sinks a lot of heat and the fuel "boils" out into the manifold... causing a flooding symptom.  Not good...

 

If you can buy non-ethanol fuel, try that and see if you get any relief.  

 

Perhaps someone can devise a better heat sink, carb spacer... an aluminum one with lots of cooling fins?

 

Ed

 

 

 

According to the engineer at Weber there's no such thing as non-ethanol pump gas regardless of what it's listed as. He said the inclusion of some percentage of ethanol is federally mandated for the purposes of resource conservation. 

 

btw the engineer I talked to came up with the sync-link. Really knowledgeable guy. I recommend everyone check in with him now and then

Edited March 23, 2020 by Mucci

[rcf925]

The main thing is to keep your cooling system running at even temp, Mine stays around 180 and since I wasn't using snorkel with dual webers I used some VW heater hose on front of snorkel down to behind grille to push air on the exhaust side, Even on hot days here in CA my carbs and manifold are nice and cool, You can just see on bottom right of pic

 

 

 

[Mike G]

Did you have this problem before rebuilding the carb

Edited March 23, 2020 by Mike G
Edit

[Mucci]

54 minutes ago, Mike G said:

Did you have this problem before rebuilding the carb

 

Bought the car in rough shape so this is the first time I've been able to drive it around.

It's been between 45-60F here in Portland lately.

 

 

[zinz]

17 minutes ago, Mucci said:

this is the first time I've been able to drive it around.

 

Does it have the thick, dark plastic spacer between the carb and manifold? ...that's the phenolic spacer I spoke about above.  You need one, with a paper gasket on top and bottom.

 

Ed

[Dick R]

This hot start problem is very reminiscent of a long-term problem I had with a 73 Saab Sonett that I sold four years ago.   Cold, it would start right up, but after driving for 20 minutes or more, it gave me lots of starting trouble.  Over a period of months I tried pretty much everything associated with the carburetor already mentioned here with glimmers of success only to be followed by failure.

 

One behavior that was always present eventually led to the ultimate fix.  When it wouldn’t start hot, it would start right up with an easy push.  Once I had three kids push me to get it going and once I had my wife push me after we had gone for a ride.  (And I think that was the last time she ever rode in that car.)   So what was causing this clue that took me far too long to figure out?  I believe that the current draw from the starter combined with the warmed-up ballast resistor of the coil reducing coil voltage, along with the trunk-mounted battery location, all conspired to produce a lousy spark when everything was warmed up.   When the car was pushed, I don’t believe it turned over any faster; it just had enough more juice going to the coil to get it going.

 

My solution - installing a vintage Mark 10 Capacitive Ignition system that I picked up on eBay.  Once that was in, it always started like a new Honda.  Never failed.   

 

To see if this has any relevance to your hot start problem, you might try a push start when it won’t start hot with the starter.  I’m not talking about a car pushing you at 20 miles an hour, just somebody pushing you by hand to get the car rolling.  For that matter, you could just park on a hill and just get it rolling a bit before letting the clutch out in 2^nd gear. 

 

[Mucci]

56 minutes ago, zinz said:

 

Does it have the thick, dark plastic spacer between the carb and manifold? ...that's the phenolic spacer I spoke about above.  You need one, with a paper gasket on top and bottom.

 

Ed

 

Nope it doesn't. Guess that explains why there's so much exposed thread on the studs...

Is the phenolic / bakelite spacer a better option than the aluminum or vice versus? 

Edited March 23, 2020 by Mucci

[zinz]

20 minutes ago, Mucci said:

Is the phenolic / bakelite spacer a better option than the aluminum or vice versus?

 

Phenolic is the one to use.  Available from lots of suppliers, like Pierce Manifolds, etc...

 

That will help you some.  

 

Best of luck... Dick's suggestion above about checking your ignition system holds merit.  You must have a hot spark (at the correct time)

 

Ed

[John76]

11 hours ago, '76mintgrün'02 said:

Did you mean to say Tank, as opposed to pump?

 

Tom,

No, I meant pump, but perhaps my thought was not very clear.

 

Of course the pump has a 1-way check valve. Otherwise it would just slosh the gas back and forth in the fuel line.

So, my thinking is:

Once the fuel leaves the pump...it cannot go back.

If the float is floating, and the float needle is sealed, then gas cannot get into the bowl.

If a fuel return valve is used, when the engine is off, the return valve is closed, so gas cannot return to the tank. Fuel is only returned to the tank when there is high manifold vacuum.

All this results in fuel trapped inside the fuel line from the pump to the carb (also in the return valve if used).

If gas evaporates from the bowl (since it is exposed to atmosphere) then the float drops, opens the float needle, and drains the previously full fuel line (by siphon), causing a air bubble, empty fuel line and/or empty bowl. 

 

What caused the float to drop?

Couple of theories to ponder:

Plastic floats get attacked by the Ethanol in our gas, causing them to become heavy and sink.

Ethanol gas is lighter than leaded gas, therefore the upward pressure (buoyancy) the float is putting on the needle valve is less....causing too much gas to enter the bowl, which overflows into the primary throat of the carb, which then pools at the bottom of the intake manifold, which then causes an over-rich mixture when trying to start, which is helped by flooring the throttle (to lean the mixture), but hindered by the squirting of more fuel from the accelerator pump!  Whew!....I'm just trying to understand this problem.

 

Solutions anyone ?

Hopefully we can collectively come up with a fix.

I would hate to put my '02 on a Carb-Free diet!

 

John

 

12 hours ago, '76mintgrün'02 said:

put a check valve inline between the pump and the tank.

I never got to try this idea. 

However, if the fuel line from the sender to the fuel pump is leak free, the pump should act as the check valve...no?

 

[Mucci]

Would this be the phenolic spacer or is this just a basic spacer? Doesn't say anything about what material it is...