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General Tech Carbs Flooding While Car Sits

KVH

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I'll admit I've posted a related question, but I can't solve the problem, so I'm reaching out again. The HS6 SU carbs in my 4A flood after I turn the engine off, and if the car sits for 20 minutes it's very hard to restart. All this started, as best I recall, after I "messed" with two things: a) the jet needle size, and b) the float adjustment. I think the floats are fine, but what about that needle. I think I installed leaner needles, and that's counter to my thought the needles could cause my flooding issue after turning off the engine. Anyway, that's my problem. Car sits, then won't start without a ton of patience and starter wear. Until I turn off the ignition, everything runs great. But if I turn it off, and then let it sit, Heavens to Betsy, I'm not going anywhere for 30 minutes. Any clues?
 

RGK

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I have a similar problem on my 250 which has HS6's fitted, if it sits overnight, but do not have the flooding at shutdown. I have to use the primer lever on the fuel pump or she cranks for a long time before firing. No gasoline in the oil sump or leaking. Thought it might be backflow, and someone mentioned evaporation. Very strange.
 

NutmegCT

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Just to clarify - are the carbs themselves flooding after engine shut off? (fuel coming over the carb's top, out the throttle shaft opening, coming out a vent tube)

Or are you saying it's the fuel bowls that are flooding and overflowing?

Either way, seems strange it would happen on both carbs at the same time. Does the problem happen if the engine is cold (left overnight)? or only after you've driven and warmed the engine?
 
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KVH

KVH

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My problem appears to occur only when the engine is hot after driving. If I pop the hood and look at the fuel line, I can see the fuel bubbling inside the fuel filter. I do not think I am having any overflow at the fuel bowls. My fuel line is located no differently then on my other TR4A. I do not believe that the location of the fuel line is the problem, and this car also does have and an ARE carb heat shield. I don’t having recall this problem until I was fiddling with the carburetors about a year and a half ago chasing down a problem that in the end really had nothing to do with the carbs. At that time I adjusted the richness and replaced the needles. Marc
 

CJD

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Hey Marc,

First off, the description sounds very much like vapor lock. Changing to a leaner needle will make the engine run a bit hotter, and I think that may have triggered vapor lock that was not happening before. BUT...let's set that diagnoses aside for the moment, as you say you do have a heat shield, which should prevent the vapor lock on all but the hottest of days and spirited of drives. So...

First there are a couple checks to make. The needles are NOT causing flooding. However, the float setting and float valve could. The way to check is to pull off the air filters so you can easily see the throats of the carbs. Then start and warm up the engine, and shut it down. Immediately look down the carbs to where the needle goes down into the jets. You should see fuel there, but it should not be high enough in the jet to overflow down the carb and intake. If you cannot see the fuel level, raise the piston to raise the needle to get a better view.

Adjust your fuel level as necessary to get the fuel level about 1/8" below the top of the jet after you just stop the engine. Note: If the engine idles roughly and fuel overflows the jet while the engine is running and when stopped, then suspect a damaged or dirty float valve.

If the 2 checks above do not turn up a fuel level problem...then you are back to probable vapor lock.
 
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KVH

KVH

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I’m going to try all of that. But I’m still curious – – why does fuel boil and bubble inside my fuel filter for several minutes after I turn the car off.
 

RGK

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I’m going to try all of that. But I’m still curious – – why does fuel boil and bubble inside my fuel filter for several minutes after I turn the car off.
Where is your fuel filter located? Have you checked the temp of it with an infrared thermometer?
 
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KVH

KVH

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Good idea. I will try that. The line, as you know, runs up near the block then in front of the thermostat housing, and the filter is a few inches before the first carb.
 

RGK

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That is a hot spot, you have the exhaust manifold and thermostat housing sitting there. If I fit a shutoff & filter, do not have one, it would be on the other side before the fuel pump. Might try to wrap the line and filter in heavy duty aluminium foil, shiny side out and see if there is a difference.
 
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DrEntropy

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Adjust your fuel level as necessary to get the fuel level about 1/8" below the top of the jet after you just stop the engine. Note: If the engine idles roughly and fuel overflows the jet while the engine is running and when stopped, then suspect a damaged or dirty float valve.

I would do this first. You're spot-on, John.

And ISTR the ethanol additive fuel will "boil" at a lower temp than gasoline without it, so p'raps relocating the entire feed line would be a "second guess" measure. But the float needle and seat ~should~ be stout enough to prevent it pushing past anyway, IMHO.
 

CJD

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I’m going to try all of that. But I’m still curious – – why does fuel boil and bubble inside my fuel filter for several minutes after I turn the car off.
I'm afraid that is a sign that you may have vapor lock. It can be caused by the fuel mix being for cooler weather...in other words, the oil company thought it would be cooler than it is, so their fuel has a lower flash point, which boils at a cooler temp.
 

NutmegCT

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An old treatment for vapor lock - toss a wet towel over the fuel line. That should condense the vaporized fuel back into liquid.

But I don't think that causes your flooding problem.
 
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KVH

KVH

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BTW. What temperature for the fuel line am I looking for when I use my infrared gun?
 

RGK

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BTW. What temperature for the fuel line am I looking for when I use my infrared gun?
Take a measurement on the line coming into the fuel pump and compare the two. Gasoline begins to vaporize at around 100F depending on the fuel blend.
 

Sarastro

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RE the fuel bubbling: this is pretty standard with modern fuels, and rarely causes problems. But sometimes...

I had a problem with my Bugeye Sprite some years ago, where it would start to miss and stumble at traffic lights on warm days. To diagnose it, I replaced a section of fuel line under the hood with vinyl (NOT recommended practice normally) to see what was happening--I got a real eyeful. The fuel looked like ginger ale, and the fuel filter was so full of vapor that i couldn't see fuel in it. Yet, most of the time, enough fuel was getting through.

The solution was to rerun the lines so they were on a continuous upward slope. That way the vapor just vented through the carb vents.

According to my father, who was a petroleum specialist, when lead was removed from motor fuels it was replaced by other antiknock additives, some of which were pretty volatile. I suspect that's the reason for the bubbling.
 
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KVH

KVH

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Hey Marc,

First off, the description sounds very much like vapor lock. Changing to a leaner needle will make the engine run a bit hotter, and I think that may have triggered vapor lock that was not happening before. BUT...let's set that diagnoses aside for the moment, as you say you do have a heat shield, which should prevent the vapor lock on all but the hottest of days and spirited of drives. So...

First there are a couple checks to make. The needles are NOT causing flooding. However, the float setting and float valve could. The way to check is to pull off the air filters so you can easily see the throats of the carbs. Then start and warm up the engine, and shut it down. Immediately look down the carbs to where the needle goes down into the jets. You should see fuel there, but it should not be high enough in the jet to overflow down the carb and intake. If you cannot see the fuel level, raise the piston to raise the needle to get a better view.

Adjust your fuel level as necessary to get the fuel level about 1/8" below the top of the jet after you just stop the engine. Note: If the engine idles roughly and fuel overflows the jet while the engine is running and when stopped, then suspect a damaged or dirty float valve.

If the 2 checks above do not turn up a fuel level problem...then you are back to probable vapor lock.
Since I’m now stuck at a shopping center with the same old problem of flooded carburetors, I thought I better ask: when you check the level of the fuel in the Jets, you do that with the jet needle remaining in the carburetor, correct? In other words, I do not remove the upper carburetor chambers and needle to check the fuel level. Instead, I check it with the needles in the Jets and I want that fuel to be an eighth of an inch below the top. Let me know if I understand this correctly. Thank you
 
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KVH

KVH

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I should report more. My jets are all the way up at the top of the jet base of the carbs. So, there's no visible puddle of fuel to see. I see no fuel running out and, in fact, both bridges, even with the engine hot, are virtually dry. When I performed my last "tune up" and adjustment, I backed off the jet setting nuts by 12 flats, so I'm puzzled why I'm seeing the jets so high. Let me know what thoughts you might have.
 

Madflyer

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Because you see bubbles looks to me as you may have a bad hose between carbs and pump letting air in to the system. Your fuel pump pressure is low say 2 lbs so may not show a leak. Also check the screw top the fuel pump and the fittings on the pump. I most always per load the fuel line to carbs with the lever and start the car in neutral with out the clutch in. Is your fuel filter ever over 1/2 fuel should never be full while running.
 
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