Heavy fire in the engine bay of my 1955 GMC truck

[Giorgio Ancona]

My carb is installed and engine runs but I got now a fuel leak at the inlet connection of the needle seat assembly , the seal of seat fitting is wet and the connection between needle assembly and fuel hose fitting is dripping. Is the gasket wrong? What can I use to stop the leak ? As you can see I used white teflon tape to prevent leakage.

I stopped because this is a potential risk of an engine fire again.

[pont35cpe]

I could be wrong, but the barbed fitting looks like an air hose fitting. The end screwed into the fitting, should be machined to match the seat, of the first fitting, that`s where they seal, not the threads. If it is an air fitting, the end is flat, and has tapered pipe threads, another miss match. Like i say, i could be wrong..

Edited November 27, 2022 by pont35cpe (see edit history)

[Bloo]

NEVER use teflon tape anywhere near a carburetor. It finds it's way into the float valve and causes fires. The float valve (and inlet fitting) accept a double flared bundyflex steel line. It is the same thing as a 5/16" steel brake line used on American cars before the change to metric. The flare does the sealing, not the threads. Brass fittings exist that imitate a steel double flare and could connect to that, but what you have doesn't look like one to me. It looks like pipe thread, and if it is, there is no way that is going to work.

 

The red gasket must seal on it's own. If it won't, you probably need another one. Look as the surfaces the gasket contacts on the carb body and float valve for possible damage. Always hold the float valve with a wrench when you tighten the gas line to it, otherwise you will have leaks.

 

 

Edited November 27, 2022 by Bloo (see edit history)

[Frank DuVal]

12 hours ago, pont35cpe said:

The end screwed into the fitting, should be machined to match the seat, of the first fitting, that`s where they seal, not the threads. If it is an air fitting, the end is flat, and has tapered pipe threads, another miss match. Like i say, i could be wrong..

I think this is right. Look into the brass fitting screwed into the carburetor. Does it look like an inverted flare fitting? Google for image    "inverted flare fitting"   and look into the pictures.

 

A 1/4" NPT thread (what is on the air hose barb fitting) starts into a flare fitting, but BUT the threads of the inverted flare fitting are straight, and NPT the T means taper and that's how they seal.

 

Pipe dope, PTFE (Teflon) tape, etc allow tapered threads to mate further together (The military calls PTFE tape Anti-Seize tape because it just makes threads more slippery). The dope/tape is not a sealant itself (yes, there are some that seal, like using Epoxy on threads, but those are specialty types), so gasoline, air, water, etc slip right past it if not used on tapered threads. Yes, in my younger years I did try to use PTFE tape to seal flare and inverted flare fittings. Nope, does not work!🙁

 

Best temporary but terrible repair is just get a piece of 5/16"  steel fuel line and cut a few inches off, stick rubber hose onto that open end and use two hose clamps. But, it will fail too at some point.

12 hours ago, Bloo said:

Always hold the float valve with a wrench when you tighten the gas line to it, otherwise you will have leaks.

YES!!!!!!  This is true of many carburetor fuel inlets, even if it is just the filter behind the inlet nut. Hold the nut with a wrench while tightening the fuel line into it.

[Giorgio Ancona]

This is the fitting. Without teflon it stops after half thread in.

Is this the correct hose fitting?

 

 

[Larry Schramm]

17 minutes ago, Giorgio Ancona said:

This is the fitting. Without teflon it stops after half thread in.

Is this the correct hose fitting?

 

 

 

I just changed the fuel filter in our Corvette which is in the base of the Rochester 4 barrel and it does not look anything like that.

[F&J]

1 hour ago, Giorgio Ancona said:

Is this the correct hose fitting?

No, that is a NPT tapered pipe threaded "barb fitting".     It cannot seal with tapered threads and no internal flared seat.    Your carb would have used a 5/16'' steel line with a "flare" on the line, and a straight thread fitting nut when it was a new truck.   

 

You can get an aftermarket design barb fitting with the correct inverted flare, which will be the straight threads that you need.

[Giorgio Ancona]

Fitting is nowhere in Germany available , so I decided to use Loctite 542 thread seal .Due to the low temprature it will take days to harden.

Will see on sunday if it solves the leakage.😄

[Giorgio Ancona]

Hi I am back with a problem after my carb overhaul.

Since the rebuild and ultrasonic cleaning the engine accelerates better but sometimes the deceleration is slow and I do not know where this effect is coming from.

A few days ago  after 25 miles driving the engine goes and on after a few seconds and it seems because of momentary missing fuel flow.

On last saturday I could not switch of the engine but I think this was an ignition switch problem and has nothing to do with the carb or am I wrong?

I will by a new ignition switch to rule out a switch problem.

 

Any ideas what to check on the carb to be sure that its proper working?

 

Thanks for any help.

 

 

[m-mman]

Fuel, compression, ignition is what it takes for any engine to run.  Eliminate any one of them and the engine stops (or wont start) 

 

Compression is 100% mechanical either the valves, rings, pistons are compressing or they are not 

 

Fuel (carburetor and mechanical pump) is also 100% mechanical. If the engine doesn't turn, the pump stops working - no fuel.

 

The carburetor is 100% mechanical. It operates by having air pass through at high enough speeds to create a vacuum that sucks the fuel into the venturi and makes a mist out of it.  Engine not spinning? Then there is no air (no vacuum) and no fuel can go into the engine. 

 

The spark (ignition) is both mechanical and electrical. The points, coil etc. make the spark but it takes the engine turning to do so. However, the ignition gets its power from the key/battery. The key SWITCH must give or withhold electricity to the ignition system. 

The reliability of giving or withholding of electricity determines whether your engine runs. 

 

Now there is ONE phenomenon that must be mentioned - dieseling - You said that "you could not switch off your engine". How well was it operating during this time?  Fuel, compression, ignition - could there be another source of ignition? YES

 

Carbon in the combustion chamber, incorrect timing, throttle plates open too far, overheated situation, etc. can result in "ignition" coming not from the spark plug but from a "hot spot" in the combustion chamber. 

These situations sound like your engine is an actual diesel engine. It runs slow with an irregular lope and knocks and stops eventually. Sometimes by emitting an exasperated hiss. . . 

 

From what you describe it sounds like your key switch was bad and continued to provide electricity after you believed it was shut off. 

[Giorgio Ancona]

Thanks for your reply , I ordered a new key switch and installed it yesterday and hope this solves the problem.

[Giorgio Ancona]

 

The problem comes again and I checked that it got fuel and ignition but it won't start , the igniton switch is replaced but the problem is still present.

It runs and during drive it shuts down than the truck rolls and sometimes it starts again sometimes I have to wait for 5- 20 minutes.

It seems like the carb is out of fuel but through the fuel filter it is visible that the mechanical fuel pump is working and fills the carb.

Some day the car runs over 50 miles without any problem and sometimes it shuts down after 5 miles driving.Yesterday it was about 27 degrees centigrade and the engine shut off after a few miles .

The igniter plugs look like they are a little bit rich running but I don't think that causes the problem.

Its really strange what happens and I don't know how to trouble shoot this problem .

 

 

 

[Oldtech]

You need to test the fuel pump. Both the pressure - which should be 4-5 pounds, and the volume. Spin the engine with the starter with the line off the carb and into a catch can, and you should get regular healthy spurts. If you want to be technical there will be a spec for how much it should pump in how many seconds  but it is actually easy to see if it is putting out, or is just sputtering and dribbling a bit.  You could also have a fuel line problem. Like a leak where it is sucking air, or the rubber flex hose to the pump could be restricted. A more remote possibility is that there is a problem in the tank but that is less likely. 

[Giorgio Ancona]

Bought a gauge and installed it , fuel pressure is between 5 PSI at idle and 4 to 4,5 psi over idle , I removed  the carb again and found the float conatminated by fuel and bought a new float.

 

The engine is running slightly rough and I am still in trouble shooting .

I tried to adjust the timing .As per shop manual  it should got three timing marks ( The first one is 0 degrees,second is 3 degrees,third one is 5 degrees) but I ‘ve got 2 marks only .

The 287 engine has to be 5° BTDC  which is the right mark?

Is the TDC mark missing or why are there two marks only?