Carb issues

-
mopar410

mopar410

Well-Known Member
Joined
Sep 14, 2011
Messages
1,086
Reaction score
30
Location
TN
Hey everyone,I'm have problems with my 6 pack carbs.To start I'm running a 340 with around 18 degree timing full advanced is unknown.As you may know the 6 pack intake is a high rise so heat transfer shouldn't be too bad but when I run the car to normal temps and shut it off the carbs will drop fuel level in 3 hours down about 3/4" or so and it all seems to go in the motor as it will not restart after sitting over night unless I use a starting spray which I have been useing carb cleaner and it still won't start easy,I usaully have to recharge the battery to get it to start from cranking way too much.However after sitting over night without running the it only dropped about 1/8" from the bottom of the site screw hole.So it seems to seep or evaporate some.
Ok heres the deal after running to temp the intake just below the front carb mount reads 165 deg and the front carb bowl lower section reads 90 deg.The other intake readings were close to the around 150 deg and all carbs read the same.Also I have a plasticish "type" base gasket to slow heat transfer.
These are the OEM carbs with OEM fuel lines except for a couple inch section from the machenical fuel pump to the carb line at the pump.These are based off the holly 2300 carbs.One with a metering block and the outter carbs have metering plates.
OEM lines from the tank forward,nothing closer than 3" to the exhaust.
Float level is just under site screw hole.
As for seeping,its not dripping from the barrels above the flaps as the barrels are dry all night.So the only place I can tell is through the mixture outlets below the flaps which shouldn't have any fuel sitting on them to seep out.Where else can it go through to get to the engine?
As for the boiling,I would assume a small amount could be pushed over the oever flows but nothing comes out of the top hole to the outside of the carb.Can the fuel really boil at the temp?Doesn't seem like it should.
I may have missed something here so ask away.So such a long post but this has been driving me crazy.Thanks in advance.
 
Also the engine is fresh and not had enough time to seat the rings in (around 20 hours idle and 10 miles max driven)and the cam and lifters are used so they are broken in already.The carbs have new gaskets also.
 
It sound to me like there are issues besides where the fuel is going.
You say that you use fluid to get it started, but it seems that if the fuel was actually going into the engine it would already have plenty of fuel in it and fluid would just make it worse.
Have you checked plugs to see if there is already to much fuel in it to start after it sits.
You can kinda see whats up if after it sits like that if you crank it like you would normally want it to start. (like 3 seconds) then pull a plug or two and see if they are wet.
Your issue sounds more like a fuel starvation problem, and I'd bet those plugs are dry.
Also, if you were loosing that much fuel into the engine it would have a gas smell to the oil.
Does it?
 
TrailBeast said:
It sound to me like there are issues besides where the fuel is going.
You say that you use fluid to get it started, but it seems that if the fuel was actually going into the engine it would already have plenty of fuel in it and fluid would just make it worse.
Have you checked plugs to see if there is already to much fuel in it to start after it sits.
You can kinda see whats up if after it sits like that if you crank it like you would normally want it to start. (like 3 seconds) then pull a plug or two and see if they are wet.
Your issue sounds more like a fuel starvation problem, and I'd bet those plugs are dry.
Also, if you were loosing that much fuel into the engine it would have a gas smell to the oil.
Does it?
Click to expand...
Thanks for the reply trailbeast.I just went out to confirm the plugs are wet without trying to start it.As for the oil the dipstick had a gas smell to it so I changed the oil last week.The gas would settle to the top I asume because the oil itself didnt smell like gas.Right now everything appears fine.
The carb cleaner acts as a catalyst as it is highly flamable and the mist is easier to ignite through the excessive gas build up.I see what you mean by starvation but the cleaner is in small amounts just to get ignition.
I've tried to do all the little things to prevent boil over but I just can't put my finger on whats happening here.Keep in mind it's only 50-60 deg here so hot summer heat (90 deg)hasn't got here yet.At first glance I would say a cracked carb but there are three with two different setups(metering block and plate) so it seems to be something else:banghead::banghead::banghead:
 
Final bump before I pull the intake and replace with a four barrel to eliminate the carb and intake.I'm not running a inline filter at the moment.I wonder if that will help?
 
mopar410 said:
Final bump before I pull the intake and replace with a four barrel to eliminate the carb and intake.I'm not running a inline filter at the moment.I wonder if that will help?
Click to expand...

Running one carb without a filter is asking for trouble.

Running 3 without a filter is 3x the trouble. I bet you have a contamination issue at the very least.

Pull each carb and blast out every port with come carb cleaner. Reinstall and readjust. That's where I would start.
 
mopar410 said:
Final bump before I pull the intake and replace with a four barrel to eliminate the carb and intake.I'm not running a inline filter at the moment.I wonder if that will help?
Click to expand...

An inline filter won't help the fuel problem unless crap is getting in one or more of the needle and seats causing it to overflow into the motor, but it sure couldn't hurt to have it in there making sure the fuel is clean.

It sure sounds like something isn't right, and that you have a good understanding as to what is going on.
It does sound like one or more of the carbs are leaking fuel somewhere.
 
I used to own an AAR cuda, so I'm very familiar with six pack set-ups, and my superbird I have now is a six pack car. If your car has backfired through the carbs at all, I would almost bet the power valve is blown and leaking fuel... My AAR used to do this on occasion, so I always carried extra parts in the glove box. Of course it could be just a bad needle/seat. I'd pull the center carb off and check it carefully.
 
Yeah I was going to put a filter on but with the factory type hard lines for the six pack so I have to figure out where to put it.As far as the needle and seat goes I have tested them and they seem to be working and if trash got in one it would pour gas out of the top of the carb while running.I've had them to stick before and they will cover the intake in a minute.fanofpetty only the center carb has a power valve and all the carbs are doing the same thing.It was new when installed a month ago but it could have blown and in theory the center could have a bad valve while the outter carbs have a different issue.Oh and i have rebuilt and cleaned each carb twice using carb cleaner and compressed air,all the passages appear clean.Any ideas are welcome and appreciated.
 
Small update the fuel level has not changed while sitting for a couple days so it doesn't seem to be leaking down after the first amount which is form a cold turn over just to fill the carbs full,didnt run the motor.
Also I noticed where the fuel line runs through the torsion bar mounts and moves inward and downward,the fuel line comes with in 1" to 1 1/2" of the exhaust running about 10".Do you think that is enough heat to cause the fuel to boil in the bowl?keep in mind the motor runs good(no vapor lock) down the road but after its shut down the problems start.I will pit some heat tape or a heat shield on and see what that does.
 
The fuel isn't being boiled out of the carb?
Sorry, late comer to the thread.
 
rumblefish360 said:
The fuel isn't being boiled out of the carb?
Sorry, late comer to the thread.
Click to expand...
On a 60 deg day after shut down I could here a squeaky sound so I got a length of hose put one end to me ear the other to the carb bowls and it sounded like a rat was inside "chattering" so I assume it's boiling over.So I rebuilt the carbs and cleaned them again.The next drive was at 50 deg but I couldn't hear anything from the carbs so I thought it was fixed but the next day the carbs were low on fuel and it wouldn't start.But after days sitting the fuel will only drop about 1/8-1/4" below the site holes.So it leads me to believe its affected by running the engine and not just seeping down.
 
Update.Found my fuel line was not clipped to the frame just pass the firewall.It was hanging down with in about 1"' of the exhaust where I stated earlier.So I wrapped the fuel line and header with exhaust wrap.The header was wrapped about 3-4" before the 4 into 1 collector back to the connection plate of the pipe.I also wrapped the fuel line over the axle as the exhaust pipe gets around 2-3" away.Now I need to try starting it later tonight at 9-10 o'clock and if it fires up it should be fixed,if not the only thing left is to replace the intake to eliminate that as a problem.If you have two of anything cross them cause I need all the help I can get.lol
 
is your accelarator pump working. Because even if your carb empties the pump cavity will not. so it should fire with whats in the pump with a couple of hits on the throttle. When its cold it will start on the choke system. Check the pump.
 
No doubt some odd things seem to be going on with the fuel system/carbs, and I can't really add much to what's been said. But, if you run out of options to try, maybe? your starting issue could be voltage related at the coil/ignition system. The fact that the volatile carb spray gets you going makes me wonder. Just something else to look at if all else fails.
 
Oldmanmopar said:
is your accelarator pump working. Because even if your carb empties the pump cavity will not. so it should fire with whats in the pump with a couple of hits on the throttle. When its cold it will start on the choke system. Check the pump.
Click to expand...
Pumps working but with all the fuel getting in the engine I can't touch the throttle to start it.
 
OldmanRick said:
No doubt some odd things seem to be going on with the fuel system/carbs, and I can't really add much to what's been said. But, if you run out of options to try, maybe? your starting issue could be voltage related at the coil/ignition system. The fact that the volatile carb spray gets you going makes me wonder. Just something else to look at if all else fails.
Click to expand...
I'm running points gapped to spec,can't remember off hand what that is though.The fire is strong and I did put a supercoil (the big yellow one)on it to make sure I was getting plenty of fire but removed it because I don't have a mounting bracket for it.The plugs are autolites 64 I believe which I plan to replace shortly.
 
Ok I just got home and after sitting for 4 hours I tried to start it after checking the fuel levels,the rear carb didn't change the front carb was down 1/8" and the center was down 1/4".Which this is consistand with how it did after sitting over night without being started.It turned over about 10 seconds and I stopped,I did pump the gas a couple times to see if it would hit any but it didn't,So I checked the fuel levels to make sure where full was on each one.Went back to start it and it turned slow like it was a little rich and hit but I put it to the floor to try and help it out but the extra pump did caused it to not start.Maybe a new set of plugs will cure it.Odd thing though as I ran it earlier in the garage I was checking temps all around and the fuel line coming out of the pump was 150 deg.But to the touch it wasn't very warm.It got cooler as it got closer to the carb which was 80-90 deg at the carb.The timing chain cover was 150deg also so it was transferring heat into the fuel line.Anyone else check the temps of their engine?I'll switch plugs tomorrow and see how that does.Getting closer.
 
I've got a 340 6 barrel setup and had problems with it. Was running too rich, rebuilt carbs and still problem. Finally rebuilt center carb and blocked off end carbs (solid plates blocking off manifolds) and did the tune up on only center carb. Then added the end carbs after center carb was adjusted and ignition and timing was correct. You can't just shut fuel off to end carbs as they pull a little air in past throttle plates and won't idle. I replaced the points system w Pertronix electronic ignition too. That helped things too.
 
this is a very common problem with the fuels that we have these days. the fuels are not designed for carb usage! modern fuel injection always has pressure on it before the fuel reaches the engine so these probs are not an issue with the new cars. Oxygenated fuel, alchohol and winter blends all contribute to the fuel magically disappearing out of the fuel bowl of a carburetor. To deal with it, some kind of insulation on the fuel line, electric fuel pump, alchohol resistant rubber parts/neeld-seat, accel pump help the situation. Remember 10% alchohol means 5% less btu in the fuel, so you have less power also. If you can find some fuel without alchohol, that would be good also. If the carb has any bottom plugs (to plug factory drillings) these must be super "leak-free" also. (cant remember if a Holley has any of these or not) you can check these by applying high pressure air from a blow gun and with some soapy water on the back side, see if any air is passing through anything. If yes air is passing, even a small amount, fuel will seep out and evaporate. Drill and replace with some new fabbed plugs installed with marine tex epoxy. bottom of carb must be leak free. On a holley, the metering block and idle passage are what to check.
 
Small break through....sorta.It seems like all the heat shielding payed off but it still loses 1/4" fuel in the center carb and 1/8" in the front carb.So I had an idea,why not try to set the floats down to that mark and see if any leaves the carbs while sitting.After readjusting the floats I ran the car some,little to much and ran it out of gas lol,after getting fuel in it and running it more to get it up to temp and the bowls full I let it for 5 hours and three pumps of the pedal and it fired up right off.So either or both "could" still be happening,1 the fuel is still boiling but with the foats set lower it can't get high enough to leave the carb and /or 2 the seeping it happening down to that point and doesn't go any lower.My opinion is that its not boiling anymore and is still seeping but with the floats set lower it cant escape into the engine.I will tinker with it some more but at aleast its useable now.The center carb appears to drop to the top of the power valve.FYI
 
You must log in or register to reply here.
-

Back
Top