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Ok...I checked the floats on my 60 dual carb 6 cyl BT7 and they look OK. It left me sit out of the blue several weeks ago. It starts and runs until the fuel in the float chambers run out and then dies. When I turn the ignition on the electronic fuel pump fills the float chamber...the car starts and the process of running for several minutes until the gas is gone repeats itself. Where do I look next?
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Fuel Problem redux
- Thread starter Rick G
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Rick, it sounds as though you have either a restriction in the fuel supply system somewhere, or a bum pump. The fuel is being delivered to the carbs at an insufficient rate, allowing the engine to use fuel faster that the system can provide it. Check for a clogged filter, or a pinched line or hose. I don't know if your car has a sock type filter in the tank or not, but if it does, this may be clogged.
Your manual should list the fuel pump test procedure, in which the delivery of the pump is measured. I don't have the info handy, but I'm sure someone has it, and will be along shortly.
Jeff
Your manual should list the fuel pump test procedure, in which the delivery of the pump is measured. I don't have the info handy, but I'm sure someone has it, and will be along shortly.
Jeff
Keoke
Great Pumpkin
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Rick, do you have any rubber hose connected in the fuel lines except the standard ones feeding the carbs and are those relatively new. You might take a look at them,make sure they are free of obstruction. This new fuel can attack rubber.-FWIW---Keoke--P.S. If you have a spare pump put it in and see what happens.
[ QUOTE ]
/ubbthreads/images/graemlins/nonod.gif Nope Jeff thats spot on 14 G/PM---Keoke /ubbthreads/images/graemlins/yesnod.gif /ubbthreads/images/graemlins/laugh.gif
[/ QUOTE ]
WOW!!!!!
As a point of reference, 16 GPM was the output of the utility hydraulic pump on an F-100 fighter. That could retract the landing gear and the flaps, simultaneously.
Of course, that was also at 3000 psi. /ubbthreads/images/graemlins/grin.gif
But, as to the original intent, I think you are going to find a simple problem, such as Keoke mentioned with the hose deterioration issue.
Jeff
/ubbthreads/images/graemlins/nonod.gif Nope Jeff thats spot on 14 G/PM---Keoke /ubbthreads/images/graemlins/yesnod.gif /ubbthreads/images/graemlins/laugh.gif
[/ QUOTE ]
WOW!!!!!
As a point of reference, 16 GPM was the output of the utility hydraulic pump on an F-100 fighter. That could retract the landing gear and the flaps, simultaneously.
Of course, that was also at 3000 psi. /ubbthreads/images/graemlins/grin.gif
But, as to the original intent, I think you are going to find a simple problem, such as Keoke mentioned with the hose deterioration issue.
Jeff
Thanks all for the quick reply. The hoses are new...I replaced the SU fuel pump several months ago as it used to stop running at the most inconvenient times. The electronic fuel pump is from Advance auto parts and has worked well to date. When I disconect the line from the front float.........it really seems to pump at fast rate with no apparent restrictions. It is rated at the proper number 2.5-4. Do you suggest I replace it and see if this is the problem?
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Hi Rick,
Just for reference, the standard SU pumps are rated at 7 gallons per hour. This is a little less than one pint per minute. Some of the later pumps such as the AZX 1300 series, are rated at 15 gallons per hour or two pints per minute.
D
Just for reference, the standard SU pumps are rated at 7 gallons per hour. This is a little less than one pint per minute. Some of the later pumps such as the AZX 1300 series, are rated at 15 gallons per hour or two pints per minute.
D
Keoke
Great Pumpkin
Offline
I do not know at the moment,but what I am thinking is that the pump may deliver fuel under no head but with a head attached it may falter. Do you still have that intermittant SU pump you might coax it to work long enough to make a comparison.-FWIW---Keoke /ubbthreads/images/graemlins/confused.gif
Unfortunately, I broke the copper line getting it off so I do not have the proper conection to put it back. I am going to try a new pump (and filter between it and the tank) to see if I get a different result. They are not expensive and it proably is worth a try.....Just went out and let it run for a few minutes before it stopped again. I think you are all on to the problem.
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Just for perspective, the average engine running on gasoline requires about .5 lb/hp/hour. This is known as "brake specific fuel consumption", BSF. Therefore, if gas weighs 6 lb/gallon, the engine will require about one gallon per hour for every 12 horsepower. An engine actually being run at 150 hp will require about 13 gallons per hour of fuel flow. Obviously the engine will not be run at it's maximum horsepower for very long, so the lesser fuel flows will usually work. The late BJ8 SU pump is rated at 15 gal./ hr.
D
D
Although this is my first post on this forum i have had similar problems with both a 100/4 and 100/6 , the solution for me was to allow the float bowls to vent to atmosphere ie breathe , it is not clear in all of the technical manuals i have but it would appear that the float bowls of these SU carbs need to be vented to air to prevent a partial vacuum being formed in the float bowl. I would suggest that slightly backing off the the central retaining bolts to the two float bowls will allow the fuel to be pumped continuosly to the carbs . Close examination of the top of the float bowl lid should show some kind of notch in the centre boss , if this has been sealed with either a replacment washer or sealant the bowl is effectively sealed and due to some law of physics or maybe nature the fuel supply does not work , I may be wrong but it might be worth investigating, it certainly workrd for me .
As an afterthought how come I am in the UK and you guys have the best Austin Healey forum in the world !!!!
As an afterthought how come I am in the UK and you guys have the best Austin Healey forum in the world !!!!
Bruce Bowker
Obi Wan
Offline
"As an afterthought how come I am in the UK and you guys have the best Austin Healey forum in the world !!!!"
We bought most of them. /ubbthreads/images/graemlins/grin.gif
Bruce
We bought most of them. /ubbthreads/images/graemlins/grin.gif
Bruce
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Greyman,
Welcome to the BCF.
You are absolutely correct. There are two types of SU bowl vent designs. Both types rely on an undersize diameter bowl hold down nut to allow passage of air around the shank of the nut. Where they differ is that one type has radial slots in the central boss on the lid to allow air passage between the hold down nut & the bowl top boss.
This type has an oversize sheetmetal cap that fits between the boss & the nut. Air passage is between this cap & carb top boss through the radial slots. No gasket should be used between lid & this cap, as the gasket will likely shut off the bowl venting.
The second type of vent relies on a banjo & vent pipe mounted between the top of the bowl & the hold down nut. It usually has no radial slots in the top boss. This type requires a special gasket between the bowl top & the banjo which has scallops cut on it's internal diameter to allow air passage through the scallops to the banjo & vent pipe.
The wrong gasket or a gasket in the wrong place can block bowl venting & cause fuel starvation as you say.
D
Welcome to the BCF.
You are absolutely correct. There are two types of SU bowl vent designs. Both types rely on an undersize diameter bowl hold down nut to allow passage of air around the shank of the nut. Where they differ is that one type has radial slots in the central boss on the lid to allow air passage between the hold down nut & the bowl top boss.
This type has an oversize sheetmetal cap that fits between the boss & the nut. Air passage is between this cap & carb top boss through the radial slots. No gasket should be used between lid & this cap, as the gasket will likely shut off the bowl venting.
The second type of vent relies on a banjo & vent pipe mounted between the top of the bowl & the hold down nut. It usually has no radial slots in the top boss. This type requires a special gasket between the bowl top & the banjo which has scallops cut on it's internal diameter to allow air passage through the scallops to the banjo & vent pipe.
The wrong gasket or a gasket in the wrong place can block bowl venting & cause fuel starvation as you say.
D
Keoke
Great Pumpkin
Offline
/ubbthreads/images/graemlins/savewave.gif
HI Greyman, Welcome to the forum ,if that bloke Bruce acts up to much ill have a talk with SWMBO if required. That was a good response you came up with and I think it will resolve the problem. I could not come up with a method of creating a head at that end of the line but as you say all you need is a depression. Cheers---Keoke
HI Greyman, Welcome to the forum ,if that bloke Bruce acts up to much ill have a talk with SWMBO if required. That was a good response you came up with and I think it will resolve the problem. I could not come up with a method of creating a head at that end of the line but as you say all you need is a depression. Cheers---Keoke
jtb55
Member
Offline
Forty years ago I had a similar problem with my first car a $125 58 MGA. It would start, run fine for 3 or 4 miles then die. After it had sat for a while it would start and repeat the sequence. It took awhile but I eventualy figured out that the electric fuel pump would get hot and short out.