confused carb
Thread Starter
Racer
Joined: Aug 2006
Posts: 420
Likes: 0
From: Pampa Texas
confused carb
I've got a 75 with a holley carb on the car. Recently it has started stumbling and backfiring at stop lights if I press the accelerator. If I hammer on the accelerator it just dies. Also after either one happens you can smell a strong smell of gasoline. From what I've read stumbling and backfiring is running lean, but what explains the fuel smell? Also what is causing this since the only thing I have changed is exhaust and distributor? I changed those two and it ran like it did before, then started acting up after a month or two. ANy help would be appreciated.
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
i just went through the same issue. check timing, check air fuel, then check wires and plugs.
mine ended up being a wire too close to the headers was burning. on the outside it looked fine but when i pulled the wire off it had gotten so hot that the boot end curled up. new wires and some heat shielding and it is running nicely.
mine ended up being a wire too close to the headers was burning. on the outside it looked fine but when i pulled the wire off it had gotten so hot that the boot end curled up. new wires and some heat shielding and it is running nicely.
Melting Slicks
Joined: Mar 2008
Posts: 2,989
Likes: 198
From: Meriden CT
i just went through the same issue. check timing, check air fuel, then check wires and plugs.
mine ended up being a wire too close to the headers was burning. on the outside it looked fine but when i pulled the wire off it had gotten so hot that the boot end curled up. new wires and some heat shielding and it is running nicely.
mine ended up being a wire too close to the headers was burning. on the outside it looked fine but when i pulled the wire off it had gotten so hot that the boot end curled up. new wires and some heat shielding and it is running nicely.
Thread Starter
Racer
Joined: Aug 2006
Posts: 420
Likes: 0
From: Pampa Texas
Thanks for the advice so far guys. I looked at the wires and didn't see anything melted through I'll have to check a little more in the daytime where I can see better.
birdsmith I"m giong to show my ignorance but what is the power valve?
Thanks again anymore advice is welcome
birdsmith I"m giong to show my ignorance but what is the power valve?
Thanks again anymore advice is welcome
Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
Most backfiring problems are NOT the carb- usual cause is an ignition/timing problem.
Get a spray bottle, put a little dish soap and fill it with water and spray the plug wires with it running- if there's a plug wire problem that will find it- guaranteed.
If you have a Holley carb that was built before the mid 90's the power valve is done too. The power valve is inside the front float bowl in the metering plate. It's job is to flow a little more gas into the carb under heavy load. It's got a rubber diaphragm in it that does NOT like backfires. No deal to change- pull the fuel line, lay some rags on the intake under the front of the carb, pull the 4 screws that hole the float bowl on, and take it off. The metering block is held on with the same screws so you get it all. get a set of gaskets, a new power valve and go.
Get a spray bottle, put a little dish soap and fill it with water and spray the plug wires with it running- if there's a plug wire problem that will find it- guaranteed.
If you have a Holley carb that was built before the mid 90's the power valve is done too. The power valve is inside the front float bowl in the metering plate. It's job is to flow a little more gas into the carb under heavy load. It's got a rubber diaphragm in it that does NOT like backfires. No deal to change- pull the fuel line, lay some rags on the intake under the front of the carb, pull the 4 screws that hole the float bowl on, and take it off. The metering block is held on with the same screws so you get it all. get a set of gaskets, a new power valve and go.
Le Mans Master
Joined: Jun 2008
Posts: 5,284
Likes: 235
From: Rockledge FL
[QUOTE=TimAT;1568557513]Most backfiring problems are NOT the carb- usual cause is an ignition/timing problem.
Get a spray bottle, put a little dish soap and fill it with water and spray the plug wires with it running- if there's a plug wire problem that will find it- guaranteed.
QUOTE]
i know you told me to do the same thing, but i found the overheated wire before i got a chance to spray. what will the wire do when you spray it with the soapy water?
Get a spray bottle, put a little dish soap and fill it with water and spray the plug wires with it running- if there's a plug wire problem that will find it- guaranteed.
QUOTE]
i know you told me to do the same thing, but i found the overheated wire before i got a chance to spray. what will the wire do when you spray it with the soapy water?
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Le Mans Master
Joined: Oct 2006
Posts: 7,123
Likes: 433
From: Gladstone MO
C3 of Year Finalist (appearance mods) 2019
The soap slows the evaporation of the water a little bit- Same old story- water and electricity. If a plug wire is bad (or going bad) the water will give the spark an easier way to go and it'll cause it to miss or jump to ground, where it may be just good enough to "make it" otherwise. Another "quick and dirty" test.
Team Owner
Joined: Aug 1999
Posts: 30,995
Likes: 99
From: Ontario
If you have a Holley carb that was built before the mid 90's the power valve is done too. The power valve is inside the front float bowl in the metering plate. It's job is to flow a little more gas into the carb under heavy load. It's got a rubber diaphragm in it that does NOT like backfires. No deal to change- pull the fuel line, lay some rags on the intake under the front of the carb, pull the 4 screws that hole the float bowl on, and take it off. The metering block is held on with the same screws so you get it all. get a set of gaskets, a new power valve and go.
Melting Slicks
Joined: Feb 2006
Posts: 3,428
Likes: 5
From: Japan
Sorry 'bout the late reply doublearrow, looks like others got there before me anyway. If and when you do decide to replace the power valve, you'll want to make sure and put the right one in there. You can simply replace the existing one by reading the barely-legible little numbers on it from left to right, or you can take a manifold vacuum reading (which might be difficult considering how badly it's running now) and then selecting a valve whose rating is 1.5 inches less than whatever your idle vacuum happens to be, i.e., if idle vac. reads 8.0 inches you'll want a "6.5" power valve. When you install it be careful to keep its circular gasket properly seated on the base of the valve; if that gets misaligned it can cause the valve to leak. Do pay attention to others' advice regarding ignition, etc., since as stated before replacing a blown power valve on an engine whose ignition or valvetrain is causing backfires will just result in more blown valves. Best of luck...
Burning Brakes
Joined: Jul 2008
Posts: 876
Likes: 0
From: Canastota Ny
one thing YOU DO NOT want to do is grab a plug wire that may be "ticking" i made that mistake in my early years! that usually mean the spark is jumping and grounding outside the boot somewhere.
the soap and water test up top with show you the little sparks as the water hits it.the car will stumble or act up too. The same problems you are having now i had on my old car. the dizzy boots were cracked on the tops. so when it rained the car would stumble. i couldnt figure it out until one day the car was acting up again in the rain, i opened the hood to find the plug boots arching everywhere. new wires problem solved!
but you said you changed the distributor, did it maybe jump a tooth on the gear?
the soap and water test up top with show you the little sparks as the water hits it.the car will stumble or act up too. The same problems you are having now i had on my old car. the dizzy boots were cracked on the tops. so when it rained the car would stumble. i couldnt figure it out until one day the car was acting up again in the rain, i opened the hood to find the plug boots arching everywhere. new wires problem solved!
but you said you changed the distributor, did it maybe jump a tooth on the gear?
Drifting
Joined: Apr 2008
Posts: 1,540
Likes: 51
From: Lexington Park Maryland
It might not have been the original cause of the backfiring (possibly timing ??) but needs to be changed now that the motor has backfired....., even one backfire and the PV is toast.
Drifting
Joined: Jul 2008
Posts: 1,873
Likes: 27
From: Sonora CA
A good variation on the water test is to do it at night in the dark, if you have bad wires, it'll look like a little miniture war going on in there. Same thing happened to me with my truck. Wouldn't run for crap in the rain, new wires and it was good to go.
Thread Starter
Racer
Joined: Aug 2006
Posts: 420
Likes: 0
From: Pampa Texas
I apologize for not having said thanks to everyone who responded. I hate asking questions and not getting back and saying thanks for the advice. Work and my business have been busy along with my first kid on the way so time has slipped faster than I wanted it to. I will use all these suggestions and start trouble shooting the car. Thanks to everyone who offered advice.