340 help!

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Trevor1991

Trevor1991

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Vermontville mi
I have what I believe is a late 60s 340 with a holly 750 carb stuffed into a 1967 barracuda fastback that I'm trying to bring to life for the first time this year. Was rebuilt last season drove all year and put it away for winter. I started it once halfway through winter (which was tough because it was cold outside) but once running ran good. Now comes spring and I go out to start it and all that happens is a cough sometimes out the exhaust but mostly through the carb and will sometimes catch fire. It will sound like it's trying to fire then all of a sudden backfire through the carb. Timing was fine before and hasn't changed so I wouldn't think that was an issue. I even tried to warm up the intake and carb with a light and poured a small amount of gas into the carbs primarys and still no go. Checked the plugs and seemed a bit wet so I dried them all off and still nothing. Can anyone please help???
 
Trevor1991 said:
I have what I believe is a late 60s 340 with a holly 750 carb stuffed into a 1967 barracuda fastback that I'm trying to bring to life for the first time this year. Was rebuilt last season drove all year and put it away for winter. I started it once halfway through winter (which was tough because it was cold outside) but once running ran good. Now comes spring and I go out to start it and all that happens is a cough sometimes out the exhaust but mostly through the carb and will sometimes catch fire. It will sound like it's trying to fire then all of a sudden backfire through the carb. Timing was fine before and hasn't changed so I wouldn't think that was an issue. I even tried to warm up the intake and carb with a light and poured a small amount of gas into the carbs primarys and still no go. Checked the plugs and seemed a bit wet so I dried them all off and still nothing. Can anyone please help???
Click to expand...
Check the inside of the distributor cap for moisture.

EDIT: added inside
 
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Alright I will do that and get back with an update. Thanks for the fast response hopefully be cruising in no time!
 
Are you getting spark???

I like to take a spare spark plug, then disconnect any spark plug wire from the engine, then connect it to the spare spark plug and hold the bottom electrode of the spare plug to a good ground and crank it over and look for spark...
 
krazykuda said:
Are you getting spark???

I like to take a spare spark plug, then disconnect any spark plug wire from the engine, then connect it to the spare spark plug and hold the bottom electrode of the spare plug to a good ground and crank it over and look for spark...
Click to expand...
It appears there is spark. Fire out the carb equates to spark.
 
does your accelerator pump squirt fuel when you open the throttle?
 
Moisture in the dist cap is a good possibility.
You said it was rebuilt last year so a timing chain shouldn't be the problem..........see if you can turn the dist. if you can then the clamp is not tight enough and timing could have changed!
 
Alright
Cudafever said:
Moisture in the dist cap is a good possibility.
You said it was rebuilt last year so a timing chain shouldn't be the problem..........see if you can turn the dist. if you can then the clamp is not tight enough and timing could have changed!
Click to expand...
yea I will check both of those things and go from there. Will report back soon! Thank you to all of your help
 
Ethanol fuel?

If so the needle seats and more may have retired. Try to find and use rec-90 or start it more often! Not a fan of the gas treatments for ethanol!
 
After the cap is all dried out nice, and the issue persists;
Push the car out into the yard.Pull all the plugs out. Disable the spark by disconnecting the power to the ECU/coil. Clamp the rubber fuel line somewhere between the carb and the pump. Bring a fire extinguisher to somewhere near the car where you can see it but no closer that a car-length away, and off to the side.
Then,crank the gas out of it. A short burst of 1 second, then another and another. Until the gas is stops pouring out. Take the extinguisher and walk away, far away. Twenty minutes later come back and crank it for 15 or 20 seconds. Go clean your plugs. If gas did come squirting out of the plug holes, you have a carb issue; take it off and fix it. If no carb issue, squirt a bit of oil in each hole. Then crank it a few revolutions to distribute the oil and blow out the excess.
Now we have only two or three options, either there is something wrong with the valves, or the gas is not 100% gas, or the valve/ignition timing has changed.
The easiest thing to do is to test for compression, I mean the plugs are already out,right. If the numbers are normal in every hole, we can rule out a jumped chain and stuck or bent valves.
The next easiest is to put the #1 piston at TDC compression, then back it up 15 degrees, Pop the cap and make sure the rotor is under the #1 tower. This too proves the chain is where it was the last time it ran, and it proves the timing is close enough to at least start and run.
Thirdly is to prove the gas is 100% gas,fresh enough to burn.To do this you will need to drain and capture the fuel from the very bottom of the bowl. On a Holley this is easy. But we especially need the very first couple of teaspoons.Drain the entire bowl into a clean transparent container. Check it for water then color. Red is bad,useless.Orange is stale,will work in your lawnmower,maybe. Light yellow will burn. Fresh gas is clear as water. There should be about 50ccs of it. So if you got clear to light yellow and no water,pour it back in, thru the bowl-vent.If the quantity was close to 50 cc,release the clamp.
Put the cap back on,reconnect the ECU/coil,put the plugs back in, and try again.
My guess is the cylinders were just dry, and the rings were not sealing and so the pistons were not pulling hard enough on the fuel circuits.But you cured that when the oil went in the plug holes. It should bark to life now.
 
Last edited:
AJ/FormS said:
After the cap is all dried out nice, and the issue persists;
Push the car out into the yard.Pull all the plugs out. Disable the spark by disconnecting the power to the ECU/coil. Clamp the rubber fuel line somewhere between the carb and the pump. Bring a fire extinguisher to somewhere near the car where you can see it but no closer that a car-length away, and off to the side.
Then,crank the gas out of it. A short burst of 1 second, then another and another. Until the gas is stops pouring out. Take the extinguisher and walk away, far away. Twenty minutes later come back and crank it for 15 or 20 seconds. Go clean your plugs. If gas did come squirting out of the plug holes, you have a carb issue; take it off and fix it. If no carb issue, squirt a bit of oil in each hole. Then crank it a few revolutions to distribute the oil and blow out the excess.
Now we have only two or three options, either there is something wrong with the valves, or the gas is not 100% gas, or the valve/ignition timing has changed.
The easiest thing to do is to test for compression, I mean the plugs are already out,right. If the numbers are normal in every hole, we can rule out a jumped chain and stuck or bent valves.
The next easiest is to put the #1 piston at TDC compression, then back it up 15 degrees, Pop the cap and make sure the rotor is under the #1 tower. This too proves the chain is where it was the last time it ran, and it proves the timing is close enough to at least start and run.
Thirdly is to prove the gas is 100% gas,fresh enough to burn.To do this you will need to drain and capture the fuel from the very bottom of the bowl. On a Holley this is easy. But we especially need the very first couple of teaspoons.Drain the entire bowl into a clean transparent container. Check it for water then color. Red is bad,useless.Orange is stale,will work in your lawnmower,maybe. Light yellow will burn. Fresh gas is clear as water. There should be about 50ccs of it. So if you got clear to light yellow and no water,pour it back in, thru the bowl-vent.If the quantity was close to 50 cc,release the clamp.
Put the cap back on,reconnect the ECU/coil,put the plugs back in, and try again.
My guess is the cylinders were just dry, and the rings were not sealing and so the pistons were not pulling hard enough on the fuel circuits.But you cured that when the oil went in the plug holes. It should bark to life now.
Click to expand...
Took out all of the the plugs took the cap off to let dry out then gave the distributor a twist and it didn't even cough. So I twisted it the other way and it came to life! Was running rough so I'm now going to get new plugs and fresh gas. But I think it was a combination of things being that there was moisture where it shouldn't be and maybe the distributor got bumped and possibly wasn't all the way tight thank you all for your help!
 
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