New guy with carb/igniting issues
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New User
Joined: May 2015
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New guy with carb/igniting issues
Hi there. I'm new to this site and fairly new to the trucks and gassers in general.
So I have a 75 f250 with a 360/390(not 100% sure which) with an edelbrock 1406.
I just picked it up two weeks ago and drove it home on a two hour ride and have been driving to work and back(ten minute drive on backroads). Since I bought it, it seemed underpowered when I punch the gas, and would even backfire through the carb when slightly getting into it. Last weekend I replaced the cap/rotor, wires, and plugs one by one. Went to start it and wouldn't Fire and now it spits gas into the hood. I rebuilt the carb thoroughly and even tried putting the old cap and rotor back on but still nothing and still fuel being pushed through the carb.
Any ideas? Any help would be greatly appreciated
So I have a 75 f250 with a 360/390(not 100% sure which) with an edelbrock 1406.
I just picked it up two weeks ago and drove it home on a two hour ride and have been driving to work and back(ten minute drive on backroads). Since I bought it, it seemed underpowered when I punch the gas, and would even backfire through the carb when slightly getting into it. Last weekend I replaced the cap/rotor, wires, and plugs one by one. Went to start it and wouldn't Fire and now it spits gas into the hood. I rebuilt the carb thoroughly and even tried putting the old cap and rotor back on but still nothing and still fuel being pushed through the carb.
Any ideas? Any help would be greatly appreciated
Fleet Mechanic
Joined: Jun 2013
Posts: 1,895
Likes: 32
Welcome to fte!
Your issues do sound like they are carburetor related.. Im not sure of you're fuel issue, can someone watch while you turn the motor over and see where the gas is spewing from? What you're describing sounds like the fuel line isnt secured properly
Your issues do sound like they are carburetor related.. Im not sure of you're fuel issue, can someone watch while you turn the motor over and see where the gas is spewing from? What you're describing sounds like the fuel line isnt secured properly
Senior User
Joined: Aug 2014
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Usually when you get a backfire thru the carb it is because you are getting spark in a cylinder while its intake valve is open. That seems to make sense now that you are getting fuel on the hood, as engine compression is pushing the fuel thru an open intake valve. A gas engine in good mechanical shape only has compression while both valves are closed. I would suggest checking your cam timing for a jumped timing chain or improper setup from a previous repair.
Postmaster
Joined: Oct 2010
Posts: 4,656
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From: Northern and Southern Cal
In my experience, lots of times ( or maybe most ) backfires are timing related.
That engine of yours is probably a 360. I think '75 might have been close to the last year on them. Double check me on that guys.
It probably has the original timing chain and gears. The upper gear was partly nylon and after all this time the nylon wears out. So the chain is at least sloppy as heck and at the most broke a tooth or jumped one.
Since it has been running the first thing I would do is give it a little advance at the distributor and see if that helps you in any way. Mark your present distributor position first so you know where you are.
That engine of yours is probably a 360. I think '75 might have been close to the last year on them. Double check me on that guys.
It probably has the original timing chain and gears. The upper gear was partly nylon and after all this time the nylon wears out. So the chain is at least sloppy as heck and at the most broke a tooth or jumped one.
Since it has been running the first thing I would do is give it a little advance at the distributor and see if that helps you in any way. Mark your present distributor position first so you know where you are.
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New User
Joined: May 2015
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Alright, I was able to get it running.
I previously I had changed every wire one at a time so everything was the same. Finally I was able to do some research on here andi found tdc #1 and then pulled the cap. The rotor was three positions off. Seeing where the rotor was, I rewired the wires on the cap accordingly. Bam!! Pickup started running! Now under a quick snap acceleration it backfires. I don't have the timing perfect due to a lack of a timing gun. In fourth gear pinned, it seems to bogg down no matter where I have the skinny pedal at. I assume it's due to the stock exhaust manifold (??)
I previously I had changed every wire one at a time so everything was the same. Finally I was able to do some research on here andi found tdc #1 and then pulled the cap. The rotor was three positions off. Seeing where the rotor was, I rewired the wires on the cap accordingly. Bam!! Pickup started running! Now under a quick snap acceleration it backfires. I don't have the timing perfect due to a lack of a timing gun. In fourth gear pinned, it seems to bogg down no matter where I have the skinny pedal at. I assume it's due to the stock exhaust manifold (??)
Cargo Master
Joined: May 2015
Posts: 2,350
Likes: 7
From: Garland, Tx
As usual, I'm late to the party. I was going to suggest the same thing you mentioned. We did the same thing to my sons 69 f100 (his grandpa gave him). My 16 year old now knows how to confirm #1 piston on a compression stroke and check TDC .
Oh, on that edlebrock, they like to go thru accelerator pumps. easy to change just keep a spare in the glove box...
Oh, on that edlebrock, they like to go thru accelerator pumps. easy to change just keep a spare in the glove box...
Fleet Mechanic
Joined: Jun 2013
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New User
Joined: May 2015
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What exactly goes out on the pump? I replaced the rubber piece that actually pushes the fuel. It's the blue rubber that came with the kit. Would I be better off trying to find a 2BBL carb and swapping it in?
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Post Fiend
Joined: Apr 2002
Posts: 19,311
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From: Waterloo, Iowa
If it were me, would want to make sure the timing/cam gear and such are straightened out before doing anything else.
Backfire through the carb indicates a timing problem. Base timing won't move unless somebody moves it - so that leaves pretty much one possibility, esp. on a high mileage engine. Not saying FOR SURE this is your problem, but sure sounds like it at a glance.
Backfire through the carb indicates a timing problem. Base timing won't move unless somebody moves it - so that leaves pretty much one possibility, esp. on a high mileage engine. Not saying FOR SURE this is your problem, but sure sounds like it at a glance.
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New User
Joined: May 2015
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Ok, I worked on it today and had a vacuum leak at the back fitting of the carb so I plugged it up. I ran it and still same symptoms.
Just for giggles I ran the engine and decided to move turn the distributor. In doing so, moving it clockwise the rpm's came up and the engine sounded healthier. I guess you can say I adjusted the timing by ear(if that's the right term). Since it idled higher, I adjusted the idle screws. Then I took it for a test drive and it drove like a champ!
Now to a new issue. With the engine warm, if I shut it off and try to start it again, it feels like the battery is low on voltage and barely cranks over but if I pump the gas while crank it eventually fires right up(~5-10 seconds). With the engine cold, battery seems fine and engine fires right up.
Any ideas? Might I have moved the timing too much?
Thanks for all the replies btw. I greatly appreciate your help
Just for giggles I ran the engine and decided to move turn the distributor. In doing so, moving it clockwise the rpm's came up and the engine sounded healthier. I guess you can say I adjusted the timing by ear(if that's the right term). Since it idled higher, I adjusted the idle screws. Then I took it for a test drive and it drove like a champ!
Now to a new issue. With the engine warm, if I shut it off and try to start it again, it feels like the battery is low on voltage and barely cranks over but if I pump the gas while crank it eventually fires right up(~5-10 seconds). With the engine cold, battery seems fine and engine fires right up.
Any ideas? Might I have moved the timing too much?
Thanks for all the replies btw. I greatly appreciate your help
Cargo Master
Joined: May 2015
Posts: 2,350
Likes: 7
From: Garland, Tx
It does sound like the timing is too far advanced. I haven't used a timing light in years. I do use a vacuum gauge. they're like $20 at an auto parts store and a good tool to have in your tool arsenal. plug it into your carb and try to set the timing where you running at 18 on the gauge. try not to go below 15. at 18 there is usually valve clatter, just back it of a pinch at a time. when you have resolved the valve clatter, use the vacuum gauge to set the carb. Adjust the air/fuel screws a little at a time. what the goal is, by watching the gauge, stop turning the screw when the gauge reaches it's highest reading on the dial. go back and forth 3 or 4 times to make sure your set.
your points play a big part in this operation too. I changed mine to pertronix electrinic ignition with a 40K volt coil.
your points play a big part in this operation too. I changed mine to pertronix electrinic ignition with a 40K volt coil.
Posting Guru
Joined: Aug 2010
Posts: 1,761
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From: Knoxville, TN
The Pertronix systems are electronic ignition systems designed to retrofit in existing distributors that came with breaker points from the factory. If you already have a Duraspark electronic/breakerless ignition system, it's not relevant. If you still have points, then it can be an easier upgrade than getting all the parts & wiring for the Duraspark system.