Lebowski

What causes a carb to backfire?

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The one barrel carb on the 6 cylinder engine on my Edsel keeps backfiring unless I pull out the manual choke a little. When I stop the car the engine idles very fast so then I have to push the choke in again until I start out again and have to pull it out so it doesn't backfire. Having to do this every time I stop is getting old so how can I fix this problem? Will turning the screws on the carb help? The previous owner said he had the carb rebuilt last year and has only put about 100 miles on it since then. Will spraying some carb cleaner in it help? Any other ideas? Thanks....

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Backfire usually means it is starving for fuel.  Check the fuel filter, pump, & possible restrictions in the fuel line from the tank.

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Backfire usually means it is starving for fuel.  Check the fuel filter, pump, & possible restrictions in the fuel line from the tank.

I'll replace the fuel filter tomorrow and see what happens. The fuel pump was replaced recently and the tank was cleaned too so hopefully it's the fuel filter. Thank you....

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Backfire usually means it is starving for fuel.  Check the fuel filter, pump, & possible restrictions in the fuel line from the tank.

Correct.  Also check the float level/height because this has a huge effect on the rich/lean condition of the carburetor.  It does sound like your carburetor is running very lean, causing the backfire.

 

Just my opinion,

Grog

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Usually. A very lean mixture or timing. Didn't hurt to check the timing regardless. Wayne

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Lean mixture, check the bolts on the intake manifold first, they tend to work loose. Sometimes all you need to do is tighten them up. If there are no intake leaks try adjusting the idle mixture a bit richer. If you are not familiar with motors best have an old mechanic check it over, there could be other problems that will be obvious to a good mechanic.

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Look for a vaccum leak. Use a 3' or so length of garden hose or equvilent. Put one end to your best ear and search around the carb and intake manifold for a leak. Manifold to head gasket is a likely spot and any vaccum accessories that run off a rubber vac hose.

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I replaced the fuel filter which was very old and the gas inside looked pretty dirty. I turned the fuel/air mixture screw on the carb to the left to lean it out. I did it one full turn, drove the car, and it seemed a little better so I turned it a second full turn. It drove a little better so I turned it a third full turn and it drives pretty good but still backfires some in third gear. I checked the nuts and bolts on the intake manifold and base of the carb and they were all tight. So what's my next move? Should I lean it out one more full turn or would that be too much? Thanks to all who have responded....

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The Edsel 6 should have a one-barrel Holley carb. The range on the adjustment screw is from 0 ~ 1 1/2 turns. Beyond 1 1/2 turns, no change. Also, this screw only controls the mixture at idle, nothing beyond idle.

 

In the years of production of the Edsel, the mixture needle would be the older short taper needle. It was not until 1968 when smog emission demanded more precise tuning that the long taper needles were regularly used.

 

I have not seen in this thread the age of the gasoline. If the gasoline is old, then issues may arise especially with a cold engine. Once the engine is totally up to normal temperature, the issues may diminish, or even disappear.

 

The fact that changing the screw is showing effect may simply be that the engine is warmer rather than any actual change from the adjustment.

 

I would suggest checking the age of the fuel (anything over 6 weeks is suspect, especially on a new engine).

 

And as others have mentioned, I would check the timing, both at idle and at higher RPM, to make certain the distributor advance unit is functioning.

 

Jon.

Edited by carbking (see edit history)
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The Edsel 6 should have a one-barrel Holley carb. The range on the adjustment screw is from 0 ~ 1 1/2 turns. Beyond 1 1/2 turns, no change. Also, this screw only controls the mixture at idle, nothing beyond idle.

 

In the years of production of the Edsel, the mixture needle would be the older short taper needle. It was not until 1968 when smog emission demanded more precise tuning that the long taper needles were regularly used.

 

I have not seen in this thread the age of the gasoline. If the gasoline is old, then issues may arise especially with a cold engine. Once the engine is totally up to normal temperature, the issues may diminish, or even disappear.

 

The fact that changing the screw is showing effect may simply be that the engine is warmer rather than any actual change from the adjustment.

 

I would suggest checking the age of the fuel (anything over 6 weeks is suspect, especially on a new engine).

 

And as others have mentioned, I would check the timing, both at idle and at higher RPM, to make certain the distributor advance unit is functioning.

 

Jon.

If you're the carb king then you're the man I need to talk to. The gas is a week old because I filled it up twice in the last two weeks. It's not a new engine. It has 108k on it and smokes pretty good so it's probably never been rebuilt. I don't have a timing light and have never used one before. I could probably buy one and find a video on YouTube on how to do it if that's what you would recommend. I appreciate the advice from you and the others so please tell me what my next move should be....

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I misunderstood your first post. When you mentioned the 100 miles on it, I assumed engine, and you meant carburetor.

 

Suggestion: buy some test equipment.

 

I would suggest any enthusiast working on older vehicles needs a minimum of 3 items of test equipment. These are:

 

(1) Timing light

(2) Compression testing gauge

(3) Dwell/tach combination meter

 

Since your engine has 100k plus miles, I would suggest (especially on a Ford 6 of this period - been there, done that!), that your backfire is much more likely to be a burned/stuck intake valve. We burned a couple by 60k miles on a 1960 Ford 223 6-cylinder that Dad bought new. A compression test would verify/deny this long distance diagnosis. The compression test is quite easy to accomplish.

 

I would also suggest the acquisation of a factory shop manual for your car. In the meantime, Motors/Chiltons aftermarket manuals have lots of useful information, and are relatively inexpensive.

 

As a general rule, engine running issues should be approached as:

 

(1) compression

(2) ignition

(3) fuel

 

And when purchasing test equipment, I personally (OPINION, others may/will differ) believe good, used made in the USA equipment from the 1960's and 1970's is vastly superior to the offshore stuff currently available new.

 

Jon.

Edited by carbking (see edit history)
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this may not apply but since you are new to old cars, any old car needs choking when cold to start and keep it choked until warmed up. as it warms up you can slowly push the choke in until warmed up. it it still backfires then follow the previous post

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 since you are new to old cars

 

When did I say that? This is the sixth Edsel I have owned. In the last 30 years I have also owned a 1930 Ford Model A, 1937 Packard, 1949 Buick, 1950 Pontiac, 1950 Studebaker, 1951 Chevy, 1952 Ford, 1956 Buick, 1957 Chevy, 1958 Mercury, 1959 Cadillac, 1961 Rambler, 1961 Mercury convertible, and several more....

Edited by Lebowski (see edit history)

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I misunderstood your first post. When you mentioned the 100 miles on it, I assumed engine, and you meant carburetor.

 

Suggestion: buy some test equipment.

 

I would suggest any enthusiast working on older vehicles needs a minimum of 3 items of test equipment. These are:

 

(1) Timing light

(2) Compression testing gauge

(3) Dwell/tach combination meter

 

Since your engine has 100k plus miles, I would suggest (especially on a Ford 6 of this period - been there, done that!), that your backfire is much more likely to be a burned/stuck intake valve. We burned a couple by 60k miles on a 1960 Ford 223 6-cylinder that Dad bought new. A compression test would verify/deny this long distance diagnosis. The compression test is quite easy to accomplish.

 

I would also suggest the acquisation of a factory shop manual for your car. In the meantime, Motors/Chiltons aftermarket manuals have lots of useful information, and are relatively inexpensive.

 

As a general rule, engine running issues should be approached as:

 

(1) compression

(2) ignition

(3) fuel

 

And when purchasing test equipment, I personally (OPINION, others may/will differ) believe good, used made in the USA equipment from the 1960's and 1970's is vastly superior to the offshore stuff currently available new.

 

Jon.

Thanks for all the info. I have a factory shop manual. My local Advance Auto Parts store has a compression tester for $25.99. Should I buy it and check the compression on all 6 cylinders or should I try to find an old one somewhere? I've seen guys use these testers before so I should be able to do that. Should I do that first or buy a timing light and try to check the timing first? I have no idea what a dwell meter is so I'll hold off on that for now I guess. Let me know and thanks again....

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I have seen ignition issues act like everything known to man. Carbs are just poorly controlled leaks and an Inline six with a 1 bbl and a log manifold is partticularly hard to get an even mixture to all cyls. Except for QJs and their tiny float bowls that often ran out of gas at the top of third (great carb for a Corsa though) most will run pretty good as long as the needle and seat are working, the float is floating, and the main is clear. Fuel line flow just needs to be "enough".

Any backfire and my first thought is timing. Second is a valve sticking. Lean runs hot and stumbles.

Of course a Rochester FI at 150 psi is different.

ps haven't seen any mention of whether the backfire is out the exhaust or the carb ?

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"Any backfire and my first thought is timing. Second is a valve sticking. Lean runs hot and stumbles."

"ps haven't seen any mention of whether the backfire is out the exhaust or the carb ?"

 

 

 

Tomorrow I'm going to buy a timing light and a compression tester. I may also make a video of the car with the engine running so you guys can see how it's smoking. 

 

It's out of the carb. Would a valve job stop the smoking or would it need a complete rebuild?

Edited by Lebowski (see edit history)

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Out the carb is almost always timing or a valve. Compression test should tell the story. If mainly at idle can also pull the plug wires one at a time with an insulated puller and see when it stops.

Timing light is used to set initial and verify advance. Dwell/Tach (I have one of these which does a lot more) is to verify the points gap (can adjust while idling on a GM car, not sure about Ford). I usually check compression with all plugs out and at cranking speed. Good compression tester will screw in the plug hole and have a reading release button.

 

As to the smoke, it depends on the color. See here. However blue smoke on startup is usually valve guides. Blue smoke on accelleration, rings. If going to do a ring job might as well do bearings at the same time.

 

ps I never turn a crank, just polish to 1 or 2 thousandths under. Replace if needs more. Factory surface hardening is just a few thousandths thick and even 10 under will remove it. Few shops can restore it.

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After watching several "how to set the timing" videos on YouTube I decided to pass on that idea because it looks too complicated for me. How much would one of you guys charge me to come to Louisville to check the timing and do a compression test?

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Not hard at all, connect the red to 12v black to negative & clip adapter on #1 plug wire. Make sure the notch in the crank balancer is visible (I use some white marker). Degree wheel is nice but I've never had one. Remove and plug hose to vaccuum advance. Clean off the marker on the timing cover. Start engine. Pull trigger & point at the block marker. Notch in balancer should appear in flashes close to the marker. Adjust (turn) distributer as needed.

 

Might see if the local junior college or high school has an auto shop class. Am sure they would love to see a 60 Edsel.

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If this problem coincides with the replacement of the carburetor 100 miles ago, I think that would be the area I would looking at.  The ignition timing seldom ever just goes off on it's own, and even less seldom to coincide  with the replacement of the carburetor

 

I had encountered a similar problem and it turned out that some paint over spray from the rebuilder was on the inside of the carb, The solvent action of the gasoline lifted it up causing it to float around the bowl until  it clogged up the metering jet. I think there is a piece of dirt stuck somewhere in the carburetor.  My problem was on a simple six cylinder GM set-up, but still similar to yours.

Edited by John348 (see edit history)
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Does your engine have solid lifters? I believe it does, if so no amount of testing equipment is going to do any good unless your valves are properly adjusted. According to my Chilton's manual hydraulic lifters were not available in that engine until 1962. I have a 1963 F150 that had a 223 cu" engine in it, which I replaced with a 262 cu" (same basic engine but a lot different!) both of which had solids. As I remember the valves were adjusted with the engine warm and running, what a frigging mess that was! Like some of my Studebakers there was so much oil that I ended up having to cut down a valve cover so I could contain the oil, while I adjusted the valves. Couldn't believe that it was the same company that built the "Y" block.

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Lots of good info so far and probably a little confusing so here is my pitch; first of all I am assuming this is not something that has immediately occurred after a recent change of anything on the car, such as plugs, points, carb etc.

 

Re the lean mixture, a good start would be to remove all of the plugs and look at the colour of the electrode ends, ideally after a reasonable run they should be a nice tan or coffee colour, too lean and they will be an off white, too rich and they will be sooty black; I emphasise this is after a good run, not idling in the drive. All of the plugs should be the same colour, if one or more are a different colour then you are probably looking at something else related to that / those cylinders.

 

Timing; just a simple test would be to loosen the clamp bolt at the base of the distributor and rotate the distributor body a few degrees one way or the other, retighten and go for a drive to see if there is any difference; mark your original position first so you can come back to it if needs be. Checking with a timing light is better, but if you don't have the confidence this may a least determine if the timing is an issue.

 

Compression; the guage check is best, but again if you want a quick check, remove the coil to distributor wire (king lead) and wind the engine over on the starter, if a particular cylinder is down on compression (possible valve leak) the engine will falter as it spins over on the starter due to there being less compression in that particular cylinder. this is not a very accurate check but if the compression loss is significant you may well pick it, of course then you have to determine which cylinder/s with a guage.

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