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Old 05-20-2013, 07:14 PM   #1
Woodie1
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Default Loss of power 7 back fire

We went to MAFFI Saturday morning. The drive down was great, coming home not so good. After about 40 miles into the trip home the A started loossing power every now & then & eventually would back fire. It did this for the rest of the 80 miles home. I took the carb apart tonight but didn't find anything plugging the jets. I did open the points a little but I don't think this was the problem. We went to MAFFI last September & had the same problem. I did notice that when I shut the gas off & close the gas adjusting needle that it took a good 2 minutes for the engine to quit. This seems like a long time. What are your thoughts on this problem? Thanks.
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Old 05-20-2013, 09:22 PM   #2
Dave Mc
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Default Re: Loss of power 7 back fire

I would be checking electrical connections and start with the battery,clean the cable connections at both ends of each cable and proceed from there until you find something loose or corroded
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Old 05-20-2013, 10:46 PM   #3
H. L. Chauvin
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Default Re: Loss of power 7 back fire

On a long trip, if carburetor is clean, sounds like fuel is well filtered from the fire wall sediment bowl to carburetor; however, also on a long trip it is possible that some deleterious material of some sort is in the gas tank, (such as rust or crud), that may possibly be collecting around the gas tank drain & impeding the flow of gas through gas shut off valve to the sediment bowl.

Are there a few more gas related details of what helped to get home; e.g., opened GAV valve, pulled choke slightly to provide more fuel?

If altering gas mixture helped, appears fuel related.

If fuel adjustments did not help & were left alone, & engine got better on its own, possible electrical problem, & more often corrosion on connections as Dave stated in above reply #2.

More of one's trip's mechanical details always lead to more meaningful help on what to check.
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Old 05-21-2013, 05:29 AM   #4
Richard Wilson
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Default Re: Loss of power 7 back fire

A common source of back firing is an air leak around the exhaust/intake manifold gasket. Easy to check.
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Old 05-21-2013, 05:36 AM   #5
Tom Wesenberg
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Default Re: Loss of power 7 back fire

I had lots of backfiring when my repro ignition switch had loose contacts. It had such poor contacts that the key fob swinging back and forth would make the switch cut out.

See how far the key turns before the ignition is open. If you barely turn the key to kill the engine, I'd fix or replace the switch.
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Old 05-21-2013, 07:02 AM   #6
Patrick L.
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Default Re: Loss of power 7 back fire

When losing power and starting to back-fire, did reducing the power help? If so, I wonder if the fuel tank is not venting properly.
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Old 05-21-2013, 07:12 AM   #7
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Default Re: Loss of power 7 back fire

all great suggestions and what tom mentioned i have seen many times..
also if your running a dreaded wireless lower plate it can give you an int and weak spark /backfire
try replacing condenser

Last edited by Mitch//pa; 05-21-2013 at 03:07 PM.
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Old 05-21-2013, 02:26 PM   #8
Woodie1
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Default Re: Loss of power 7 back fire

In years past if I had this problem, opening the gas valve would help some. In this case it didn't seem to help. The lower plate is the original type with the wire. If I let up on the gas pedal it did seem to help to some degree. I have the stand pipe filter in the shut off & the tank was almost full of gas so it shouldn't have been something plugging the gas flow. I did not make any adjustments to the carb during the time it was back firing. It was back firing all the way home but sometimes the pause was longer. We might get 5 miles before it would do it again.
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Old 05-21-2013, 02:45 PM   #9
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Default Re: Loss of power 7 back fire

I'm shocked (!) that nobody has suggested a condensor going bad.
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Old 05-21-2013, 03:01 PM   #10
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Default Re: Loss of power 7 back fire

But, you haven't tried opening the gas cap or checking the to make sure the vent is clear ?
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Old 05-21-2013, 03:06 PM   #11
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Default Re: Loss of power 7 back fire

Quote:
Originally Posted by JBill View Post
I'm shocked (!) that nobody has suggested a condensor going bad.
...x2
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Old 05-21-2013, 05:15 PM   #12
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Default Re: Loss of power 7 back fire

Condenser, change it. It happened to me, thought it was gas related but it finely quit on me. And that was it. I always carry two with me.
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Old 05-21-2013, 06:26 PM   #13
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Default Re: Loss of power 7 back fire

Quote:
Originally Posted by JBill View Post
I'm shocked (!) that nobody has suggested a condensor going bad.
X3

Usually that's the solution for any problem.
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Old 05-22-2013, 12:51 AM   #14
H. L. Chauvin
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Default Re: Loss of power 7 back fire

One (1) spark plug not firing now & then, (intermittent fire), is just one cause of backfire.

For example, knew a show-off teenager with an almost perfect Model AA truck who used to always turn the switch off & quickly turn it back on to "make" it backfire.

In this case, unburned fuel mixture is pumped into the exhaust manifold & when this fuel mixture is later ignited in the exhaust manifold, it caused the backfire.

The "Rest of the Story" with his backfiring truck & a murder case is just too long to mention.
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Old 05-22-2013, 07:18 AM   #15
Tom Wesenberg
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Default Re: Loss of power 7 back fire

"For example, knew a show-off teenager with an almost perfect Model AA truck who used to always turn the switch off & quickly turn it back on to "make" it backfire."

I did that with my 55 Chevy when I was in high school.
After a few loud explosions I blew out the muffler. This wasn't a smart thing to do, like I thought it was.
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Old 05-22-2013, 07:27 AM   #16
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Default Re: Loss of power 7 back fire

Maybe ttry replacing the plugs??
Paul in CT
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Old 05-22-2013, 07:36 AM   #17
luckyal
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Default Re: Loss of power 7 back fire

I had exactly the condition described and it was a poorly vented gas cap. Replaced cap and problem disappeared immediately.
Al
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Old 05-22-2013, 05:01 PM   #18
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Default Re: Loss of power 7 back fire

Check the coil. Diagnostics with a "cold" coil don't count. Just replace it with a known good coil and see if that doesn't fix the problem.
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