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11-27-2012, 05:58 PM | #1 |
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Lean Condition back fire .
Any ideas on this 30 Model A New motor ,on a run accelerating at 40 MPH car looses power gives a small back fire ,then picks up a bit .We have found a lot of crud in the tank cleaned it out .Changed to known good Carb,running a filter just before the carb ,We have ruled out electrical .Thank Ted
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11-27-2012, 06:20 PM | #2 |
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Re: Lean Condition back fire .
Did you re-torque the manifold nuts? Usually this is for low RPMs. Check that the gas supply line is not bottomed in carb shutting off gas flow.
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11-27-2012, 06:23 PM | #3 |
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Re: Lean Condition back fire .
Hi Ted,
What kind of filter? Many fuel filters were manufactured for fuel supplied with the pressure of fuel pumps as opposed to fuel provided by gravity flow which can cause fuel starvation -- the paper NAPA #3039 one in the glass sediment bowl works well. Last edited by H. L. Chauvin; 11-27-2012 at 06:29 PM. Reason: added: #3039 |
11-27-2012, 06:43 PM | #4 |
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Re: Lean Condition back fire .
Hi,H,L , Thanks for the comments so far ,Yes we did re-torque the manifold.It has a temporary plastic filter timed on cc per minute checks outs OK .I am thinking a obstruction floating over the fuel out let .We water blasted inside the tank -over flowed .
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11-27-2012, 06:48 PM | #5 |
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Re: Lean Condition back fire .
Hello Ted ,
When you say you are running a new motor, does it now have a much larger cylinder bore than before?, the reason I ask is that a few years ago I did some flow testing on my carb jets as per instructions , and ended up with poor power and back firing at higher RPMs, I gradually increased the flow until it ran OK. I later found that the engine was bored .090" over thus needing that extra fuel for the larger cylinder replacement. The only fuel filters I use are the finger filter in the tank and the fine mesh in the sediment bowl, I removed the filter in the carb, as I had never seen it trap anything. Regards Brian.
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11-27-2012, 06:57 PM | #6 |
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Re: Lean Condition back fire .
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Last edited by FlatheadTed; 11-27-2012 at 11:03 PM. |
11-27-2012, 07:03 PM | #7 |
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Location: Largo Florida
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Re: Lean Condition back fire .
Adjusting the GAV makes no difference ?? Once it backfires,, will it continue to backfire if throttle position doesn't change ?? Have you checked the fuel flow, gas cap vent ?? Try it with the gas cap off or loose..
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11-27-2012, 07:16 PM | #8 | |
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Re: Lean Condition back fire .
Quote:
Steve |
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11-27-2012, 07:17 PM | #9 |
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Re: Lean Condition back fire .
I second the gas cap . Had the same problem you are having and it was the gas cap not venting as it should ,
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11-27-2012, 07:29 PM | #10 |
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Re: Lean Condition back fire .
Patrick& Duffy , I did try the cap but its worth looking at again .
Steve Thanks for allthe filter posts,it had the problem prior to attaching the filter but there was crud in tank then. |
11-27-2012, 07:47 PM | #11 |
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Re: Lean Condition back fire .
Ted,
Also, with the see through filters, (as Steve mentions in reply # 8 above), have experienced that everything can appear fine with the filter full of fuel for a spell; then all of a sudden, one sees an air pocket inside the see through filter & the engine begins missing. How did the tank dry after filling it with water? Any possibility of droplets of water settling to the bottom of the tank? Always takes a while to clean out a tank that set up for some time -- sometimes: 1. Fill tank with about 4 gallons of fuel & slightly shake car sideways; &, 2. Drain through a white cotton sock into 5 gallon container; &, 3. Then Repeat 1. & 2. several times until white sock stays clean. |
11-27-2012, 08:33 PM | #12 |
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Re: Lean Condition back fire .
H,L We added a quart of alcohol between drinks and 3-4 gallons gas only, no flushing ?
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11-27-2012, 08:40 PM | #13 |
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Location: Illinois
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Re: Lean Condition back fire .
I have not tried this,but the dirty leg looks like a great solution to crud in the tank.
http://www.fordgarage.com/pages/kellyshutoff.htm John |
11-27-2012, 09:06 PM | #14 |
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Re: Lean Condition back fire .
I like that one John ,Thanks
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11-27-2012, 09:33 PM | #15 |
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Re: Lean Condition back fire .
You have probably heard; "90% of carburator problems are electrical". Something to think about! Ron W
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11-27-2012, 10:06 PM | #16 |
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Re: Lean Condition back fire .
Ted,
That's the main problem -- between drinks, you did not "drink" the quarts of alcohol -- it probably would have helped. Flushing works. |
11-27-2012, 10:47 PM | #17 |
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Re: Lean Condition back fire .
I have heard that John ! I said the same thing to the owner, it certanly proves true with FH v8s ,
Yeah H,L . Maybe it was just the fumes .LOL This is the offending vehicle ,Checking the Diz. Last edited by FlatheadTed; 11-27-2012 at 10:53 PM. |
11-27-2012, 11:34 PM | #18 |
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Re: Lean Condition back fire .
Adjusting the GAV makes no difference .not really .Once it backfires,, will it continue to backfire if throttle position doesn't change.I think it does, and then it slows down .Its gets worse when you are accelerating
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11-28-2012, 10:17 AM | #19 |
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Re: Lean Condition back fire .
You probably checked this, but remember that the tank shut off valve has or should have a small screen in it to stop crud, and if its plugged it will slow down the flow. Iceman
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11-28-2012, 10:58 AM | #20 |
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Re: Lean Condition back fire .
check your points and codenser you never know does not sound like gas
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