Backfire through carb -Help !
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From: Lancaster SC ,
Backfire through carb -Help !
OK fellow Y blockers. 272 recently rebuilt, installed in a 55 Effie. Put on new wires, dizzy cap, rotor, points, condy , plugs whole schlmeel. Engine developed a putt putt and would put blue flame out pipes at idle. Finally tracked down a cracked dizzy cap. Problem solved. However, now, Idle is fine, but when pushing accelerator at idle, I get a popping back through carb. I have adjusted timing by marks on pulleys. Idle is perfect and cranks when looking at the starter button, much less a small touch of the starter button.I have an idea the timing is not advancing. The carb has a port on the side and I plugged it to the dizzy. When removing the line to the dizzy in order to set timing, I don't feel a lot of vacuum from the port. as a matter of fact almost none.
My pulleys only have a single mark on both pulleys. I am aligning my pointer with that. Am I timimg right or is there another mark somewhere?
Thanks for your help.
Bubba
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From: Southern New Hampshire
That vacuum port on the back of the carb bowl is venturi vacuum and controls the 54-56 Lodomatic distributors. The vacuum works exactly in reverse of the later style dizzies. It must be plugged when using a 57 and later dizzy.
A backfire thru the carb usually takes out the power valve. You can replace with a similar one or get the new style that wont blow. You need to do a slight bit of grinding to get it to fit as it is wider; nothing fancy involved.
Since the damper is a 2 piece affair with a rubber seperator they have a habit of seperating over time. This will give erratic timing readings. If you have the points and dwell set properly then you can pretty much time by ear anyway. A Y doesnt need rocket science.
A backfire thru the carb usually takes out the power valve. You can replace with a similar one or get the new style that wont blow. You need to do a slight bit of grinding to get it to fit as it is wider; nothing fancy involved.
Since the damper is a 2 piece affair with a rubber seperator they have a habit of seperating over time. This will give erratic timing readings. If you have the points and dwell set properly then you can pretty much time by ear anyway. A Y doesnt need rocket science.
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From: Lancaster SC ,
312 I have taken the wires off and redone them 3 times. I believe it is a timing issue more than a carb issue. I may switch carbs and try it and see if I still get the backfire.
286Merc Thanks for your info, I probably ought to just go ahead and put a kit in it anyway, just to eliminate any problems. You're right about the Y not being rocket science, they are just good dependable low tech engines with awesome torque.
Bubba
286Merc Thanks for your info, I probably ought to just go ahead and put a kit in it anyway, just to eliminate any problems. You're right about the Y not being rocket science, they are just good dependable low tech engines with awesome torque.
Bubba
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From: S.C.
Bubba, What kind of carb are you running? I run the original Holly (ford script) in my 54 and had to go thru the car a couple of times to make sure all of the ports were clear....then I got good vaccume from it.
Also have you had the dizzy out to check the condition of the dizzy drive gear for wear? Some of these older carbs like mine also had a "backfire valve" kind of like the power valve....are the passeges clear to it as well?
Hope any of this helps, good luck... Ed
Also have you had the dizzy out to check the condition of the dizzy drive gear for wear? Some of these older carbs like mine also had a "backfire valve" kind of like the power valve....are the passeges clear to it as well?
Hope any of this helps, good luck... Ed
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From: Southern New Hampshire
All Y block 3 bolt Holleys had a spark control valve in the cast iron base. It is NOT a backfire valve but instead adjusts the vacuum signal to the venturi port in conjunction with the vacuum pulled down the air horn. Spark control means adjusting the advance diaphram.
These valves do get carboned up and become non functional after time but the result is usually pinging under WOT.
These valves do get carboned up and become non functional after time but the result is usually pinging under WOT.
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From: S.C.
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From: Lancaster SC ,
I'm running a later model Motorcraft 2 barrel carb. I believe to be a 2100 model.
It does wonderfully at idle but when you hit the accelerator hard at idle it pops back. I may just go ahead and rebuild it anyway. My goal is to acquire a 4 barrel carb and intake.
Bubba
It does wonderfully at idle but when you hit the accelerator hard at idle it pops back. I may just go ahead and rebuild it anyway. My goal is to acquire a 4 barrel carb and intake.
Bubba
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From: Maryland
Did you change your distributor with your carb? If not you will need to get a 57 or newer distributor if you want to run a more modern carb. I think that may cause your back fireing problem.
Last edited by 57_ford; Oct 24, 2004 at 03:14 PM.
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From: Lancaster SC ,
Thanks guys. I was running a later model carb but I think I'm going back to the old one. Just can't seem to ID it. No tags, just the number 102 on the side of it. Gonna take it to the local autoparts guy and let him get a kit for me and hopefully he can ID the thing.
57 Ford, No the distributor wasn't changed
Thanks
Bubba
57 Ford, No the distributor wasn't changed
Thanks
Bubba
More Turbo
Joined: Mar 2004
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From: Salem
Work on the carb just as you have and everyone has suggested. If that does not do the trick, then..... many years ago I too had this problem. I picked up a couple extra carbs and went through two rebuilds of them - still, pop, pop, pop (sounded like an old two stroke engine). I was perplexed. I worked at a filling station at the time and the lead mechanic started messing around and noted that the intake manifold was sucking air at one of the heads - not much, but just a little tiny bit. We pulled it and put in a new gasket - worked like a charm and I had a nice new carb to boot. Gas milage picked up as well.
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From: Houston U.S.
Originally Posted by 55Bubba
OK fellow Y blockers. 272 recently rebuilt, installed in a 55 Effie. Put on new wires, dizzy cap, rotor, points, condy , plugs whole schlmeel. Engine developed a putt putt and would put blue flame out pipes at idle. Finally tracked down a cracked dizzy cap. Problem solved. However, now, Idle is fine, but when pushing accelerator at idle, I get a popping back through carb. I have adjusted timing by marks on pulleys. Idle is perfect and cranks when looking at the starter button, much less a small touch of the starter button.I have an idea the timing is not advancing. The carb has a port on the side and I plugged it to the dizzy. When removing the line to the dizzy in order to set timing, I don't feel a lot of vacuum from the port. as a matter of fact almost none.
My pulleys only have a single mark on both pulleys. I am aligning my pointer with that. Am I timimg right or is there another mark somewhere?
Thanks for your help.
Bubba
The backfiring through a carburetor is ussually points that are closed, or crossed wires on yhe distrubuter wires or cap, it can also be the usiing of pluugshat arenonresiston......Janet
MAKE SURE YOU ARENT USING RESISTOR PLUGS, with a points system that will cause backfiring, look on your plugs and see if it has an R on it, if it does, this is your problem
Last edited by Janet40; Oct 30, 2004 at 09:31 PM.
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If you have checked carb, wires and timing and still have backfiring, check the hold down screw on the condenser in the distributor, I had a 390 that drove me crazy for weeks back firing through the carb, rebuilt everything including installing new carb. Finaly gave up and took it to local shade tree mechanic shop, told him my problem and he went straight to the distrbutor and tightened up that hold down screw and all my back firing went away.
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