back fire 31 model a

What is your procedure when you start your A? Where are the levers, do you use the choke, where is the GAV set?

Let us know what procedure you use.
 
Any un-burned fuel escaping through an exhaust valve during compression can cause an after fire (explosion in the exhaust system). Causes could be a sticky or burned valve, valve not seating well, cam timing could be off, or intermittent ignition troubles.

A back fire through the carburetor is usually caused by a lean condition with the carburetor. This can also be caused by a leaky or sticky intake valve. May also be an intake valve adjustment or cam timing problem.
 
ajusted timeing spark is up choke is out i will have to check timeing when it was running no power under load len
 
if it did not backfire prior to adjusting the timing, there's the problem. follow this procedure:
http://www.abarnyard.com/workshop/timing.htm

do you use the Ford dist body, or a cap with wires to the spark plugs? With a cap, the wires can get crossed and it will backfire when trying to start, but will not start. To get the timing that far off using the original dist body, you have to position the rotor incorrectly.
 
lenmissy said:
what causes back fire when trying to start 31 model a len
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From yesterdays thread Backlash 31, It seems that you have got the timing way off. after reading Pat in Santa Cruz post it occured to me that you may be tring to set the rotor tip with the wrong contact in the distributor cap body. I will try again to walk you through the timing process that I use. If you are standing on the passenger side of the engine snap the clamps and remove the top distributor cap that the coil wire connects to. Leave the distributor cap body that the plug wire straps connect to in place. You can look in to the distributor and observe the rotor and the contacts in the distributor cap body that run through the cap body to where the spark plug wires connect. The front contact on the passenger side in the distributor cap body is the number one contact. When the timing pin drops into the indentation on the timing gear, lift off the rotor and loosen the slot head screw that holds the distributor cam. place the rotor back in place and rotate the cam untill the trailing or rear edge of the rotor tip is pointing at the number one contact in the distributor cap body with no clockwise backlash. Go back and read my posts yesterday on backlash and maybe it will be easier to understand. If you try my method and try to add in part of someone elses method you will end up with an engine that probably won't run at all .

I know it can be challenging for a person to set the timing for the first time, But you gotta get tough, its not that hard and setting points and timing is something that you really need to be able to do as a model A owner.

If you have an old rotor cap that is no good you can break off the little thin steel contact strip on top, then turn the rotor cap over and drill a hole about 7/16 through the rotor. you can install it on the distributor cam and you cou tighten the screw that holds the cam while holding the rotor in place with the pointer correctly pointed. After tightening the screw check that you don't have any clockwise backlash. You may need to repeat the loosen, adjust, tighten process a few times before you get the back lash out. This makes a good cheap timing tool that you can take with you in your tool bag. Good Luck.
 
lenmissy said:
When i tighten the screw the rotor can still move rotor back and forth one half in will try again today len
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you have a worn drive gear and/or shaft, and there is a lot of backlash. It is important to remove all backlash in order to get accurate timing. The cam moves counterclockwise when the engine is running. When timing it, rotate the rotor clockwise to remove the backlash until the points just close as the point rubbing block is moving down the lead edge of the cam. Then tighten the screw. If it moves further clockwise when tightening it, not all the backlash was removed. You want it so the points are just at the point of opening when all backlash is removed. It will still have the movement when rotated counterclockwise, but when the engine is running that will not be much of an issue. Using a tool like the one Purdy describes, or one of the metal rotor wrenches common from suppliers will help hold it in place as you tighten it.
 
lenmissy said:
When i tighten the screw the rotor can still move rotor back and forth one half in will try again today len
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Yes it will. If you re read my previous posts on backlash , the object is to move ALL of the backlash to the counter clockwise side where it does not effect the timing. You need to keep trying untill when you tighten the cam screw the trailing or back edge of the rotor tip is pointing at the number one contact and won't move back or in the clockwise direction. You will still have the 1/2 inch backlash but it will all be in the counter clockwise or foward direction, where it WILL NOT effect timing. It is also VERY important to check the points. I always set mine at .022 for optimum results. If the points gap is very much less than .018 it will cause you to loose power.

If you wanted to remove all of the backlash you may have to replace the distributor shafts, oil pump and distributor drive gear and maybe even the camshaft. If you are having trouble setting the timing, you can only imagine the problems and EXPENSE you would have with a procedure like that. If you adjust the distributor cam so that ALL of the backlash is in the foward or counter clockwise direction, the backlash will have NO effect. Keep trying, if it gets TOO stressfull stop and meditate. It is not that hard, My wife can do it and so can you.
 
lenmissy said:
thanks day 3 coming up i an getting close len
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I hear you!!! Probably one of the problems can be that when you tighten the cam screw the distributor shaft is turning a little bit and putting clockwise backlash at the cam and rotor tip. It may help if you hold the cam a little past the point that you want it to arrive, after tightening. This method will give the shaft a little room to turn as you tighten the cam screw without adding clockwise backlash. It will be trial and error for a couple of tries until you find the correct amount to lead the cam so that after tightening you won't have clockwise backlash. Any clockwise backlash at all will contribute to retarded timing and loss of power. Good luck.
 
Most vendors now sell a dist cam wrench (w/inst) that is simple to use and I think fool proof. After finding TDC on #1 And setting point gap, w dist cap on the dist but top off, install the tool over the cam, loosen screw, turn tool 2 turns CLOCKWISE until edge of tool touches #4 pin on the cap, tighten cam screw, Job done. Approx $10. Works for me
Paul in CT
 
OK so i have a question if the point gap spread is from .018 - .022 what is the difference in spark at the plug for each gap .018-. 019. 020. 021. 022 im trying to understand if the gap is wider at .022 than at .018 than the spark lasts a micro second longer? how does that help or hinder the performance ? also if the spark is jumping a wider gap doesnt that diminish the strength of the spark at the plug wouldnt some of the energy dissipate in the transfere through the points ?curious minds want to know and i too am trying to get my engine set just perfect enough that i can hand crank it with minimum number of trys, so far my engine starts anywhere between the 4th to 7th crank up from 9oclock to 12 position .
 
Points gap is all about dwell time or how long the points are closed and/or open. The condenser has to charge to specs during that period when the points are closed. If the point gap is wider, the dwell time is shorter. If points dwell time is erratic then the high tension spark will also be erratic. The condenser resists current flow if working properly so it keeps the primary side of the ignition from trying to jump the point gap as the points open. This keeps arcing of the points to a minimum and the points last much longer

Kerby
 
rollingsculpture said:
OK so i have a question if the point gap spread is from .018 - .022 what is the difference in spark at the plug for each gap .018-. 019. 020. 021. 022 im trying to understand if the gap is wider at .022 than at .018 than the spark lasts a micro second longer? how does that help or hinder the performance ? also if the spark is jumping a wider gap doesnt that diminish the strength of the spark at the plug wouldnt some of the energy dissipate in the transfere through the points ?curious minds want to know and i too am trying to get my engine set just perfect enough that i can hand crank it with minimum number of trys, so far my engine starts anywhere between the 4th to 7th crank up from 9oclock to 12 position .
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The wider gap of .022 gives the coil more time to build up before the next firing, it is only miliseconds but everything counts and it gives a stronger spark at the spark plugs. In other words more dwell and it has a similar effect of adding a model B distributor cam. The other advantage is with the wider gap, it gives more time before having to re set the points. as the fiber block wears down on the points the gap begins to close and you slowly lose power untill it gets to the point that it gets harder and harder to crank and sombody will have to re set the points. It is said that the points wears the most in the first 1000 miles
 
lenmissy said:
update still have not got the tin can running a friend is coming out on thurs hope he can len
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Sorry that my advise hasn't helped more. I don't know what else that I can say about backlash and the trailing edge of the rotor tip. I am already sounding like a broken record. Maybe by now, you have the timing correct and other problems are keeping it from running. Maybe the spark plugs are wet and the battery is getting low. If the battery is low, in many cases it won't have enough power to turn the starter and fire the distributor. You need a strong blue spark. Maybe you have the dreaded so called modern points, they are hell to adjust and famous for shorting out with no visable reason.The list could go on an on. All I can say is good luck and keep us posted.
 
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