Free start backfire question

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Model T Ford Forum: Forum 2015: Free start backfire question
Top of pagePrevious messageNext messageBottom of page Link to this message  By paul iverson freeport ill. on Thursday, June 25, 2015 - 06:57 pm:

on our 16 after tightining the swivil on spark advance rod it was only held on by cotter pin very loose. there is now no play. before no free starts. now I get 4-5 in a row. but if it is not a free start its a big backfire I dont want to blow out muffler. the only thing that changed is I guess it retards a little bit more. I dont think it should backfire should it? it starts very easy cold on crank with batt.fully retarded. when warm on mag. with lever advanced 9 notches no kick 2 or 3 pulls to start


Top of pagePrevious messageNext messageBottom of page Link to this message  By R. S. Cruickshank on Thursday, June 25, 2015 - 07:39 pm:

It could be that someone put beans instead of corn in the gas! (I couldn't resist it)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Harold Schwendeman - Sumner,WA on Thursday, June 25, 2015 - 07:59 pm:

Paul - Assuming that the loose spark advance linkage condition had existed for quite a long period of time, it's reasonable to assume that the ignition timing had been adjusted in such a way as to compensate for the sloppy linkage. Now that the linkage is tightened up, I'd bet that your ignition timing is at least a bit "out of whack".

P.S. Makes me think of George Carlin, who always said that he'd often heard of things "out of whack", but never heard of anything "in whack"! Ha, ha,.....harold


Top of pagePrevious messageNext messageBottom of page Link to this message  By Allan Bennett - Australia on Thursday, June 25, 2015 - 10:24 pm:

Paul, you can expect a change in the timing when you take the slack out of the linkages. A backfire means your car is firing before top dead centre, driving the crank backwards rather than forwards. You need either to crank faster so momentum takes the crank over TDC, or safer, a little more retard on the spark. If you can't get this just moving the lever, you will need to make the adjustment at the linkage to the timer.

Hope this helps.

Allan from down under.


Top of pagePrevious messageNext messageBottom of page Link to this message  By paul iverson freeport ill. on Thursday, June 25, 2015 - 11:13 pm:

thanks Harold and Allan about the timing but what I meant to say was with out cranking eng I put switch on batt. and then I move lever down slowly to get a free start so it would be far advanced when it backfires. mabey I should not do it that way.it looks like operator error! I think if it wont start on 4or 5 notches advanced I will retard it and lift crank it starts easy


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gustaf in Idaho on Thursday, June 25, 2015 - 11:22 pm:

As you move the lever down, you advance the timing, if the crank is stopped at before tdc then you will get a back fire. If I do not get a free start with the lever fully retarded, I can move the lever down very quickly and then back up quickly and sometimes it will fire and go backwards one cylinder and the hit on the previous cylinder and start, but you have to move the lever faster than the crank moves. This works about 10% of the time for me.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Georgetown TX on Friday, June 26, 2015 - 06:25 am:

You should not have to move the lever down to get a free start.


Top of pagePrevious messageNext messageBottom of page Link to this message  By paul iverson freeport ill. on Friday, June 26, 2015 - 11:54 am:

I think I got it figured out. when I had the play it was advanced like 1 or 2 notches now I get full retard it does start some times on turning on key if I advance 1 to 3 notches it starts often. then when I advance it all the way it backfires or sometimes starts. my anwser is if no freestart in 4 notches advance retard all the way and lift crank for a easy start.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Walker, NW AR on Friday, June 26, 2015 - 06:58 pm:

OT -- Gustaf -- I sent you an email message through the Forum system yesterday. Please check your junk mail folder, as those messages sometimes go there. I'd like to visit with you about WW-I Ambulances. Thanks.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, June 28, 2015 - 11:21 am:

When you pull the spark lever down the spark is occurring before top dead center not after = back firing. When staring the car on battery, the spark needs to be set to fire just after top dead center on full retard.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce in Georgetown TX on Sunday, June 28, 2015 - 11:33 am:

What Mark is saying is true. Your timing is not set properly. It should be set like this when the spark lever is all the way up:



I see folks talking about setting the timing using the position of the pin on the crankshaft. That scares me, because you don't know where the piston is when spark happens. You can easily measure the piston going down the hole using any object that can be inserted in the spark plug hole that allows you to feel the piston moving downward. A plastic coffee stir stick works perfectly.

Also, the diagram above shows a dimension of 1/4" and the roller just touching the contact in the timer. You should ignore the dimension, and set the timing so that the coil buzzes at exactly when the piston moves 3/16" down from TDC on the compression stroke with the switch set to BATT.

The diagram is OK if you have original Ford camshaft, crankshaft, timing gears, and timer. If you don't have all that, you should set the timing by piston position and when the spark really happens.

(Message edited by royce on June 28, 2015)


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Rose on Sunday, June 28, 2015 - 01:36 pm:

To me "Backfire" means that one or more cylinders are firing with a valve open.

I have seen lots of people assemble an engine and when trying to start it, Kerboom, then keep cranking until the battery is discharged and recharge it and crank until the starter is junk. bottom line when you hear kerboom, quit cranking until you find the problem.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Sunday, June 28, 2015 - 02:00 pm:

to backfire; to cause an explosion behind or before where it should be. To load up the muffler with too much raw fuel and have it fire back behind me! To have an engine fire back behind where is should causing it to try and run backwards! In both cases making a loud boom possibly injuring operators ears or parts on car :-)


Top of pagePrevious messageNext messageBottom of page Link to this message  By paul iverson freeport ill. on Sunday, June 28, 2015 - 06:49 pm:

thanks guys for all the info. what I was doing wrong was advancing all the way after I got a buzz it was the next coil that sparked is why it back fired. I have not had a back fire since. it never back fired when running I have checked the spark timming there is no fan belt on car so it is easy to see pin in crank. also I didnt understand the diff. with batt. and mag. and how to start it. I read a lot of old posts and I think I got it now I have learned a lot. a t is not like anything I worked on before


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Rose on Tuesday, June 30, 2015 - 04:37 am:

Mark: If the cylinder fires before top dead center or after dead center when you are cranking or running it, the pressure from the explosion will be trying to turn the engine counterclockwise or clockwise. You only hear a backfire when a cylinder has a valve open when the explosion happens. If your thinking was correct you would hear a backfire anytime the engine is running.


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