Doodlebug, magneto and carb

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Model T Ford Forum: Forum 2013: Doodlebug, magneto and carb
Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron on Thursday, September 05, 2013 - 11:46 am:

Got a lead from someone who knows I like T conversion tractors - so I went to take a look at this T doodlebug (see pictures). Guy who owns it and brought it this far over the last 15 years has never started it (non-starter engine and he can no longer crank). Very unusual intake/exhaust setup. Mag was just rebuilt and was putting out a spark (but being unfamiliar with external mags, that's all I can say - cannot vouch for the timing). Carb was a rebuild as well. Soooo....after putting in some gas, I spent about 2.5 hours exercising my cranking arm, trying to help him get it started. Nothing. The owner's prodigious use of starting fluid down her throat produced a couple of coughs and precipitated at least 4 carb fires, but that was about it. At various intervals, I would pull plugs (1, 3, 2) and all were largely dry - so my question: does the inverted intake and a standard NH carb setup prevent a mixture from being sucked into a combustion chamber? Oh, cannot vouch for the compression either (the old gentleman's compression gauge was inop).


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob McDonald-Federal Way, Wa. on Thursday, September 05, 2013 - 12:04 pm:

Did you check fuel flow to the carb.? How high is the gas tank?

Bob


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron on Thursday, September 05, 2013 - 12:23 pm:

Roger - bowl contained fuel - steady stream would come out when I'd open petcock on bottom.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron on Thursday, September 05, 2013 - 12:26 pm:

Tank is mounted to firewall - above the height of the sediment bowl. You can just make the cap out in the first picture and see the side of it on the far left in the second.

I'm just wondering if a standard NH can even deliver a mixture given this setup?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Kenneth W DeLong on Thursday, September 05, 2013 - 12:40 pm:

I think i would take the hot air pipe off the carb so with help you could check for strong suction? Dry plugs on 3 cyls suggest to me stuck valves?? Bud.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron on Thursday, September 05, 2013 - 12:52 pm:

These are older pictures. The pipe was off for the attempts to start. Owner previously had the head off and said valves were good. All of this is leading me to question the intake setup.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth from NC on Thursday, September 05, 2013 - 01:38 pm:

I would do a few things before you try again -
This is mainly about the mag since I think your intake setup is probably ok as long as carb is getting gas and is adjusted even remotely close (adjustment needle all the way in, then back out 1.5 turns, maybe just 1 turn.)


1. Pull the plugs and verify that none are gapped more than .018": the gap has to be closer for the high tension magneto. If they are not, and say something like .025" or more, then it's time to stop and pull magneto and have it rebuilt - the secondary is fried - may be worth trying as is though after you run through rest of list.

2. While plugs are out, turn engine over and verify that all valves are moving.

3. Do a "rough" compression check with thumb over spark plug hole while turning engine over.

4. Verify that magneto is wired correctly to plugs: if you are sitting in the passenger seat looking at the face of the magneto, the firing order is 1243, but starting on the far right and moving counter-clockwise - 3 oclock is #1, 1 oclock is #2, 11 oclock is #4, 9 oclock is #3.

5. Lay plugs on the head and turn engine over to verify you are getting spark.

6. Assuming you've made it this far and everything is ok - that looks like an impulse coupler on the back-side of the magneto (front side - grey part is magneto, black circular part is impulse coupler). You should fell that when you crank, there will be a spring loading and then the coupler will snap forward.

Turn the engine until you get #1 on TDC on compression - then go backwards until crank pin is at about .45 degrees. Remove shaft from engine block to magneto. Then take off the brown/black distributor face plate (this is what the spark wires are hooked up to - two screws, far right and far left). Be careful taking it off as the inside is essentially like a New Day timer, the block you are taking off is the face and there is a brush on a rotor connected to the magneto - it is sprung and may want to fall out if you snatch the cover off. With the shaft on the back disconnected, slowly and gently turn the magneto backwards until the rotor is at 6 oclock, then slowly turn forward until you feel the impulse coupler stop you. You are now setup to fire on #1. Re-install cover plate and make sure everything is hooked back up and ready to go.

Before re-installing the plugs, I'd remove the carb and blow through the manifold just to make sure nothing managed to nest in there.

Last but not least I'd hook everything back up - make sure spark lever on mag is fully retarded, pull gas down 3 notches, with the mag grounded (aka OFF) 2 quarter pulls with the choke, then turn mag on and give it a rip. Might take a few rips but if you went through all that other and it STILL doesn't work, then the manifold is probably the issue.

There's no reason to have the shaft that long - you could dramatically shorten the shaft put the magneto up where a generator normally is and go with a conventional exhaust manifold and intake.

Let me know what happens!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth from NC on Thursday, September 05, 2013 - 01:42 pm:

On #4 - I said that but I assumed that the mag normally spins clockwise (when viewed from the passenger seat) but after looking at the pic, if the gear driving the mag runs straight off the cam gear, then the mag spins counter-clockwise and thus reverses the order of the distributor rotation.

Something like this may also be the source of your problem - the mag can be set up to turn either way, but it doesn't work both ways, it has to be changed to rotate the opposite direction. I don't know enough about them to tell which way it needs to rotate - I just asked the guy at Mainely Magnetos to make mine rotate correctly based on my gear drive.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ron on Thursday, September 05, 2013 - 03:20 pm:

Seth - thank you for all of that. If I get the opportunity again, I will run through the list you laid out above.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Thursday, September 05, 2013 - 08:22 pm:

Also make sure to check your fuel mixture. Turn the adjustment screw clockwise until it bottoms out and you feel it stop. DON'T FORCE IT! Then open it up about 1-1/2 turns, and that should be enough to at least get it started (I would assume). When you get it running, you can tweak it from there.

Just something else to check.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Thursday, September 05, 2013 - 09:25 pm:

I suggest you oil the cylinders (teaspoon in each cylinder). You need some compression (which this will help) and it will reduce the drag. If you could tow it so the engine is spinning at about 500 rpm would really help. A tow bar would make half ways safe!! Oiling the cylinders has worked for me more than once


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Dumas on Thursday, September 05, 2013 - 10:18 pm:

Unless the mag has an impulse coupling, it will take a hellacious spin to get sufficient spark. As Les suggested, if you are sure about the timing, tow it to start.


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