Super MD question...

Adam Wiles · Apr 19, 2011

So I finally got some money and time together and started to work on the SMD. When I got the tractor, the gas side was in pieces. I've rebuilt the carb, new fuel line, new plugs and wires, replaced the mag with a battery dist., and adjusted the decompression linkage (which was WAY out). I went for a start and she took off and ran solid for about 5 seconds and shut off... After cranking for a bit she started again, but only for 5 seconds. It's almost as if the ignition timing is "running out". I put a distributor off of a IH M (gas) on the tractor. I don't know if they used the same distributor for both or not.

Any help would be great! Thanks

andymd · Apr 19, 2011

a md dist.rotates oppisite direction of a gas motor need to get the correct distributer

pete 23 · Apr 19, 2011

Dist on a gas m turns opposite direction of a MD so if you use a gas dist, when engine picks up a little speed the spark will retard, not advance. Also, the diesel has a very small degree of spark advance, like 8 degrees whereas a gas m may have 40, 30, or 22 depending on dist.

Adam Wiles · Apr 19, 2011

Gotcha. Thanks for the quick and informative replies!

Bob M · Apr 19, 2011

Could be it's not an ignition problem. Rather I suspect the carb's running out of gas.

Try starting it again. Then when it quits, immediately pull of a plug wire, stick a spare plug on it then crank the engine and check for spark. If you see a spark you know the problem is fuel-related.

I'd then check for fuel flow into the carb bowl. Try opening the bowl drain with the starting lever in "gas" mode - you should get a steady stream of gas out the drain.

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Incidentally the SMD and M distributors are NOT interchangeable. The they rotate in opposite directions (the M clockwise, the SMD counterclockwise). Consequently the M distributor will give an advance that's opposite what the engine requires. In addition they have different vastly different advance timings which only makes the timing mismatch worse.

Farmaller · Apr 19, 2011

It's running out of gas, check float and fuel line.

Adam Wiles · Apr 19, 2011

I will check the fuel again but I believe its a timing issue. You can hear the engine change as the timing comes back in as its cranking, she fires off for 5 seconds and then the timing runs away from it again. Its consistant. But I totally understand what you guys are saying. I will check the fuel system again as well.

Bob M · Apr 19, 2011

OK - if you have an M distributor, the "timing going away" could indeed be the problem. Here's what I'm thinking:

The stock SMD distributor has an 7 deg advance. The stock M distributor has 40 deg advance. However since the M distributor is being spun "backward" on an SMD, the 40 deg advance actually becomes 40 deg RETARD.

Consequently if the distributor is timed at correctly at TDC with the engine stopped, when the RPMs come up the timing will be 40 deg AFTER TDC, not the 7 deg BEFORE TDC the engine requires. Ie. the timing will be retarded 47 deg from ideal at speed.

Ideally installing the correct distributor for the SMD is the fix. However you can probably get it to run using the M distributor if you disable the centrifugal advance mechanism so the spark occurs at TDC regardless of RPM.

Adam Wiles · Apr 19, 2011

That makes perfect sense! I'm hoping to get to it Saturday. Ill keep you all posted. Thank you for all your help! You guys are great!

Adam Wiles · May 4, 2011

Just to update you all... I got a MD dist and put it on yesterday and she fired right off and ran great!

Thanks again for everyones help and input!

Super MD question...

Adam Wiles

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andymd

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pete 23

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Adam Wiles

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Bob M

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Farmaller

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Adam Wiles

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Bob M

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Adam Wiles

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Adam Wiles

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