706 won't stay running

Dayermaker · Aug 29, 2022

I recently tuned up a 706 gasser that had
been sitting for several years. I installed new plugs
and wires, added an electronic ignition
coil and rebuilt the carb. I Had it
running fine for a few weeks but the
engine ran away 1 day while I was mowing.
So I shut it down immediately, I thought
it was unusual for a gasser to run away
like it did. After that it only runs if
the starter button is being held down, but
it runs full bore no matter where the
throttle or choke is set at, so now its
been sitting again, any ideas on what I
should look at?

James Babcock · Aug 30, 2022

The butterfly valve on the throttle shaft might have come off.

casecollectorsc · Aug 30, 2022

Had that happen on a 1930 model L I bought. Started missing on one cylinder. Took the intake off and found the throttle plate from the carb covering the intake port. Previous owner must have had a runaway as the carb on it was intact.

Steve@Advance · Aug 30, 2022

Sounds like 2 separate problems.

The only running while the starter is held in is an electrical problem, the ciol is only getting power when the starter is engaged.

The runaway is either the throttle plate has come off the shaft, or there is a problem with the governor or linkage.

Roger Tomfohrde · Aug 30, 2022

Hopefully who ever put the electronic ignition on removed the ballast resistor. I am not sure that the electronic ignition would survive on 6 volts though. sounds like the resistor gave up. Agree with two problems.

rvirgil_KS · Aug 30, 2022

Only runs when starter button is held down is due an open dropping resistor or wire connection between ignition switch and coil input.

(An open is a broken path where there should be continuity, a short is a continuity path where there should not be one.)

My 706 diagram shows 2 wires off input coil post(+) One is bypass wire going back to starter solenoid, the other wire goes to the resistor and then through a couple of plugs and junctions back to ignition switch. Open connection could be anywhere in that path.

Resistor is used to drop voltage/current from 12 volt battery to operate 6 volt coil. Wire from start solenoid bypasses resistor when starter cranks the engine giving temporary 12 volts to the coil for hotter starting spark.

rvirgil_KS · Aug 30, 2022

added an electronic ignition coil

Did you change to complete electronic ignition system or just change the coil?

rustred · Aug 30, 2022

appears u got 2 things going on there. the run away is governor or carb problem. the no start is electrical.

706 won't stay running

Dayermaker

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James Babcock

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casecollectorsc

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Steve@Advance

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Roger Tomfohrde

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rvirgil_KS

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rvirgil_KS

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rustred

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