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Merc 700 Ignition Problem

M

marathon60

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"I have a 1961 Merc 700 that w

"I have a 1961 Merc 700 that will not run. Fires immediately when key switch turned to "start" but dies when key released and moved to "ignition." Have 12 volts at coil when in "start" and 3.3 volts when in "ignition" (after current passes through resistor). With starter disconnected and switch held in "start" can pull start the motor and it runs fine (as fine as a 45-year-old motor can run, anyway)--as long as key is held in start. Motor dies when key is released and returns to "ignition" position. Any ideas on what to check next will be highly appreciated."
 
Sounds like you have a ballast

Sounds like you have a ballast resistor. Put a jumper wire across the resistor and try it again.
 
"Partial success--I tried the

"Partial success--I tried the jumper and it worked (thanks, IBNFISHN). The motor runs fine with the jumper in place--but is that a permanent solution? The repair manual seems to indicate that full voltage at the coil can burn out the breaker points at low RPM.

Since jumping the resistors worked, I focused on them. The resistors are 3.2 ohms each in a parallel circuit. They look like coiled wires in a rectangular ceramic sleeve.

I checked the power with the key in the run/"ignition" position (thanks, Guest) and it seems OK. Initially, with the key in the "ignition" (run) position, I was getting 12 volts before the resistors and 3.3 volts at the coil after the resistors. I measured each resistor at 3.4 ohms--a little high but within tolerance according to the manual. In parallel the set is about 1.7 ohms. I cleaned all the terminals and reassembled. Afterwards I got about 6.2 volts at the coil but she still would not run with the key in the "ignition" position.

Does anyone know how many volts the coil should be getting through the ignition circuit? I found another post for a different engine (of questionable relevance, I know) that said the coil should be getting 9-10 volts.

Also, these are almost-new coils. They are of a new part number that superceded the old part number. They say "external resistor" on the casing, so I don't think the problem is that the coils have their own internal resistors.

Thanks again for any ideas on what to try next."
 
M. Dwyer
My Mercury repair ma

M. Dwyer
My Mercury repair manual states that some 700 models use the Merc 1000 type ignition system. The ballast resistors are connected in series
for these. You do not say what type you have. This pertains to the full gear shift 850 and 700. From the KIEKHAEFER repair manual.
Nothing sounds like a straight SIX at 5500 RPM.
Nick in TX
 
"Thanks for the reply, Nick.

"Thanks for the reply, Nick. I have the Merc 700 FGS with resistors connected in parallel. I do not have my manual with me at this time, but the wiring matches one of the Merc 700 configs shown in the manual (I think also by Keikhaefer--got it from Grubbs Marine). It is an awesome motor when running, and looks impressive and BIG even when not running (must have been designed by a Texan!). I have it pushing a 15-foot 1960 Glasspar Marathon. Hopefully will be out on the water again soon.
Mike"
 
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