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maa37maa

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I have a 86 350/260hp and when i am running wide open for a while i will start to lose power constantly losing rpms til it goes dead. It is also missing when it is trying to plane out but clears up after on plane. Ive replaced coil, rotor, dist cap, plugs, wires, fuel water sep, and put a new accelerator pump in carb, and cleaned the filters but they looked good. Any ideas what cld be causing this problem? Thanks
 
When it's dead is there spark? Have you checked compression? You have replaced every ignition part but the sensor assy. under the rotor and the amplifier. If the sensor is rusted it could be the problem. But, since it slowly loses RPMs it sounds like the amplifier is dying.

Check the sensor first; replace if rusted. Check the wiring to the amplifier for a crack or corrosion at the connectors. I recently posted TB ignition test procedures. Search for them and perform them when it dies.

Tests for Thunderbolt Ignition:


W/ignition key on AND BILGE WELL VENTILATED OF GAS FUMES!!!


Check the kill switch first!


#1 - Connect your voltmeter neg. lead to the engine ground and pos. lead to the white/red wire terminal at the dist. It should read 12 volts.

#2 - If 12 volts are present, remove the coil spark wire from the distributor and connect it to a spark gap tester to ground. Remove the white/green lead from the dist. terminal. Turn the ign. key to on and strike the white/green lead to ground. If there is spark, replace the ignition sensor in the dist.

#3 - If there is no spark, substitute a new coil and repeat test #2. Now if you get spark, install a new coil. NO SPARK, replace ign. amp.

#4 - In #2, if there is No voltage present, disconnect the white/red wire and check it again for 12 volts. If 12 volts is present, replace the ignition sensor inside the dist. cap. If no 12 volts present w/it disconnected--ignition amplifier is shot and must be replaced.
 
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Why is it that some people wouldn`t think of running their car or truck wide open but think nothing of doing it to their boat?
 
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