Merc 5.7 Hiccup

[wryork25]

I need some help from the group, I have a carbed 5.7, I recently did a bunch of maintenance because it was running like trash (carb rebuild, plugs, wires, rotor, sensor in dizzy). It has a thunderbolt V in it. It is running very smooth other than a little hiccup, for lack of a better term. When I performed the timing adjustment I noticed it. At idle it has a little hesitation, you can see it with the timing light. It sporadically jumps timing from about 8 degrees to 10 degrees about every 30 seconds or so. When I set it to 10 it would jump from 10 to 12. I didn't want to over advance it so I backed it off enough that the high side was 10. Other than this the motor sounds great on the muffs and seems to do fine when I advance the throttle, which I can only do so much on the muffs. I have not had a chance to put it in the water yet. Does anyone have any ideas on what this might be or where to start?

 

[Scott Danforth]

have you checked the fuel filter contents in a clear container looking for contaminates?

 

[wryork25]

have you checked the fuel filter contents in a clear container looking for contaminates?

I drained the gas tank and put a fresh filter before this issue.

 

[Scott Danforth]

have you checked the filter contents? the new fuel could have loosened up crud in the tank and plugged up the new filter

could also have clogged the anti siphon valve.

 

[wryork25]

have you checked the filter contents? the new fuel could have loosened up crud in the tank and plugged up the new filter

could also have clogged the anti siphon valve.

Yes sir checked both

 

[kd4pbs]

I am trying to remember exactly how the thunderbolt V works. Does it have a flyweight advance mechanism in the distributor or is it electronic depending on RPM?

 

[Scott Danforth]

TB ignition is hall effect trigger with digital advance. The trouble shooting tree is in the stickies
However there was a design change from a 2-wire trigger sensor to a 3-wire (extra ground)

@wryork25 does your dizzy have the 2-wire trigger sensor or the 3- wire?

 

[wryork25]

TB ignition is hall effect trigger with digital advance. The trouble shooting tree is in the stickies
However there was a design change from a 2-wire trigger sensor to a 3-wire (extra ground)

@wryork25 does your dizzy have the 2-wire trigger sensor or the 3- wire?

originally it had the two wire sensor but I replaced it when I did the cap and rotor because it was looking real rough! It now has the extra ground.