Logo
FULL SITE MENU

1975 15 hp vibration or miss at part throttle

D

Dieter

Advanced Contributor
Hi folks,

spent a a good amount of time last summer getting a 1975 15 hp model 15554c, serial E0002504 back in good working order. Main issues were starting and stalling out. idle mix screw had no effect on performance so rebuilt carb with new float, new water pump, new fuel pump, was not perfect but running very smooth. Next week wouldn't start, ohm'd the coils and they were both bad. Replaced both coils fired right up and started amazingly easy(obviously coils were big part of issues). Didn't test it on the lake and decided to go the next step and replace the points and condensers. Set .020 gap when on the set part of the crank etc. ever since then at low throttle settings tends to vibrate until throttle is 1/3 open then smooths out and engine has good top end power. Also should not replaced plugs with iridium S that were one step hotter as my brother trolls a lot for trout and wanted to keep plugs from fouling.

Any my ideas why it may vibrate? Recheck the points?
 
On both sides of the magneto plate are two sets one for each cylinder, the single mark on the bottom of the flywheel should fall between the two marks on the plate.
 
Thanks for the replys , assuming it is off where do I adjust to get it back in time? Does the magplate have adjustment or do I have to readjust the points?

Thanks for your help
 
Point gap is the way to adjust timing. With that ignition start with setting the points at exactly .022 and then see where it sits there ia a special tool for setting the points with the flywheel off but probably not cost effective to purchase one. You can use a ohm meter just disconnect the condensers from the points. Then connect a ohm meter set to diode hook one lead to ground and the other to the points. Put the flywheel back on and turn the flywheel slowly until the points open. The mark on the flywheel should be in between the two marks on the plate the moment the points open. Oh yea you need to disconnect the points wire from the ignition coil that wire tells you when the points open.
 
Last edited:
Ok got it thanks.

Should have just left the old points in as it was running fine after coils, never started so fast, never saw such a hot spark on this engine.

In the 40 years this motor has been in my family, never adjusted the points so I appreciate the tip.
 
Dieter said:
Hi folks,

spent a a good amount of time last summer getting a 1975 15 hp model 15554c, serial E0002504 back in good working order. Main issues were starting and stalling out. idle mix screw had no effect on performance so rebuilt carb with new float, new water pump, new fuel pump, was not perfect but running very smooth. Next week wouldn't start, ohm'd the coils and they were both bad. Replaced both coils fired right up and started amazingly easy(obviously coils were big part of issues). Didn't test it on the lake and decided to go the next step and replace the points and condensers. Set .020 gap when on the set part of the crank etc. ever since then at low throttle settings tends to vibrate until throttle is 1/3 open then smooths out and engine has good top end power. Also should not replaced plugs with iridium S that were one step hotter as my brother trolls a lot for trout and wanted to keep plugs from fouling.

Any my ideas why it may vibrate? Recheck the points?
Click to expand...

engine not synchronized
 
The timing fixture is nothing but a " dummy flywheel "------------You can use the timing marks on your flywheel to accomplish the same thing !
 
Back
Top