spark advance 100 hp

[B.D]

1989 100 hp #oc135219: Just cleaned the carbs and rebuilt the fuel pump. This took care of the preformance problem I was having. After repairs I put it back into the water and the idle was high (1600), and the idle was rough. I tried to adjust the throttle cable which didn't help, tried to adjust the low speed jets (in gear), didn't help. So I started playing the throttle lever or spark advance lever?? It made the idle come down and the idle to smooth out. Looked like the a adjustment screw cam loose. So I adjusted the screw so the idle is about 800 rpms and then readjusted that screw until it ran smooth; to much it would start to miss and die, the screw I adjusted was the second one from the bottom on that lever. Not even sure what the idle should be set at for this modle.
Seems to be running great now.

Question: Could I get engine damage if the advance timing is off? And how do you set it? I have a picture of the screw if someone needs to see it.

The other question was why didn't adjusting the slow speed screws do much. The only change I noticed was when they where almost turned in all the way. I put them out about 1 1/8 turns.

 

[hkeiner]

Re: spark advance 100 hp

It is generally not a good idea to adjust things at random. There is a specific link and sync procedure for your motor and it should be followed in the order specified in the manual. Each step is dependent on the previous step being done correctly. If a previous step (setting) is incorrect, then you may be over compensating with a latter step (setting) to get the idle RPMs right. However, this is not the way to get optimal performance or results. The missing could be the result of the idle jets being adjusted too lean. A too lean idle mixture can cause missing that sounds like a sneeze.

It is very important to set the WOT timing according to the specs for your motor. If timing is advanced too much, you can get knock and eventual cylinder damage. You may not hear the knock until it is too late. If timing is too late, you lose performance.

The idle speed timing is a different matter. An idle timing range (rather than a specific value) is specified in the manual (such as 0 to 9 degrees ATDC) and your idle timing should set somewhere in this range to get your idle speed RPMs to be within the specified RPM range (such as 650rpm - 750 rpm) while in forward gear. You can use an inductive tachometer clamped to a spark plug wire to measure low speed RPMs. The tach on your boat's dash is not accurate or detailed enough to use.