1989 90 HP missing

[heyblue]

Good compression on all three cylinders, and all within a few lbs of each other.
Spark on all three, used timing light on each cylinder one at a time while engine was running.
Seems to be missing, so blocked the inlet to each carburetor one at a time. blocked #1 engine bogged down from flooding, recovered after removing block. blocked #2 same results. blocked inlet to #3 carburetor and no change in engine performance. What would be the most likely reason? Thanks in advance

 

[Bosunsmate]

Good compression on all three cylinders, and all within a few lbs of each other.
Spark on all three, used timing light on each cylinder one at a time while engine was running.
Seems to be missing, so blocked the inlet to each carburetor one at a time. blocked #1 engine bogged down from flooding, recovered after removing block. blocked #2 same results. blocked inlet to #3 carburetor and no change in engine performance. What would be the most likely reason? Thanks in advance

Can you see the fuel getting sucked up and out of the jets in the throat of that 3rd one?
You could swap the carbs around and see if it follows the carb then you know if its a carb or a reed, lower seal etc problem

 

[heyblue]

I did two things. The first, as I mentioned, I blocked the inlet to carb 3. When I removed my hand there was excess fuel in the throat, just like the top two. Second, I squirted starter fluid in each carb while the motor was running. Doing so in the top two caused the engine to bog (flooding I guess), squirting it in the bottom one had no effect on the engine speed. I though about an intake leak, but think shooting the starting fluid in would have had some effect.
Short answer to your question is maybe.

 

[enginepower]

I had the same issue on my 90hp and blew 2 switch boxes. I had a partially shorted trigger so I changed that but still blew the 2nd box. I found a bad coil causing feedback voltage and I haven't changed that yet but I'm sure it's the culprit. Before the box went down, I would get an unstable idle at times where the cylinder with the bad coil would not work but at high speed, everything runs fine. I noticed while checking voltage on #1 cyl with my homemade DVA, my multimeter would always freak out.

 

[Texasmark]

I noticed while checking voltage on #1 cyl with my homemade DVA, my multimeter would always freak out.

What do you mean freak out and what schematic and component part values did you use on your DVA?

 

[enginepower]

What do you mean freak out and what schematic and component part values did you use on your DVA?

The lcd characters go all over the place or mostly blanks out and i have to turn it off then back on (suspecting over 1KV is doing this which would have to be coil back feed. It will only do this when I take a reading on my #1 cylinder which I found has high/sometimes open circuit on the coil secondary resistance. I used 22uf cap with 1meg resistor. I haven't changed coil yet but I'm sure a new coil will fix this situation. High secondary resistance is deems it bad anyway.

 

[Texasmark]

The lcd characters go all over the place or mostly blanks out and i have to turn it off then back on (suspecting over 1KV is doing this which would have to be coil back feed. It will only do this when I take a reading on my #1 cylinder which I found has high/sometimes open circuit on the coil secondary resistance. I used 22uf cap with 1meg resistor. I haven't changed coil yet but I'm sure a new coil will fix this situation. High secondary resistance is deems it bad anyway.

Pull your test leads out slightly at your meter, just enough to get some metal showing and wrap a 1kv .01 uf or so, (not critical on size) ceramic disc capacitor right across the leads. 2 things could be affecting you: Voltage higher than scale selected (400v scale is what's recommended in the maint. manual) or high frequency interference picked up on the test leads from the ignition firing. The cap will fix the high frequency pickup, changing scales will fix the rest.
Oh....keep your fingers off the exposed leads.....but you knew that. Grin

Mark