Re: Pulsating 15hp detuned down to a 9.9 question

[johnyrude200]

I figured out the issue. After tracing my way back all the way to the end of the fuel system, I found the leaf plate (not the leaf valves) actually had wear spots where the end of the leaves flutter against that plate. It was allowing about a 1/2mm gap to stay open in 3 of the 4 leaf valves. Instead of the plate being perfectly square where the leaf valve flaps lay flat and rest, it was rounded off. This would explain the irratic operation at mid range. Either they were allowing enough fuel to idle OK, or they were wide open for WOT. But in between, FORGET IT!

After checking the carb 3 times, checking the pickup 5-7 times, double checking fuel lines and pump, I had no other choice than to get more invasive. Thankfully this solved the issue.

The motor still has a little bit of flutter at the mid range sometimes (no rhyme or reason for it have a small RPM fluctuation, even despite holding the throttle steady), but it is running at an acceptable level.

The customer wanted a 9.9 for a 10 foot inflatable for his kids, and also the option to switch back to a 15hp in the future if necessary. This 15hp manifold did not have shims on the leaf plate. The donor motor I took for a new leaf plate from was a mid 80’s 15, and had the shims.

If interested, I can post some pictures of the worn reed plate next to a known good one.