Hi, I have a Lowell ported 1390 GPR.

The last time I was out (91.3RAD) it ran great for 30 minutes then I took a 10 minute break on the water. Started it up and it was bogging off the line (wet plugs but sounded like a lean bog) when you pin it off the line and continued to bog the rest of the day off the line. This has happened in the past testing with different jetting setups. It has never happened with an overly rich part throttle jetting only when i try to lean it out so it does not load up at idle.

I took the ski out for another ride today (92.5 RAD). I did not change anything except that I added 6 more gallons of gas to fill up the tank. It ran great no loading up(plugs were dry) and a peak of 7280 rpm with a 15/25. This was with the 120/95g/157.5 and BR9ES plugs. I did high speed runs prolonged idling and let it sit after running it. I could not get it to bog.

The cylinder head was slightly warm and the cylinders and the stinger were a little bit warmer. The carbs/fuel pumps were cold. So that rules out vapor lock and heat soak ofthe fuel system.

Any ideas on what would cause this?