Hi,
This is my first time posting on this forum so I hope I have my protocols correct. I recently purchased a 2000 Donzi 35ZFC with two Mercury 250XS Optimax engines. The engines are a bit of a mix and match where the mid section and bolts ons were originally from a 2005 JP XL and the powerhead and mapping are from a 2006 250 XS 1E01045. It has taken me a bit of time just to sort that out. The previous owner bought them as a re-power from an offshore performance store in Fort Myers.
One of the engines seems to run very well. Smooth and strong all the way through. The other seems to pull well but misfires and runs quite rough at idle. I should mention the ECU's are only indicating that the pair have 85 hours of running time. So far I have swapped coils around with no improvement, changed spark plugs with the NGK iridiums properly gapped. took out the add on Racor fuel water separators and checked compression which is even at 120 across all cylinders on both powerheads. My pressures are as follows:
Air Fuel
Running 94 108
5 sec off 92 98
10 sec off 88 88
15 sec off 88 82
I've read in the forums that the tracker valve is often to blame for poor idling issues. Does that sound like it might be the issue here? If not where would you start?