Here's my problem ....I have a 632" BBC with 13.7:1 naturally aspirated (no start retards or motor reatrds). My boat worked fine when I put it on the trailer for the winter last year....move forward to May of this year and i decided to install a MSD Digital 7 programable #7531 so i could take advantage of a launch program and a diverter timer.
For the last 12 years I had been running a MSD Digital 7 Programmable Plus with a crank trigger that worked just fine (but you couldn't run a launch control out of my old MSD box). Swapping out the 2 boxes was easy and all the same wiring plugged right in......1st time out the boat would hardly run off idle finally diagnosed that the crank trigger went bad over winter (bad luck)...replaced the crank trigger boat worked good for 1 day, then the following weekend (at the CP Regatta) it wouldn't run over 7,000 rpms.....it runs hard up to 7k but almost acts like theres a Rev limit and the boat surges. I went to the lake last Monday and screwed around and still have issues.
I checked the the MSD program and had 2 other people that have been using the programs for a few years and all of my Rev Limits are set correctly (7,800 rpm) so its not that...I sent the box and coil (I run a HVC #8251 but I ordered a #8261 yesterday to try) back to MSD to get checked out and their fine....checked the float level and fuel pressure an everything is good there too....did a plug check and they look great (same jetting/set-up I had for the last 3 years)...I checked the timing, rotor phasing, ect. everything good there....when you put a timing light to the motor it doesn't jump around so I wouldn't think the pick-up polarity swicthed??...I run the shielded gray crank trigger pick-up so interference should be an issue....I replaced the spark plugs (gapped at .040), wires, checked ground at the box and the cyl. heads, ect.... Now I'm to the point of trying another coil, replacing the cap and rotor (they looked fine), and flipping the polarity of the crank trigger pick-up, after that there's nothing else to replace or check except trying another box.....the motor should pull around 7600rpm.....The only thing I changed from last year to this year was the MSD box....any help or ideas would be great...thanks guys