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I am trying to fix up a basket case of a Challenger boat. It had previously sunk, and was not taken care of. We have repaired most things, and at least have it running again. The original engine was more or less a small boat anchor, so I cobbled an engine together from pieces/parts I had on the shelf, for the most part. The bottom end I wound up using is an RFI bottom end. I adapted the MAG housing, flywheel, magnet and stator/pickup, and got what was needed to make it a running engine. The top end is 97 carb 787, along with the rotary valve cover, and carbs. The original carbs were more corrosion than metal, so I acquired another set from another Challenger, rebuilt them with SBT rebuild kits, and new 1.5mm Needle/seats. The pilot jets installed were 65, but most everything I could find called for a 70. The Main jets are 142.5. I set pop off pressure at about 30psi, which should be in the middle of the range I found listed for other PWCs of the same vintage. Got the engine running, and it will start and idle OK, but as soon as you advance the throttle, it begins 4 stroking terribly, and will not rev cleanly. I have tried both the 65 and 70 pilot jets.
I found TDC (and marked the PTO flywheel), and rechecked the rotary valve timing, and it looks good. Put a timing light on it, and it sits at about 22 degrees at 3000 rpm. Timing and ignition pulses look steady and even at all speeds the engine will operate at. Tried replacing the spark plugs and the wires, no change. Plugs come out looking clean, but soaked with fuel. I have been through the carbs several times, and I cannot find an obvious issue. Does this with water running from the hose, or even if the water is cutoff. Tried choking it, to see if anything would change, and all it does is slow the engine down a bit. Tried hand pumping the accel pump, to see the effect of dumping raw fuel, and saw no effect.
I am thinking that possible problems are that the pop off pressure may need to be higher, and also that there could be some obstruction in the muffler somewhere. Lastly, the only other thing that could make sense is that I installed the pistons backwards, and the window of the piston is facing wrong, but I highly doubt I would have done that (or that it would run at all this way). Looking for any suggestions or input more experienced folks may have.
I found TDC (and marked the PTO flywheel), and rechecked the rotary valve timing, and it looks good. Put a timing light on it, and it sits at about 22 degrees at 3000 rpm. Timing and ignition pulses look steady and even at all speeds the engine will operate at. Tried replacing the spark plugs and the wires, no change. Plugs come out looking clean, but soaked with fuel. I have been through the carbs several times, and I cannot find an obvious issue. Does this with water running from the hose, or even if the water is cutoff. Tried choking it, to see if anything would change, and all it does is slow the engine down a bit. Tried hand pumping the accel pump, to see the effect of dumping raw fuel, and saw no effect.
I am thinking that possible problems are that the pop off pressure may need to be higher, and also that there could be some obstruction in the muffler somewhere. Lastly, the only other thing that could make sense is that I installed the pistons backwards, and the window of the piston is facing wrong, but I highly doubt I would have done that (or that it would run at all this way). Looking for any suggestions or input more experienced folks may have.
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