BoLongo
Active Member
I sold my jets skis and bought a Seadoo Challenger 1800 twin 787s. The boat was a mess; after rebuilding the carburetors with Mikuni rebuild kits (learned that lesson on my jet skis) and flushing the old TC-3 oil and switching to Mystik JT-4 and new spark plugs I headed to the lake. My compression was in the low 130s so the engines were ready for top-end rebuilds and one of the cranks was making a lot of bearing noise. Within forty-five minutes of running on the lake, I burned a hole in the exhaust side of the starboard rear cylinder. I assumed it was a crank seal; the boat had sat in a field for a couple of years. I pulled both engines; the seized engine got new pistons and a rebuilt crank with new crank seals the other engine got new crank seals, honed and new piston rings. I pressured tested both engines, put everything together and headed to the lake.
I wanted to make sure the carburetors were calibrated right; I had three sets of new spark plugs. I motored through the no wake zone varying RPMs between 1500 and 2500 for about 5 minutes; checked all the spark plugs chocolate brown coating. Let the engine cool and installed a new set of spark plugs, varying the engine RPMs between 2500 and 4000 for about five minutes, checked the spark plugs chocolate brown coating. Let the engine cool, Re-torqued the heads and installed the last set of spark plugs. I was not going to take the engine over 6000 PRMs until the engines had more time to set the rings, so I varied the RMPs between 4000 and 5800 about four minutes in the starboard engine died, I knew I had just seized another piston. I pulled the Rave Valve, and I could see some light scoring on the piston skirt. Limped the boat back to the launch ramp and pulled it apart when I got home. Piston seized on the rear starboard engine. The jug will need honing and a new set of rings, so the damage was not that bad.
Here is where I need some help. I believe I am getting a lean condition in the high-speed circuit in the starboard rear carburetor. I remember when I rebuilt the carburetors the high speed adjust screw was a turn and half out. I thought that was strange (stock setting is 0). I know I was the first to rebuild the carburetors the screws still had the factory paint. I checked the jets; they are the stock jets, and the pop off pressure was within specs.
Is it reasonable to have a carburetor that needs the high-speed adjustment screw turned out one and a half turns to operate correctly?
Is there any way that the timing could be advancing on just the rear cylinder to create the lean condition at the higher RPMs, this seems very unlikely to me, but I am searching for answers.
I wanted to make sure the carburetors were calibrated right; I had three sets of new spark plugs. I motored through the no wake zone varying RPMs between 1500 and 2500 for about 5 minutes; checked all the spark plugs chocolate brown coating. Let the engine cool and installed a new set of spark plugs, varying the engine RPMs between 2500 and 4000 for about five minutes, checked the spark plugs chocolate brown coating. Let the engine cool, Re-torqued the heads and installed the last set of spark plugs. I was not going to take the engine over 6000 PRMs until the engines had more time to set the rings, so I varied the RMPs between 4000 and 5800 about four minutes in the starboard engine died, I knew I had just seized another piston. I pulled the Rave Valve, and I could see some light scoring on the piston skirt. Limped the boat back to the launch ramp and pulled it apart when I got home. Piston seized on the rear starboard engine. The jug will need honing and a new set of rings, so the damage was not that bad.
Here is where I need some help. I believe I am getting a lean condition in the high-speed circuit in the starboard rear carburetor. I remember when I rebuilt the carburetors the high speed adjust screw was a turn and half out. I thought that was strange (stock setting is 0). I know I was the first to rebuild the carburetors the screws still had the factory paint. I checked the jets; they are the stock jets, and the pop off pressure was within specs.
Is it reasonable to have a carburetor that needs the high-speed adjustment screw turned out one and a half turns to operate correctly?
Is there any way that the timing could be advancing on just the rear cylinder to create the lean condition at the higher RPMs, this seems very unlikely to me, but I am searching for answers.
