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    New Rider - Need Some Tuning Advice

    Hello!
    I purchased a pair of 1999 GP1200s a few months ago, and I'm hoping to get a little input/advice on getting the carbs set up. Back story first.

    The kids are off to college, so the wife and I were looking for something fun to fill the garage with, and maybe entice them to come home from time to time in the summer. We'd rented jet skis on vacation a couple of times in the past, and everyone really enjoyed it. Other than that, and a small ski boat in college, I really didn't have much experience on the water.

    I found this pair on Craigslist for what I think is a good price. The PO told me one ski (we'll call it Ski#1) was good to go, but Ski#2 had low compression in the rear cylinder. I do a lot of motorcycle restoration projects including engine work, so I have a little experience and a good set of tools. I wasn't scared by the prospect of an overhaul.

    We brought them home and the wife and I took Ski#1 out for a test ride. It ran flawlessly and was a total blast. Much faster that the rentals we'd ridden. They must govern those down to ~35 mph for liability reasons.

    Next step was to dig into the engine issues. Ski#1 compression was 120 psi on all three cylinders. No surprise. Ski#2 was 120 psi on the front two and 100 on the rear. Not as bad as I expected, and it would actually start but sounded terrible. So I pulled the engine and tore it apart. It turned out to be worse than expected. One of the piston skirts on #3 had broken off, made it to the bottom of the engine and punched a hole in the lower crank case. I took the parts to a local speed shop, had the cylinders bored (they were still stock bore) and had the case welded up. Installed a new set of Wiseco pistons and put it back together.

    I also bought carb kits and rebuilt those while it was apart. As far as I could tell, the carbs had never been messed with. They were disgusting. It looked like there was mud in the pumps, surfaces were corroded and just an overall mess. Since Ski#2's carbs were so bad, I bought a set of kits for Ski#1 as a winter project. I also found a plugged oil feed check valve on the rear cyclinder. Culprit identified!

    The carb overhaul went fine, but I had trouble finding the factory spec to set pop-off. As near as I can tell it should be 50-55 psig, but searching forums I found several recommendations to go with 40 psig to improve starting (Ski#1 is a bear to start the first time). So I set pop-off at 40 and put it back together. I also set the low and high screws to the middle of the factory ranges rather than the "as-found" settings. I figured enough had changed that I might as well start from scratch.

    I put 10 gallons of 50:1 premix in the tank (oil system also cleaned, new hoses and in operation) and took it to the lake for break-in. It's got some hesitation off the bottom, but above 3-4000 rpm it hauls. According to the speedometer, it's a bit faster than Ski#1 (63 mph vs 60 mph). Toward the end of the day, it started to bog a bit more, and I had to play with the choke to get it to plane out. I suspect fouled plugs due to the break-in oil, but I ran out of time and it was starting to rain. I played with the low screws on the carbs a bit, but wasn't able to improve the situation. So there's still some fine tuning to do, but the good weather is over. It'll be next spring before I can get back to it.

    Now I've turned my attention to the carbs on Ski#1. I pulled those off last night, and they've obviously had some work done to them at some point in the past. Zip ties on the hoses are day-glo orange rather than black like on Ski#2. I haven't take the pump sides apart yet, but I did pull the coves off the N/S so I could check pop-off pressures before I completely disassemble. I can already tell these carbs are quite a bit cleaner than on Ski#2.

    Here's where my question comes in. I found pop-off on Ski#1 all in the 55-60 psig range. As I mentioned before, I've set Ski#2 to 40 psig. What do people with tuning experience find works best? Should I stick with higher pressure and live with hard starting? Could the lower pressure be contributing to the stumble at low rpm pn Ski#2? I'm not opposed to tearing back into Ski#2's carbs if necessary. I've got all winter. Thanks in advance.

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