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  1. #1

    Waveblaster 760 Engine Rebuild Any Advice Appreciated

    So I bought a cheap waveblaster 2. The guy said he had rebuilt the engine but couldn’t ever get it to run right and already had replaced one piston that he put a hole in after the rebuild. So it ran when I got it but not very good and had around 150 psi compression on both cylinders. I first checked the carbs and the high and low speed were way off around 3 to 3.5 turns out on both so I pulled the carbs and went completely through them. I called Riva and set the carbs to their specs because it has a Riva red pipe exhaust on it. Their carb specs called for Main 110, primary 125, needle 1.5, spring 115, pop off 55, low speed 1 3/4 turns, high speed 1/2 turn. So now with the rebuilt carbs the ski ran a lot better than before, but it still wasn’t right. It was weak on bottom end just pretty slow on take off, then once you got going it would take off and seem to run really good. Well I ran around on the lake with it for maybe 10 minutes at the most and it just suddenly died, no weird engine noises or anything, it just seemed like it lost all spark. I came coasting to a stop and it would then only turn over and no attempt at firing. So I thought it was electrical for a while but finally I just decided I would check compression again. Front cylinder 140, rear cylinder maybe at the most around 10 or 15. Here are the pics. The first pic is the rear cylinder (no compression), the next pic is front cylinder. Looks like the front cylinder is starting to do the same thing that the rear has done. I know I need to do some sort of a rebuild at this point but I just wanted some advice on where to go from here. I would really like to figure out what has caused this problem so it doesn’t happen again when I do the rebuild. Whether it’s an internal air leak, carb settings, etc. Also, I’m running premix gas. Sorry for the long post, just wanted to share all the information I had. I really appreciate any input and advice from anyone! Thanks, Ryan.

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  2. #2
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Madison, WI, USA
    My feeling is air leak lean meltdown.
    So now you can try to put it together, air leak test it, and try to find a leak. Or you can rebuild it and completely reseal it...then air leak test it.
    I prefer to find the problem before I rebuild.

  3. #3
    Thanks for the reply. I would like to find the problem if possible before I rebuild. In your experience, where are common areas to cause such an air leak meltdown? In the sad shape my pistons are in, how would I do a leak down test in its current state?

  4. #4
    Yamaha artisan Cutlass's Avatar
    Join Date
    Oct 2010
    Madison, WI, USA
    Not a leak down test. You need to do a crankcase leak test.
    You need to somewhat reassemble the engine, seal off the intake and exhaust, and put air pressure into the crankcase. Spray soapy water around the suspect leak areas. Look for bubbles.
    If you aren’t familiar with what I’m talking about, the entire engine is part of the air intake “manifold” and needs to be air tight. Search around this site for air leak testing ideas.

  5. #5
    swlamarshrunner's Avatar
    Join Date
    Dec 2014
    Lake Charles, Louisiana
    The cost is pretty low to completely rebuild a 760 and the engine is pretty easy to take all the way down. I would strip it down to inspect crank then start fresh with new crank seals, all new gaskets, fresh bore etc. Once the engine were back together with all new parts I would do a leak test. This is pretty much exactly what I do with all of my engines and they get hours and hours of racing on them.

  6. #6
    Thanks for the replies, the entire engine leak test makes sense now, I will do some more research on here to get some ideas on that.

    Since I'm going to do a full rebuild, any tips on who you think provides the best rebuild kits and if I should consider doing any head work, etc for a small performance gain? I'm not trying to make a racer or anything just a decent ski to ride around on and if there's a few little things here and there I can do during the rebuild to help with power then great. It's got a Riva red pipe exhaust, stock style air filter, riva intake grate, ocean pro ride plate, not sure about the impeller but visually it looks to be in decent condition.

    Last question would be do you think my carb settings should be ballpark? The only thing thing I am considering at the moment is possibly lowering my pop off to help some with bottom end from what I have read on here.

  7. #7
    butterbean_29512's Avatar
    Join Date
    Sep 2013
    Bennettsville, SC
    All of the 760's had the same carb settings IIRC, just look the settings up and plug them in. Don't change any pop off settings. Install 1.5 needle and seat and 115gr springs (factory settings.) The rear carb main jetting is larger than the front carb to account for the torsional twist of the crank. When you rebuild the engine/reseal the cases use only three bond 1211. It's the gold standard. As part of your prep process once you have your cases clean use a fine sharpening stone and "level" all the aluminum sealing surfaces that must be sealed or gaskets. Both cases, case to cylinder sealing surfaces, top of cylinder, and head. Keep the stone wet with WD40 or equivalent. It is kinda like clay barring a car. You quickly get the hang of it, and you can feel when you have the sealing surface perfectly flat. If you have any burrs (aluminum burrs easily) they will prevent a good seal. I have rebuilt a ton of these motors, they are easy to rebuild, and are very reliable. They make a ton of HP. The original 760 exhaust is the best exhaust for it by far.

  8. #8
    Myself's Avatar
    Join Date
    May 2007
    North Central Arkansas
    Definately a lean meltdown as the pistons are burnt up on the exhaust side. There is also no fuel wash on those piston tops to speak of. The 110 pilot and 125 main jetting sounds too small, I'm thinking more like 115 and 135.

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