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  1. #1

    Angry Yamaha LX 210 Starboard Eng Problem

    I bought a used LX210 and I am having problems with the Starboard eng.

    The number one cylinder had O compression and the piston was scored on the inlet side.
    Cylinder was honed out, new piston and rings and I now have #1 cyl 115, #2 cyl 125 #3 cyl 120 (also my port eng has almost the same compression)

    My carb was rebuilt by a independent and also by the dealer.

    The eng. run fine at idel at at full throttle.

    But at mid range about 45 seconds or at the end of the ski coarse the starboard eng. drops from 4000 RPM to 2500 RPM for 15 seconds and then return to 4000 RPM. At 5000 RPM on the same ski course it will drop down to about 3200 RPM and stay at that RPM for about 30 seconds before recovering.

    The dealer tech says low compressing on #1 cylinder is causing the problem, but I do not have that problem with the port eng. with similar compression

    I have also installed 2 new fuel filters, but no changes.

    Help befor I spend $2000 with the dealer new pistons anc cylinders!!!

  2. #2
    i will get all the rest i need when im dead corkycat's Avatar
    Join Date
    Jan 2009


    sounds to me like a carb situation, at mid rpm those engines will be seing a lot of load and the standard jetting on the carbs may be to lean hence no#1 going low on each engine.
    osidebill will be the best person to speak to regarding this, he sorted my ski right out.

  3. #3
    Moderator OsideBill's Avatar
    Join Date
    Mar 2006
    United States
    Sounds like a fuel issue and here is a good read on the boat fuel systems. Your compression sounds fine.
    Fuel System Issues

    Engine Starting - Since PWCs routinely get upside down in the water, the Coast Guard regulations have always mandated that they have a fully sealed fuel system. The PWC makers have used this mandate to their advantage. As a pwc fuel tank gets agitated, a small amount of internal pressure builds (exactly as shaking a 5 gallon can of fuel results in built up internal pressure). In PWCs, this natural pressurization is utilized to help feed fuel through the fuel lines to the carburetors. Furthermore, when a PWC is shut off, this sealed fuel system holds fuel in place where it is immediately available for the next restart.
    Ironically, Coast Guard regulations “”mandate” all traditional pleasure boats (including the Yamaha Jet-boats) utilize an un-sealed “vented to the atmosphere” fuel system. Overall, such a system can work okay, however it does represent one big inconvenience … hard starting.
    In the “unsealed” system used on the jet-boats, most of the fuel in the fuel lines is often siphoned back into the gas tank when the engine is shut off for a few hours. In order to re-start, the fuel pumps on the carbs must re-fill the long empty fuel lines in order to get the engine to fire. This often requires lengthy runs on the ignition starter key. Since the fuel lines to the port (left) engine is a longer run, the port motors usually take alot more cranking to get their fuel. Since the starters are not designed for long usage, these lengthy starter uses (to re-fill the fuel lines) can cause premature starter motor failures.
    Air in the Fuel Lines
    High performance PWCs (and jet-boats that use pwc engines) all have a shared problem. As fuel level gets low, air bubbles routinely make their way into the fuel pickups and then into the fuel lines. Since there is no way for this air to be purged out (once it has entered) the air is passed through the carburetor jets where it causes a momentary, but serious, lean condition. As more and more bubbles are admitted, these moments of lean condition becomes so prevalent that the operator experiences a noticeable “bog” or hesitation.
    On low performance pwc engines, these “lean moments” are of little consequence. However on high performance PWCs (particularly 3 cylinder engines), these lean moments often result in momentary detonation, and “more than occasionally” result in piston scoring or piston seizure. Countless times, owners of high performance PWCs and jet-boats have experienced a sudden unexplainable engine “shut down”. Examination afterwards shows the shut-down was the result of a scored piston … but why??
    Our testing showed that in many cases these mysterious scored-piston shut-downs are a result of a “more than momentary” lean condition being caused by air entering the fuel pickups when fuel levels are below 1/2 tank. To resolve this problem, we created a fuel/air separator kit that assures an “air free” supply of fuel to the carbs at all times. This kit can be easily fitted to most PWCs and jet-boats, and brings with it improved starting abilities reduced carburetor maintenance, and total elimination of all air bubbles in the fuel lines.
    About Air in the Fuel Lines – The Technical Background
    We purchased a single motor Yamaha Exciter135 jet-boat for performance increase tests. After spending a few weeks of testing with various props, compression ratios, porting formats, etc, we got down to doing the carburetor fine-tuning. Like all our fine-tuning tests, the boat was equipped with a gps, digital tachometer, and a detonation sensor that had a lead to each cylinder. We were in the second day of fine-tuning, and the boat was operating perfectly, even under the heaviest high speed loads we could inflict upon it.
    Mid way through our test session, another boat we had at the water needed fuel. We pulled up the jet boat (with it’s 35 gallon tank about half full) and siphoned out 6 gallons to put in our other boat. We figured we still had at least 12 gallons of fuel on board, which would easily be enough to complete our testing. With the siphoning done, we headed our Exciter jet-boat back out on the water to finish our fine tuning. Immediately, we started seeing mild detonation on all three cylinders as the jet-boat ran across the bumps of some small boat wakes. We then ran the boat to peak speed for our standard “full speed left turn” test (this test loads the engine harder than any other kind of operation). As soon as we snapped the wheel to full left, all three cylinders showed heavy detonation that would have easily scored a piston if we maintained the turn for a couple of more seconds. We were stunned that this engine, that had been performing flawlessly for days, was suddenly on the verge of burning down a piston. We checked our entire engine compartment to make sure that some random component failure or fuel restriction wasn’t causing this new and very lethal detonation. After exhausting all possibilities, we went back to the launch ramp and added back the 6 gallons of fuel we had just siphoned off. Back out on the water, our jet-boat once again performed flawlessly with no visible detonation, even under the heaviest high rpm operation and hardest turns.
    For us, the message was clear. The fuel in the long and narrow fuel tank of our jet-boat could easily be ”sloshed” away from the fuel pickup tubes. Once the pickup ends are exposed to air, that air enters the fuel lines. Our jet-boat (like all pwcs) has no way to purge out this air in the fuel lines, other than passing it through the jets in the carburetors. As soon as these air bubbles reach the jet circuits, they create a very brief, but very serious, lean condition. These brief lean conditions were causing the mild detonation our jet-boat exhibited as we drove across the bumpy boat wakes. However, our full-speed left-turn sloshed virtually all the fuel to one side of the tank, causing an instant and very lengthy lean condition. A lean condition of this order can easily score a piston in less than 3-4 operating seconds (under load).
    The Solution

    We decided to create a fuel/air separator for our project jet-boat to purge all air bubbles from the fuel lines “before” they reached the carbs. “All” fuel/air separator setups require the use of a remote fuel pump. We tested with both electric and “pulse” type fuel pumps, and various separator chamber designs. Through the whole process we maintained a “keep it as simple as possible” mindset.
    We finalized on two separate designs. (A) The crankcase “pulse” fuel pump kit, and (B) the electric fuel pump kit. The electric fuel pump kit is intended primarily for the twin-engine jet-boats (Yamaha and Sea Doo), however it could be used on any pwc with a strong charging system as well. The “Pulse” fuel pump Kit is the more simple setup intended for PWCs, and it does mandate the installation of a primer pump (or carbs with an accelerator pump feature to prime the carbs).
    After installing our finished separator on our Exciter 135 test jet boat, we re-ran our tests with only 5 gallons of fuel in the tank (the earlier tests showed heavy detonation with 12 gallons on board). This is a level that would have certainly delivered heavy detonation during high-speed rough-water operation, and piston seizing detonation during our “full speed left turn” test. No matter how hard we ran our test jet-boat with this low fuel level, we never experience even the slightest detonation, or “low fuel” hesitations. The fuel/air separator was obviously doing a perfect job of purging all the air from the fuel input lines to the carbs. With this separator in place, we could run the fuel level down to virtually zero without experiencing any “engine harming” detonation or lean conditions.
    We consider this fuel/air separator to be absolutely mandatory for any Yamaha jet boat that gets operated in any fashion with less than a half tank of fuel.
    In addition to the above mentioned benefits, we also found that our hard-starting problems were also eliminated. Our electric fuel pump (which was wired in to the ignition key) would immediately fill the fuel lines that had been siphoned empty, and our Exciter started almost instantly.

    The Yamaha Jet-boat fuel/air separator consists of the electric fuel pump, separator canister, and all the hoses & fittings required for installation.

    (note: electrical

  4. #4

    Red face Lx 210 Problems

    I think you might of solved the problem.

    If the wheather is nice on Saturday I will take the boat out and run a new fuel line to a one gallon fuel tank and see if the problem goes away.


  5. #5

    Angry LX210

    I just got a chance to run the boat

    Full tank of gas Problem still is happening.

    This time we run boat straight out no turns problem sitll happens

    Switched full line to see if it is a feuel line pick up issue, problen stays with engine.

    What would happen if I were to put a fuel pump on that eng. for testing and run the hose to a 5 gallon can. Would I damage the carb and mech fuel pump?

  6. #6
    [quote=355Ferrari FI;979358]Hi
    I just got a chance to run the boat?

    Full tank of gas Problem still is happening.

    This time we run boat straight out no turns problem sitll happens

    Switched full line to see if it is a feuel line pick up issue, problen stays with engine.

    What would happen if I were to put a fuel pump on that eng. for testing and run the hose to a 5 gallon can. Would I damage the carb and mech fuel pump?

  7. #7

    Smile lx210 Problem Resolved

    Problem resolved: Using a laser temperature gauge found the area causing the problem to be the last bend of the exhaust header by the thermal couple. I disassembled the header and found the last chambers to be 95% blocked with salt build up an one of the three passages to be completely blocked.

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