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Dominick, Marine Mechanic
Category: Boat
Satisfied Customers: 1009
Experience:  25 Years Experience as Mechanic, 20 Yrs Boat Yard Owner/Mechanic, Factory Certified
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Have a 2003 yamaha LST 1200AB engine in a LX210 jet boat, Starboard

Customer Question

have a 2003 yamaha LST 1200AB engine in a LX210 jet boat, Starboard engine will be running at 4000 and lugs down to 3000 rpm but is not in limp mode, does not seem to be overheating, on the ramp with boat on trailer will peg at 5500 RPM no fluctuation, will idle but rpms are erratic in the 4000 range, drop to 3 then up to 5 with a little throttle.
comp tested both engines all cylinders between 122 and 125, pulled the plugs, cleaned and gapped at .026
tested fuel, looks clean, filters are see through, i see no dirt, both engines pull from same tank.
when on the ramp it seems like the port engine tries to move the boat when in nuetral, but does not happen with the starboard is it possible the coupler is slipping also?
Submitted: 1 year ago.
Category: Boat
Expert:  RSRBOB replied 1 year ago.
Hi and thank you for your question.I am not sure what you mean when you say you have an LST engine in an LX210. All of those boats used the 65U engine so compatibility should not be an issue.However, since you mentioned it, it sounds like what you are also saying is there was an engine swap at some point and the starboard engine is no longer the original engine. If that is true, is the replacement engine a rebuilt engine or short block from an aftermarket manufacturer? I am also going on the assumption that the engine in question was not doing this prior to needing to replace it. Please correct me or fill in as many details as you can here please, you never know what might help us get to the bottom of this problem quickly.Since you said the compression was consistent, we will look in other areas for now. Mainly, the carburetion. Since carbs have different circuits that they use to meter fuel flow at various throttle settings, it is plausible that it could start and idle fine, yet under a load demonstrate a running problem. This would indicate the high speed circuit has issues. The first thing I would suggest is checking to make sure the high speed screws are set correctly. The #1 and #3 carb have their high speed screws set at 3/4 turn out from LIGHTLY seated. The #2 carb has its high speed screw set at 1 turn out from LIGHTLY seated. Unfortunately you about have to pull the carbs to be able to check that. The high speed screws are on the sides of the carbs that are facing the cylinders. The screws that are on the same side as the throttle linkage are your low speed screws.If the high speed screws are set correctly, then you will need to take the carbs apart and inspect and clean them. You want to pay special attention to any kind of debris that would restrict fuel flow on the high speed circuit. The high speed main jet is sized 135. In case someone has been in here before you, remove the high speed screw and blow compressed air or contact cleaner through the high speed screw hole in towards the carb. Make sure it is coming out inside the carburetor where the 135 main jet was.Lastly, I would check to make sure the vacuum lines for the fuel pumps were all connected and stick your fingers down the intake manifold and make sure you dont have any bro***** *****s.If you have any more questions, feel free to ask.ThanksRSRBOB
Customer: replied 1 year ago.
The Boat is an LX210, i thought it came with these engines, but their serial numbers or models were LST200AB which I have found that number when looking for parts. I am pretty sure these are original engines.
I pretty much figure by now I will be cleaning and rebuilding the carbs, or may have it done at a shop.
Any idea what the book hours would be on a job like that?
Is there any procedures documents for removal and install of the carbs?
When I look at Yamaha parts on their web page it shows carb 2 & 3 NLA do you know if the internal rebuild parts are the same as # ***** for all 3
Expert:  RSRBOB replied 1 year ago.
Without actually consulting the flat rate, and it being a boat and not a personal water craft, you are probably going to be looking at 3-4 hours per engine to get the carbs cleaned. One bugaboo is that the exhaust has to come off to get to the carbs to be able to take them off. Flat rate really only applies when a dealer is getting paid by the manufacturer. Most shops bump flat rate 50% because typically the factory flat rate times aren't terribly realistic.If you decide to do it for yourself, make sure you get the Mikuni 44mm carb kits for Yamaha engines (if you don't go OEM). Mikuni makes the same size (44mm) but the carb body is much smaller than the Yamaha carb body and the o rings and gaskets won't fit.If you have any more questions, feel free to ask.ThanksRSRBOB
Customer: replied 1 year ago.
Thanks still deciding, when I look at OEM do not see actual kits,all I see is an ala cart list
Expert:  RSRBOB replied 1 year ago.
Here is what I was looking at. Typically, aftermarket distributors sell the Mikuni rebuild kits for less than the boat manufacturer. This shows the repair kit as $267. That is per carb. I believe that includes a lot of components that you would not automatically need to replace. This is a link to an aftermarket distributor that sells Mikuni brand rebuild kits. I am not a fan of 3rd party rebuild kits howeve. I do suggest sticking with Mikuni genuine parts, just not necessarily from Yamaha. :)Let me know if you have any more questions.ThanksRSRBOB

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