1991 YAM 250TURP IGNITION

[FHARVELL]

Ok, I posted this three months ago and still have not been able to figure this out. Keep in mind, I've rebuild just about every kind of gasoline combustion engine you can imagine, automotive, marine, lawn mowers, chain saws, the small cox toy engines, even the big detroit 671 diesels - I've seen a few. I bought the SELOC manual which explained the ignition system and tested everything in the book, by the book (using a fluke). I ruled out the charging system and battery, verified proper voltage levels, I pulled, checked, cleaned all the plug connections and wires, everything that could be adjusted - I tried - only made things worse. I checked every sensor, CP, TP, Knock, TSwitch, TSensor. I tried higher Octane fuel(93). I've merticulously cleaned all 6 carbs - twice, I re-adjusted the carb linkage and oil injector linkage - FOUR times, verified fuel delivery, no blockage or cracks in the fuel lines. (a new fuel tank was installed early this summer when I got the boat) I finally got the chance to have the previous owner take the boat out last weekend, He hadn't been in it for over two years but by his recollection - it did the same thing with him for as long as he owned it, only he recalled the motor only pulling back once. Anyway, I have a see-through fuel filter plus the one in the engine that are both perfectly clean - Nothing, and I mean nothing I've done has had any affected WHAT SO EVER on this particular problem. It performs EXACTLY the same way EVERY SINGLE TIME, I can duplicate the problem every single time I throttle up to WOT. I'm convinced the YMIS is advancing the timing to the full 22 BTDC at WOT (like its' suppose too), going immediately to WOT, the boat plains and reaches a TS Of 42MPH, RPMS reach 54 (takes about 8 seconds, no cavitation), 5 seconds later, the RPMs INSTANTLY drop back to 49, boat slows to 36MPH, five seconds after that, RPMS INSTANTLY drop again to 46, boat slows to 31MPH, where it will remain ALL DAY LONG for as long as I am running the boat. If I slowly throttle up to WOT, the RPMS never reach above 46. Other than that, the motor has been completely reliable, NO other problems what-so-ever that I can tell. Someone told me the motor is still in the "Break-in mode" that the YMIS is not allowing the motor to reach full potential to allow for a "Break-in Period" set by the dealer. Is there such a thing? I plan on wringing out the pulser coil next (the boat is stored in another state, so I can only work on it during the weekend - which interfers with my fishing) I think maybe one of the pulsers is defective (???), Then again, This is a smooth strong clean running engine - NO MISSING, (yes, I checked the plugs, they ALL look normal) I did find a bad Spark plug cap and replaced it, but it made no difference what-so-ever to the main problem, other than it did seem to run just a little smoother. I checked all 6 Ignition Coils with a meter, (which is how I found the bad cap) I just can't figure it out. Another Idea I had was the Knock sensor, it shows 580Mohms, it should be infinity, but when I disconnected it - the motor ran considerably worse. The book says the YMIS only takes input from the KS input if not getting input from the CP and TP sensors. There is no O2 sensor. I have not checked compression but judging the way it jumps out the hole (will throw you out the boat if you don't hold on) I don't see this being a compression problem, plus hot or cold the problem does not change. I also intend to put a timing light on it to verify if it is indeed the timing, hard to do on the water at WOT though. The P owner also told me he blew a fuse once (the small round one, next to the two big square ones) and ended up having to replaced the computer. (it is the correct PN) I need some real technical insight here, not backyard warrior feedback. I've spoken to several outboard motor mechanics and dealers and they all gave me a different answer (I checked everything they suggested). The 250 seems to be a rare engine (???) Nobody I talked to seemed to have much experiance with that model. Keep in mind, the 225 and 250 is way different from other YAMI models (it is the most advanced YMIS covered - unquote). I'm also looking into getting a diagnostic test harness.

 

[bigbrownbuku]

Re: 1991 YAM 250TURP IGNITION

sounds like its running out of gas( these engines use an insane amount of gas). have you done a fuel vacuum test? have you rekitted your fuel pumps? what happens when you prime the primer while underway at wot? try running with a separate gas tank, find a friendly dealer that will let you borrow his boat in a box and rule out any main harness problems also. dont replace any electrical parts until you have tried the above.<br />a side note its almost the same price to buy the complete pump vs the individual parts.

 

[seahorse5]

Re: 1991 YAM 250TURP IGNITION

A common problem with older Yamahas is debris gets trapped inside the fuel passageway between the carb inlet fitting and the 2 needle and seats. It is a blind passageway and no way to clean it out. The steel screws inside the fuel pump rust and the "rust dust" packs in there also.<br /><br />While you are running, the debris will float around then plug up or restrict the fuel flow to one needle and seat, dropping that cylinder. You can also see it by removing the airbox while the motor is running. Don't run it long as the cylinder is lean and hot, and you know what lean and hot means to a 2-stroke piston!<br /><br />Yamaha came out with a service letter years ago about drilling out the carbs for access to the passageway and gave the part numbers for a gasket and screw to seal it back up. See a dealer for a copy of the procedure.

 

[rodbolt]

Re: 1991 YAM 250TURP IGNITION

ok now ya gotta post a model; number<br /> if you have a 2.6L 225 its a non smart motor does not have YMIS. if its a 3.1L motor I will bet odds I know the problem<br /> glad your such a wonderful tech but thjis moptor will kick your rumpus until you study all the control systems. but without a model number I cant tell what motor you winging

 

[FHARVELL]

Re: 1991 YAM 250TURP IGNITION

Thanks everyone for the tips, these are really excellant suggestions worthy of checking out. <br /><br />Hey rodbolt I see you're a water-bound North Carolinian, I too grew-up on the NC coast, Beaufort to be exact, I spent 95% of my youth fishing crab-pots and trawling for shrimp/fish/crab/flounder off the beaufort bar Adams creek, P and C Sound (the other 5% I spent sleeping). I don't think there's any place I haven't been in an outboard or shrimp trawler in Carteret or Craven county. Now I teach weapon systems and Combat direction systems for all of the Navy's big deck ships, destroyers and Frigates. As I said, the boat is in NC, next time I'm there I'll double check the name plate data, but to the best of my knowledge (the number on the plate, port side motor bracket, is 250TURP (250 HP, 3130 cc, (250 Vx 76 degree, Micro Computer Ignition System is what's on the cowling), power tilt, trim, 30" shaft, remote (704) control, 1991 model) I have the full digital instrumentation package. It's mounted on a 23' 1975 SeaRay via an external bracket mount (everyone seems to stop and admire). I don't have access to another box which is forcing me to pin-point the cause before I go buy parts. OK - I CAN fix thing right now for about $1500.00, but I'm trying really hard to shrink this number - The government does not pay all that great ya know, and with the cost of GAS, I can barely affort to take the thing out /// So, I came to a new discovery last weekend. After tinkering with everything on the engine (to no avail) My son was running up the throttle - He got up to 36 rpm and hung out there, 10 seconds latter, it dropped to 33 rpm, 10 seconds after that, it dropped to 31 rpm. No missing, no surging, more like someone flipped a switch. (sounds like it's dropping two cyclinders Huh?) He then took it on up to WOT, the motor topped out at an even 45 without any more dropping off. OK then we backed down to idle and did the HOLE-SHOT WOT thing - same as always, 53, 48, then settling at 45. I'm still thinking it's in the pulser coil (high speed side). I suppose this could be a carb issue if the problem wasn't so predictable at so many different speeds, and, I'm even more skeptical now, that this could be a fuel delivery problem. I do notice less power after the motor drops back. I'd appreciate any ideas - AND - Is there any such "Break-In-Period" setting designed to hold the motor back?

 

[rodbolt]

Re: 1991 YAM 250TURP IGNITION

hahahaha<br /> another aouto tech goes down in flames<br /> I love it<br /> its a very simple system, almost.<br />you can run that motor with the air boxes removed and spray premix in the carbs to check for one running lean, the timing must be verified with a light at WOT not guessed at, the ign system can be checked with a DVA meter and only a DVA meter. the diagnostic lamp is about 70 dollars and will tell you in 30 seconds whats not broke.<br /> that motor kicks arse on a bunch of backyard monkeys, its actually funny to watch.<br /> if you disconnect the knock sensor it should default to 7*BTDC.<br /> the v76x motors are kinda outdated technology now.<br /> but they worked well.<br />I will be in NY and VE for the next week.<br /> I will try to check your progress from VE. you will need a tune up spec guide or the factory service manual, a DVA meter and the diagnostic lamp will help. there were some stator issues that as it ran the charge coil output voltage would fall and RPM would suffer. wont see it on the winky blinky.

 

[FHARVELL]

Re: 1991 YAM 250TURP IGNITION

Well,,, I suppose that's why I'm here... As far as engines go, I ain't never seen nothing like this thing ... If Virginia Beach didn't have so many rediculus ordinances, I'd be able to park the thing at my home and have time to work on it. I'm using a Fluke 77 digital voltage meter and I think the end is in sign now. I won't get a chance to work on it until the following weekend, but my plan is to check for lean carbs then take resistance readings (I've been procrastinating this) on the stator and timing base, I have the SELOC to help me out. Worse comes to worse, Budget Boats in Chesapeake has a mountain of used discount outboard motor (and boat)parts. I bought a clymer once for my Kawasaki LTD454 and it left alot to desire. I don't mind working on engines, I hate having to work on my own, preventive yes, corrective no. - thanks again for the help. I'll definitely post what's been causing this once I find it (and how much it cost me to fix) Personnally, I'll take a Chevy 350 any day...