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ContinuousWave Whaler Moderated Discussion Areas ContinuousWave: Whaler Performance Yamaha 90 Tune Up
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Author | Topic: Yamaha 90 Tune Up |
btb |
posted 10-07-2007 09:47 PM ET (US)
I have a 1991 Yamaha 90 on my Whaler and it has started to die while idling in neutral. The plugs look black and wet when removed. I have not been putting any RingFree or Techron in my gas, so maybe that's the long-term cause. This weekend I did the basics: checked ignition timing, spot on; checked "synchronization" and adjusted that a bit; advance was leading carbs opening; adjusted the idle mixture adjuster needles per the book; open 1-1/2 turns; one carb was WAY out with about 3 turns open. When running at idle in neutral in a test tank, the engine speed would slowly build up for a couple of seconds, then there would be a muffled "phut" accompanied by a big splash of water in the test tank, and the revs would plummet, then it would build again, then another "phut" and so on. I ran some carb cleaner into the carbs for a while, then ran some RingFree through it, then just gas again, but this cycling mentioned stayed pretty constant and didn't improve. Any ideas? Would anyone recommend a more Yamaha-focused forum to get some ideas where to look next? I plan to run a few tanks of RingFree at the "shock" level, I have a few sets of plugs so I can change those - any other major advice on what this might be, or does it sound more like a carbon-buildup problem I just have to battle through? Thanks! btb |
rmart |
posted 10-07-2007 10:39 PM ET (US)
Of you want a yamaha based forum.... |
Clark Roberts |
posted 10-08-2007 06:24 AM ET (US)
Suggest you decarb with Mercury "Power Tune" or Yamaha "Combustion Deposit Cleaner" per instructions on the can and then (with boat in water, in fwd gear, running and at idle) readjust the idle mixture needle valves...in succession top carb to bottom carb turn clockwise (leaner) until rpm drops then counterclockwise (richer) until same and then try to set at midpoint (1 1/2 turns is just the starting point). I think your plugs should be NGK B8HS-10 (10 signifies factory gap setting at .040 inches). If not new plugs then check that gap. Good luck... Clark... Spruce Creek Navy Note: idle adjustments are best made with boat in water as described above since you need water up in the mid-section to provide proper back pressure and in gear to provide proper load. |
seahorse |
posted 10-08-2007 08:15 AM ET (US)
Clark is absolutely correct about decarbonizing the motor. Not only should it be done every 100 hours, but if the rings are only slightly stuck, after decarbonizing, the idle should improve. In addition, the thermostat is probably not warming up the motor enough. If you can hold your fingers on top of the cylinderhead for more than 3 seconds, the motor is too cold. The small passages in the Yamaha carbs will gum up very quickly with today's fuels, sometimes in as little as 6 weeks of non-use if the gas is not stabilized. The idle passages and jet are the smallest and gum up first. You may need a carb clean and rebuild kit if all fails. |
btb |
posted 10-08-2007 11:18 AM ET (US)
Ahah! So the needles control gasoline, rather than air - so the further in, the less gas gets through - that changes my understanding so thanks for that clarification. |
btb |
posted 10-12-2007 12:39 PM ET (US)
I used the de-coke spray, and ran the motor with some Ring Free. Took it to the bay and gave it a good run. Then did my best to adjust the idle on the carbs. Every now and again it still misses - and this misfire sometimes stops the motor, but at other times knocks the revs right down. Is this likely to be an ignition circuit problem - I don't think [the problem is caused by] carburetor jets and blocked airways from the nature of it. It just hits out of the blue in a random fashion. The engine runs better than it did - but this intermittent misfire is still present. Also, when running it at WOT, my max speed and revs were down about 5-MPH and 400-RPM. Any suggestions? I will check over the ignition electrics, but I am very grateful for any pointers where to start. Thanks for previous comments! Bill |
Clark Roberts |
posted 10-16-2007 05:59 AM ET (US)
Bill, suggest that you do a compression test (also a leak-down test) to determine if you have a cylinder(s) that's scoured or broken ring, etc. Hate to mention this but that would be my next step. The loss of 400-RPM and some speeds makes me suspicious. Fingers crossed... Clark... Spruce Creek Navy |
seahorse |
posted 10-16-2007 07:30 AM ET (US)
btb wrote: >>>> When running at idle in neutral in a test tank, the engine speed would slowly build up for a couple of seconds, then there would be a muffled "phut" accompanied by a big splash of water in the test tank, and the revs would plummet, then it would build again, then another "phut" and so on...<<<<<<<
Decarbon the motor as suggested previously as slightly stuck rings will free up and allow a better idle. If all else fails, then the carbs will need cleaning and new gaskets, orings, and float valve. The removable idle jets clog up very easily in those styles of carburetors. |
jimh |
posted 10-16-2007 08:57 AM ET (US)
In the REFERENCE section there is a procedure for evaluating an outboard motor. I think this might be useful in assessing your outboard motor problem. http://continuouswave.com/whaler/reference/outboardCheck.html |
btb |
posted 10-16-2007 11:21 AM ET (US)
Thanks to everyone for guiding me through this. I ran another bunch of Quicksilver power tune into the spark plug holes on a warm motor, then ran it in an improvised test tank for a while. I then ran the suggested compression check and all 3 cyls registered the same pressure - around 125 psi if I recall. I examined as much of the ignition wiring per Jim's suggestion as I could, undid and cleaned all the connections/terminals. Removed the coils and cleaned those of trapped crusting here and there, but didn't really find anything I thought was a problem - glad I did it though. So then figured its time to fix the obvious stuff - so I removed the carbs - which was much easier to do than I thought it would be - and am working through them one by one right now. The first carb has visible crud/varnish/brown stuff here and there inside and at least one of the tiny holes near the throttle plate was blocked. I am spraying everything with carb cleaner and blowing it out with compressed air. I bought a couple of 12 oz bottles of Ring Free from my local Yamaha place (for $17 apiece) then found Chevron Techron at the local Autozone for $6.99, AND a mail-in rebate for $3 off two bottles - so that's a deal so bought a bunch of that and plan to run 3 tanks (22 gal) with 2oz Techron through the motor, then revert to a can now and again going forward. I will let you know how it works out this weekend (its not winter here yet!) Bill |
btb |
posted 10-16-2007 11:32 AM ET (US)
Forgot to add: when zooming around the bay I tried putting my hand on the cylinder head - and I could keep it there more than 3 seconds - maybe its running too cold. I will replace the thermostat. When I bought this boat last August the guy showed me receipts for some engine work which included a new thermostat - but who knows what work was actually done. I found several things amiss on this motor over the year plus I have had it - blocked oil filter, incorrect setting on the oil pump linkage resulting in too little oil getting to the engine, now one of the carbs idle jets way too open - so I am thinking the mechanic was setting things up for more work for him! Looking through Jim's checklist I think I have addressed everything now - so will finish the carbs and take it out again..... Thanks again for your help, encouragement and patience. Bill |
btb |
posted 10-19-2007 10:40 AM ET (US)
Seahorse - I pulled the thermostat out of the motor. There was minor salt here and there but overall the waterways looked open in there. I tested the 'stat and found it is performing to spec - the manual specifies a 118-126 degree thermostat and this was opening up around 125 and fully open at 130 degrees. As a separate check, after letting the pot with the hot water stabilize its temp, I tried the hand test and found that at 130 degrees I could comfortably hold my hand on the pan for more than three seconds. The magic temp for your test seemed to be around the 140 degree mark. So the thermostat is working to spec, and the motor seems to be operating at its designed temperature. As I said, I cleaned out the carbs. It seemed to run better during a quick test on the hose but I plan to take it out this weekend and set it all up again per the instructions posted earlier. I will let you know how it works out. Thanks again, Bill |
seahorse |
posted 10-19-2007 10:57 AM ET (US)
You are correct, your 90 hp uses a 118-126° thermostat whereas most ouboards use 135-145° ones. |
PeteB88 |
posted 10-19-2007 11:02 AM ET (US)
Gents - is this same procedure for my 92 Yamaha 40 2S Precision lube? thx What is strange about my motor is 1) I always warm it up while ie if launching I let idle at ramp while parking the rig. 2) I run easy for the first few minutes and work throttle up past planing speed to nice cruise. Say after 5 or 10 minutes I push throttle up to what feels like a detent in the throttle linkage I can expect a miss or blahhhhhh from motor until I back it off and it runs nice. Push forward, same. I have learned to pump the throttle sometimes vigorously to correct. It sometimes takes many efforts but if it goes blahhhhh (no real loss of power, just doesn't want to go higher revs) I back off instantly. Inevitably after 20 minutes or so it will run perfectly at higher speeds the rest of the day. If consecutive days, no problem. It's as if some crud builds in one of the carbs or resides there. Ideas? thanks |
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